b9 edge ion guide ed1
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Domain : NETWORK OPTIMISATION
Product : 2G B9
Division : METHODS
Rubric : EDGE
Type : GUIDELINE
Distrib. codes Internal: External:
PREDISTRIBUTION
NE J. ANDRES NE/Quality & Partnership LF.GONNOT
NE/Romania S. BODEA NE/GSM F. Colin
NE/Egypt N. GEORGE NE/GSM/Egypt S. Abdel-Wahab
NE/GSM/Romania C. Inta
ABSTRACT
This document presents the EDGE optimisation methodologies, for B9 release.
KEYWORDS
GSM, EDGE, EGPRS, B9, Optimisation
Approvals
NE J. ANDRES NE/GSM F. Colin
Date:
Signature:
Date:
Signature:
Date:
Signature:
Date:
Signature:
Site
CASCAIS
WIRELESS BUSINESS GROUP
NETWORK ENGINEERING
Originator
Pedro Henriques B9 EDGE Optimisation Guide
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HISTORY
Edition Status Date Comments
01 Draft May. 23rd, 2007 Draft Creation
1 Release June, 29th, 2007 First edition
DISTRIBUTION LIST
NE
END OF DOCUMENT
TABLE OF CONTENTS
1 INTRODUCTION ....................................................................................................... 5
2 ALGORITHMS AND PARAMETERS ................................................................................. 6 2.1 MAIN EDGE CONCEPTS......................................................................................................................... 6 2.2 HARDWARE AND POWER ASPECTS ......................................................................................................... 7 2.3 ENHANCED TRANSMISSION RESOURCE MANAGEMENT ............................................................................. 8 2.3.1 M-EGCH STATISTICAL MULTIPLEXING....................................................................................................................... 8 2.3.2 DYNAMIC ABIS ALLOCATION .................................................................................................................................. 10 2.3.3 ATER RESOURCE MANAGEMENT ............................................................................................................................ 12 2.3.4 DL RETRANSMISSION IN THE BTS .......................................................................................................................... 13 2.4 AUTONOMOUS PACKET RESOURCE ALLOCATION (RAE4) ........................................................................ 13 2.5 M-EGCH LINK MANAGEMENT .............................................................................................................. 22 2.5.1 DEFINITIONS........................................................................................................................................................ 22 2.5.2 ABIS SELECTION IN M-EGCH LINK.......................................................................................................................... 22 2.5.3 M-EGCH LINK SIZE ............................................................................................................................................... 23 2.5.4 PERIODICAL GCH ESTABLISHMENT PROCESS .......................................................................................................... 23 2.5.5 FAST INITIAL PS ACCESS ....................................................................................................................................... 24 2.5.6 HANDLING OF UNUSED GCH ................................................................................................................................. 24 2.5.7 M-EGCH LINK CAPACITY DECREASE ....................................................................................................................... 25 2.6 TBF RESOURCE ALLOCATION/REALLOCATION ...................................................................................... 25 2.6.1 TBF RESOURCE ESTABLISHMENT PROCESS............................................................................................................. 25 2.6.2 RADIO RESOURCE ALLOCATION PRINCIPLES........................................................................................................... 26 2.6.3 TRANSMISSION RESOURCE AVAILABILITY STEP ....................................................................................................... 28 2.6.4 TRX LIST COMPUTING .......................................................................................................................................... 28 2.6.5 BEST CANDIDATE ALLOCATION COMPUTATION ....................................................................................................... 28 2.6.6 PDCH CAPACITY ALLOCATION ............................................................................................................................... 31 2.6.7 TBF REALLOCATION CASES ................................................................................................................................... 32 2.7 ENHANCED SUPPORT OF EGPRS IN UL................................................................................................. 34 2.7.1 SUPPORT OF 8-PSK IN UPLINK .............................................................................................................................. 35 2.7.2 SUPPORT OF INCREMENTAL REDUNDANCY AND RESEGMENTATION IN UPLINK.......................................................... 36 2.8 EXTENDED UL TBF MODE ................................................................................................................... 37 2.9 ENHANCED PACKET CELL RESELECTION............................................................................................... 39 2.9.1 NETWORK ASSISTED CELL CHANGE PROCEDURES (NACC) ...................................................................................... 39 2.9.2 PACKET (P)SI STATUS PROCEDURE ........................................................................................................................ 42
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2.9.3 NC2 IMPROVEMENT ..............................................................................................................................................44 2.9.4 DL LLC PDU REROUTING.......................................................................................................................................46 2.10 TELECOM PARAMETERS .....................................................................................................................47
3 NETWORK DIMENSIONING........................................................................................54 3.1 ABIS ..................................................................................................................................................55 3.2 ATER .................................................................................................................................................57 3.2.1 METHOD 1 ...........................................................................................................................................................57 3.2.2 METHOD 2 ...........................................................................................................................................................58 3.2.3 NUMBER OF GCH NEEDED.....................................................................................................................................59 3.2.4 HSDS IMPACT .......................................................................................................................................................59 3.3 GPU/GP ............................................................................................................................................62
4 NETWORK PRIORITIES.............................................................................................64 4.1 PHASE 1 ............................................................................................................................................64 4.2 PHASE 2 ............................................................................................................................................64 4.3 PHASE 3 ............................................................................................................................................65
5 QOS FOLLOW-UP....................................................................................................66 5.1 TBF LIFE TIME ...................................................................................................................................66 5.1.1 TBF ESTABLISHMENT ............................................................................................................................................66 5.1.2 TBF DATA TRANSFER.............................................................................................................................................67 5.1.3 TBF REALLOCATION .............................................................................................................................................70 5.2 RLC STATISTICS..................................................................................................................................71 5.2.1 (M)CS DISTRIBUTION ............................................................................................................................................71 5.2.2 LLC/RLC TRAFFIC AND RETRANSMISSION...............................................................................................................74 5.3 RADIO RESOURCES .............................................................................................................................76 5.4 TRANSMISSION RESOURCES.................................................................................................................77 5.5 RNO REPORTS....................................................................................................................................77 5.6 END-USER STATISTICS.........................................................................................................................79
6 OPTIMISATION METHODS AND CONSTRAINTS .............................................................81 6.1 LOW DL THROUGHPUT OBSERVED .......................................................................................................81 6.1.1 END-TO-END ANALYSIS..........................................................................................................................................81 6.2 DL MCS FLUCTUATION ........................................................................................................................88 6.2.1 RADIO CONDITIONS ..............................................................................................................................................88 6.2.2 UNCONTINUOUS LLC TRAFFIC ..............................................................................................................................90 6.3 UL PERFORMANCE..............................................................................................................................90 6.3.1 RESEGMENTATION VS IR .......................................................................................................................................90 6.3.2 EXTENDED UL TBF MODE ......................................................................................................................................90 6.4 ACCESS TIME OPTIMIZATION ...............................................................................................................91 6.5 EDGE PERFORMANCE VERSUS FREQUENCY PLANNING...........................................................................91 6.6 ABIS CONGESTION..............................................................................................................................91 6.7 ATER CONGESTION.............................................................................................................................92 6.8 GSS OPTIMISATION FOR GMM/SM SIGNALLING......................................................................................95
A TABLE OF FIGURES .................................................................................................97
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REFERENCED DOCUMENTS
Table 1: Referenced Documents
[1] EDGE Field Trial Guideline, ed4 3DF 01902 2015 VAZZA
[2] B9 MR1 Features Review, Methodology and Field Feedback 3DF 01906 2913 VAZZA
[3] 3GPP TS 05.08, Radio subsystem link control
RELATED DOCUMENTS
Table 2: Related Documents
[i1] (E)GPRS Radio Interface - RLC sub-layer 3BK 11202 0392 DSZZA
[i2] (E)GPRS Radio Interface - RRM sub-layer (PRH) 3BK 11202 0390 DSZZA
[i3] (E)GPRS Radio Interface - RRM sub-layer (PCC) 3BK 11202 0391 DSZZA
SCOPE
PURPOSE OF THE DOCUMENT
This document is a guideline of EDGE optimisation methods, for B9 release. It gives the direction for the
optimisation process and it tries to focus in the main topics and issues.
AREA OF APPLICATION
This template should be used within NE and RSC for all ALCATEL-LUCENT, it is an internal document.
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1 INTRODUCTION This document is a guideline for EDGE optimization for B9 MR1. It does not include the B9MR4 software
features (PS in extended cell, QoS handling) and the B9MR4 hardware features (Twin module). It has a
theoretical introduction of the PS features, follow by a chapter of network dimensioning and QoS follow-up.
To finalize there is a chapter explaining possible optimisation methods.
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2 ALGORITHMS AND PARAMETERS
2.1 MAIN EDGE CONCEPTS
EDGE introduces some new aspects that fatally distinguish it from the “classical” GPRS service:
o New coding schemes are introduced – EDGE uses MCS1 to MCS9 (MCS meaning Modulation and
Coding Scheme).
o New modulation – besides the GMSK modulation, which is still used in MCS1 to MCS4, EDGE uses 8-
PSK modulation. This modulation has a variable envelope, which impacts the available output
power.
o New LLC PDU segmentation – while in GPRS the LLC PDU is segmented in RLC blocks taking into
account the used coding scheme, in EDGE the LLC PDU is segmented in payload blocks (new concept
in EDGE) taking into account the used MCS family – in EDGE the RLC block can carry one or two
payload blocks.
o The coding scheme family concept, referred just above is also new in EDGE. Besides what was
already referred, this new concept changes the way retransmission is done. Table 1 presents the
different coding scheme families available (currently missing in the table below), as well as its
theoretical throughput.
o Puncturing Schemes – new concept in EDGE also used in the retransmission mechanisms.
Table 3: Coding Schemes
Coding scheme Coding scheme Family Modulation Theoretical throughput per PDCH (kbit/s)
CS1 GMSK 8
CS2 GMSK 12
CS3 GMSK 14.4
CS4
-
GMSK 20
MCS1 Family C GMSK 8.8
MCS2 Family B GMSK 11.2
MCS3 Family A/
Family A padding GMSK 14.8 / 13.6
MCS4 Family C GMSK 17.6
MCS5 Family B 8-PSK 22.4
MCS6 Family A/
Family A padding 8-PSK 29.6 / 27.2
MCS7 Family B 8-PSK 44.8
MCS8 Family A padding 8-PSK 54.4
MCS9 Family A 8-PSK 59.2
Retransmission mechanism, or ARQ (Automatic Repeat request), has been greatly modified in EDGE.
The first modification comes from the introduction of the payload concept. In an EGPRS TBF the RLC block
can be retransmitted either by using the same MCS or by using a MCS from the same coding scheme family.
A side effect from this is that even if Link Adaptation (algorithm that changes the coding scheme according
to radio conditions) is disabled, we can observe RLC blocks with different coding schemes (although always
with the same family).
Still in the ARQ mechanism, EDGE introduces a new type of ARQ. Now we have:
o Type 1 ARQ – the decoding of a re-transmitted RLC block does not take into account the previously
transmitted versions of this same RLC block. It is always used in GPRS.
o Type 2 hybrid ARQ (used only in EGPRS) – also known as Incremental Redundancy (IR), it is always
used in downlink EGPRS and for uplink, in B9, it can be activated by a flag. This mechanism works
as follows:
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o The first emission of the RLC block is done with a first puncturing scheme (PS1).
o If the RLC block needs to be retransmitted, the same MCS or a MCS from the same family
will be used. The block may or may not be re-segmented (depending on parameterisation).
The transmitter will also select the Puncturing Scheme to use.
o The receiver will use the information in all versions of the received block to increase its
decoding probability.
Note that 3GPP states that:
o IR is mandatory in MS’s receiver;
o There is no way to activate/de-activate IR in the MS receiver by signalling over the air-interface – IR
can only be de-activated in the case of insufficient memory in the mobile;
o The soft combining can be done between MCSx and MCSx blocks (same MCS used), a MCS9 and a
MCS6 block (RLC data blocks with the same number of payload units) or between a MCS7 block and
a MCS5 block (RLC data blocks with the same number of payload units).
The RLC Window management also changes in EDGE. While in GPRS the RLC window size is fixed at 64
blocks, in EDGE:
o It is variable and determined for each TBF depending on the MS multi-slot class;
o It varies between 64 and 1024 blocks (512 blocks in Alcatel-Lucent implementation);
o It is increased following an increase on the number of PDCH’s, but not decreased in the case of a
reduction.
2.2 HARDWARE AND POWER ASPECTS
In terms of HW compatibility, EDGE is available (i.e. 8-PSK is supported) in all TRE from G4 (also called TRA)
onward.
In all cases the output power available in GMSK is always greater than in 8-PSK – this is due to design issues
concerning the fact that GMSK is a constant envelope modulation, while 8-PSK is not. Table 2 presents the
output powers of the different EDGE capable TRE’s available.
Table 4: Power characteristics from the different available TRA (EDGE capable TRE’s).
TRA GMSK output power 8-PSK output power 8-PSK output power
(EDGE+ TRA)
900 Medium power 45 W / 46.5 dBm 15 W / 41.8 dBm 30 W / 44.8 dBm
900 High power 60 W / 47.8 dBm 25 W / 44 dBm 30 W / 44.8 dBm
1800 Medium power 35 W / 45.4 dBm 12 W / 40.8 dBm 30 W / 44.8 dBm
1800 High power 60 W / 47.8 dBm 25 W / 44 dBm 30 W / 44.8 dBm
Because GMSK output power is often different from 8-PSK output power, there is a new concept introduced
with EDGE – the Average Power Decrease (APD).
According to the 3GPP specs, there are some constraints on this parameter when the TRE responsible for
the EDGE service is also carrying the BCCH. [3] it states that:
“Furthermore, 8-PSK modulated timeslots on the BCCH carrier may use a mean power which is at most 4 dB
lower than the mean power used for GMSK modulated timeslots, with the exception of the timeslot
preceding a slot used for BCCH/CCCH where at most 2 dB lower mean power is allowed.” (3GPP 45.008
5.i.0, section 7.1)
3GPP also predicts some specific problems for fast moving mobiles, in [3]:
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“In the case that 8-PSK modulation is allowed on the BCCH carrier and frequency hopping including the
BCCH carrier is used, the reception quality in connected mode for some fast moving MS (meaning MS
experiencing Doppler frequencies of 100 Hz or more) may be degraded. This may be seen as a backwards
compatibility problem for some existing MS, most likely occurring if the used APD is larger than 2 dB.
”(3GPP 45.008 5.i.0, section 7.1)
The field tests performed didn’t show any negative impact, which just confirms that only older mobiles are
prone to have problems, we can say that:
It is possible to use normally the BCCH TRX for EDGE without any re-configuration or output power
modification.
2.3 ENHANCED TRANSMISSION RESOURCE MANAGEMENT
The Enhanced Transmission Resource Management is a feature which assembles 4 sub-features. These sub-
features fit together to create the new transmission concepts brought by B9.
2.3.1 M-EGCH STATISTICAL MULTIPLEXING
The definition of an M-EGCH link (Multiplexed Enhanced GPRS CHannel) is a bi-directional link defined per
TRX and established between the MFS and the BTS. The M-EGCH link is a set of 16kbits/s GCH and its size is
dynamic depending of the GCH established number. The algorithms to dynamically decrease or increase the
size of an M-EGCH link correspond to the Dynamic Abis allocation.
The M-EGCH link of a TRX is necessary:
o To carry TBF traffic and PACCH signalling when TBFs are established on some PDCHs of the TRX,
o To carry signalling messages when MPDCHs are defined on the TRX,
o To carry UL signalling messages after one-UL-block allocation (UL two-phase access),
o To carry some BTS-MFS signalling.
The next figure explains the evolution between B8 and B9 release. The EGCH defined per RTS (PDCH) is
swapped by the new concept of the M-EGCH link per TRX, defined in B9. This enhancement allows the
dynamic of the GCHs among the PDCHs of a TRX. With the change, it is possible to have better reuse of the
existing resources.
Figure 2–1: B8 release EGCH vs B9 release M-EGCH
B8: one EGCH per RTS B9: one M-EGCH link for the whole TRX
0 1 7 6 2 3 4 5
EGCH
0 1 7 6 2 3 4 5 TRX
M-EGCH link
1 to 36 GCHs
composed of
GCH
EGCH
EGCH
EGCH
EGCH
EGCH
EGCH
EGCH
GCH
GCH
GCH
GCH
1 to 5 GCHs depending on the TRX class
GCH
composed of
GCH
GCH
GCH
GCH
TRX
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The location of the M-EGCH and L1-GCH layers is show in the figure below. The M-EGCH layer offer a service
of data transport to the upper layer the RLC/MAC layer.
Figure 2–2: M-EGCH and L1-GCH layers location
The way the RLC/MAC PDU are filling an M-EGCH link is explained by the next figure.
Figure 2–3: GCH filling with RLC/MAC PDUs
In this example 2 RLC/MAC PDUs are not enough to fill the 5 GCH, therefore the M-EGCH fills it with
padding bits or with a dummy message. Important to mention is the dynamic of the process which lead to a
RLC header
MEGCH header (next segments)
MEGCH header (first segment)
SYNC pattern + Z bit indicator
Padding bits
CRC + Tail bits
MEGCH header (/NHP and addr byte)
Dummy Filling PDU
LEGEND
320 bits 320 bits 320 bits
320 bits
20 ms 20 ms 20 ms
GCH1
GCH2
GCH3
GCH4
RLC/MAC PDU 1 for DBN=x
320 bits
GCH5 Dummy Filling PDU
Dummy Filling
Dummy Filling
Dummy Filling
RLC/MAC PDU 2 for DBN=x
DBN=x+1DBN=x DBN=x+2
MEGCH layer segmentation
sub-layer
RLC/MAC layer
MEGCH layer
framing sub-layer
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better bandwidth usage. The RLC/MAC PDU is segmented through several M-EGCH frames and one M-EGCH
can transport segments from different RLC/MAC PDUs.
In B8, due to the static approach the number of GCHs needed per PDCH was higher than in B9, see next two
tables.
Table 5: Number of GCH per GPRS coding scheme.
Max_GPRS_CS Nb_GCH in
B8 Nb_GCH in
B9
CS-1 1 0,73
CS-2 1 1,00
CS-3 2 1,25
CS-4 2 1,64
Table 6: Number of GCH per EGPRS coding scheme.
Max_EGPRS_MCS Nb_GCH in
B8 Nb_GCH in
B9
MCS-1 1 0,89
MCS-2 1 1,00
MCS-3 2 1,33
MCS-4 2 1,50
MCS-5 2 1,86
MCS-6 3 2,36
MCS-7 4 3,49
MCS-8 4 4,14
MCS-9 5 4,49
The dynamic transportation of the RLC/MAC PDU brings a more efficient resource usage also due to:
o Instantaneous reaction to radio variations (MCS variations).
o The resources not used by delayed DL TBFs, extended UL TBFs, … are used by other TBFs.
2.3.2 DYNAMIC ABIS ALLOCATION
In B8, the Abis interface has a static allocation of the Abis nibbles (basic + extra) into the RTS. They can
only be used in the EGCH of this RTS, several Abis nibbles are wasted due to the static allocation.
The 64 kbit/s extra Abis TS are mapped per TRX creating the TRX class concept.
As example of the waste of Abis nibbles in B8, for a TRX class 2, there is the next figure:
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Figure 2–4: Abis resources concept in B8
In this B8 release example, 50% of the Abis resources are wasted, in B9 all the Abis nibbles can be used, as
explained after.
In B9, the following Abis nibbles are usable for PS traffic:
o The basic Abis nibbles mapped to a RTS currently available for PS traffic (see “Autonomous Packet
Resource Allocation" feature to know the list of those RTSs) or mapped to a RTS used as MPDCH.
o The “bonus” basic Abis nibbles are the ones not used by the BCCH or static SDCCH channels, these
channels are mapped in the RSL TS. Depending on the cell configuration more or less “bonus” Abis
nibbles are available.
o All the extra Abis nibbles of the BTS, can be used by the PS. A number of 64k extra Abis TSs
(4x16kbit/s extra Abis nibbles) is defined for each BTS by O&M (N_EXTRA_ABIS_TS). The list of extra
Abis TSs of a BTS is provided by the BSC to the MFS.
To have a better view of the B9 dynamic Abis concept, see the follow example applied in B9:
Figure 2–5: Abis resources concept in B9
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The 16kbit/s Abis nibbles can be used/shared between M-EGCH link, the share follows specific rules
depending the Abis nibble type:
o The basic Abis nibbles mapped on a RTS allocated to MFS can be used in the M-EGCH link of any TRX
of the CELL.
o The extra Abis nibbles can be used in the M-EGCH link of any TRX of the BTS.
o The “bonus” Abis nibbles can be used in the M-EGCH link of any TRX of the BTS.
This new algorithm/concept leads into a modification of the GCH establishment and release. Two new
scenarios to distribute GCH resources are created:
o Intra-cell GCH pre-emption : between TRXs of a cell
o Inter-cell GCH pre-emption : between cells of a BTS
To be able to implement the dynamic Abis algorithm new signalling messages were created, they are sent to
the BTS via GSL and RSL interface to notify each TRE which Abis nibbles are associated.
2.3.3 ATER RESOURCE MANAGEMENT
In this sub-chapter is resumed the Ater resource management in load situation, anticipation and defence
mechanism. A strong requirement, in B9 implementation, is to ensure GPRS access in all the cells of the
GPU (no cell shall be blocked due to Ater congestion).
In a given GPU the resource management is based on two complementary algorithms:
o GPU Ater TS margin
o “High Ater usage” handling.
GPU 64KBIT/S ATER TS MARGIN
The aim of the GPU Ater TS Margin, managed in each GPU, is to ensure that priority requests can never be
blocked in a cell due to a lack of Ater resources in the GPU.
The priority requests are the GCH establishment requests for the “first PS traffic in a cell” (first TBF to
establish in a cell). E.g when the first One-UL-Block or best-effort TBF has to be established in a cell.
The GPU Ater TS Margin mechanism is trigger to release some GCHs when the remaining number of free 64k
Ater TSs in the GPU becomes lower than a threshold defined by the parameter N_ATER_TS_MARGIN_GPU.
The parameter N_ATER_TS_MARGIN_GPU is defined in the O&M and can be tunable.
HIGH ATER USAGE HANDLING
The Ater usage of a GPU represents the consumption of Ater nibbles (by GCH channels) among the PCM links
connected to the GPU. The state of the Ater usage can be either “normal” or “high”.
The decision to evaluate the Ater usage state is based on the comparison of the Ater nibble consumption
with a threshold. This threshold is the O&M parameter Ater_Usage_Threshold.
If Ater usage is “high”, there is an impact in the packet switch transmission resources. The Target_Nb_GCH
values associated to TRXs of the GPU supporting some PS traffic will be reduced, taking in account the
parameter GCH_RED_FACTOR_HIGH_ATER_USAGE.
The reduction factor is only applied on PDCHs newly open, e.g. no radio resources were previously
allocated on this PDCH.
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In the next example the reduction method is presented:
1)Hypothesis:
o Max_EGPRS_MCS = MCS-9,
o GCH_RED_FACTOR_HIGH_ATER_USAGE = 0,5
2) Ater usage = “normal”
3) Establishment of an EGPRS DL TBF on RTS0-3
o Target_Nb_GCH = 4 * Nb_GCH(Max_EGPRS_MCS) = 4 * 4,49 = 18
4) Ater usage = “high”
5) Establishment of an EGPRS DL TBF on RST4-7
(Ater usage high and newly open PDCH => reduction will be applied)
o Target_Nb_GCH =
• = 4 * Nb_GCH(Max_EGPRS_MCS) + 0,5 * 4 * Nb_GCH(Max_EGPRS_MCS) =
• = 4 * 4,49 + 4 * 0,5 * 4,49 = 27 (< 36)
2.3.4 DL RETRANSMISSION IN THE BTS
The feature DL Retransmission in the BTS was developed with the aim to avoid consuming transmission
resources (Abis + Ater) in case of DL RLC data block retransmissions.
The principles of the feature is simple, the DL RLC data blocks, received from the MFS to a MS, are store in
a buffer. These blocks are keeped in the memory of the TRE involved in the packet transfer mode with the
MS, during a pre-define period. Then, if Dl retransmission is needed, the RLC/MAC layer (in the MFS) ask
the TRE (in the BTS) to retransmit the specific DL RLC data blocks.
This mechanism is enabled / disabled at TRX/TRE level, however respecting the following constrains
specified in the next table:
Table 7: DL retransmission constrains.
HW generation of the TRE
CS-2 CS-4 CS-4+MCS-9 EN_DL_RETRANS_BTS Round_Trip_Delay
(DRFU) (G3 or M4M) (G4 or M5M)
Enabled < 500 ms Disabled Disabled Enabled
Enabled ≥ 500 ms Disabled Disabled Disabled
Disabled - Disabled Disabled Disabled
2.4 AUTONOMOUS PACKET RESOURCE ALLOCATION (RAE4)
Before the explanation of the new B9 resource allocation a brief review of the B8 resource allocation is
done.
In B8, the BSC evaluates the maximum number of timeslots (load indication) that the MFS could use to carry
PS traffic (Max_SPDCH_Dyn). This value is sent periodically to the MFS, however the MFS does not have the
information of which timeslots are usable for PS traffic, it just knows the number. To serve a new TBF, MFS
needs to request new timeslots mapping to the BSC. This “Event-triggered” mechanism creates delays in
the PS access time.
With the introduction of the Enhanced Transmission Resource Management feature in B9, a new resource
allocation was developed. This new algorithm is named Autonomous Packet Resource Allocation (RAE4) and
allows taking all the benefit of the new B9 concepts.
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The development took in consideration the following new needs:
o Need to know the list of basic Abis nibbles which are currently available to establish GCHs,
o Need to know which basic Abis nibbles are preemptable / not-preemptable for CS traffic by the
BSC. This information is useful:
• For the QoS feature (in order to be able to ensure a given GBR for an RT PFC).
• To define some priorities in the Abis nibble selection (preference is given to the non-
preemptable basic Abis nibbles in order to limit the interaction of CS over PS traffic).
o Need to accelerate TBF establishment times (the B8 round trip delay between MFS and BSC to
allocate some PDCHs can be avoided).
In the Autonomous Packet Resource Allocation (RAE4) algorithm the BSC evaluates the CS and PS load at cell
level and calculates a number of timeslots that the MFS can use to carry PS traffic (Max_SPDCH_Limit). The
resources sharing between the CS and the PS is then based on the evaluation of Max_SPDCH_Limit.
The Max_SPDCH_Limit value is a comprised value between the Min_SPDCH and the Max_SPDCH and takes in
account the O&M parameters (Max_PDCH, Min_PDCH, Max_PDCH_HIGH_LOAD, HIGH_TRAFFIC_LOAD_GPRS,
THR_MARGIN_PRIO_PS).
Exists a periodical exchange of messages between the BSC and the MFS, with the aim to inform the MFS
which timeslots can be used to serve a new TBF and to inform the BSC of the present status of PS allocated
resources.
The periodical exchange of messages has the following information:
o RR Allocation Indication message from BSC to MFS: provide to the MFS the mapping of the allocated
SPDCHs, the periodicity of this message is TCH_INFO_PERIOD * RR_ALLOC_PERIOD.
o RR Usage Indication message from MFS to BSC: With a periodicity of TCH_INFO_PERIOD or in
response of the previous message RR Allocation Indication message, informs the BSC with the
current usage of the allocated SPDCHs.
CELL LOAD EVALUATION
The BSC evaluates for each cell the CS and PS load, the process starts with the calculation of the current
usage of the resources, e.g a sample of the current usage on TCH, TCH/SDCCH and TCH/SPDCH TS. This
cyclic process is done every TCH_INFO_PERIOD.
Figure 2–6: Cyclic calculation of the usage of the cell resources
The TCH usage samples calculate by the BSC every TCH_INFO_PERIOD are map in the internal parameters:
o NB_USED_CS_TS(k) - SPDCH State is deallocated
o NB_USED_PS_TS(k) - SPDCH State is allocated or de-allocating
o NB_USED_TS(k) = NB_USED_CS_TS(k) + NB_USED_PS_TS(k)
o NB_UNUSED_TS(k)
TCH_INFO_PERIOD = 5s NB_USED_CS_TS(k) NB_USED_PS_TS(k) NB_USED_TS(k)
NB_UNUSED_TS(k)
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Every RR_ALLOC_PERIOD * TCH_INFO_PERIOD, the BSC computes three averaged values through a sliding
window of size LOAD_EV_PERIOD_GPRS (default value = 3), these averages of the previous internal
parameter give the following internal parameters, used to calculate Max_SPDCH_Limit:
o AV_USED_CS_TS(k)
o AV_USED_PS_TS(k)
o AV_UNUSED_TS(k)
Figure 2–7: Cyclic calculation of the average usage of the cell resources
MAX_SPDCH_LIMIT CALCULATION
The calculation of the Max_SPDCH_Limit follows the diagram below:
Figure 2–8: General diagram of the Max_SPDCH_Limit calculation
TCH_INFO_PERIOD = 5s
AV_USED_CS_TS(k) AV_USED_PS_TS(k) AV_UNUSED_TS(k)
NB_USED_CS_TS(k) NB_USED_PS_TS(k) NB_USED_TS(k) NB_UNUSED_TS(k)
k k-k-
LOAD_EV_PERIOD_GPRS = 3
k+ k+
AV_USED_CS_TS(k+2) AV_USED_PS_TS(k+2) AV_UNUSED_TS(k+2)
RR_ALLOC_PERIOD * TCH_INFO_PERIOD
MAX_SPDCH_HIGH_LOAD
Computation of CS/PSMargin
AV_USED_CS_TSAV_USED_PS_TSAV_UNUSED_TSNB_TS_DEFINED
NB_TS_SPDCH
Computation ofThresholds
THR_MARGIN_PRIORITY_CSTHR_MARGIN_PRIORITY_PS
NB_TS
MARGIN_PRIORITY_CSMARGIN_PRIORITY_PS
Computation ofMAX_SPDCH_LIMIT
MAX_PDCH_HIGH_LOADMAX_PDCHMIN_PDCH
NB_TS_MPDCH
MAX_SPDCH_LIMIT
MIN_SPDCHMAX_SPDCH
O&M parameters
O&M parameter
= 100 – HIGH_TRAFFIC_LOAD_GPRS
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1) Computation of thresholds
The calculation of MIN_SPDCH, MAX_SPDCH and MAX_SPDCH_HIGH_LOAD is done every RR_ALLOC_PERIOD *
TCH_INFO_PERIOD to take into account possible TRX failures. The O&M parameters (MIN_PDCH, MAX_PDCH
and MAX_PDCH_HIGH_LOAD) are multiply by the ratio:
o AVAILABILITY_TS_RATIO(k) = NB_TS(k) / NB_TS_DEFINED
Where:
NB_TS: Total number of TCH/VGCH, TCH/SDCCH, or TCH/SPDCH/VGCH timeslots available in the cell. This
parameter is re-computed every RR_ALLOC_PERIOD * TCH_INFO_PERIOD to take into account possible TRX
failure.
NB_TS_DEFINED: total number of TCH, TCH/SDCCH or TCH/SPDCH timeslots available in the cell if there is
no TRX failure. This parameter is retrieved from the O&M configuration of the cell.
In case there isn’t master channel (NB_TS_MPDCH=0) and there is no TRX failure
(AVAILABILITY_TS_RATIO=100%) then there is simply:
o MAX_SPDCH_HIGH_LOAD = MAX_PDCH_HIGH_LOAD
o MIN_SPDCH = MIN_PDCH
o MAX_SPDCH= MAX_PDCH
2) Computation of CS/PS Margin
Two new margins, one for CS traffic and one for PS traffic are introduced to guarantee that a certain
number of timeslots are kept available for the arrival of new calls between two transmissions of the RR
Allocation Indication message:
o the first margin, named MARGIN_PRIORITY_CS (k), is dedicated to CS traffic
• = (THR_MARGIN_PRIO_CS * (NB_TS(k) – MAX_SPDCH_HIGH_LOAD(k)) / 100
o the second margin, named MARGIN_PRIORITY_PS(k), is dedicated to PS traffic
• = (THR_MARGIN_PRIO_PS * MAX_SPDCH_HIGH_LOAD(k)) / 100
Where:
THR_MARGIN_PRIO_PS is O&M parameter, It is the margin of radio timeslots reserved for PS traffic between
two sendings of the BSCGP RR Allocation Indication messages. The threshold is expressed in percentage of
radio timeslots. This margin only applies in case of high CS load and low PS load.
THR_MARGIN_PRIO_CS is equal to the 1- High_Traffic_ Load_GPRS.
High_Traffic_ Load_GPRS: Load threshold used to determine a certain margin of radio timeslots reserved for
CS traffic between two sending of the BSCGP RR Allocation Indication messages. The threshold is expressed
in percentage of the radio timeslots available in the cell.
These two margins are re-evaluated every RR_ALLOC_PERIOD * TCH_INFO_PERIOD, before the computation
of MAX_SPDCH_LIMIT
3) Computation of MAX_SPDCH_LIMIT
The basic idea to evaluate MAX_SPDCH_LIMIT is to estimate the number of unused TS and to share them
between CS and PS traffic, taking into account both margins (for CS and PS traffics) defined to guarantee a
certain number of TS available to serve incoming calls.
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Figure 2–9: Detailed diagram of the Max_SPDCH_Limit calculation
3.1) Computation of MAX_SPDCH_LIMIT_CS
The MAX_SPDCH_LIMIT_CS determines the maximum number of SPDCHs that can be allocated to the MFS in
order to ensure that a certain number of timeslots (margin) is kept in the BSC to serve possible incoming CS
requests, received between two sends of the RR Allocation Indication message. It is given by:
o MAX_SPDCH_LIMIT_CS(k) = RoundDown [ NB_TS(k) – AV_USED_CS(k) - MARGIN_CS(k) ]
Where:
o MARGIN_CS(k) = max(MARGIN_PRIORITY_CS(k), AV_UNUSED_TS(k) / 2)
3.2) Computation of MAX_SPDCH_LIMIT_PS
The MAX_SPDCH_LIMIT_PS determines the minimum number of SPDCHs that should be allocated to the MFS
in order to ensure that a certain number of timeslots (margin) is kept in the MFS to possibly serve incoming
PS requests.
If AV_USED_PS_TS(k) ≤ MIN_SPDCH then
o MAX_SPDCH_LIMIT_PS(k) = MIN_SPDCH(k)
else
o MAX_SPDCH_LIMIT_PS(k) = RoundUp (AV_USED_PS_TS(k) + MARGIN_PRIORITY_PS(k))
3.1) Computation of MAX_SPDCH_LIMIT
The MAX_SPDCH_LIMIT calculation can be in the range of [MIN_SPDCH, MAX_SPDCH] and its value can be
either MAX_SPDCH_LIMIT_CS or MAX_SPDCH_LIMIT_PS.
Computation ofMAX_SPDCH_LIMIT_CS
MARGIN_PRIORITY_CS
AV_USED_CS_TS(k)AV_UNUSED_TS(k)
MAX_SPDCH_LIMIT_CS(k)
Computation ofMAX_SPDCH_LIMIT_PSAV_USED_PS_TS(k)
MAX_SPDCH_LIMIT_PS(k)
MIN_SPDCHMARGIN_PRIORITY_PS
Computation ofMAX_SPDCH_LIMIT
MAX_SPDCHMAX_SPDCH_HIGH_LOAD
MAX_SPDCH_LIMIT(k)
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Figure 2–10: Max_SPDCH_Limit CS and PS zones
MAX_SPDCH_LIMIT TS SELECTION
Every TCH_INFO_PERIOD * RR_ALLOC_PERIOD, the BSC sent to MFS the Radio Resource Allocation Indication
message. This message contains the SPDCHs Allocation bitmap, e.g the information whether a timeslot is
allocated to the MFS or not. In response to the RR Allocation Indication message or every
TCH_INFO_PERIOD, the MFS sent to BSC the Radio Resource Usage Indication message.
The RR Usage Indication message contains 3 different bitmaps, the analysis of the bitmaps gives the present
status of the timeslots:
o The SPDCHs_Confirmation bitmap is used to update the SPDCH allocation state of each timeslot.
o The SPDCHs_Usage and SPDCHs_Radio_Usage bitmaps allow to update the occupancy state of the
timeslot at “unused” or “used” (from radio and/or transmission point of view for the SPDCHs_Usage
bitmap and from radio point of view only for the SPDCHs_Radio_Usage bitmap).
The TS selection, e.g the Radio TCH allocation, uses the TRX ranking table. This table takes in account both
HW capability and design O&M parameters. The way to set the priority of the PS capable TRX
(TRX_PREF_MARK = 0) is slightly modified in B9 release with the introduction of a frequency band criterion:
o PS_PREF_BCCH_TRX
o HW TRE capability (G4 HP -> G4 MP -> G3)
o DR TRE capability (FR TRX -> DR TRX)
o E-GSM TRX preference (new in B9, E-GSM TRX -> P-GSM/GSM850/DCS TRX)
o TRX having the maximum number of consecutive SPDCHs
o TRX identity (low TRX id -> high TRX id)
With the PS capable TRX list performed, the next step consists in ordering the PS timeslots and the PS
capable TRX, to obtain an ordered list of TCH/SPDCH timeslots. The selection of the TRX is done, selecting
first the TRX having the lowest rank in the TRX ranking table. Once the TRX has been selected, the
Zone where MAX_SPDCH_LIMIT = MIN( MAX_SPDCH,
MAX_SPDCH_LIMIT_CS)
Zone where MAX_SPDCH_LIMIT = MIN (MAX_SPDCH_LIMIT_PS,
MAX_SPDCH_HIGH_LOAD)
0
MAX_SPDCH
MAX_SPDCH_HIGH_LOAD
MIN_SPDCH
MIN_SPDCH
MAX_SPDCH_LIMIT_CS
MAX_SPDCH_HIGH_LOAD MAX_SPDCH
MAX_SPDCH_LIMIT_PS
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TCH/SPDCH timeslots is selected preferentially to the lowest timeslot index, i.e. the one located at the
most left side of the TRX is selected first.
The SPDCHs are allocated according to the different PS TS zones, the zones definitions are:
o MAX_SPDCH_HIGH_LOAD zone: this zone corresponds to the MAX_SPDCH_HIGH_LOAD consecutive PS
capable TS that are preferred for PS allocation. In this zone, allocated TBFs cannot be pre-empted
o Non pre-emptable PS zone: this zone is always inside the MAX_SPDCH_HIGH_LOAD zone, in this
latter zone, we search for the right most TS allocated to the MFS and used, then all the TS located
at its left define the non pre-emptable PS zone. Inside this zone, a TS:
• remains allocated to the MFS if already allocated to the MFS
• is allocated to the MFS if previously allocated to the BSC and unused
• remains allocated to the BSC if already allocated to the BSC and used
o MAX_SPDCH_LIMIT zone: this zone corresponds to the MAX_SPDCH_LIMIT consecutive PS capable TS
that are preferred for PS allocation. Inside this zone, a TS:
• remains allocated to the MFS if already allocated to the MFS
• is allocated to the MFS if previously allocated to the BSC and unused
• remains allocated to the BSC if already allocated to the BSC and used
o PS traffic zone: this zone corresponds to the larger zone between the non pre-emptable PS zone
and the MAX_SPDCH_LIMIT zone
As examples of the PS TS zones follows the next two:
Example 1: MAX_SPDCH_HIGH_LOAD = 8, MAX_SPDCH_LIMIT = 10
Figure 2–11: PS TS zones – example 1
This feature should be enhanced, so that the number of allocated PDCH corresponds to MAX_SPDCH_LIMIT
Example 2: MAX_SPDCH_HIGH_LOAD = 8, MAX_SPDCH_LIMIT = 3
Figure 2–12: PS TS zones – example 2
TRX2 TRX11 3 42 5 6 7 8 9 10 1211 13 14 15 16
MAX_SPDCH_LIMIT zone
PS CSPS CS CSCS CS
MAX_SPDCH_HIGH_LOAD zone
PS PS PS PS
Non pre-emptable PS zone
PS traffic zone
TRX2 TRX11 3 42 5 6 7 8 9 10 1211 13 14 15 16
MAX_SPDCH_LIMIT zone
PS CSPS CS CSCS CS
MAX_SPDCH_HIGH_LOAD zone
PS CS CS
Non pre-emptable PS zone
PS traffic zone
CS
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The selection of the TCH/SPDCH TS begins with the non pre-emptable PS zone. All the TS in this zone, that
can be or are allocated to the MFS, will be allocated to the MFS. The verification in terms of number of TS
allocated to the MFS is done only when all the TS inside this zone have been handled. If at the end of the
non pre-emptable PS zone, the number of selected TS for the MFS is strictly lower than MAX_SPDCH_LIMIT
then the process of selection continues in the MAX_SPDCH_LIMIT zone
If at the end of the MAX_SPDCH_LIMIT zone, the number of selected TS for the MFS is still lower than
MAX_SPDCH_LIMIT, the process continues outside this zone until this number reaches MAX_SPDCH_LIMIT.
Once MAX_SPDCH_LIMIT TS have been selected, all the remaining TCH/SPDCH TS are now allocated to the
BSC, even if they were previously allocated to the MFS. This means that a TS with a SPDCH allocation state
set to “allocated” has its SPDCH allocation state set to “de-allocating”.
To improve the SPDCH allocation, two parallel algorithms to PS TS selection exist:
1) Pre-reservation mechanism in the PS traffic zone:
In order to increase the PS capacity and limit the occurrence of holes in the SPDCHs_Allocation bitmap,
each TCH/SPDCH capable TS carrying CS traffic and located inside the PS traffic zone, has its pre-
reservation state set to “pre-reserved for PS”. No new incoming CS call can be served on this TS, if it
becomes unused once it is “pre-reserved for PS”. This is valid until the TS becomes “not pre-reserved for
PS” again and of course still handled by the BSC. The modification of the value of the pre-reservation state
can only occur when the SPDCHs_Allocation bitmap is built, every TCH_INFO_PERIOD * RR_ALLOC_PERIOD
seconds.
2) CS calls in the Non pre-emptable PS zone:
To speed up the release of TS carrying a CS call inside both the non pre-emptable PS zone and the
MAX_SPDCH_LIMIT zone, it is proposed to reallocate the concerned CS call in the CS zone using an intra-cell
handover.
If EN_RETURN_CS_ZONE_HO = enabled, each time MAX_SPDCH_LIMIT is calculated, the BSC shall check
whether TCHs are allocated in both the MAX_SPDCH_LIMIT zone and the non pre-emptable PS zone. In this
case, it shall send a ‘Start HO (cause 30)” message to the HO Preparation entity, to trigger an intracell
handover, to move these TCHs into the CS zone
If for any reason, the handover fails, the TCH will remain in the PS zone, until the next calculation of
MAX_SPDCH_LIMIT, where a new HO could be triggered, if still needed.
The TS will be considered as unused only once the handover will have been successfully performed. As the
pre-reservation state of such TS is set to “pre-reserved for PS”, no new incoming CS call can be allocated
on it.
CS PREEMPTION PROCESS
The CS pre-emption process is triggered when some radio TS are reported by the BSC as no longer allocated
to the MFS. The principle can be explained by 5 steps:
1. MFS receives a RR Allocation Indication message from the BSC, and uses the SPDCHs_Allocation
bitmap to determine which SPDCHs shall be given back to the BSC
2. then, MFS shall immediately send a RR Usage Indication message to the BSC with the
SPDCHs_Confirmation bitmap
• SPDCHs not used are immediately given back to the BSC (Note : SPDCHs are considered not
used if no TBF resources are allocated on those SPDCHs and their basic Abis nibbles are
free). The associated basic Abis nibbles are also given back and others TBFs using these
basic Abis nibbles can be impacted (see below).
3. After RR Usage Indication, TCH_INFO_PERIOD timer is restarted. Remaining impacted SPDCHs,
which are in use (at least one TBF is established on those SPDCHs or the basic Abis nibbles of those
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SPDCHs are used by a GCH channel), are marked as “de-allocating”.
4. The CS pre-emption process shall be completed before the TCH_INFO_PERIOD expiry, in order to
confirm the deallocation of all the remaining pre-empted SPDCHs in the next RR Usage Indication
message to be sent to the BSC. For that purpose, the internal T_PDCH_Preemption timer is set to
TCH_INFO_PERIOD - 1s
5. When T_PDCH_Preemption expires, the fast preemption is launched.
Then, once the impacted best-effort TBFs have been determined, the following steps shall be played in
sequence:
1) TBF release in case of too high number of TBFs
If, due to the CS preemption, the number of best-effort TBFs established on a TRX will become too high
according to the remaining number of GCHs in the M-EGCH link of the TRX, then some best-effort TBFs shall
be released (in order to guarantee that the T_MAX_FOR_TBF_SCHEDULING constraints / the PACCH
signalling traffic constraints will still be possible to fulfil for all the remaining best-effort TBFs established
on the TRX).
On a given TRX, the number of TBFs to be released in the XL direction is called Nb_TBFs_To_Release_XL.
The Nb_TBFs_To_Release_XL TBFs which shall be released are selected as follows:
o Release preferentially the best-effort XL TBFs which are impacted by the CS preemption (i.e. the
best-effort TBFs established in the XL direction and whose PACCH is impacted or whose on-going
max allowed (M)CS is no longer possible to serve).
o Then, release preferentially the best-effort XL TBFs which were established (or reallocated) on the
TRX the most recently (i.e. the “newest” best-effort TBFs established in the XL direction on the
TRX).
2) T1 TBF reallocation
The not released TBFs are attempted to be T1 reallocated (soft-preemption process).
Figure 2–13: T1 reallocation
The TBFs impacted by the CS preemption are managed by the soft preemption process, the impacted best-
effort TBFs are:
o The best-effort TBFs having their PACCH impacted, i.e. their PACCH is supported by a preempted
RTS (that case is valid for both Evolium and DRFU BTSs),
o The best-effort TBFs for which it will no longer be possible to serve their on-going max allowed
(M)CS because of the subsequent reduction of the M-EGCH link size of their TRX. Note: the M-EGCH
DL
0 1 2 3 4 5 6 7
UL
0 1 2 3 4 5 6 7
No T1 candidate
T1 candidate
M-EGCH EGPRS TBF
TRX
2 preempted GCHs Max_EGPRS_MCS = MCS9 ⇒ 5 GCHs needed
4 GCHs
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links whose size will be reduced can be on the TRX containing the preempted RTSs or on any of the
other TRXs of the cell (because basic Abis nibbles are shareable among all the TRXs of the cell).
2.5 M-EGCH LINK MANAGEMENT
2.5.1 DEFINITIONS
The following concepts are used in the M-EGCH link management:
o TRX capabilities for GPRS (maximum CS) and for EGPRS (EGPRS possible or not, maximum MCS) are
defined at MFS side using:
• HW PS capability for each TRX,
• Max_GPRS_CS O&M parameter,
• En_EGPRS O&M parameter,
• Max_EGPRS_MCS O&M parameter.
Table 8: HW PS capability
TRE generation HW PS capability of the TRX
G2 (TRE in a DRFU BTS) CS-1/2
G3 (TRE in an Evolium BTS) CS-1/4
G4 (TRE in an Evolium BTS) CS-1/4 + MCS-1/9
o TRX is said “established” if there is an M-EGCH link associated to this TRX with GCHs.
o Non CS Preemptable GCH: GCH, whose Abis nibble is not CS preemptable:
• Extra Abis nibble,
• “Bonus” Abis nibble,
• Basic Abis nibble mapped on a RTS inside the “Max_SPDCH_High_Load” zone.
o CS Preemptable GCH: GCH, whose Abis nibble is CS preemptable:
• Basic Abis nibble mapped on a RTS outside the “Max_SPDCH_High_Load” zone.
2.5.2 ABIS SELECTION IN M-EGCH LINK
When establishing new GCHs in the M-EGCH link of a given TRX, the free Abis nibbles are selected with the
following priorities:
1. Free basic Abis nibbles mapped to RTSs currently available for PS traffic and within the
Max_SPDCH_High_Load zone of the cell,
2. Free extra Abis nibbles and free bonus Abis nibbles,
3. Free basic Abis nibbles mapped to RTSs currently available for PS traffic and out of the
Max_SPDCH_High_Load zone of the cell.
If there aren’t enough free Abis nibbles, or free Ater nibbles, then GCH preemption will be used:
o The inter-cell GCH preemptions for PS traffic (the “source TRX” and the “target TRX” belong to two
different cells of the same BTS).
o The intra-cell GCH preemptions for PS traffic (the “source TRX” and the “target TRX” belong to the
same cell)
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2.5.3 M-EGCH LINK SIZE
As mention in the chapter 2.3.1 the M-EGCH link is defined per TRX, its size in the TRX is expressed in
number of GCHs. For each TRX, the following variables are defined:
o Established_Nb_GCH: Number of GCHs that are activated in the M-EGCH link.
o Established_Non_CS_Preemptable_Nb_GCH: Established_Nb_GCH when only GCHs using extra Abis
nibbles, bonus basic Abis nibbles and basic Abis nibbles mapped to RTSs within the non preemptable
PS zone of the cell are considered.
o Target_Nb_GCH: An estimation of the number of GCHs necessary in a given M-EGCH link to carry the
signalling and data PS traffic. A target number of GCHs, which may of course not be reached in
transmission resource (Abis and/or Ater) congestion situations.
• Target_Nb_GCH is a function of:
� Number of PDCHs on the TRX, on which radio resources have been allocated for BE
TBFs.
� Max_GPRS_CS and Max_EGPRS_MCS O&M parameter values.
� Number of GCH needed per PDCH for Max_GPRS_CS / Max_EGPRS_MCS
(Nb_GCH(Max_GPRS_CS / Max_EGPRS_MCS)).
� Whether Ater Usage in the GPU is high or not. If it is high, the value of
Target_Nb_GCH is reduced so as to decrease the global Ater resource consumption
in the GPU.
• The following example explains the Target_Nb_GCH evaluation for a EGPRS TBF and for
GPRS TBF (In this example, it is supposed that the Ater usage of the GPU is not “high”):
� M–EGCH link of a TRX supporting one 4-TS EGPRS TBF (Max_EGPRS_MCS = MCS-9)
• Target_Nb_GCH = 4 * 4.49 = 18 GCHs
� M-EGCH link of a TRX supporting one 4-TS GPRS TBF (Max_GPRS_CS = CS-4)
• Target_Nb_GCH = 4 * 1.64 = 7 GCHs
o Min_Nb_GCH: An estimation of the minimum number of GCHs, necessary in a given M-EGCH link, is
used as threshold when GCH preemption is performed. It ensures that all the TBFs established on
the TRX will always be able, on at least one PDCH, to send a Radio Block with their
Max_Allowed_(M)CS.
The Target_Nb_GCH and Min_Nb_GCH are updated at TBF allocation / reallocation and at TBF release.
A new M-EGCH link is established each time there is new PS traffic in a TRX without a M-EGCH link
established. It can also be due to the “Fast Initial PS Access” feature.
Some GCHs are added to an existing M-EGCH link, when new TBF is allocated on the TRX and
Target_Nb_GCH becomes strictly higher than Established_Nb_GCH. Also it can be due to the “Fast Initial PS
Access” feature or when performing the “Periodical GCH establishment” process.
2.5.4 PERIODICAL GCH ESTABLISHMENT PROCESS
A periodical GCH establishment process aims at periodically attempt to increase the M-EGCH link size of
TRXs, which have not yet reached their Target_Nb_GCH. It is defined in each cell of a BTS.
The “periodical GCH establishment process” allows:
o The usage of the recently freed Abis/Ater transmission resources in the BTS/GPU due to GCH
releases.
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o The usage of the free basic Abis nibbles mapped to RTSs out of the “non preemptable PS zone” of
the cell.
o To guarantee that, following some abnormal GCH releases, new GCHs will be established in the
impacted M-EGCH links.
o To guarantee a balance between the M-EGCH link sizes of the TRXs of a given cell after some TBFs
(established on those TRXs) have been released.
o To guarantee that some GCHs are inter-cell preempted towards the M-EGCH links of the cell. This
can be useful for example following the release of an RT PFC in another cell of the same BTS.
o To guarantee that some GCHs are always established for the “Fast Initial PS Access” feature
2.5.5 FAST INITIAL PS ACCESS
The aim of the feature Fast Initial PS Access is to speed up the TBF establishment time in a cell. It ensures
that one M-EGCH link is always established on the first TRX of the cell having some allocated TSs, i.e. for
the most PS-prioritary TRX of the cell having some TSs available for PS traffic. The feature is enabled at
cell-level with the EN_FAST_INITIAL_GPRS_ACCESS O&M parameter and the number of GCHs to establish on
this M-EGCH link is tunable by the N_GCH_FAST_PS_ACCESS system parameter.
2.5.6 HANDLING OF UNUSED GCH
When a TBF is released and Target_Nb_GCH of M-EGCH link becomes strictly lower than
Established_Nb_GCH, there is in the M-EGCH link (Established_Nb_GCH- Target_Nb_GCH) unused GCHs, e.g
established GCHs that are considered to be no more needed in the M-EGCH link.
Each time the previous condition happens, the T_GCH_Inactivity timer of the M-EGCH link is started. This
timer is useful to:
o “Anticipate” the arrival of new PS traffic on a given TRX.
o Provide some time for the “radio defragmentation” process to be completed in the cell (cf. T3 TBF
reallocations).
o Optimize ping times.
o Make the Ater nibbles of the released GCHs (on T_GCH_Inactivity timer expiry) usable by other
BTSs, or by other DSPs (if all the 4 nibbles of the 64k Ater TS are freed).
o If there is some PS traffic on another TRX in the cell while the T_GCH_inactivity timer is running,
then the “unused GCHs” can be intra-cell preempted to meet the GCH needs (if any) of that other
TRX. That avoids an Abis-Ater deswitching operation followed by a reswitching operation in the BSC.
This principle is only applicable to intra-cell GCH preemptions, not to inter-cell GCH preemptions.
At timer expiry, if Target_Nb_GCH is still strictly lower than Established_Nb_GCH, the unused GCHs are
released, the choice of GCHs to release is the reverse order than the one used for GCH establishment.
If the last TBF in the cell is released, a number of GCHs shall be kept established during the
T_GCH_Inactivity_Last time. The number of GCHs is defined at O&M by the parameter
N_GCH_Fast_PS_Access_GCH. Those GCHs will be useful in case of (E)GPRS traffic resumption in the cell
(when the “Fast Initial PS Access” feature is not enabled).
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Figure 2–14: Handling of unused GCHs
2.5.7 M-EGCH LINK CAPACITY DECREASE
There can be four reasons to have a M-EGH link capacity decrease, e.g a number of GCH is removed from an
M-EGCH link of a TRX:
o When a TBF is released and Target_Nb_GCH becomes strictly lower than Established_Nb_GCH
(unused GCHs and inactivity timer mechanism).
o GCH preemption: inter-cell and intra-cell.
o CS preemption: a basic Abis nibble used in the M-EGCH link is mapped on a RTS that must be given
back to the BSC (“CS preempted” RTS).
o Abnormal GCH release.
2.6 TBF RESOURCE ALLOCATION/REALLOCATION
In this chapter only Best-effort TBF (Non Real Time) resource allocation is considered.
2.6.1 TBF RESOURCE ESTABLISHMENT PROCESS
The TBF resource establishment process operates in two steps:
1. Radio Resource Allocation Algorithm: the objective of this algorithm is to find the best candidate
timeslot allocation and verify if enough transmission resource are available. This topic is discussed in
the next sub-chapter
2. TBF Establishment: if the RR allocation is performed then the TBF establishment is possible according
to the following conditions:
o TBF allocation policy:
• ASAP: used for BE (Best Effort) TBF establishment, T1, T2 and T4 reallocation. Its goal is to
serve the request as soon as possible.
� If it is possible, an ASAP request is served immediately on a TRX having already
Nb_GCH_For_TBF_Estab established GCHs. Otherwise, the establishment of
M-EGCH link
7 “used” GCHs
GCH1 B ≤ HL
GCH2 B ≤ HL
GCH3 B ≤ HL
GCH5 Extra
GCH4 Extra
GCH7 B > HL
GCH6 B > HL
Established_Nb_GCH = 10
3 “unused” GCHsGCH9 B > HL
GCH8 B > HL
GCH10 B > HL
Established_Nb_GCH = 7
Target_Nb_GCH = 7
M-EGCH link
7 “used” GCHs
GCH1 B ≤ HL
GCH2 B ≤ HL
GCH3 B ≤ HL
GCH5 Extra
GCH4 Extra
GCH7 B > HL
GCH6 B > HL
GCH1 B ≤ HL
GCH2 B ≤ HL
GCH3 B ≤ HL
GCH5 Extra
GCH4 Extra
GCH7 B > HL
GCH6 B > HL
Established_Nb_GCH = 10
3 “unused” GCHsGCH9 B > HL
GCH8 B > HL
GCH10 B > HL
Established_Nb_GCH = 10
3 “unused” GCHsGCH9 B > HL
GCH8 B > HL
GCH10 B > HL
GCH9 B > HL
GCH8 B > HL
GCH10 B > HL
Established_Nb_GCH = 7
Target_Nb_GCH = 7“B > HL”: GCH uses a basic Abisnibble mapped on a RTS out of the “non preemptable PS zone” of the cell.“Extra”: GCH uses an extra Abisnibble or a “bonus” basic Abis nibble.“B ≤ HL”: GCH uses a basic Abisnibble mapped on a RTS within the “non preemptable PS zone” of the cell.
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Nb_GCH_For_TBF_Estab GCHs on a TRX of the cell will be necessary to serve the
request.
• OPTIMAL: used for T3 reallocation. Its goal is to ensure that a significant bandwidth will be
offered to the MS upon T3 reallocation, even if it takes some time to establish all the
necessary GCHs
� All the possible GCHs (Target_Nb_GCH) are systematically requested to be
established before serving the request, and an “Optimal” request will only be
served if the total number of GCHs successfully established on the TRX is greater
than Nb_GCH_For_TBF_Estab (see below).
o Max allowed (M)CS determination of a TBF depends on the type of TBF (GPRS / EGPRS) and of the
direction of the TBF (UL / DL). It is limited by the:
The number of established GCHs: Nb_GCH
Table 9: Maximun allowed CS.
Nb_GCH Max_Allowed_CS
1 CS-2 (UL) / CS-1 (DL)
2 ≥ CS-4
Table 10: Maximun allowed MCS.
Nb_GCH Max_Allowed_MCS
1 MCS-2 (UL) / MCS-1 (DL)
2 MCS-5
3 MCS-6
4 MCS-7
5 ≥ MCS-9
• GPRS / EGPRS TRX capability
• Max_GPRS_CS and Max_EGPRS_MCS (O&M parameters)
Nb_GCH_For_TBF_Estab is the minimum number of GCHs which are required on the TRX (M-EGCH) to serve
the request.
Table 11: Number of GCH required on the TRX.
Type of request Policy Nb_GCH_For_Estab
TBF establishment (without concurrent) ASAP 1
TBF establishment (with concurrent) ASAP 1 to 5 (Max_Allowed_(M)CS of concurrent TBF)
T1 TBF reallocation ASAP 1
T4 TBF reallocation ASAP 1 to 2 (Max_Allowed_CS of concurrent TBF)
T3 TBF reallocation Optimal 1 to 5 (Max_Allowed_(M)CS of concurrent TBF)
2.6.2 RADIO RESOURCE ALLOCATION PRINCIPLES
The Radio Resource Allocation Algorithm is used to find the radio and transmission resources in the Evolium
BTS case for (E)GPRS best-effort TBF establishment and in the case of TBF reallocation.
The Radio Resource Allocation Algorithm aims to:
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o Find the best candidate timeslot allocation, depending on:
• Type of request (GPRS / EGPRS)
• Multislot class
• Bias
• Traffic type
o Compute the number of GCHs which can be established:
• With free Abis and Ater resources,
• With inter-cell GCH preemptions,
• With intra-cell GCH preemptions.
The next figure summarizes the radio resource allocation algorithm.
Figure 2–15: RAE4 diagram
The description can be done by four steps:
o Find the best candidate timeslot allocation (steps 2, 3 and 4)
o Verify if there are enough transmission resources (steps 1, 5 and 6)
TRX list sorted by BSC
DSP congestion state
candidate TS allocation
- rejected request - or L4 queuing - or L5/L6 queuing - or L7 queuing (11) - or try to change TBF mode EGPRS case (12)
Type of the TBF request
n_MS_requested n_MS_requested_concurrent
TRX list
MS class, Bias, Traffic type
Best-effort TBF allocation/reallocation request
Number of radio TSs determination
(3)
TRX list computing
(2)
Best candidate TBF allocation computation (4)
no candidate TS allocation
Cell Transmission Equity (5)
Available_Nb_GCH_With_Equity
Test if enough GCHs (6)
“Enough GCHs “
“ALLOC OK” case “ALLOC FAILED” case
Transmission Resource
Availability (1)
TFI/TAI/USF allocation (7)
Available_Nb_GCH
Transmission resource reservation (8)
“Not enough GCHs “
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o Allocate the radio resources (step 7)
o Reserve the transmission resources (step 8)
2.6.3 TRANSMISSION RESOURCE AVAILABILITY STEP
The goal of the Transmission resource availability is to compute the total number of new GCHs which are
possible to be established in a given cell. That number is called Available_Nb_GCH. The process is done by
two steps:
1. Compute the number of free Abis and Ater resources:
o Nb_Free_GCH = Min( Nb_Free_Basic + Nb_Free_Extra, Nb_Free_Ater, 25)
• Where “25” is the maximum number of GCHs allowed in the Transmission-Allocation-
Request message on BSCGP interface for G2 BSC
2. Compute the number of possible inter-cell GCH preemptions. The principles of this algorithm are:
o “Source” TRX and “Target” TRX on different cells of the same BTS,
o Only the GCHs using extra or “bonus” Abis nibbles are considered.
o Only cells using more extra or “bonus” basic Abis nibbles are considered.
o On “source” TRX, the following constraints shall be respected:
• Established_Nb_GCH ≥ Min_Nb_GCH
o The iterative process stops when:
• No more GCH to preempt
• Or Available_Nb_GCH = Nb_Free_GCH + Nb_Preempted ≥ 36
2.6.4 TRX LIST COMPUTING
The goal of the TRX list computing step is to determine the TRX list on which the TBF or one UL block
candidate allocations will be searched.
The conditions for a TRX to be inserted into the TRX list are:
o The TRX shall be PS capable.
o If the TRX is not already mapped to a DSP and no DSP can be associated to the TRX, then the TRX
shall not be considered.
Opposite to B8, in B9 there is no longer some “restricted EGPRS capable TRX lists” (i.e. selection of the
EGPRS TRX of highest class (that is which offer the highest throughput) as long as the maximum number of
EGPRS TBF per PDCH on these TRX is not higher than a threshold). Indeed, all the EGPRS capable TRXs can
offer the same potential throughput: they are all mapped on G4 TRE, and the B8 concept of “TRX pool
type” has disappeared.
2.6.5 BEST CANDIDATE ALLOCATION COMPUTATION
In the radio resource allocation/reallocation algorithm, the computing of the best candidate TBF allocation
consists in searching which are the best PDCHs onto which to establish (or reallocate) the TBF, according to
various radio related criteria.
Once all the usable PDCHs are determined, the different candidate timeslot allocations are sorted
according to their respective “available throughput”, in order to choose the one offering the highest
throughput to serve the considered request. This is a complete change compared to the previous BSS
releases (B6, B7 and B8).
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The input data for the best candidate TBF allocation computation are:
o A sorted list of TRXs,
o n_MS_requested and n_MS_requested_concurrent,
o Type of the radio resources allocation request.
The output of the best candidate TBF allocation computation is a candidate TS allocation on a given TRX, as
it is defined in the next sub-sections.
Definition: PDCH states
The PDCH states are:
o Allocated:
• new in B9: the PDCH is a SPDCH indicated as usable for PS traffic by the BSC.
• B8 definition: radio resource allocated to the MFS, but associated transmission resources
are not allocated.
o Active:
• new definition in B9: an allocated PDCH is active if it supports at least one radio resource
allocated for a TBF.
• the B8 definition was considering the parameter N_TBF_PER_SPDCH which is removed in B9
release.
o Full:
• As in B8 release
� For GPRS Best Effort TBFs:
• An allocated PDCH is full in a given direction (XL: UL or DL) if and only if:
o Nb_BE_TBF_XL ≥ MAX_XL_TBF_SPDCH.
� For EGPRS Best Effort TBFs:
• An allocated PDCH is full in a given direction (XL: UL or DL) if and only if:
o Nb_BE_EGPRS_TBF_XL ≥ MAX_XL_TBF_SPDCH.
o EGPRS:
• An allocated PDCH is in the “EGPRS” state if some radio resources are allocated in DL, for
an EGPRS TBF. Only used when running the radio resource (re)allocation algorithm in GPRS
mode and when considering the UL direction of the candidate TBF allocations.
Remark: the “busy” PDCH state (number of established TBF on the PDCH higher than N_TBF_PER_SPDCH) is
no more used by the allocation algorithm.
Candidate timeslot allocation:
A candidate timeslot allocation is a double list of contiguous PDCH in a TRX (one list for the direction of the
request, one list for the opposite direction), which verifies the concurrent constraints as defined by the MS
multislot class.
To be included in a candidate timeslot allocation in order to serve a best effort TBF, a PDCH on a given TRX
must verify the following conditions:
o The PDCH shall be allocated in the MFS. This condition is new in B9 release and comes from the fact
that the MFS does not request PDCH to the BSC
o The PDCH shall not be in the “Full” state in the considered direction
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o The PDCH shall not be “locked” due to a CS pre-emption process
Available throughput of a candidate timeslot allocation:
This is a completely new metric introduced in B9 release and with high impact in the timeslot allocation. In
the past releases the idea was already to give the highest possible throughput to a TBF (allocating the
highest number of TS not busy, if possible) but there was no explicit metric evaluating the available
throughput provided by a candidate TS allocation. The available throughput of a given candidate timeslot
allocation (available_throughput_candidate_XL) is the overall throughput provided by its PDCHs. It depends
on the potential throughput of its PDCHs (potential_throughput_PDCH) and on the available capacity on
each of its PDCHs (available_capacity_PDCH_XL).
The potential throughput of a PDCH (potential_throughput_PDCH) is calculated as follows according to O&M
parameters for the Evolium BTS case:
o GPRS best effort TBF: R_AVERAGE_GPRS ( default = 12kbit/s )
o EGPRS best effort TBF: R_AVERAGE_EGPRS ( default = 30kbit/s )
This “potential throughput” and its associated parameters are only used in the computation of the best
allocation.
The available capacity on a given PDCH (available_capacity_PDCH_XL) is calculated as follows:
o For a GPRS TBF (XL corresponds to either UL or DL) :
• 1 / Nb_BE_TBF_SAME_PRIOR_XL
o For an EGPRS TBF (XL corresponds to either UL or DL) :
• 1 / Nb_BE_EGPRS_ TBF_SAME_PRIOR_XL
Where:
o Nb_BE_TBF_SAME_PRIOR_XL indicates the total number of Best Effort TBFs (GPRS or EGPRS) which
have some radio resources allocated on the considered PDCH in the XL direction
o Nb_BE_EGPRS_TBF_SAME_PRIOR_XL only take into account EGPRS TBF (the best effort GPRS TBF are
not taken into account)
The available capacity of a given candidate timeslot allocation for n PDCH (n≥1) is computed as follows, for
each direction (XL corresponds to either UL or DL):
o ∑=
=n
1i
DCHi_XLcapacity_Pavailable_ Landidate_Xcapacity_cavailable_
Finally, the available throughput of a candidate timeslot allocation is computed as follow, for each
direction (XL corresponds to either UL or DL):
o available_throughput_candidate_XL =
potential_throughput_PDCH * available_capacity_candidate_XL
Candidate time slot allocations sorting
A candidate timeslot allocation, to be valid, needs to ensure enough resources for PDCH capacity, TFI, TAI
and USF in the direction(s) in which the TBF has to be established. If no candidate timeslot allocation is
found, the best effort TBF (re)allocation request is failed and the process is aborted. Otherwise, all the
valid candidate timeslot allocations are sorted according to the following list of ordered criteria (from the
highest priority to the lowest). This list of criteria is valid in all cases: for GPRS or EGPRS service (contrary
to the B8 release case where two lists were used), and in a cell belonging to an Evolium BTS or to a DRFU
BTS:
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o [ALPHA]: For “ASAP” policy only: the candidate timeslot allocations, which are on some TRXs for
which (Established_Nb_GCH - Nb_MPDCH) is greater than Nb_GCH_For_TBF_Estab” are preferred.
o [A]: For UL GPRS TBF establishment / reallocation only: the candidate timeslot allocations, which
have the lowest number of PDCHs in the “EGPRS” state are preferred.
o [B]: the candidate timeslot allocations, which have the highest available throughput in the
direction of the bias are preferred.
o [C]: the candidate timeslot allocations, which have the highest available throughput in the
direction opposite to the bias are preferred.
o [D]: the candidate timeslot allocations, which are on the TRX with the highest priority, are
preferred.
o [E]: for EGPRS TBFs establishments only: the candidate timeslot allocations, which have the lowest
number of GPRS TBFs in the direction of the bias, are preferred.
o [F]: combinations with the PDCHs that have the lowest index are preferred.
Remarks:
o The A criterion is only relevant for an UL GPRS TBF establishment / reallocation (i.e. when
considering the UL direction of a candidate TS allocation in GPRS mode)
o When evaluating criterion F, the concurrent constraints imposed by the MS multislot class (if it is
known) or by the default multislot class (if the MS multislot class is not known) shall be taken into
account
2.6.6 PDCH CAPACITY ALLOCATION
Once a candidate TS allocation has been found (in the “best candidate allocation computation” step), the
following radio resources are allocated to the MS in the directions in which a TBF has to be established:
o PDCH capacity
o TFI
o PDTCH / PACCH
o TAI
o USF (only in the UL direction)
This first step is new in B9 release, the PDCH capacity allocation is performed on the best candidate TS
allocation, it has to guarantee a minimum bandwidth for the corresponding TBF(s) (data throughput and
throughput generated on PACCH channels in DL and in UL). The PDCH capacity allocation should always
succeed, because the candidate TS allocations for which the PDCH capacity allocation cannot be performed
have been excluded during the “best candidate allocation computation” step.
PDCH capacity needed for a TBF:
In a given direction (UL or DL) and on a given PDCH, the minimum capacity (in terms of radio block
scheduling in MAC layer) that is required for a best effort TBF is called needed_capacity_Best_Effort_XL (XL
corresponds to either UL or DL). This capacity corresponds to a minimum bandwidth that shall be
guaranteed for the best effort TBF and it is computed as follows:
o needed_capacity_Best_Effort_XL = 20 / T_MAX_FOR_TBF_SCHEDULING
with T_MAX_FOR_TBF_SCHEDULING an O&M parameter in ms
This calculation of needed_capacity_Best_Effort_XL approximates the minimum load which can be
generated by the data traffic and the signalling traffic of the TBF (signalling traffic on the PACCH in the
direction of the TBF). To simplify, it is considered that:
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o needed_capacity_Best_Effort_DL = needed_capacity_Best_Effort_UL
Algorithm to allocate the PDCH capacity needed for a TBF:
In a given direction (XL corresponds to either UL or DL) and on a given PDCH, the maximum PDCH capacity
which can be allocated is equal to:
o 1 - USED_CAPACITY_BEST_EFFORT_XL
Where:
USED_CAPACITY_BEST_EFFORT_XL indicates the total PDCH capacity that has already been allocated to best
effort TBFs (both GPRS and EGPRS) on the PDCH in the XL direction in order to ensure a minimum
bandwidth for those best effort TBFs.
In the direction(s) in which a TBF has to be established, a PDCH capacity equal to
needed_capacity_Best_Effort_XL shall be allocated on each PDCH included in the best candidate TS
allocation. Then, on each of these PDCH, the value of USED_CAPACITY_BEST_EFFORT_XL shall be increased
accordingly (incrementation by needed_capacity_Best_Effort_XL).
2.6.7 TBF REALLOCATION CASES
Four different TBF reallocations exist:
o T1: reallocation to maintain a TBF alive despite the CS preemption of some RTSs or of some GCHs in
the cell.
o T2: reallocation of an on-going TBF when establishing a concurrent TBF.
o T3: reallocation useful to
• Provide a higher throughput, if it is possible, to a TBF,
• Establish a new M-EGCH link for one of the TRXs of the cell,
• Perform a “radio de-fragmentation” process.
o T4: reallocation to move an UL GPRS TBF sharing one PDCH with a DL EGPRS TBF onto PDCHs which
do not support a DL EGPRS TBF. It concerns only GPRS TBFs.
In particular, it is presented the T3 and T4 reallocation cases.
T3 TBF reallocation Cases
The BSS systematically requests a T3 reallocation for any MS which has an established TBF in the direction
of the bias verifying the following conditions:
o More than N_CANDIDATE_FOR_REALLOC bytes have been sent on the DL TBF or received on the UL
TBF since their establishment
o T3192 is not running
A T3 TBF reallocation is based on the following principles:
o Computing of a THROUGHPUT_RATIO (= Allocated_Throughput / Optimal_Throughput) to know “how
sub-optimal a TBF allocation is”.
o A T3 TBF reallocation will only be allowed if a significant THROUGHPUT_RATIO gain is reached. The
minimal gain is set by the system parameter: MIN_THROUGHPUT_GAIN (= 40%).
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T3 reallocation attempts occur at each expiry of the T_CANDIDATE_TBF_REALLOC timer and up to
N_MAX_PERIODIC_REALLOC_T3. T3 reallocation attempts can take place at each
T_CANDIDATE_TBF_REALLOC timer expiry.
In case of successful T3 reallocation attempt, no new attempt takes place until the next
T_CANDIDATE_TBF_REALLOC timer expiries. Even if less than N_MAX_PERIODIC_REALLOC_T3 attempts have
occurred and up to two T3 TBF reallocations can be successfully played at each T_CANDIDATE_TBF_REALLOC
timer expiry.
A specific case of T3 reallocation is explained in the next example:
Initial situation:
o 3 MSs (MSa, MSb, and MSc), all GPRS and (4+1),
Figure 2–16: T3 reallocation - initial MSs allocation.
o MSc is the most impacted by the multiplexing in terms of throughput.
In B8:
o MSc is not candidate for T3 reallocation because its allocation is optimal (4 TS in DL),
In B9:
o MSc is candidate for T3 reallocation,
o A new TRX will be established (cf. “Optimal” policy) and MSc will then be reallocated on this new
TRX.
Figure 2–17: T3 reallocation - final MSs allocation for B9.
A second example is a T3 TBF reallocation trigger due to radio defragmentation purpose, as shown in the
next figure:
0 1 2 3 4 5 6 7
DL
UL
MSa MSa MSa MSa MSb MSb MSb MSb
MSc MSc MSc MSc
MSc MSb MSa
0 1 2 3 4 5 6 7
DL
UL
0 1 2 3 4 5 6 7
DL
UL
MSa MSa MSa MSa MSb MSb MSb MSb
MSb MSa
0 1 2 3 4 5 6 7
DL
UL
MSc MSc MSc MSc
MSc
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Figure 2–18: T3 reallocation - defragmentation purpose.
T4 TBF reallocation cases
The goal of the T4 reallocation is to avoid the “UL GPRS - DL EGPRS” TBF multiplexing situations, e.g. some
dummy DL GPRS TBF(s) may have to be managed by MAC in order to schedule the USFs of the UL GPRS
TBF(s), which can induce a throughput reduction for the DL EGPRS TBFs
A GPRS MS becomes candidate for a T4 reallocation as soon as its UL GPRS TBF shares at least one PDCH
with a DL EGPRS TBF
The MS remains candidate for a T4 reallocation, after an UL TBF release, if a DL TBF is still ongoing. This
means that a DL TBF can be T4 reallocated even if it has currently no UL concurrent TBF
In the best candidate allocation computation algorithm:
o The candidate timeslot allocations do not require having the same number of PDCHs than the
current allocation.
o In the UL direction, the candidate timeslot allocations cannot contain PDCHs in the “EGPRS” state.
o The radio resource allocation algorithm is run with the ASAP policy. Thanks to the allocation
criterion ALPHA, the candidate TS allocations located on the TRXs having already
Nb_GCH_For_TBF_Estab established GCHs are favored.
Upon T_CANDIDATE_TBF_REALLOC timer expiry it shall be attempted to reallocate a maximum of
N_MAX_PERIODIC_REALLOC_T4 candidate MSs queued within a list. If a reallocation succeeds, the next
request within the list shall be played (up to the N_MAX_PERIODIC_REALLOC_T4 limit).
2.7 ENHANCED SUPPORT OF EGPRS IN UL
This feature is part of EGPRS package, for more details see [2]. It is divided into two sub features:
o Support of 8-PSK in Uplink
• The "8-PSK in UL" feature proposes to introduce the 8-PSK modulation in UL, which permits
to use the MCS-5 to MCS-9 coding schemes in the BSS (in B8 only the MCS-1 to MCS-4 are
supported in UL).
o Support of Incremental Redundancy and resegmentation in Uplink
TBF
TBF
Initial
Final situation
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• The "Incremental Redundancy in UL" feature proposes to introduce the incremental
redundancy in UL which permits to improve the decoding performances of the BTS with
EGPRS. This is particularly useful when mobiles are at the border of the cells where a gain
up to 15 % of throughput can be expected according to simulations.
2.7.1 SUPPORT OF 8-PSK IN UPLINK
The feature introduces 8-PSK modulation supported in UL, for more details see [2] The 8-PSK is a
modulation technique that compare to GMSK allows up to 3 times more data to be transmitted over the
GSM air interface. The 8-PSK modulation supports MCS-5 to MCS-9 coding schemes, which permit to achieve
higher throughput when the radio conditions are good enough.
Table 12: Theoretical throughput per UL MCS.
Modulation Coding Scheme
Throughput (kbits/sec)
GMSK MCS-1 8.4
GMSK MCS-2 11.2
GMSK MCS-3 14.8
GMSK MCS-4 17.6
8-PSK MCS-5 22.4
8-PSK MCS-6 29.6
8-PSK MCS-7 44.8
8-PSK MCS-8 54.4
8-PSK MCS-9 59.2
If an EGPRS mobile station wants to initiate the UL EGPRS TBF establishment and if the mobile supports the
8PSK in uplink, then it shall send an EGPRS Packet Channel Request using TS1 alternative training sequences
to request the resources in EGPRS mode. The EGPRS capability is indicated using alternative training
sequences (see 3GPP TS 45.002), as presented in the next table.
Table 13: Training sequence.
Training sequence
Packet Channel Access
TS1 EGPRS with 8PSK capability in uplink
TS2 EGPRS without 8PSK capability in uplink
The MCS-5 to MCS-9 coding schemes will be used both in RLC acknowledged and unacknowledged mode. The
link adaptation mechanism in uplink is based on measurements (MEAN_BEP, CV_BEP) done by the BTS on the
radio blocks received from the mobile. To take into account MCS-5 to MCS-9 in uplink, the B9 BSS algorithm
for link adaptation has new link adaptation MEAN_BEP/CV_BEP tables, which are the same as the ones
already used for downlink. Then, the MCS selected by the BSS is indicated in the "EGPRS modulation and
coding" IE included in the PACKET UPLINK ACK/NACK message. The TRX shall transmit the MEAN_BEP and
CV_BEP of the RLC data block which is received with a correctly decoded RLC/MAC header, whether the
payload is correctly decoded or not. The TRX will discard the RLC/MAC blocks when the header has not
been successfully decoded.
The Link Adaptation tables depend on the APD (Average Power Decrease) of the mobile station, the APD of a
mobile station is the difference between the maximum output power in GMSK and the maximum output
power in 8-PSK and the maximum output powers are known by "GMSK Power Class" and "8-PSK Power Class"
fields of the MS Radio Access capability IE. The Link Adaptation tables also depend of the Incremental
Redundancy if it is activated or not.
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As examples of APD in case of GSM 900 and GSM 850, there is the following table:
Table 14: Average Power Decrease.
8-PSK: Power Class E1
8-PSK: Power Class E2
8-PSK: Power Class E3
Max. output
power = 33 dBm Max. output
power = 27 dBm Max. output
power = 23 dBm
GMSK: Power Class 2
Max. output power = 39 dBm APD = 6 APD = 10 APD = 10
GMSK: Power Class 3
Max. output power = 37 dBm APD = 4 APD = 10 APD = 10
GMSK: Power Class 4
Max. output power = 33 dBm APD = 0 APD = 6 APD = 10
GMSK: Power Class 5
Max. output power = 29 dBm APD = 0 APD = 2 APD = 6
2.7.2 SUPPORT OF INCREMENTAL REDUNDANCY AND RESEGMENTATION IN UPLINK
The incremental redundancy (type II hybrid ARQ) is used with EGPRS data blocks sent on RLC acknowledged
mode using MCS-1 to MCS-9. The incremental redundancy is based on reception of RLC data blocks coded
with different puncturing schemes, so that the BTS may enhance the decoding of the RLC data block with
soft combining. By taking into account the erroneous RLC data blocks and combining them with the
retransmitted RLC data blocks, the BTS receiver increases the probability of decoding them correctly and
reduces the number of times it uses a slower coding scheme compared to the situation where incremental
redundancy is not used and therefore the average throughput is increased.
The RLC data block re-segmentation in UL is a new B9 feature, which can be activated in the O&M. As in DL
the re-segmentation of radio block is only possible inside the same coding scheme family, as presented in
the next figure. The objective of this algorithm is to retransmit a RLC block in a lower and more robust
coding scheme.
Figure 2–19: Coding scheme families.
MCS5 MCS6 MCS7 MCS8 MCS9MCS1 MCS2 MCS3 MCS4
FamilyC
FamilyB
FamilyA
padding
FamilyA
28
22
34+3
22 22
28 28
34+3 34+3
28 28
28 28
34 34
34 34
37 37 37 37 37
37 37
GMSK 8PSK
28RLC data block unit of payload (in bytes)
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The incremental redundancy cannot be applied when the RLC datablocks are re-segmented with a different
number of payloads
For more details see [2].
2.8 EXTENDED UL TBF MODE
The aim of this feature is to extend the duration of the UL TBF in order to quickly restart data transmission
in UL if higher layers in the MS deliver new data, without having to re-establish a new UL TBF, after the
countdown procedure has started. E.g. to maintain the UL TBF established, some time after the last block
(CV=0) has been acknowledged by the network. During inactivity period the BSS should keep the USF
scheduling and the reception of uplink RLC data block as long as the uplink TBF is in extended phase.
This feature allows improving access time to the GPRS network. It also improves the throughput in cases
where the traffic is discontinuous. The extended UL TBF mode (EUTM) is supported by mobiles which are
indicating support of 3GPP “GERAN Feature Package 1”. The GERAN Package 1 is mandatory for Rel-4 MS
and optional for Rel-99 MS (so, there can be also MS Rel-99 that supports EUTM), for more details see [2].
The BSS shall indicate to the MS that the network supports the extended uplink TBF mode. The MS is aware
of the BSS capability by the NW_EXT_UTBF parameter that is broadcast on either BCCH (SI13)or PBCCH
(PSI1). So the MS is always aware of the BSS capability before establishing an Uplink TBF. On the contrary
the BSS does not always know the MS radio access capability when the first Uplink TBF is established at the
beginning of a session. The detection whether or not a given MS supports the Extended Uplink TBF Mode is
received at downlink TBF establishment in the first downlink PDU. In case of cell reselection for an uplink
transfer and if the MS radio access capability stays unknown the “Radio Access Capability Update”
procedure is used to obtain the information.
If the MS does not support the Extended Uplink TBF Mode or if the BSS does not know MS capability, the
network will apply the Normal release mode (with delayed final PUAN).
During an UL transfer in a MS having MS context without the support of the Extended Uplink TBF Mode, if a
Radio Access Capability update message is received allowing the Extended Uplink TBF Mode, then the MS
context is overwrite and update.
The Extended uplink TBF mode is activated through an O&M parameter, EN_EXTENDED_UL_TBF and an
inactivity period duration of extended uplink TBF mode is configured T_MAX_EXTENDED_UL by the
parameter.
The release of the uplink TBF is trigger upon the expiry of the timer T_max_extended_UL.
The Radio Access Capability Update on the Gb is activated by the flag EN_RA_CAP _UPDATE. If the
EN_EXTENDED_UL_TBF is enabled and the Radio Access Capability update is supported by SGSN, it is
recommended to enable the flag EN_RA_CAP _UPDATE.
At UL TBF establishment, immediately after the “contention resolution” procedure, the “radio access
capability update” procedure is triggered in the BSS. The BSS request an MS’s current Radio Access
capability and/or its IMSI by sending to an SGSN a RA_CAPABILITY_UPDATE, which includes the TLLI of the
MS and a Tag. Then it starts timer T5_RA_CAPABILITY_UPDATE. In case of the timer expiry, BSS shall repeat
the request up to RA_CAPABILITY_UPDATE_RETRIES times (value = 3). The SGSN shall respond by sending a
RA_CAPABILITY_UPDATE_ACK, which includes the TLLI of the MS, the Tag received in the corresponding
RA_CAPABILITY_UPDATE. When the SGSN answers, the MS Radio Access capability is updated and the
Extended UL feature can be used if the “GERAN Feature Package 1” bit is set. Otherwise, the MS does not
support the extended uplink feature.
If MS supports Extended UL TBF mode and when entering the extended uplink phase the MS begins to run
out of LLC data, it begins the countdown normally. When the BSS receives the last RLC block (CV =0), and if
all the previous blocks have been correctly received, the BSS sends a Packet Uplink Ack/Nack with
Final_Ack_Indicator set to 0, with the SSN incremented like for an active TBF (SSN = last received BSN +1).
All RLC numbering variables are kept as TBF was still active. The uplink TBF is now extended and will not be
released by the mobile. The BSS starts the timer T_max_extended_UL to monitor the maximum duration of
the extended phase.
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Figure 2–20: Trigger of the timer T_max_extended_UL.
The BSS continues to schedule USF, so that the MS is able to resume an uplink transfer when required. While
the UL TBF is in extended phase, the reception of an uplink dummy block from the MS, shall not cause the
N3101 counter to be incremented in the BSS. Only the reception of an invalid block increment N3101. While
the UL TBF is in extended phase, the reception of an uplink dummy block from the MS shall not cause the
N_UL_dummy counter to be incremented.
Figure 2–21: Schedule USF.
After the expiry of the timer T_max_extended_UL the network ends the TBF permanently by sending a
Packet Uplink Ack/Nack with FAI = 1 and polling. When receiving PUAN with FAI=1 and polling, the MS sends
the Packet Control Ack in response to polling, and then aborts the uplink TBF. When the timer
T_max_extended_UL expires, the BSS shall wait for all the radio blocks corresponding to already
transmitted USF, before transmitting FAI =1.
Figure 2–22: Expiry of the timer T_max_extended_UL.
RLC block, BSN=n, CV=0
MS BSS
PUAN, SSN=n+1, FAI=0 Enter TBF extended phase.Start T_max_extended_UL
RLC block, BSN=n, CV=0
MS BSS
PUAN, SSN=n+1, FAI=0 Start T_max_extended_UL
USF
USF
Dummy block
USF
Dummy block
MS BSS
T_max_extended_UL expiry
USF
Dummy block
PUAN, FAI=1, S/P=1
PCA
TBF is releaseNominal case
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If the radio blocks corresponding to the last scheduled USF carry RLC data block, then the BSS shall restart
the uplink TBF.
Figure 2–23: Restart the uplink TBF.
The USF for extended mode are scheduled only on the PDCH, which carries PACCH.
IF the PDCH supports uplink TBF, which all are in extended mode and the flag EN_FAST_USF_UL_EXTENDED
is enable then the throughput in radio blocks is equally shared between MS (round robin of one RLC block
per MS). So USF are scheduled as follows:
o One MS in extended mode on PACCH: USF scheduled every 20ms
o Two MS in extended mode on PACCH: USF scheduled every 40ms
o n MS in extended mode on PACCH: USF scheduled every n x 20m
Otherwise, a polling period T_extended_UL_TBF_POL is used for all MS in extended phase with a default
value of 200ms and the remaining bandwidth is used for MS in transfer.
2.9 ENHANCED PACKET CELL RESELECTION
The “Enhanced Packet Cell Reselection” feature includes two sub-features allowing to reduce cell
reselection duration and to avoid (NC2 mode) to direct MS towards high loaded cells.
The sub features to reduce the service outage during packet cell reselection (NC0 and NC2 modes) are:
o Network Assisted Cell Change Procedures (NACC): MS acquires target cell (P)SI in the serving cell.
Only for R4 MS.
o Packet (P)SI Status procedure : access to a new cell without having previously acquired the full set
of P(SI). Mainly for R4 MS.
In NC2 mode, the algorithm was improve to take in consideration the cell ranking with load criteria, to
prevent MSs to be directed towards high loaded cells, where the MS can be served with non-optimum
resources, or even worse, rejected due to congestion.
For details see [2].
2.9.1 NETWORK ASSISTED CELL CHANGE PROCEDURES (NACC)
The NACC takes place in serving cell and consists of 2 independent procedures:
o CCN mode procedure (Cell Change Notification): Procedure in MS to notifies the network when the
cell reselection is decided in Packet Transfer Mode and delays the cell reselection to let the
network act on need, eventually through the Cell System Information distribution procedure.
o Cell System Information distribution: Procedure to assist an MS in Packet Transfer Mode with target
cell system information required for initial packet access after a cell change. This information is
sent to the MS in the serving cell and before the cell change is performed.
MS BSS
T_max_extended_UL expiry
USF
Radio block, BSN=n+1
USF
Radio block, BSN=n+2, etc…
TBF is active again
Transfer resumption after timer expiry
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Figure 2–24: NACC.
Network Assisted Cell Change - NC0
When EN_NACC is enable, the CCN mode is ordered through System Information to all R4 MSs supporting
GERAN feature package 1 in the cell. The next scenario describes the NACC procedure in NC0 mode:
Figure 2–25: NACC procedure in NC0 mode.
(1) T3206 monitors the sending of the Packet Cell Change Notification.
(2) At receipt of the PACKET CELL CHANGE NOTIFICATION message, the MFS checks whether the proposed
cell belongs to the same BSS as the serving cell. If the proposed cell does not belong to the same BSS
(BSC_ID(n) (target cell) <> BSC_ID (serving cell)), a PACKET CELL CHANGE CONTINUE (PCCC) message is sent
to the mobile station without sending any neighbor cell system information.
(3) In the case, the neighbor cell belongs to the same BSS, RRM starts the timer T3208n (T3208 – RTD) that
monitors the sending of the PCCC and retrieves the SI13 / SI1 / SI3 or PSI14 / PSI1 / PSI2 instances currently
broadcast in the neighbor cell and requests MAC to send the relevant (P)SI to the MS
o if the target cell supports a PBCCH channel, RRM encodes the PSI14, PSI1 and PSI2 instances of that
cell in one or multiple instances of the PACKET NEIGHBOR CELL DATA message which are sent to the
MS, followed by a PACKET CELL CHANGE CONTINUE message .
CCCeeellllll AAA CCCeeellllll BBB Partial Sys Info. of Cell
Cell BMS Cell A
Ongoing data transfer
Target cell choice (1)
T3206
RLC data block polling
Packet Cell Change Notification (2)
Packet Neighbor Cell Data (PSI14)
Packet Neighbor Cell Data (PSI1)
Packet Neighbor Cell Data(PSI2-first instances)
Packet Neighbor Cell Data(PSI2-intermediate instances)
Packet Neighbor Cell Data(PSI2-last instances)
Packet Cell Change continue (4)
T3210
T3208
T3208n
Retrieval PSI instancesof the chosen cell (3)
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o if the target cell does not support a PBCCH channel, RRM encodes the SI13, SI1 and SI3 instances of
that cell in one or multiple instances of the PACKET NEIGHBOR CELL DATA message.
o When the MS sends the Packet Cell Change Notification message, the MS activates the timer T3210
to wait for a response from the BSS, if timer expiry, the Packet Cell Change Notification is
retransmitted. The MS also activates the timer T3208 to wait for PACKET CELL CHANGE CONTINUE
from the BSS (at timer expiry, the MS will continue the cell reselection in NC0 mode).
(4) When RLC has sent all the instances of the PACKET NEIGHBOUR CELL DATA message, the PACKET CELL
CHANGE CONTINUE (PCCC) message is sent on the PACCH of the MS and the timer T3208n is stopped. It is to
be noted that no PCA is requested to acknowledge the PCCC (No T_Ack_Wait timer is launched by the BSS
when sending the PCCC because at the timer expiry, the mobile station has already left the CCN mode
either because it has received the PCCC or because T3208 has already expired and it is not necessary to
send the PCCC again).
When the mobile station receives the PACKET CELL CHANGE CONTINUE message, it shall leave CCN mode
and continue cell reselection in NC0 mode.
Note: The figure above covers the case where there is a PBCCH in the target cell. When there is no PBCCH
channel in the target cell, the same scenario takes place with BSS sends the SI13, SI1 and SI3 messages
instead of the PSI14, PSI1 and PSI2 messages.
Network Assisted Cell Change - NC2
NC2 cell reselection execution with Cell System Information Distribution is described in the next figure:
Figure 2–26: NACC procedure in NC2 mode.
(1) An UL or DL TBF is assumed on-going.
(2) The MS sends a Packet Measurement Report message on one of the allocated UL block on PACCH
(3) Upon receipt of the Packet Measurement Report message, the BSS detects that a cell reselection must
be triggered. It finds out that the target cell, belongs to the same BSS, and the MS supports the acquisition
of neighbor cell (P)SI.
(4) The BSS sends the PNCDs to the MS, on all the PDCHs of the TBF, to transmit the (Packet) System
Information for the target cell:
o SI13, SI1 and SI3 for a target cell without PBCCH
o or PSI14 (containing the same information as SI13), PSI1 and a consistent set of PSI2 for a target cell
with a PBCCH.
In case both a UL and a DL TBF exist, PNCDs are sent on the DL TBF.
MS BSS Serving cell BSS Target cell
Ongoing UL or DL TBF (1)
Packet Measurement Report / PACCH (2)
Packet Neighbor Cell Data / PDCHs (4)
Packet Neighbor Cell Data / PDCHs
Packet Cell Change Order / PACCH (5)
Packet Control Acknowledgement / PACCH (7)T_ACK_WAIT
(3)
(6)
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(5) When all the PNCDs have been sent, the BSS orders the MS to reselect a new cell by sending a Packet
Cell Change Order message on the PACCH of the DL or UL TBF. If both an UL and a DL TBFs are on-going, the
message is preferentially addressed by a DL TFI.
The Packet Cell Change Order message is sent in acknowledged mode and contains the ARFCN and the BSIC
of the target cell.
When sending the Packet Cell Change Order message, the BSS starts the timer T_ACK_WAIT to monitor the
receipt of the Packet Control Acknowledgement message.
(6)-(7) Upon receipt of the Packet Cell Change Order message, the MS aborts its on-going TBF in the serving
cell and sends the Packet Control Acknowledgement message, then switches to the new cell.
2.9.2 PACKET (P)SI STATUS PROCEDURE
Packet (P)SI status feature allows MS to make an access to a new cell without having previously acquired
the full set of SYSTEM INFORMATION (resp. PACKET SYSTEM INFORMATION if PBCCH is present in the target
cell) messages sent on the BCCH channel (resp. PBCCH) of the target cell.
The Packet (P)SI Status procedure takes place in the target cell if in this cell, EN_PSI_STATUS = Enable.
o Packet PSI Status procedure is a feature standardized from Release 97 onwards, optional for Release
97, Release 98 and Release 99 MS, and mandatory for Release 4 onwards MS supporting GERAN
Feature Package 1.
o Packet SI Status procedure is a new feature standardized in Release 4, mandatory for Release 4
onwards mobile stations supporting GERAN Feature Package 1.
Figure 2–27: Packet (P)SI status.
Packet SI Status
The scenario of the Packet SI Status procedure is described in the next figure:
Figure 2–28: Packet SI Status procedure.
CCCeeellllll AAA CCCeeellllll BBB
Partial Sys Info.
Remaining
Sys Info.
Cell BMS Cell A
RLC data block (1)
Packet SI status (SI2, SI2bis, SI2ter message type missing) (2)
Scheduling of the serving cell SI message to MS
Packet serving cell data (SI2 message) (4)
Packet serving cell data (SI2bis message)
Packet serving cell data (SI2ter message)
Completion of UL LLC PDU transfer
RLC data block
Packet Uplink ACK/NACK
T_P
SC
D_S
CH
ED
ULE
_AC
K (3)
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(1) When reselecting a new cell without a PBCCH channel and supporting the PACKET SI STATUS procedure
(EN_PSI_STATUS = enable), the MS can immediately request the establishment of an uplink TBF provided it
has acquired the SI13, SI3 and SI1 message (if present) of this new cell. It can then send a cell update or
restarts its on-going data transfer.
(2) The MS asks BSS to provide the missing system information by sending a PACKET SI STATUS message on
PACCH.
(3) When receiving the MS request, if a downlink TBF is already established, or if a downlink TBF is being
established, or if a downlink TBF will soon be established (DL LLC PDU are being rerouted to the new cell),
then the BSS shall wait until full establishment of the DL TBF to send requested SIs on all the downlink
PDCHs allocated to the MS. Otherwise, SIs are sent on all the PDCHs of the uplink TBF.
A supervision timer (T_PSCD_SCHEDULE_ACK) is started to monitor the sending of the SI messages to the
mobile.
(4) The SI instances are encapsulated in one or multiple instances of a PACKET SERVING CELL DATA message
and sent individually to the mobile station.
When the last SI is sent to the mobile, T_PSCD_SCHEDULE_ACK is stopped (RLC indicates to RRM that all SIs
have been sent).
Packet PSI Status
The scenario of the Packet PSI Status procedure is in the next figure:
Figure 2–29: Packet PSI Status procedure.
(1) When reselecting a new cell with a PBCCH channel and supporting the PACKET PSI STATUS procedure
(EN_PSI_STATUS = enable), the MS can immediately request the establishment of an UL TBF, provided it has
acquired the PSI14, PSI1 and PSI2 messages of this new cell. It can then send a cell update or restarts its
on-going data transfer.
(2) The MS asks the BSS to provide the missing system information by sending a PACKET PSI STATUS message
on a PACCH block.
(3) When receiving the MS request, if a DL TBF is already established, or is being established, or will soon
be established (DL LLC PDU are being rerouted to the new cell), then the BSS shall wait until full
establishment of the DL TBF to send requested PSIs on all the downlink PDCHs allocated to the MS.
Cell BMS Cell A
RLC data block (1)
Packet PSI status (PSI3, PSI3bis missing) (2)
Scheduling of the serving cell PSI messages to MS
Packet serving cell data (PSI3bis message) - first instance
Packet serving cell data (PSI3bis message) - intermediate instance
Packet serving cell data (PSI3bis message) - last instance
Completion of UL LLC PDU transfer
RLC data block
Packet Uplink ACK/NACK
T_P
SC
D_S
CH
ED
ULE
_A
CK
(3)
Packet serving cell data (PSI3 message)
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Otherwise, PSIs are sent on all the PDCHs of the uplink TBF. A supervision timer (T_PSCD_SCHEDULE_ACK) is
started to monitor the sending of the PSI messages to the mobile.
(4) When the last PSI is sent to the mobile, T_PSCD_SCHEDULE_ACK is stopped.
2.9.3 NC2 IMPROVEMENT
Cell load evaluation
The NC2 load is sampled every T_NC2_LOAD_RANKING seconds by dividing the used bandwidth by the total
bandwidth available in the cell
with:
UL_PS_used_Bandwidth: the bandwidth used by PS traffic in the UL direction,
DL_PS_Used_Bandwidth: the bandwidth used by PS traffic in the DL direction,
CS_Used_Bandwidth: the bandwidth used by CS traffic,
Total_PS_Bandwidth: the total bandwidth available in the cell.
The UL PS used bandwidth is defined as the sum of the bandwidth used by the UL TBFs over all the PDCHs
allocated to the MFS.
Where the bandwidth per PDCH calculation is given by:
With:
nULTBF,i: defines the number of UL TBFs on the allocated PDCH i.
NULTBF: is the maximum number of UL TBFs that can be pilled up on the PDCHs (defined by the parameter
MAX_UL_TBF_SPDCH).
In the DL direction, the DL_PS_Used_Bandwidth is computed in a similar way as the UL direction.
The bandwidth used by the CS traffic (CS_Used_Bandwidth) is defined by the difference between the
maximum number of slave PDCHs that can be allocated in the cell (number of slave PDCHs = MAX_PDCH -
NB_TS_MPDCH) and the number of slave PDCHs currently allocated to the MFS in the cell
Next, it is a example of the Cell load evaluation. It is assumed, he following repartition of the DL TBFs is
used:
o The UL_PS_Used_Bandwidth is lower than the DL_PS_Used_Bandwidth. Thus, it is not computed.
o Number of PDCH allocated = 7;
o MAX_DL_TBF_SPDCH = 3;
o MAX_SPDCH = 8.
( )∑=
=OCATEDN_PDCH_ALL
1ii , ULUL BB
Nn
BT B F U L
i , T B F U Li , U L =
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Time Slot 0 1 2 3 4 5 6 7
3
2 DL TBF3
1 DL TBF1 DL TBF2
CS
BDL , i 1/3+1/3=
2/3 1/3+1/3=
2/3 1/3+1/3=
2/3 1/3 1/3 1/3 1/3 0
Figure 2–30: PS used bandwidth.
In this example, the total bandwidth is equal to 8, the DL_PS_used_bandwidth is equal to 4x1/3 + 3x2/3 =
10/3.
Therefore, the NC2_load is equal to [(10/3)+ 1]x100/8 = 13x100/24 = 54.16 %
The NC2 load samples are further averaged using a sliding window. The size of the sliding window is defined
by the parameter NC2_LOAD_EV_PERIOD.
The load evaluation of internal BSS cells is calculated every T_NC2_LOAD_RANKING, the BSS compares the
computed NC2 load of the cell to the threshold THR_NC2_LOAD_RANKING:
o If the NC2 load average is lower than or equal to the threshold, the cell is considered in a low load
situation.
o If the NC2 load average is higher than the threshold, the cell is considered in a high load situation.
The MFS shares the NC2 load situation information among the different cells of the BSS (or at least between
the cells having a cell reselection link to the serving cell), i.e. low/high load. That exchange of information
is taking place every MULTI_GPU_INFO_BROADCAST_PERIOD.
All external cells to the BSS will always be considered as in low load situation, because of the threshold
THR_NC2_LOAD_RANKING of an external cell is unknown for the BSS.
NC cell reselection ranking
The NC2 cell ranking process consists of 2 cases.
o Case 1: there is a PBCCH in the serving cell
• Cells with C31NC2 > 0
� NC2_Load situation [low => high PS load];
� Cell PRIORITY_CLASS [high => low];
� C32NC2 [high => low]
• Cells with C31NC2 < 0
� C32NC2 [high => low]
Figure 2–31: NC2 cell ranking process – case 1.
NC2_load
PRIORITY_CLASS
C32NC2
high
low
priority
C31NC2
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o Case 2: there is no PBCCH in the serving cell
• Cells with C31NC2 > 0
� NC2_Load situation [low => high PS load];
� C2NC2 [high => low]
• Cells with C31NC2 < 0
� C2NC2 [high => low]
Figure 2–32: NC2 cell ranking process – case 2.
2.9.4 DL LLC PDU REROUTING
The DL LLC PDU rerouting feature process is explained in the next message flow:
Figure 2–33: DL LLC PDU rerouting feature process.
(1) The MS is in packet idle mode in the serving cell (the old cell).
(2) The MS starts it own cell reselection towards the new cell.
(3) The MS acquires the SI or PSI of the new cell.
(4) While the MS acquires the system information, a DL LLC PDU is received in the old cell for the related
MS.
(5) RRM initiates the DL TBF establishment procedure upon receipt of the DL LLC PDU.
(6) When the MS has finished the system information acquisition in the new cell, it performs an uplink data
transfer in the cell in order to inform the SGSN of its new cell location.
(7) The BSS forwards the new cell identity to the SGSN.
(8) The SGSN analyses the uplink PDU and deduces that the MS has changed of cell.
C31NC2
NC2_load
C2NC2
high
low
priority
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(9) The SGSN sends a Flush message to the old cell.
(10) RRM re-routes the MS context and then all the stored DL LLC PDU’s according to the conditions defined
above. Otherwise RRM discards the DL LLC PDUs.
(11) RRm sends FLUSH-LL-ACk to SGSN.
If the flag EN_DL_LLC_PDU_Rerouting is set to enable the MFS behaviour follows the conditions of the next
table:
Table 15: MFS behaviour with activation of DL LLC PDU rerouting
Old and New Cell
SGSN INR En_Autonomous_Rerouting FLUSH-LL information MFS behaviour
Old BVCI and New BVCI MS Context rerouted DL LLC PDU rerouted Same RA
Same NSE NA NA
Old BVCI DL LLC PDU deleted
Old BVCI, New BVCI and New NSEI
MS Context rerouted DL LLC PDU rerouted Yes NA
Old BVCI DL LLC PDU deleted
Enable Old BVCI
MS Context autonomous rerouted DL LLC PDU autonomous rerouted
Same RA Different NSE
No
Disable Old BVCI DL LLC PDU deleted
If the DL LLC PDU rerouting feature is disabled the DL LLC PDU in the old cell will be deleted.
2.10 TELECOM PARAMETERS
The telecom parameters associated to the previous description are aggregated in the next table, the
optimised values are the ones were an optimisation is recommended, the optimised values should be
analysed before widely implementation in a network:
Table 16: Telecom parameters
GPRS/EGPRS configuration
Logical name Definition Instance Type Range Default value
Optimised value
TRX_PREF_MARK Preference mark assigned to a TRX to favour or disfavour CS radio resource allocations on a TRX.
TRX Number 0 to 7 1 0
Resource allocation/reallocation
Logical name Definition Instance Type Range Default value
Optimised value
EN_RES_REALLOCATION Enabling / disabling of the resource reallocation feature.
BSS Number 0 to 15 NA
T_PDCH_PREEMPTION
Timer to limit the duration of the soft pre-emption process (at its expiry, a fast pre-emption is undertaken).
Cell Number 0 to 240
NA
MAX_DL_TBF_SPDCH Maximum number of DownLink (E)GPRS connections per Slave PDCH.
Cell Number 1 to 10 8 5
MAX_UL_TBF_SPDCH Maximum number of UpLink (E)GPRS connections per slave PDCH.
Cell Number 1 to 6 5
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EN_RETURN_CS_ZONE_HO
Flag enabling the intracell handovers allowing to move TCH from the PS zone to the CS zone of PDCH/TCH allocation
Cell Flag Enable
/ Disable
Enable
R_AVERAGE_GPRS average bitrate per PDCH for non-Edge capable terminals in this cell
Cell Number 0 to 20000
12000
R_AVERAGE_EGPRS average bitrate per PDCH for Edge capable terminals in this cell
Cell Number 0 to 59000
30000
GPRS/EGPRS radio resources
Logical name Definition Instance Type Range Default value
Optimised value
MAX_PDCH Maximum number of slave and master PDCHs that can be established in the cell.
Cell Number 0 to 127
0
MIN_PDCH Minimum number of master and slave PDCHs that are always allocated to the MFS.
Cell Number 0 to 127
0 1
MAX_PDCH_HIGH_LOAD
Maximum number of slave and master PDCHs that can be allocated to the MFS when the CS traffic is high.
Cell Number 0 to 127
0 1
MAX_PDCH_PER_TBF Maximum number of PDCH allocated to a single (E)GPRS connection
Cell Number 1 to 5 5
MAX_PDCH_PER_TBF_High_Ater_Usage
Maximum number of PDCH allocated to a single (E)GPRS connection, when the Ater usage is “high”.
Cell Number 1 to 5 NA
EGPRS activation / TBF handling
Logical name Definition Instance Type Range Default value
Optimised value
ACCESS_BURST_TYPE Format of the access burst used by MS
cell Flag 8 bits or
11 bits 8 bits
BEP_PERIOD Filter constant for EGPRS channel quality measurements.
cell Number 1 to 25 10
EN_EGPRS Enables/Disables EGPRS traffic in the cell.
cell Flag Enable
/ Disable
Disable Enable
MAX_EGPRS_MCS Maximum Modulation and Coding Scheme used for EGPRS traffic in the cell.
cell Number MCS1 to
MCS9 9
MAX_GPRS_CS Maximum coding scheme used for GPRS traffic in the cell.
cell Number 2 to 4 2
NB_EXTRA_ABIS_TS
Number of all extra Abis (64k) timeslots of all the pools defined on the 2 possible sectors on which the cell is mapped.(virtual changeable)
cell Number 0 to 96 NA
N_EXTRA_ABIS_TS Number of extra Abis (64k) timeslots configured for a BTS.
BTS Number 0 to 60 0
NB_TS_MPDCH (BSC) Number of radio timeslots reserved for the primary and secondary master PDCHs defined in the cell.
cell Number 0 to 4 0
PS_PREF_BCCH_TRX
Indicates whether or not the PS requests shall be preferentially served with PDCH(s) of the BCCH TRX
cell Flag Enable
/ Disable
Disable
T_DL_EGPRS_MeasReport Time period to request for an EGPRS Packet Downlink Ack/Nack with measurements.
cell Timer 60 to 3000m
s 200ms
TBF_DL_INIT_CS
Value of the downlink coding scheme when the link adaptation algorithm is disabled or initial value of the coding scheme otherwise.
cell Number CS1 to CS4
CS-2
TBF_UL_INIT_CS
Value of the uplink coding scheme when the link adaptation algorithm is disabled or initial value of the coding scheme otherwise.
cell Number CS1 to CS4
CS-2
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TBF_DL_INIT_MCS
Value of the downlink coding scheme when the link adaptation algorithm is disabled or initial value of the coding scheme otherwise.
cell Number MCS1 to
MCS9 MCS-3
TBF_UL_INIT_MCS
Value of the uplink coding scheme when the link adaptation algorithm is disabled or initial value of the coding scheme otherwise.
cell Number MCS1 to
MCS9 MCS-3
NETWORK_CONTROL_ORDER(n) This parameter defines whether the MS or the BSS controls the cell reselections.
cell Number 0 to 4 0
TX_EFFICIENCY_ACK_THR
Threshold below which the TBF is released because of a bad transmission efficiency in acknowledged mode.
cell Percentage 0 to 100
10
TX_EFFICIENCY_NACK_THR
Threshold below which the TBF is released because of a bad transmission efficiency in unacknowledged mode.
cell Percentage 0 to 100
15
EN_EXTENDED_UL_TBF Flag to disable/enable the extended TBF mode feature on the uplink
cell Flag Enable
/ Disable
DISABLE
Enable
T_MAX_EXTENDED_UL Maximum duration of the extended uplink TBF phase
cell Timer [100, 4000]
2000
EN_FAST_USF_UL_EXTENDED Flag to disable/enable the transmission of USF every 20ms in extended mode
BSS Flag Enable
/ Disable
ENABLE Enable
EN_RA_CAP_UPDATE Flag to enable/disable the Radio Access Capability update on Gb
BSS Flag Enable
/ Disable
DISABLE
DRX_TIMER_MAX Maximum value allowed for the MS to request for non-DRX mode after packet transfer mode.
BSS sec 0 to 4 2
BS_CV_MAX
Number of remaining RLC data blocks sent (per assigned PDCH) by the MS, below which the Count Down procedure is entered. One third of the number of RLC data blocks per assigned PDCH before the MS checks if the resolution contention has failed.
cell Number to 15 9
Coding scheme and radio link control
Logical name Definition Instance Type Range Default value
Optimised value
CS_QUAL_UL_2_3_FH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the uplink direction when the RLC mode is acknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 4
CS_QUAL_DL_2_3_FH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 4
CS_QUAL_UL_2_3_FH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the uplink direction when the RLC mode is unacknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 2
CS_QUAL_DL_2_3_FH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 2
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CS_QUAL_UL_2_3_NFH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the uplink direction when the RLC mode is acknowledged and the TBF is established on a non-hopping TRX.
BSS Theshold 0 to 7 3.5
CS_QUAL_DL_2_3_NFH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a non-hopping TRX.
BSS Theshold 0 to 7 3.5
CS_QUAL_UL_2_3_NFH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the uplink direction when the RLC mode is unacknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 2
CS_QUAL_DL_2_3_NFH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS2 to CS3 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 2
CS_QUAL_UL_3_4_FH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the uplink direction when the RLC mode is acknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 0.5
CS_QUAL_DL_3_4_FH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 0.5
CS_QUAL_UL_3_4_FH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the uplink direction when the RLC mode is unacknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 0
CS_QUAL_DL_3_4_FH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 7 0
CS_QUAL_UL_3_4_NFH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the uplink direction when the RLC mode is acknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 0.5
CS_QUAL_DL_3_4_NFH_ACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 0.5
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CS_QUAL_UL_3_4_NFH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the uplink direction when the RLC mode is unacknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 0
CS_QUAL_DL_3_4_NFH_NACK
Threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 7 0
CS_SIR_DL_3_4_FH_ACK
Signal to Interference Ratio threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 15 14 10
CS_SIR_DL_3_4_FH_NACK
Signal to Interference Ratio threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a hopping TRX.
BSS Threshold 0 to 15 15 10
CS_SIR_DL_3_4_NFH_ACK
Signal to Interference Ratio threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is acknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 15 13 10
CS_SIR_DL_3_4_NFH_NACK
Signal to Interference Ratio threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the RLC mode is unacknowledged and the TBF is established on a non-hopping TRX.
BSS Threshold 0 to 15 15 10
CS_SIR_HST_DL
Signal to Interference Ratio hysteresis used in the link adaptation algorithms to change the Coding Scheme from CS4 to CS3 in the downlink direction.
BSS Number 0 to 15 1
CS_BLER_DL_3_4
CS3 BLER threshold used in the link adaptation algorithms to change the Coding Scheme from CS3 to CS4 in the downlink direction when the SIR measurements are not reported by the MS.
BSS Percentage 0 to 100
5
CS_BLER_DL_4_3
CS4 BLER threshold used in the link adaptation algorithms to change the Coding Scheme from CS4 to CS3 in the downlink direction when the SIR measurements are not reported by the MS.
BSS Percentage 0 to 100
15
TBF_CS3_BLER_PERIOD
Defines the window size required to estimate the CS3 BLER. The window size is expressed as a number of DL RLC data blocks
BSS Number 1 to 512
32
TBF_CS4_BLER_PERIOD
Defines the window size required to estimate the CS4 BLER. The window size is expressed as a number of DL RLC data blocks
BSS Number 1 to 512
32
EN_FULL_IR_DL Enables/Disables Incremental redundancy for the downlink TBF in the cell.
BSS Flag Enable
/ Disable
DISABLE
Enable
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EN_IR_UL Enables/Disables Incremental redundancy for the uplink TBF in the BSS.
BSS Flag Enable
/ Disable
DISABLE
Enable
EN_RESEGMENTATION_UL Enables/Disables the re-segmentation for the uplink TBF in the BSS
BSS Flag Enable
/ Disable
DISABLE
Disable
E_TX_EFFICIENCY_PERIOD Number of received radio blocks for an EGPRS TBF after which E_TX_EFFICIENCY is computed.
BSS Number 0 to 500
200
EN_CS_ADAPTATION_ACK Enables / disables the link adaptation in RLC acknowledged mode.
Cell Flag Enable
/ Disable
Enable
EN_CS_ADAPTATION_NACK Enables / disables the link adaptation in RLC unacknowledged
Cell Flag Enable
/ Disable
Enable
TBF_CS_DL
For a monoslot TBF alone on its PDCH, threshold defining the number of consecutive Packet Downlink Ack/Nack not received above which the coding scheme of a downlink acknowledged or unacknowledged TBF is changed to CS1 (only in downlink). For a multi-slot TBF or a TBF which shares its PDCH(s), the limit is proportional to the instantaneous bandwidth allocated to the TBF.
BSS Number 0 to 15 8
TBF_CS_UL
Threshold defining the maximum number of consecutive times the network receives an invalid UL RLC data block or nothing from the MS having a monoslot GPRS TBF before changing the coding scheme to CS1. For a multislot GPRS TBF, TBF_CS_UL_limit := TBF_CS_UL x n_allocated
BSS Number 0 to 64 32
TBF_MCS_DL
For a monoslot TBF alone on its PDCH, threshold defining the number of consecutive EGPRS Packet Downlink Ack/Nack not received above which the coding scheme of a downlink acknowledged or unacknowledged TBF is changed to MCS1 (only in downlink). For a multi-slot TBF or a TBF which shares its PDCH, the limit is proportional to the allocated bandwidth at the TBF establisment.
BSS Threshold 0 to 15 12
TBF_MCS_UL
Threshold defining the maximum number of consecutive times the network receives an invalid UL RLC data block or nothing from the MS having a monoslot EGPRS TBF before changing the coding scheme to MCS1. For a multislot EGPRS TBF, TBF_MCS_UL_limit := TBF_MCS_UL x n_allocated_timeslots.
BSS Threshold 1 to 192
32
GPRS/EGPRS Transmission
Logical name Definition Instance Type Range Default value
Optimised value
EN_FAST_INITIAL_GPRS_ACCESS
This flag indicates whether or not one Slave PDCH for (E)GPRS traffic usage will be statically established in the cell.
cell Flag Enable
/ Disable
Disable
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T_GCH_INACTIVITY
- For Non Evolium BTS : Timer to postpone the release of one slave PDCH, when it does not support any (E)GPRS traffic. - For Evolium BTS : Timer to postpone the release of the "unused" GCHs of the M-EGCH link of a TRX (the condition for some GCHs of the M-EGCH link of a TRX to become "unused" is that some TBFs
BSS Number 1 to 100
3 2
T_GCH_INACTIVITY_LAST
- For Non Evolium BTS : Timer to postpone the release of the last established slave PDCH of a cell, when it does not support GPRS traffic anymore. - For Evolium BTS : Timer to postpone the release of the last N_GCH_FAST_PS_ACCESS GCHs established in a cell, when the last TBF has been released in the cell.
BSS Number 1 to 200
20 8
N_GCH_FAST_PS_ACCESS
Two definitions are possible : - If EN_FAST_INITIAL_GPRS_ACCESS = “enabled” : number of GCHs required to be established due to the “Fast Initial PS Access” feature, - If EN_FAST_INITIAL_GPRS_ACCESS = "disabled” : number of GCHs to keep established when there is no more (E)GPRS traffic in a cell (while the T_GCH_INACTIVITY_LAST timer is running). Those GCHs will be useful in case of (E)GPRS traffic resumption in the cell.
MFS Number 1 to 5 1
GPRS_MULTISLOT_CLASS_DEF_VALUE
Default value of the (E)GPRS multislot class assumed at TBF establishment when the actual MS (E)GPRS multislot class is unknown.
BSS Number 1 to 8 8
ATER_USAGE_THRESHOLD Threshold (percentage of used Ater nibbles, in a GPU) above which the Ater usage is said “high”.
BSS Percentage 1 to 100
70
N_ATER_TS_MARGIN_GPU
Number of free 64k Ater TSs that are kept “in reserve” in order to be able to serve some prioritary requests in cells managed by the GPU. The prioritary requests are the GCH establishment requests launched when the first TBF has to be established in a cell.
BSS Number 0 to 10 2
GCH_RED_FACTOR_HIGH_ATER_USAGE Reduction factor of the number of GCHs targeted per PDCH, when the Ater usage is “high”.
cell Number 0 to 1 0.75
Enhanced Packet Cell Reselection
Logical name Definition Instance Type Range Default value
Optimised value
EN_NACC Enables the Network Assisted Cell Change feature.
cell Flag Enable
/ Disable
Disable 1
EN_PSI_STATUS
Enables the Packet SI Status feature in cells w/o PBCCH or the Packet PSI Status feature in cells with a PBCCH.
cell Flag Enable
/ Disable
Disable 1
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3 NETWORK DIMENSIONING
The BSS network architecture and dimension had a high improvement with B9 release. Dynamic Abis and the
new Ater resources usage, along with the M-EGCH, allowed the dynamically of the transmission resources
and prepared the Alcatel-Lucent BSS to the future.
The BSS architecture in B9 can be summarize in the next figure:
Figure 3–1: BSS Architecture in B9 release.
And with the introduction of the Mx platform and TWIN TRA:
Figure 3–2: BSS Architecture in B9 release with Mx platform.
The BSS dimensioning explained in this chapter is only an overview and the document of the reference
should be used for a deeper understanding.
The traffic profile and the operator objectives are external variables, impacting the network dimensioning.
Simple cases will be considered in the examples.
The dimensioning will be focus in the 3 main interfaces/equipments:
o Abis
o Ater
o GPU/GP
BSC Abis TSU
Ater TSU
Abis TSU
Ater TSU
Abis TSU
Ater TSU
speech
data
A-ter mux
Gb
A
CS
CS+ PS
PS
CS A-bis
Air
MFS
GPU board
DSP DSP DSP DSP
GPU board
DSP DSP DSP DSP
TC
MT120
SMU TRCU TRCU
TRCU
MT120
SMU TRCU
TRCU
TRCU
TRX 2 M-EGCH link 1
PS traffic
TRX 3 M-EGCH link 2
M-EGCH link n
BTS
Dynamic Abis
allocation GCH Extra
GCH Basic
GCH Basic
GCH Extra
GCH Bonus
TCH
TCH TRX 1 CS
traffic
TRX n
TCUC
Up to 12 TRXs per BTS
speech
data
A-ter mux
Gb
A
CS
CS+ PS
PS
CS A-bis
Air
TC
MT120
SMU TRCU TRCU
TRCU
MT120
SMU TRCU
TRCU
TRCU
TRX 2 M-EGCH link 1
PS traffic
TRX 3 M-EGCH link 2
M-EGCH link n
BTS
Dynamic Abis
allocation GCH Extra
GCH Basic
GCH Basic
GCH Extra
GCH Bonus
TCH
TCH TRX 1 CS
traffic
TRX n
MxBSC CCP board
CCP board
SSW board
TP board
LIU board
LIU board
VTCU
MxMFS
GP board
DSP DSP DSP DSP
GP board
DSP DSP DSP DSP
Up to 24 TRXs per BTS with Twin Modules
Capacity 1 GP = 4xGPU
(B9 MR4)
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3.1 ABIS
The Abis dimensioning in B9 is at BTS level, as explained in chapter 2.3.2, this is due to the fact that the
bonus and extra Abis nibbles are shared by all TRXs of the BTS.
The bonus Abis nibbles are mainly depended of the BTS configuration, number of cells and number of
SDCCH configured. The extra Abis nibbles are depended of the Abis resources “load” and they can be
mapped by the parameter N_extra_Abis_TS.
For Abis dimensioning three examples are proposed, the first one is applied to Abis dimensioning
computation based on operator requirements; the second presents an impact of the defined dimensioning
and the third example is an easy explanation how to dimension an Abis interface based in statistical data.
Example 1
The proposal of this example is to determine the number of extra Abis TS required in a BTS to accomplish
the operator objectives.
Operator objectives:
o 2 users with Class 10 MS simultaneous in a BTS
o DL data transfer in MCS9
BTS configuration:
o 3 cells with 2 TRX and 1 SDCCH per cell.
o No limitations of radio resources allocation (Max_SPDCH_Limit)
Based on the operator objectives the number of GCH required is:
o 4.5 GCH per radio TS in MCS9 x 4 PDCH per user x 2 users = 36 GCH (16 kbit/s Abis nibbles)
The present number of available GCH in the cell is:
o 6 bonus nibbles available for PS (from the 3 BCCH and the 3 SDCCH)
o 4 PDCH per user x 2 users x 1 GCH from basic nibbles = 8 GCH
o 6 nibbles + 8 basic = 14 GCH
The number of GCHs in deficit is:
o number of GCH required - number of available GCH in the cell = 36 – 14 = 22 GCH
The number of required extra Abis TS is given by the number of GCHs in deficit:
o 22 GCH in deficit (16 kbit/s Abis nibbles) / 4 Abis nibles per Abis TS = 5.5 Extra Abis TS
o As a conclusion: The N_EXTRA_ABIS_TS should be set to 6 to fulfil the requirement
Example 2:
For the previous configuration including the N_extra_Abis_TS = 6, the impact in the DL throughput
performance of a third user with MS class 10 will be explained in the example:
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Assumption:
o Each user is alone in one of the cells.
o Cell transmission equity is not possible, since the users are served by different cells
o Max_SPDCH_limit = 4 per cell.
The total number of GCHs available in the BTS is:
o Total number of GCHs - The number GCH already in use by the 2 users = 42 -36 = 6 GCH
Where the:
o Total number of GCHs = 6 nibbles + 12 basic + 6*4 extra Abis nibbles = 42 GCH
o 12 basic = 4 PDCH per user x 3 users x 1 GCH from basic nibbles = 12 GCH
The required number of GCH for the third user is:
o 4.5 GCH per radio TS in MCS9 x 4 PDCH per user x 1 users = 18 GCH
The 6 GCH available to be established in the M-EGCH will allowed a maximum MCS of MCS9.
The expected DL RLC throughput should be around 6 / 18 = 33.3% of the maximum DL RLC throughout
without transmission constrains.
Example 3:
This example explains the method to calculate the number of extra Abis nibbles needed for a cell. It is an
easy method, however it is only applied for PS dimensioning of the Abis. The method is applied when
congestion in the Abis is observed, it takes in consideration that the traffic not allowed due to the
congestion should be carry by the extra Abis nibbles.
The input variables are indicators from O&M counters.
Figure 3–3: Calculation of the Number of Extra Abis TS.
Where:
o %)30,__(%1
__&___&_Re
CongAbisTBFMin
TrafficAbisBonusExtraMeasuredTrafficAbisBonusExtraquired
−=
o GoS = Grade of Service
With:
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o 3600
466__&_
PTrafficAbisBonusExtraMeasured =
o )___,%___(%__% CongAbisTBFULCongAbisTBFDLMaxCongABISTBF =
o %100919191919191
105___% ×
+++++=
fPePdPcPbPaP
iPCongAbisTBFDL
o %100438626262
105___% ×
−++=
cPcPbPaP
jPCongAbisTBFUL
After the calculation of the number of required extra & Bonus Abis nibbles using the Erlang C formula, it is
needed to remove the bonus Abis nibbles and dividing per four the total number of extra Abis TSs needed
are found.
3.2 ATER
In the computation of the number of needed AterMux links the capacity of 112 GCH per link is taken in
order to be able to support GSL carrying
The goal of the AterMux interface dimensioning assessment is to estimate the needed number of GCH
resources in order to be able to support the estimated Required_GCH_traffic (the traffic in Erlang that
AterMux interface should handle for not having congestion).
Figure 3–4: Calculation of the needed GCHs in the Atermux interface.
The proposal methods for Atermux dimensioning take as input variables the real data. 2 different methods
can be used for dimensioning estimation:
o Method 1: driven by the estimation of the required traffic as a function of the measured GCH traffic
and of Ater/GPU congestion
o Method 2: driven by the estimation of the required traffic as a function of the measured GCH and
radio PS traffic
3.2.1 METHOD 1
The method 1 is a function of existing GCH traffic and Ater/GPU congestion and it is only valid if the GCH
congestion is lower than 30%. The measured GCH traffic is given by the counter P100c and the Ater/GPU
congestion is given by the counters P383a, P384, P201, P202 and P404, these counters are explained in the
chapter 5.4.
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Figure 3–5: Calculation of the Required_GCH_Traffic by Method 1.
The Required_GCH_Traffic is calculated by the formula:
Congestion
TrafficGCHMeasuredTrafficGCHquired
−=
1
____Re
Where:
o Measured_GCH_Traffic = P100c / 3600
o Congestion = Max(Ater_or_GPU_limitation, 30%)=Max(Max(P383a,P384,P202,P201,P402) / 3600; 30%)
3.2.2 METHOD 2
The method 2 is function of the relation between the GCH traffic and the PDCH traffic, if a saturation of
the GCH resources is observed a new Ater dimensioning should be performed.
Figure 3–6: Measured GCH traffic vs Measured PDCH traffic.
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The Required_GCH_Traffic is quasi linear relationship of the PDCH traffic, before there is congestion or
reduction due to High Ater load. If saturation is observed with n Atermux link some extra links should be
added, up to 5 Atermux per GPU. The Required_GCH_traffic can be found doing an extrapolation of the
linear relationship between GCH and PDCH traffic and taking the GCH traffic value corresponding to the
maximum observed PDCH traffic.
The formula is given by the:
Figure 3–7: Calculation of the Required_GCH_Traffic by Method 2.
With P38b as the PDCH traffic.
3.2.3 NUMBER OF GCH NEEDED
After the Required_GCH_Traffic is calculated, the Erlang C formula should be used to calculate the number
of GCHs needed and by association the number of Atermux to add.
3.2.4 HSDS IMPACT
With the activation of HSHS (EDGE and CS3/CS4) the consumption of AterMux transmission resources (GCH)
per radio resource (PDCH) increases.
The calculation of the Required_GCH_Traffic is impacted by an increase factor if HSDS is activated; the
process is in the next figure:
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Figure 3–8: Increase factor
The increase factor will be a function of:
o The transition type
o The target service penetration (i.e. %EDGE with respect to GPRS)
o The traffic profile
A transition type is explained by the following figure, depending on the path (a, b, c, d and e) different
increase factor is applied:
Figure 3–9: Transition type
If no reference BSC exists the increase factor is calculated taking in account assumption of the EGPRS
penetration at cell level. The increase factor is given by the relation between the number of GCHs per
PDCH before and after the service activation:
o initial
final
r_PDCH_nb_GCH_peAvg_target
r_PDCH_nb_GCH_peAvg_targetactorIncrease_f =
CS1 / CS2
CS3 / CS4
EDGE
CS3 / CS4 And EDGE
a
b
c
d
e
Increase_factor estimated on the basis of the Avg_target_nb_GCH_per_PDCH (depending on the target service
penetration)
Increase_factor =
Avg_target_nb_GCH_per_PDCHfinal /
Avg_target_nb_GCH_per_PDCHinitial
Increase_factor =
increase_factor (reference BSCs)
Execute transition
Dimensioning assessment for
fine tuning
Update reference BSCs set
Does a (set of) reference
BSC(s) Exist?
No
Yes
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Where:
o _PDCH_MCSynb_GCH_per S%_PDCH_GPR_PDCH_MCSxnb_GCH_per RS%_PDCH_EGP
r_PDCH_nb_GCH_peAvg_target
×+×==
o %_PDCH_EGPRS: % of Radio Resources (PDCH) supporting at least one TBF established in EGPRS
mode on a cell with MAX_EGPRS = MCSx
o %_ PDCH_GPRS: % of Radio Resources (PDCH) supporting only TBF established in GPRS mode on a
cell with MAX_GPRS = CSy
o Nb_GCH_per_PDCH_MCSx: given by table 6
o Nb_GCH_per_PDCH_CSy: given by table 5
For the different transition type the increase factor is given by:
Table 17: Increase_factor
Transition Type Increase_factor
a [(%_PDCH_EGPRS*4,49)+(%_PDCH_GPRS*1,64)]/1
b [1,64]/1
c [(%_PDCH_EGPRS*4,49)+(%_PDCH_GPRS*1)]/1
d [(%_PDCH_EGPRS*4,49)+(%_PDCH_GPRS*1,64)]/ 1,64
e (%_PDCH_EGPRS*4,49)+(%_PDCH_GPRS*1,64)/(%_PDCH_EGPRS*4,49)+(%_PDCH_GPRS*1)
For method 1 the application of the increase factor is by the simple formula:
o actorIncrease_f_trafficquired_GCH_trafficquired_GCH currentfinal ×= ReRe
For method 2 the impact of the increase factor is applied in the slope, as explained in the next graphic:
Figure 3–10: Method 2 – increase_factor
Where
o a2= a1 * Increase_Factor and b2 = b1 (approximation !)
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3.3 GPU/GP
The number of GPU/GP boards can be estimated thanks to the computed Needed GCH and to the computed
GPU_GCH_Capacity.
The GPU_GCH_Capacity is the number of GCH that a GPU/GP can handle. It is given by the minimum of
three variables:
{ }CapabilitySWHWGPUperGCHULMaxGPUperGCHDLMaxMin
CapacityGCHGPGPU
_/,____,____
__/
∑∑
=
The variables are defined by:
o HW/SW capability - Maximum number of GCH per GPU is:
• B9MR1:
� 480 – N_ATER_TS_MARGIN_GPU*4
• B9MR4:
� Legacy MFS: 480 – N_ATER_TS_MARGIN_GPU*4
� MxMFS: 1560 – N_ATER_TS_MARGIN_GPU*4
o Max_DL_GCH_per_GPU and Max_DL_GCH_per_GPU – The maximum number of GCHs that the GPU
will be able to handle can be obtained knowing the (M)CS distribution of the analyzed network:
• ( )( ) ...H_MCS1 max_DL_GCMCS1 max_PDCH_%MCS1
...H_CS1 max_DL_GCCS1 max_PDCH_%CS1
_GPUMax_DL_GCH
+××++××
=
• ( )( ) ...H_MCS1 max_UL_GCMCS1 max_PDCH_%MCS1
...H_CS1 max_UL_GCCS1 max_PDCH_%CS1
_GPUMax_UL_GCH
+××++××
=
• Where
� Max_DL/UL_GCH_CSy is defined in table 5.
� Max_DL/UL_GCH_MCSxP57x is defined in table 6
� The maximum number of PDCH per GPU/GP is dynamic depending on the used
coding schemes and on the HW/SW capability:
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Table 18: max_PDCH_CSy per GPU/GP determination for GPRS
GPRS max_PDCH_CSy: Max nb of PDCH per GPU/GP
Max CS GPU (A9135) & GP (A9130) up
to B9MR1
GP (A9130) from B9MR4 Case 12 E1 links per GP
GP (A9130) from B9MR4 Case 16 E1 links per GP
GP (A9130) from B9MR4 Case 10 E1 links per GP
CS1 240 960 960 896
CS2 240 960 960 896
CS3 224 892 892 716
CS4 200 684 804 544
Table 19: max_PDCH_MCSx per GPU/GP determination for EGPRS
EGPRS max_PDCH_MCSx: Max nb of PDCH per GPU/GP
Max MCS GPU (A9135) & GP (A9130) up
to B9MR1
GP (A9130) from B9MR4 Case 12 E1 links per GP
GP (A9130) from B9MR4 Case 16 E1 links per GP
GP (A9130) from B9MR4 Case 10 E1 links per GP
MCS1 224 860 860 860
MCS2 224 836 836 836
MCS3 208 796 796 672
MCS4 200 748 776 596
MCS5 184 604 704 480
MCS6 172 476 664 380
MCS7 136 320 452 256
MCS8 116 272 380 216
MCS9 108 252 352 200
The number of GPU/GP needed is then given by dividing the needed GCH per the GPU_GCH_Capacity.
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4 NETWORK PRIORITIES
With the introduction of the packet switch, in GSM networks, the radio and transmission resources available
have to be shared between the circuit and packet switch, it is a compromise between different variables:
the CS accessibility, PS accessibility, PS performance and most important with the operator network
capacity.
Normally, when PS is activated in a network, the traffic is mainly due to signalling (GMM/SM), with the time
and with the new services arriving, the end user customers begin to use these services as a daily routine
and the PS traffic starts to have more weight in the network. Two major reasons are associated to a rapidly
increase of PS traffic in a network, flat rates and short data traffic (e.g. chat, MMS, etc). With the increase
of PS traffic the network architecture and dimensioning have to be reviewed, parameters values
implemented during the EDGE activation have to be optimised to the new reality. The increase of capacity
in a network, either radio or transmission, impacts the costs and due to that the operators are quite
sensitive to this issue. That’s why, a consistent and rigorous approach has to be considered on this topic.
Three different main phases exist for the PS dimensioning and optimisation:
o Phase 1 - PS implementation/activation, the network is dimensioning for low PS traffic, mainly
signalling traffic.
o Phase 2 - Increase of PS traffic without enough radio and transmission resources – parameters
optimization needed to minimize the impact
o Phase 3 – Re-dimensioning of the network architecture.
In all the three phases the CS is the service with more priority, it is only considered the CS accessibility
since the performance is not impacted by PS access and traffic.
4.1 PHASE 1
For the phase 1, the network is carrying the first data traffic, it is mainly signalling (GMM/SM). The few
customers using user data service are spread in time and location. The traffic load created by them is low.
In this way the operators define their network priorities as:
1. Circuit Switch accessibility
2. Packet Switch performance
3. Packet Switch accessibility
The operators want to give to the few users the best performance as possible, not only throughput but also
small establishment time. Due to this, the configuration and parameterization is optimized to achieve the
better performance as possible. In order to reduce the GPRS signalling traffic and their impact in the radio
and transmission resources load some GSS optimisations are possible, for more information see sub-chapter
6.8
In this phase the parameters are in their default value, for best performance. For the default parameters
values see sub-chapter 2.10.
4.2 PHASE 2
The PS traffic increases with the new services, the capacity dimensioned during the PS implementation is
not enough. Congestion problems appear in the transmission and degradation of the PS accessibility and
performance begins due to the under dimensioned radio resources. The operator should react and it should
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optimize the network in accordance. This phase is a transition phase; it should be used for only a short
time.
The PS performance is no longer a major priority, important is to give PS access to all users and the
priorities are redefined as:
1. Circuit Switch accessibility
2. Packet Switch accessibility
3. Packet Switch performance
The BSS parameters should be optimised to able the implementation of the new network priorities. This
phase is when the PS traffic had increase to a critical situation; the major problem observed is congestion
at transmission level Ater and Abis and at DSP side. The parameter tuning proposed for this situation is
explained in chapters 6.6 and 6.7.
4.3 PHASE 3
With the upgrade of the transmission and radio resources, the network priorities are again reordered to
similar to phase 1:
1. Circuit Switch accessibility
2. Packet Switch performance
3. Packet Switch accessibility
The PS performance is again an operator priority, the user want to have his service with a good quality. The
BSS parameters should be optimised to allow a better throughput, e.g. more bandwidth in radio and
transmission resources. It is proposed to get back the parameter values to the default ones. For the default
parameters values see sub-chapter 2.10
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5 QOS FOLLOW-UP In this chapter is presented the main RNO indicators for QoS follow-up, they are grouped in three specific
RNO reports called dashboards:
o Alc_Mono_DashBoard_(E)GPRS_QoS
o Alc_Mono_DashBoard_(E)GPRS_Traffic_1
o Alc_Mono_DashBoard_(E)GPRS_Traffic_2
The Main RNO indicators are also included in several RNO reports and in this way it is also presented in this
chapter the main RNO reports to analyse.
An overview of end-user statistics is described in the sub-chapter 5.6.
5.1 TBF LIFE TIME
5.1.1 TBF ESTABLISHMENT
The next indicators allows to follow the success of the TBF establishment and the possible existing failures,
this ones can be due to radio, transmission interface, BSS internal failures or to congestion. It is not
possible in the current BSS release to distinguish the TBF establishments between GPRS and EDGE TBFs, this
lack of information can hide problems related to only one technology.
For DL:
Table 20: DL TBF Establishment RNO indicator Description Unit Comments
GPRS_DL_TBF_success_rate Rate of DL TBF establishment -successes (seized by the mobile)
%
GPRS_DL_TBF_request Number of DL TBF establishment -requests. nb
The absolute number of requests is important to validate the statistics
GPRS_DL_TBF_estab_allocated_rate Rate of DL TBF allocated per cell. % This indicator measure the impact of the congestion
GPRS_DL_TBF_estab_fail_BSS_rate Rate of DL TBF estab - failures due to BSS problem per cell. Reference: number of DL TBF estab -requests
%
GPRS_DL_TBF_estab_fail_GB_rate Rate of DL TBF estab -failures due to Gb interface problem per cell. Reference: number of DL TBF estab -requests
%
GPRS_DL_TBF_estab_fail_radio_rate Rate of DL TBF estab -failures due to radio problem per cell. Reference: number of DL TBF estab -requests
%
GPRS_DL_TBF_estab_fail_cong_rate
Rate of DL TBF establishment failures due to congestion per cell. Reference: number of DL TBF establishment requests.
%
Split of failures during DL TBF establishment
GPRS_DL_TBF_estab_fail_abis_cong Number of DL establishment failures due to congestion of Abis.
nb
GPRS_DL_TBF_estab_fail_ater_cong Number of DL establishment failures due to congestion of Ater(Mux).
nb
GPRS_DL_TBF_estab_fail_cpu_cong Number of DL establishment failures due to CPU processing power limitations of the GPU.
nb
GPRS_DL_TBF_estab_fail_dsp_cong Number of DL establishment failures due to congestion of DSP.
nb
GPRS_DL_TBF_estab_fail_radio_cong Number of DL TBF establishment failure due to radio congestion per cell.
nb
Split of the congestion failures, this information is important for BSS dimensioning
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For UL:
Table 21: UL TBF Establishment RNO indicator Description Unit Comments
GPRS_UL_TBF_success_rate Rate of UL TBF estab success. Reference: number of UL TBF estab -requests
%
GPRS_UL_TBF_request Number of UL TBF establishment -requests per cell.
nb The absolute number of requests is important to validate the statistics
GPRS_UL_TBF_estab_allocated_rate Rate of UL TBF allocated per cell. % This indicator measure the impact of the congestion
GPRS_UL_TBF_estab_fail_BSS_rate Rate of UL TBF estab -failures due to BSS problem per cell. Reference: number of UL TBF estab -requests
%
GPRS_UL_TBF_estab_fail_GB_rate Rate of UL TBF estab -failures due to Gb interface problem per cell. Reference: number of UL TBF estab -requests
%
GPRS_UL_TBF_estab_fail_radio_rate Rate of UL TBF estab -failures due to radio problem per cell. Reference: number of UL TBF estab -requests
%
GPRS_UL_TBF_estab_fail_cong_rate
Rate of UL TBF establishment failures due to congestion per cell. Reference: number of UL TBF establishment requests.
%
Split of failures during UL TBF establishment
GPRS_UL_TBF_estab_fail_abis_cong Number of UL establishment failures due to congestion of Abis.
nb
GPRS_UL_TBF_estab_fail_ater_cong Number of UL establishment failures due to congestion of Ater(Mux).
nb
GPRS_UL_TBF_estab_fail_cpu_cong Number of UL establishment failures due to CPU processing power limitations of the GPU..
nb
GPRS_UL_TBF_estab_fail_dsp_cong Number of UL establishment failures due to congestion of DSP.
nb
GPRS_UL_TBF_estab_fail_radio_cong Number of UL TBF establishment failure due to radio congestion per cell.
nb
Split of the congestion failures, this information is important for BSS dimensioning
When performing an investigation in the TBF establishment performance, a typical threshold to consider is
for DL is 95%, however for UL the threshold is lower 92% mainly due to signalling impact.
These values are high depended of the network configuration and overall performance. The different
failure causes should be analysed:
o Failures due to Gb – this might indicate problems at Gb link side (no BVC available, which would
affect the cell – this implies that the cell’s operational state is “disabled”);
o Failures due to BSS – this might indicate a system problem (e.g.: faulty board at MFS side). Verify
also if CS traffic is being affected due to BSS causes (e.g. TCH assign failures due to BSS);
o Failures due to congestion: these can also be divided in other sub-causes:
• Radio congestion – this might be due to badly functioning resources (like a TRE not working,
with unavailable TS or even 0 available TS), from too much CS traffic, or even from too
much PS traffic.
• Abis congestion, Ater congestion, DSP congestion and CPU congestion – either due to lack of
GCHs resources or not enough DSP and/or CPU processing power.
o Failures due to radio – might indicate radio problems (e.g. bad frequency plan, bad coverage
planning)
5.1.2 TBF DATA TRANSFER
These indicators evaluate the release of a TBF, they reflect possible failures during data transfer and TBF
releases due to reselection for moving MS.
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For DL:
Table 22: DL TBF Data Transfer RNO indicator Description Unit Comments
GPRS_DL_TBF_normal_release_rate Rate of DL TBF normal release. Reference: number of DL TBF establishment - successes
%
Rate of DL TBF not impacted by failures or reselection during data transfer
GPRS_DL_TBF_acceptable_release_rate
Rate of DL TBF release due to: - DL TBF release due to radio preemption - DL TBF release due to suspend resume procedure - DL TBF release due to cell reselection. Reference : number of DL TBF successes
%
Rate of DL TBF impacted during data transfer due to features to favour CS or cell reselection.
GPRS_DL_TBF_drop_rate Rate of DL TBF drops. Reference: number of DL TBF establishment - successes
%
GPRS_DL_TBF_normal_release Number of DL TBF normal release. nb
GPRS_DL_TBF_acceptable_release
Number of DL TBF release due to : - DL TBF release due to radio preemption - DL TBF release due to suspend resume procedure - DL TBF release due to cell reselection
nb
GPRS_DL_TBF_drop Total number of DL TBF drops. nb
GPRS_DL_TBF_radio_preemption_release_rate
Rate of DL TBF releases due to fast preemption in case of need of radio resources. Reference: number of DL TBF establishment successes.
%
GPRS_DL_TBF_release_suspend_rate
Rate of suspend messages for a DL TBF received from MS (via BSC). Reference: number of DL TBF establishment successes.
%
GPRS_DL_TBF_release_NC2_reselect_rate
Rate of DL TBF releases due to NC2 cell reselection Reference: total number of DL TBF establishment success
%
GPRS_DL_TBF_release_NC0_reselect_rate
Rate of DL TBF releases due to NC0 cell reselection Reference: total number of DL TBF establishment success
%
Split of acceptable release causes
GPRS_DL_TBF_drop_BSS_rate Rate of DL TBF drops due to BSS problems. Reference: number of DL TBF establishment - successes
%
GPRS_DL_TBF_drop_GB_rate
Rate of DL TBF drops due to Gb interface problems. Reference: number of DL TBF establishment - successes
%
GPRS_DL_TBF_drop_blocking_rate
Rate of DL TBF drops due to blocking situation at the beginning or at the end of DL TBF ( including blocking situation following NC2 cell reselection) . Reference: number of DL TBF establishment successes.
%
GPRS_DL_TBF_drop_N_stagnatingWindow_rate
Rate of DL TBF drops due to N_StagnatingWindow (including N_StagnatingWindow following cell reselection in transfer mode). Reference: number of DL TBF establishment successes
%
Split of TBF drop causes
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GPRS_DL_TBF_realloc_execution_fail_radio_rate
Rate of DL TBF drops due to radio failures during radio resource reallocation execution. Reference: number of DL TBF establishment successes.
%
GPRS_DL_TBF_drop_radio_rate Rate of DL TBF drops due to radio problems. Reference: number of DL TBF establishment - successes
%
For UL:
Table 23: UL TBF Data Transfer RNO indicator Description Unit Comments
GPRS_UL_TBF_normal_release_rate Rate of UL TBF normal releases. Reference: number of UL TBF establishment - successes
%
Rate of UL TBF not impacted by failures or reselection during data transfer
GPRS_UL_TBF_acceptable_release_rate
Rate of UL TBF releases due to: - TBF release due to radio preemption - TBF release due to suspend resume procedure - TBF release due to cell reselection. Reference : number of UL TBF success.
%
Rate of UL TBF impacted during data transfer due to features to favour CS or cell reselection.
GPRS_UL_TBF_drop_rate Rate of UL TBF drops. Reference: number of UL TBF establishment - successes
%
GPRS_UL_TBF_normal_release Number of UL TBF normal releases. nb
GPRS_UL_TBF_acceptable_release
Number of UL TBF releases due to : - UL TBF release due to radio preemption - UL TBF release due to suspend resume procedure - UL TBF release due to cell reselection
nb
GPRS_UL_TBF_drop Number of UL TBF drop. nb
GPRS_UL_TBF_radio_preemption_release_rate
Rate of UL TBF releases due to fast preemption in case of need of radio resources. Reference: number of UL TBF establishment successes.
%
GPRS_UL_TBF_release_suspend_rate
Rate of suspend messages for an UL TBF received from MS (via BSC). Reference: number of UL TBF establishment successes.
%
GPRS_UL_TBF_release_NC2_reselect_rate
Rate of UL TBF releases due to NC2 cell reselection Reference: number of UL TBF establishment successes
%
GPRS_UL_TBF_release_NC0_reselect_rate
Rate of UL TBF releases due to NC0 cell reselection Reference: number of UL TBF establishment successes
%
Split of acceptable release causes
GPRS_UL_TBF_drop_BSS_rate Rate of UL TBF drops due to BSS problems. Reference: number of UL TBF establishment - successes
%
GPRS_UL_TBF_drop_GB_rate
Rate of UL TBF drops due to GB interface problems. Reference: number of UL TBF establishment - successes
%
GPRS_UL_TBF_drop_blocking_rate
Rate of UL TBF drops due to blocking situation at the beginning or at the end of UL TBF (including blocking situation following NC2 cell reselection). Reference: number of UL TBF establishment successes.
%
Split of TBF drop causes
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GPRS_UL_TBF_drop_N_stagnatingWindow_rate
Rate of UL TBF drops due to N_StagnatingWindow (including N_StagnatingWindow following cell reselection in transfer mode). Reference: number of UL TBF establishment successes
%
GPRS_UL_TBF_realloc_execution_fail_radio_rate
Rate of UL TBF drops due to radio problems during radio resource reallocation execution Reference: number of UL TBF establishment successes.
%
GPRS_UL_TBF_drop_radio_rate Rate of UL TBF drops due to radio problems Reference: number of UL TBF establishment - successes
%
It is acceptable to have as lower as 95% for DL/UL TBF normal release rate, in case of DL/UL TBF drop rate
is expected to have value up to 4%.These value can change with the network design and interference noise
level in the network.
To perform an investigation in the data transfer, verify how TBF’s are being abnormally released. The
following causes are possible:
o RLC blocks are being lost during the GPRS connection
o RLC blocks are being retransmitted too many times – check the TBF Retransmission Ratio KPI;
o Connection drop is high – this might be due to 3 other sub-causes:
• System drop – indicating a system problem. Verify other KPI (GSM included);
• Gb drop – indicating problem on Gb interface;
o Radio drop – this might be due either to real radio drops or to acceptable releases (due to cell
reselection; suspend/resume procedure; PDCH pre-emption).
5.1.3 TBF REALLOCATION
To understand the TBF reallocation indicators is important to read the subchapter 2.6. The B9 release
brought new triggers to the reallocation comparing to B8, not only the PDCH allocation and soft pre-empted
are considered but also in B9 the GCHs reallocation and pre-emption.
Table 24: TBF Reallocation RNO indicator Description Unit Comments
GPRS_DL_TBF_realloc_T1_success_rate Rate of DL TBF reallocation Trigger 1 success over the number of DL TBF trigger 1 requests
%
GPRS_DL_TBF_realloc_T2_success_rate Rate of DL TBF reallocation Trigger 2 success over the number of DL TBF trigger 2 requests
%
GPRS_DL_TBF_realloc_T3_success_rate Rate of DL TBF reallocation Trigger 3 success over the number of DL TBF trigger 3 requests
%
GPRS_DL_TBF_realloc_T4_success_rate DL T4 reallocation success rate. %
GPRS_DL_TBF_realloc_T1_request Number of DL TBFs candidate for resource reallocation (trigger T1).
nb
GPRS_DL_TBF_realloc_T2_request Number of DL TBFs candidate for resource reallocation (trigger T2).
nb
GPRS_DL_TBF_realloc_T3_request Number of DL TBF candidate for resource reallocation (trigger T3).
nb
GPRS_DL_TBF_realloc_T4_request Number of DL TBF candidate for resource reallocation (trigger T4).
nb
The absolute number of requests is important to validate the statistics
GPRS_UL_TBF_realloc_T1_success_rate Rate of UL TBF reallocation Trigger 1 success over the number of UL TBF trigger 1 requests
%
GPRS_UL_TBF_realloc_T2_success_rate Rate of UL TBF reallocation Trigger 2 success over the number of UL TBF trigger 2 requests
%
GPRS_UL_TBF_realloc_T3_success_rate Rate of UL TBF reallocation Trigger 3 success over the number of UL TBF trigger 3 requests
%
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GPRS_UL_TBF_realloc_T4_success_rate
Rate of UL TBF resource reallocation successes for trigger T4. Reference: number of UL TBF candidate for resource reallocation for trigger T4.
%
GPRS_UL_TBF_realloc_T1_request Number of UL TBF candidate for resource reallocation (trigger T1).
nb
GPRS_UL_TBF_realloc_T2_request Number of UL TBFs candidate for resource reallocation (trigger T2).
nb
GPRS_UL_TBF_realloc_T3_request Number of UL TBF candidate for resource reallocation (trigger T3).
nb
GPRS_UL_TBF_realloc_T4_request Number of UL TBF candidate for resource reallocation (trigger T4).
nb
The absolute number of requests is important to validate the statistics
The investigation of the reallocation indicators is complex due to the high number of variables impacting
the reallocation algorithm performance. Depending on the trigger of each reallocation there is impact of
the PS traffic type and load, CS traffic load, network architecture, telecom parameters and MS type. For
one reallocation the trigger can also be due to two different reasons radio resources or transmission
resources, as possible analyses:
o High frequency of occurrence of T1 might indicate that the cell is sub-dimensioned to
accommodate all CS and PS traffic;
o The high number of T2 requests can be a consequence of the value of the parameter
GPRS_Multislot_Class_Def_Value and the traffic type (user data or GMM /SM).
For the reallocation indicators is not possible to define global thresholds since the performance of these
indicators will change from network to network.
5.2 RLC STATISTICS
5.2.1 (M)CS DISTRIBUTION
There are large possibilities to calculate/present the distribution of CS and/or MCS blocks. But all
ratios/rates/useful throughput/etc. indicators will be based on the number of useful blocks received per
(M)CS. Here we propose the MCS distribution statistics given its ratio, e.g. the number of transmitted useful
RLC blocks by overall useful RLC blocks, for DL and for UL.
The throughput indicators calculated using the (M)CS distribution are important for stability, since it
doesn’t represent the available maximum or average throughput in the cell, The throughput indicators are
impacted by small amount of data transfer
For DL:
Table 25: DL (M)CS Distribution RNO indicator Description Unit Comments
GPRS_DL_useful_RLC_blocks_CS1_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in CS-1, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_DL_useful_RLC_blocks_CS2_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in CS-2, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
Split of the CS distribution
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GPRS_DL_useful_RLC_blocks_CS3_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in CS-3, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_DL_useful_RLC_blocks_CS4_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in CS-4, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_DL_useful_RLC_blocks_MCS1_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-1, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS2_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-2, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS3_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-3, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS4_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-4, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS5_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-5, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS6_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-6, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS7_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-7, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS8_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-8, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_DL_useful_RLC_blocks_MCS9_ack_ratio
Ratio of useful DL RLC blocks sent on PDTCH encoded in MCS-9, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
Split of the MCS distribution
GPRS_DL_useful_throughput_radio_EGPRS_TBF_avg
Average DL useful throughput (in kbit/s) in RLC acknowledged mode. The DL retransmissions are not counted. Reference Time: Cumulated time duration of all active DL TBFs established in EGPRS mode.
kbit/s
GPRS_DL_useful_throughput_radio_GPRS_TBF_avg
Average DL useful throughput (in kbit/s) in RLC acknowledged mode. The DL retransmissions are not counted. Reference Time : Cumulated time duration of all active DL TBFs established in GPRS mode.
kbit/s
High impacted by the small data transfer, such as GMM and SM.
For UL:
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Table 26: UL (M)CS Distribution RNO indicator Description Unit Comments
GPRS_UL_useful_RLC_blocks_CS1_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in CS-1, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_UL_useful_RLC_blocks_CS2_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in CS-2, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_UL_useful_RLC_blocks_CS3_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in CS-3, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
GPRS_UL_useful_RLC_blocks_CS4_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in CS-4, in RLC acknowledged mode (the retransmitted blocks are not counted). Overall number of useful RLC data blocks encoded in CS1-2-3-4
%
Split of the CS distribution
GPRS_UL_useful_RLC_blocks_MCS1_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-1, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS2_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-2, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS3_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-3, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS4_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-4, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS5_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-5, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS6_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-6, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS7_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-7, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS8_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-8, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
GPRS_UL_useful_RLC_blocks_MCS9_ack_ratio
Ratio of useful UL RLC blocks sent on PDTCH encoded in MCS-9, in RLC acknowledged mode (the retransmitted blocks are not counted).
%
Split of the MCS distribution
GPRS_UL_useful_throughput_radio_EGPRS_TBF_avg
Average UL useful throughput (in kbit/s) in RLC acknowledged mode. The UL retransmissions are not counted. Reference: Cumulated time duration of all UL TBFs established in EGPRS mode.
kbit/s
High impacted by the small data transfer,
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GPRS_UL_useful_throughput_radio_GPRS_TBF_avg
Average UL useful throughput (in kbit/s) in RLC acknowledged mode. The UL retransmissions are not counted. Reference Time: Cumulated time duration of all UL TBFs established in GPRS mode.
kbit/s
such as GMM and SM.
The (M)CS distribution may be impacted by the radio conditions, telecom parameters but they are almost
not impacted by the transmission resources in B9 release.
It is normal to have the major sample in the (M)CS corresponding to the TBF_DL/UL_INIT_(M)CS, default for
GPRS is CS2 and for EDGE is MCS3. The impact of the initial (M)CS is high due to the high number of TBFs
with small data transferred, GMM/SM and MMS,…
A high number of MCS1 or CS1 can be due to the existing radio conditions or due to limit transmission
resources.
In B9 and in cells covering an area with good radio conditions, the MCS9 should have weight in the overall
distribution.
5.2.2 LLC/RLC TRAFFIC AND RETRANSMISSION
The overall user traffic in a cell should be measured by the next 2 indicators one for DL another for UL.
Table 27: LLC traffic
RNO indicator Description Unit Comments
GPRS_DL_LLC_bytes Number of DL LLC bytes received from the SGSN at BSSGP level per cell.
nb Overall DL LLC traffic
GPRS_UL_LLC_bytes Number of UL LLC bytes sent to the SGSN at BSSGP level per cell.
nb Overall UL LCC traffic
The split of LCC traffic by the Radio Access Capabilities are in the next 2 tables.
For DL:
Table 28: DL LLC traffic
RNO indicator Description Unit
GPRS_DL_LLC_bytes_EGPRS_ack_mode Number of DL LLC bytes transmitted and acknowledge on established DL TBF in EGPRS mode and RLC acknowledged mode
nb
GPRS_DL_LLC_bytes_EGPRS_unack_mode Number of DL LLC bytes transmitted and acknowledge on established DL TBF in EGPRS mode and RLC unacknowledged mode
nb
GPRS_DL_LLC_bytes_GPRS_ack_mode Number of DL LLC bytes transmitted and acknowledge on established DL TBF in GPRS mode and RLC acknowledged mode
nb
GPRS_DL_LLC_bytes_GPRS_unack_mode Number of DL LLC bytes transmitted and acknowledge on established DL TBF in GPRS mode and RLC unacknowledged mode
nb
For UL:
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Table 29: UL LLC traffic
RNO indicator Description Unit
GPRS_UL_LLC_bytes_EGPRS_ack_mode Number of UL LLC bytes received on UL TBFs established in EGPRS mode and RLC ackowledged mode
nb
GPRS_UL_LLC_bytes_EGPRS_unack_mode Number of UL LLC bytes received on UL TBFs established in EGPRS mode and RLC unackowledged mode
nb
GPRS_UL_LLC_bytes_GPRS_ack_mode Number of UL LLC bytes received on UL TBFs established in GPRS mode and RLC ack mode
nb
GPRS_UL_LLC_bytes_GPRS_unack_mode Number of UL LLC bytes received on UL TBFs established in GPRS mode and RLC unackowledged mode
nb
The indicators for RLC traffic are the next tables
For DL:
Table 30: DL RLC traffic RNO indicator Description Unit Comments
GPRS_DL_useful_bytes_CSx_ack Number of useful RLC data bytes sent on PDTCH, in GPRS and RLC ack modes.
nb
GPRS_DL_useful_bytes_MCSx_ack Number of useful RLC data bytes sent on PDTCH, in EGPRS and RLC ack modes.
nb
GPRS_DL_RLC_bytes_PDTCH_CSx_retransmission_ratio
In RLC ack mode, ratio of downlink RLC retransmitted data bytes sent on PDTCH and encoded in CS-x. Reference : overall number of DL RLC data bytes transmitted in GPRS mode
%
This indicator is an overall indication, however some CS may be more retransmitted than others.
GPRS_DL_RLC_bytes_PDTCH_MCSx_retrans_ack_ratio
In RLC acknowledged mode, ratio of DL RLC data bytes encoded in MCS-x and retransmitted due to unacknowledgement of the MS. RLC blocks containing LLC dummy UI commands are not counted. Reference: overall number of DL RLC data bytes transmitted in EGPRS mode.
% This indicator is an overall indication, however some CS may be more retransmitted than others.
For UL:
Table 31: UL RLC traffic
RNO indicator Description Unit Comments
GPRS_UL_useful_bytes_CSx_ack Number of useful RLC bytes sent on PDTCH in GPRS and RLC ack modes
nb
GPRS_UL_useful_bytes_MCSx_ack Number of useful RLC bytes sent on PDTCH in EGPRS and RLC ack modes
nb
GPRS_UL_RLC_bytes_CSx_retransmissing_ack_ratio
In RLC ack mode, ratio of uplink RLC bytes retransmitted on PDTCH and encoded in CS-x. Reference : total number of UL RLC data bytes sent on PDTCH in RLC ack mode
%
This indicator is an overall indication, however some CS may be more retransmitted than others.
GPRS_UL_RLC_bytes_PDTCH_MCSx_retrans_ack_rate
In acknowledged mode, ratio of UL RLC data bytes encoded in MCS-x and retransmitted due to unacknowledgement of the MFS. Reference : overall number of UL RLC data bytes sent on PDTCH encoded in MCSx in RLC ack mode
%
This indicator is an overall indication, however some CS may be more retransmitted than others.
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For both DL and UL the MCS retransmission rate can be up to 10%, this value is due to the fact of the higher
MCS being less robust and so more sensible to interference.
5.3 RADIO RESOURCES
One main reason for the existence of the radio resources indicators is to allow a good PS radio dimensioning
in a cell. It is possible to monitor the use of the PDCH not only the time they are established but also the
number of pilled TBF per PDCH.
Table 32: Radio Resources RNO indicator Description Unit Comments
GPRS_PDCH_EGPRS_traffic_time Cumulative time during which the slave PDCHs are established and carry at least one UL or DL TBF.(established in EGPRS mode)
s
GPRS_PDCH_traffic_time Cumulative time during which the slave PDCHs are established and carry at least one UL or DL TBF.(established in GPRS mode or EGPRS mode).
s
GPRS_PDCH_active_avg
For B8: average number of established slave PDCHs. For B9: average number of slave PDCHs carrying at least one UL or DL TBF.(established in GPRS mode or EGPRS mode). Reference: observation period
nb
GPRS_PDCH_used_max
Maximum number of PDCHs used in the cell Note: B8: It count the established PDCHs. An established PDCH is a PDCH to which one (several) transmission resource(s) is (are) connected. B9: It count the used (active) PDCH. An used PDCH is a PDCH that carries at least one UL or DL TBF. Consolidated in Day/Week/Month with the MAX value.
nb
These indicators are important for radio dimensioning
GPRS_DL_connection_time_avg Average connection time of established DL TBF (active and delayed). Reference : Number of DL TBF successes.
s
GPRS_UL_connection_time_avg Average connection time of established UL TBF. Reference : Number of UL TBF successes.
s
GPRS_DL_TBF_Pilled_avg
Average number of DL TBF on PDCHs active with DL transfers (TBF active and delayed phases are taken into account). An active PDCH with DL transfer is a PDCH carrying at least one DL TBF.
nb
GPRS_UL_TBF_Pilled_avg
Average number of UL TBF on PDCHs active with UL transfers (TBF active and delayed phases are taken into account). This indicator gives a measure of the number of UL TBFs piled up on a PDCH for all the PDCH. An active PDCH with UL transfer is a PDCH carrying at least one UL TBF.
nb
These indicators are important for radio dimensioning
GPRS_DL_TBF_estab_avg Average number of DL TBF simultaneously established over the granularity period. Consolidated in Day/Week/Month with the MAX value.
nb
GPRS_UL_TBF_estab_avg Average number of UL TBF simultaneously estab over the Granularity period. COnsolidated in day-week-month with the MAX value.
nb
GPRS_PDCH_per_DL_TBF_avg
Average number PDCHs (active with DL transfers) per DL TBF (TBF active and delayed phases are taken into account). An active PDCH with DL transfer is a PDCH carrying at least one DL TBF.
nb
GPRS_PDCH_per_UL_TBF_avg
Average number PDCHs (active with UL transfers) per UL TBF (TBF active and delayed phases are taken into account). An active PDCH with UL transfer is a PDCH carrying at least one UL TBF.
nb
These indicators are important for radio dimensioning
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GPRS_PDCH_used_DL_TBF_GMM_signalling_time_ratio
Ratio of time during which a DL TBF established for GMM signaling purposes uses a PDCH, compared with all DL PDCH established, for all PDCHs and for all the TBFs of the cell.
%
GPRS_DL_biased_and_DL_optimal_alloc_percent
Percentage of time during which downlink TBFs are granted the maximum number of PDCHs they support and the corresponding MSs are engaged in downlink-biased transfers. Reference: time during which MSs are engaged in downlink-biased transfers and served by DL TBFs.
%
GPRS_UL_biased_and_UL_optimal_alloc_percent
Percentage of time during which uplink TBFs are granted the maximum number of PDCHs they support and the corresponding MSs are engaged in uplink-biased transfers. Reference: time during which MSs are engaged in uplink-biased transfers and served by UL TBFs.
%
GPRS_BSC_high_load_percent Percentage of time during which the BSC is in high load situation in the cell. Reference: Granularity period
%
GPRS_MAX_PDCH_nb_avg
Maximum number of PDCHs that can be allocated in the cell. This indicator is consolidated in Day/Week/Month with the average of Hour/Day/Week values.
nb
This indicator is a function of the parameter Max_PDCH
GPRS_MIN_PDCH_nb_avg
Minimum number of PDCHs that can be preferentially allocated in the cell. This indicator is consolidated in Day/Week/Month with the average of Hour/Day/Week values.
nb
This indicator is a function of the parameter Min_PDCH
The pilled indicators are in restriction up to B9 MR4 ed6.
5.4 TRANSMISSION RESOURCES
The main indicators for transmission resource are impacted by Abis and Ater interface.
Table 33: Transmission Resources
RNO indicator Description Unit Comments
GPRS_transmission_GCH_busy_average Average number of GIC 16k busy (i.e. operational and used).
nb
GPRS_transmission_GCH_deficit_average Average number of GCH resources in deficit in the cell.
nb
Monitor the lack of transmission resources, Abis and Ater interface
GPRS_transmission_GCH_excess_average Average number of GCH resources in excess in the cell.
nb
GPRS_transmission_GCH_use_bonus_and_extra_average
Average number of extra and bonus Abis nibbles used in the cell.
nb
GPRS_transmission_GCH_use_bonus_and_extra_avg_max
Average number of extra and bonus Abis nibbles used in the cell. This indicator is consolidated in Day/Week/Month with the MAX value.
nb
These transmission indicators are very wide and for a deeper investigation there is in RNO a few number of
indicators for CELL, BSS and GPU. It is also recommended to read sub-chapters 6.6 and 6.7.
5.5 RNO REPORTS
The RNO reports for (E)GPRS QoS follow up are presented below:
o Alc_Mono_GPRS_telecom: This report provides details about main GPRS Telecom procedures.
• DL TBF establishment
• UL TBF establishment
• DL TBF Release
• UL TBF Release
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• DL TBF Acceptable Release causes
• UL TBF Acceptable Release causes
• DL TBF Drop Causes
• UL TBF Drop Causes
• DL TBF state
• UL TBF state
• DL session
• UL session
o Alc_Mono_GPRS_Throughput: This report provides details of GPRS/EGPRS throughputs.
• Radio throughput per cell
• DL GPRS radio throughput
• UL GPRS radio throughput
• DL EGPRS radio throughput
• UL EGPRS radio throughput
o Alc_Mono_GPRS_Resource_Reallocation_DL: This report provides details about the procedures
related to the DL resource reallocation feature
• DL resource realloc
• DL resource realloc T1
• DL resource realloc T2
• DL resource realloc T3
• DL resource realloc T4
o Alc_Mono_GPRS_Resource_Reallocation_UL: This report provides details about the procedures
related to the UL resource reallocation feature
• UL resource realloc
• UL resource realloc T1
• UL resource realloc T2
• UL resource realloc T3
• UL resource realloc T4
o Alc_Mono_GPRS_RLC_Ack_Traffic_Coding_Schemes: This report provides all the views related to RLC
traffic and efficiency in RLC acknowledged mode.
• RLC traffic in Acknowledge Mode
• DL EGPRS useful RLC traffic
• UL EGPRS useful RLC traffic
• GPRS DL useful RLC traffic
• GPRS UL useful RLC traffic
• DL RLC Ack retransmitted traffic per CS
• UL RLC Ack retransmitted traffic per CS
o Alc_Mono_GPRS_PDCH_Use_B9: This report provides all views related to PDCH allocation B9.
• Load Report
• Traffic time and Active number of PDCHs
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• DL TBF Pilled
• UL TBF Pilled
• PDCH per DL TBF
• PDCH per UL TBF
• DL TBF establishment per MS type
• UL TBF establishment per MS type
• GMM Signaling
• PDCH Preemption
o Alc_Mono_GPRS_Transmission_Resources: This report provides details about main GPRS transmission
resources.
• GPRS GCH resources
• Extra and Bonus Abis nibbles
• GCH in deficit
• GCH in excess
5.6 END-USER STATISTICS
The majority of the EDGE analyses go through the end user tests and their results. Three indicators are
considered as the main ones for QoS follow-up, they are from FTP and Ping test:
o DL FTP Application Throughput
o UL FTP Application Throughput
o Ping Application time
The EDGE protocol for end-user tests is detailed in reference [1]. The recommended protocol by NE should
be followed to allow the proper support from NE team. A deviation from the protocol may lead to results
different from the ones expected.
The expected values for these indicators are presented in this subchapter, they are the processed data
collected from different field trials. The analysis is based in statistical values and due to that it is highly
dependent of samples quality. A method was considered to validate in a first step the samples and then the
final results.
During an end-user field trial several external variables can impact the results:
o Upper layers (TCP/IP and FTP) performance
o Radio conditions (good, normal, radio)
o RF load (high CS traffic, high PS traffic)
o Radio resources allocation (number of PDCHs allocated, number of TBFs per PDCH)
o Transmission resources allocation (number of GCH)
Three different radio conditions are considered and they are based in the indicators RxLev and Mean_BEP.
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Table 34: Radio Conditions
Radio Conditions RxLev Mean_BEP
Good [-55 dBm, -65 dBm] [31, 25]
Normal [-65 dBm, -85 dBm] [25, 15]
Poor [-85 dBm, -100 dBm] [15, 0]
In the expected results is considered that no impact exist from the radio and transmission resources.
Table 35: Expected Application Throughput
Radio Conditions Expected DL Applic Throughput
per PDCH interval (kbit/s) Expected UL Applic Throughput
per PDCH interval (kbit/s)
Good 40.0 - 53.5 28.9 - 40.0
Normal 35.7 - 43.6 26.5 - 38.1
Poor 28.2 - 38.0 14.9 – 22.8
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6 OPTIMISATION METHODS AND CONSTRAINTS
6.1 LOW DL THROUGHPUT OBSERVED
The main “complain”, during end-to-end tests, is the observation of low DL throughput at application layer
and at RLC layer. In 80% of the cases this issue is not associated with BSS network, the major problems
observed are in the PDP context negotiation and in the FTP server configuration. This complains comes
when non prepared end user tests are done, in services such as FTP download.
FTP is the best option to measure the throughput in a network.
6.1.1 END-TO-END ANALYSIS
In end-to-end analysis all parts of a network are analysed and their performance evaluated. The analysis
can be split in two, the impact of the radio layers and the impact of the upper layers (LLC layer up to
Application layer).
Test preparation
The correct use of tools and test preparation is necessary to have a reliable analysis of the results. When a
low DL throughput is observed, the tests should be repeated several times to give as much as possible
statistical consistency of the results.
A set of tools is proposed:
o Deutrip: Generates application traffic automatically (FTP, WEB, Streaming, etc.) and records
statistics (application throughput, access time, etc.)
o Ethereal: Protocol analysis (TCP/IP but also many others), developed by the Open-source
community (GNU license) and works on top of a capture library (WinPcap, for Windows)
o Agilent E6474A (Nitro): Tool to collect and process air interface trace
o K12/K15: they are used to collect data from different interfaces, one important for PS analysis is
the Gb.
o Compass: tool used mainly to post-process the data from Gb traces, two possible usages : global
analysis of user traffic and deep analysis of traffic generated during tests.
The layer where these tools are used is explained by the figure below.
Figure 6–1: Network Architecture.
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When performing the test, first it is important to eliminate possible impact of the radio conditions and
network load (radio and transmission), a way to do it is to perform the test in good coverage cells, well
dimensioned and in low traffic hours. Second, the FTP server configuration and location should be verified.
With these previous constrains removed, the test is performed and the results can easily be analysed.
First step: Ethereal trace analysis
The Ethereal gives a global view of the transfer, the light investigation performs in this first step will give a
direction to a deeper analysis:
a) Pollution traffic
Check possible pollution traffic, e.g. packet traffic generated by windows update, anti-virus update, etc.
This extra traffic can have an impact in the end-user application throughput, by “stealing” bandwidth.
Check in the message transfer window the IP Source address and the IP destination address, it should be
only from your PC and from the FTP server.
If polluted traffic is observed, before repeating the test, remove all possible source of background packet
switch traffic. For example disable the windows update.
b) Main TCP parameters
To go deeper in the TCP/IP analyses check the main TCP parameters (MTU, RWIN):
o MTU recommended value is 1500 Bytes = MSS + 40 Bytes => MSS = 1460 Bytes.
• To check the used MSS see as example the figure below (note: MSS is only available in SYN,
ACK/SYN messages):
Figure 6–2: Ethereal example - MSS.
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o RWIN is recommended to be set to 64kBytes (64520 Bytes)
• Also this TCP parameter can be checked in the message layer.
Figure 6–3: Ethereal example - RWIN.
If the TCP parameters are not correct checked and if the limitation is in the drive test PC, you can use
Dr.TCP (it is freeware tool that can be found in http://www.dslreports.com) to correct the TCP parameters.
The setting should be similar to the ones presented in the figure below.
Figure 6–4: Dr. TCP example – TCP parameters
If the TCP parameters are not correct in the PC you can use the same tool to implement the right values.
After, it is recommended to repeat the tests.
c) FTP transfer - data flow
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The next step in the investigation is to analyse the overall data flow during FTP transfer. The process is to
filter one of the bad FTP download transfer by using the function “Follow TCP Stream”. These enables 3
main functions which give graphic representation of the round trip time, TCP throughput and packet flow
(data and ack).
The importance of a graphic representation is to have a better global view of the data transfer and a fast
identification of the bottlenecks and problems. The graphic time-sequence as the major information and
existing problems can be split in two, the next examples are representative of the most reported issues:
o BSS/Radio layers impact, for example due to bad radio conditions or cell-reselections.
Figure 6–5: Ethereal example – Time/Sequence graphic 1
Figure 6–6: Ethereal example – Time/Sequence graphic 2
Expected slope with throughput = 200kbit/s
Good throughput with small perturbations
(high MCS with BLER ?)
throughput is decreasing (MS going towards the edge of the cell, and MCS are decreasing ?)
2-3 seconds hole, with TCP losses (radio drop and LLC-FLUSH due
to reselection ?)
Retransmission of lost data
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o Upper layers impact, observed by TCP losses and retransmissions.
Figure 6–7: Ethereal example – Time/Sequence graphic 3
Figure 6–8: Ethereal example – Time/Sequence graphic 4
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Second step: in-depth analysis
In this step the investigation can follow two different ways, analysis of possible radio impact and analysis of
upper layers impact.
a) For the radio impact the process is to analyse the traces collected in the air interface, for example using
Nitro. The key indicators to investigate are:
o Radio conditions, given by Rx Level, mean_BEP and CV_BEP, define the radio conditions during the
test.
o MCS distribution, typical cases:
• High usage of MCS3, normally associated to TBF_DL_INIT_MCS
o Block Error Rate, high BLER can be due to bad radio conditions or equipment problems.
o DL RLC throughput per TS, the value of this indicator is dependent of the previous indicators values
and should be compared with the expected throughput per radio conditions presented in the
previous chapter.
b) The upper layer investigation is performed by analysing traces from different points, mainly they are
from TCP/IP trace at client side, Gb traces and TCP/IP at FTP server side.
During a FTP DL, see in Ethereal on the client side that some TCP segments are lost, and retransmitted.
This causes a big impact on the throughput. Most often the TCP segments are not lost by the BSS, but by
some other elements above it (Frame relay of the Gb interface, SGSN, IP backbone, etc.).
The principle of the analysis is to take an Ethereal trace on the PC client side, simultaneously with a Gb
trace (with K12/K15) and preference collect also Ethereal trace at FTP server side
First identify the TCP segment lost at client side.
Then try to see if they were already lost on Gb interface or not.
-> at client side, it should be seen something like this in DL :
A - B - [previous segment lost] - D - E - F - G - H - I - J - K - C - L - M - N - O...
-> at Gb side, either you have:
A - B - C - D - E - F - G - H - I - J - K - C - L - M - N - O... (segment not missing, so was lost after Gb)
Or:
A - B - D - E - F - G - H - I - J - K - C - L - M - N - O... (segment missing, so was lost before Gb).
TCP segments numbers have a unique identifier, which can be seen in both traces.
Beware that in Ethereal, it should be set the option to see the absolute value, not the relative one:
-> Menu Edit -> Preferences -> Protocols -> TCP -> Unselect "Relative sequence numbers and window scaling"
The steps of the analysis are:
a) In Ethereal, click on any DL frame with FTP-DATA.
b) Menu Statistics -> TCP Stream graph -> Time-sequence graph (tcptrace)
c) Identify in the trace a TCP segment lost and retransmitted. Click hold CTRL and click a segment in the
graph to go to the position in the trace.
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d) Identify the segment number of the retransmitted (lost) segment. (which was called "C" in the example
earlier).
e) Identify also the segment numbers "B" and "D"
NB: There should be: B = C - MSS, and D = C + MSS, with MSS=Max segment size, often 1380 or 1460.
f) Open the Gb trace for example with K12 record viewer and look for the TCP segments number B, C, D.
NB: in K12 record viewer, once the correct decoding stack is used, it should be possible to see the decoding
of TCP layer, and the TCP segments number. Find the TCP segment number (be careful to choose a DL one,
and to select the Segment number, not the ACK number). Then right mouse button click -> Add column.
That way you get the TCP segment number as a new column in the synthetic view.
g) check if there is :
A - B - C - D - E - F - G - H - I - J - K - C - L - M - N - O... (segment not missing, so was lost after Gb)
A - B - D - E - F - G - H - I - J - K - C - L - M - N - O... (segment missing, so was lost before Gb).
If the problem is before Gb, e.g. in the CN or IP network, forward the problem to the GSS team. If the
problem is after Gb it can be associated with the LLC layer parameterization and configuration.
Typical cases and solutions
a) BSS Network:
o Case: Less number of the DL PDCH allocated than the MS capability, due to the impact of load in
the cell
• Solution: Check cell configuration and radio dimensioning:
� Cell configuration and parameters such as:
• Number of TRX
• Number of TRA - EDGE capable
• Max_PDCH
• MAX_PDCH_High_Load
• Min_PDCH
• High_Traffic_Load_GPRS
� Check number of T1 reallocation
� GSM indicators, traffic load and congestion
� GPRS Radio resources allocation indicators, see sub-chapter 5.3
o Case: Gb Congestion noticed by NSE (UL congestion control), pre-emption of one PDCH per each
T_UL_Congestion seconds until the end of the Gb congestion.
• Solution: Check BVC parameters
o Case: Lifetime parameter is changing during DL LLC PDU transfer in the Gb.
• Solution. With Ericsson SGSN
� Set PDU_Lifetime_Order to disable
o Case: Low throughput observed due to lack of transmission resources.
• Solution: Perform BSS architecture and dimensioning, see chapter 3.
b) GSS Network
o Case: Wrong QoS parameters in the HLR and/or in the client side:
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• Solution: The QoS parameters are negotiated during the PDP context activation; they are
defined by the minimum of the client or the network. Check in the PDP context negotiation
L3 messages the QoS parameters:
� RLC: ack
� LLC: unack
� Mean Throughput: Best-effort
� Peak throughput: Up to 256 000 octets/s (2 048 kbit/s).
• In the client side the QoS parameters can be tuning by the AT command:
� +CGDCONT=1,"IP","APN";+CGQREQ=1,3,4,3,0,0
c) IP Network
o Case: Wrong TCP/IP parameters, client side and FTP side.
• Solution: Using Dr. TCP correct the parameters values
� MTU = MSS + 40 = 1460 + 40 = 1500 Bytes
� RWIN > RTT * Bandwidth, recommended RWIN = 64520 Bytes
o Case: MTU bottleneck in IP network
• Solution: Find the largest non-fragment MTU in the network. Test the network by pinging
the server:
� “ping –l MSS –f target_name”
� Find the largest possible non-fragmented packet
• to compensate the difference between ICMP and TCP headers,
o add 28 Bytes (ICMP 8 Bytes & IP 20 Bytes headers) to the MSS to get
the MTU
o the MSS for TCP/IP to be configured for FTP DL or UL is MTU – 40
Bytes for headers (TCP 20 Bytes & IP 20 Bytes).
o Case: FTP server misconfigured:
• Solution: Check buffer size
• Solution: TCP parameters
• Solution: Check the FTP server load, number of clients connected, etc.
6.2 DL MCS FLUCTUATION
One common complain and also associated with the low throughput is the DL MCS fluctuation, normally
observed between MCS9 and MCS6.
This fluctuation could be due to the radio conditions or to uncontinuous LLC traffic.
6.2.1 RADIO CONDITIONS
The interference/bad quality in the network will generate some not well decode blocks leading to a need
of block retransmissions.
As example, it is considered that MCS9 is used in a DL data transfer. There is 2 RLC blocks per radio blocks
with the same number of payload as MCS6, see following table and figure:
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Table 36: MCSx structure
Figure 6–9: Radio Block structure
In case of RLC block is not well decoded from the MCS9 radio block, only this block will be retransmitted
and using MCS6. In the next example, it is considered that RLC block 1 is not well decoded and so it will be
retransmitted.
Figure 6–10: RLC block not well decoded
37 Bytes 37 Bytes 37 Bytes 37 Bytes
RLC Block 1 RLC Block 2
Radio Block
MCS9
37 Bytes 37 Bytes MCS6
RLC Block 1 - Retransmitted
Radio Block
37 Bytes 37 Bytes 37 Bytes 37 Bytes
RLC Block RLC Block
Radio Block
MCS3
MCS6
MCS9
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To confirm the DL MCS fluctuation is due to radio conditions the BLER should be check.
6.2.2 UNCONTINUOUS LLC TRAFFIC
A second possible hypothesis for the DL MCS fluctuation is due to an uncontinuous LLC traffic. If the LLC
PDU traffic coming from the SGSN by the Gb is not continuous, the BSS is able to adapt the MCS according
the data size to be sent in the RLC/MAC data block. If there is no more DL LLC PDUs stored for the MS, RLC
sends the last segment of the last useful RLC data block. This radio block contains the last segment of the
last useful DL LLC PDU, completed by an LLC UI Dummy command in order to maintain the DL TBF alive.
If the radio block consists of two RLC data blocks (i.e. if the current MCS is MCS-7 or MCS-8 or MCS-9) and
the last segment of the last useful DL LLC PDU fits into the first part of the radio block, then the MCS shall
be decreased from MCS-9, 8 or 7 to MCS-6 or 5. Indeed, the first LLC UI Dummy command has already been
inserted into the end of the LLC queue in order to be send as last useful LLC PDU segment.
6.3 UL PERFORMANCE
As explained in sub-chapters 2.7 and 2.8, in B9 there was an improvement in the UL performance due to
three new features:
o Support of 8-PSK in uplink.
o Support of incremental redundancy and resegmentation.
o Extended UL TBF mode.
The feature “support of 8-PSK in uplink” is subject to optimisation as for DL, in terms of usage of highest
MCS.
6.3.1 RESEGMENTATION VS IR
With the introduction of 8-PSK modulation in uplink, two sub-features were introduced the incremental
redundancy and resegmentation, the first one is activated by the flag En_IR_UL and the second by the flag
En_Resegmentation_UL.
The default values for these parameters are:
o En_IR_UL = Disable
o En_Resegmentation_UL= Disable
Based in results from field trials, a NE recommendation is proposed:
o En_IR_UL = Enable
o En_Resegmentation_UL= Disable
This parameter set provides the best performances, whatever the radio conditions. The significant gain is
observed in medium and bad radio conditions. In good radio conditions the performance impact of the
parameter setting is neglected.
6.3.2 EXTENDED UL TBF MODE
The benefit of the feature extended UL TBF mode is measured by accessibility tests, e.g. pings. With small
interval between iteration the gain brought by the feature could be up to 60% of the time to ping a server.
The gain is depended of the ping size and the iteration interval. This achieve is possible due to keeping the
UL TBF established and to maintain the higher MCS between iteration. For more details see [2].
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6.4 ACCESS TIME OPTIMIZATION
The access time of a network is measured by the application service “ping”, a few parameter optimizations
are possible to improve ping performance, however all the parameter proposals have impact in the
transmission resources and there will be increase of load if applied:
o For all pings:
• TBF_DL/UL_Init_MCS - Increase the initial MCS from MCS3 to MCS6.
� Better throughput in the first blocks and lower ping time.
� Ping test are to be performed in good radio condition, so no impact in the tests are
expected due to radio conditions, for example retransmission due to a not well
decoded RLC block.
o Mainly for ping with small interval between iteration:
• EN_EXTENDED_UL_TBF – Enable the Extended UL TBF mode feature to maintain the UL TBF
alive
• T_MAX_EXTENDED_UL – The default is 2s, but can be increase if need for better ping
performance.
o Mainly for ping with medium and large interval between iteration:
• EN_FAST_INITIAL_GPRS_ACCESS – The feature will guarantee transmission resources are
keep established for the cell, along with the next parameter it will be possible to optimize
the transmission for the cell having ping test. It consume transmission resource even
without PS traffic in the cell
• N_GCH_FAST_PS_ACCESS – The increase of the parameter value from 1 to 5 will guarantee
enough resources in the cell for allowing good ping performances.
6.5 EDGE PERFORMANCE VERSUS FREQUENCY PLANNING
Since EDGE was launched in Alcatel Networks, there were several field trials and drive test campaigns, the
results retrieved from those measurements were analysed and processed.
From the analysis performed the Frequency Hopping can degraded EDGE performance in average less than
5%.
When an operator plans to implement EDGE several dimensioning decisions has to be done, such as the
radio resources and transmission resources, these major decisions have higher impact in the EDGE
performance than the frequency type. For example, 2 TBFs sharing the same PDCHs degraded 50% in the
EDGE performance, 3 PDCHs allocated in DL instead of 4 PDCHs have 25% of impact.
To conclude the design and the parameterization in a network have higher importance in the EDGE
performance, than the frequency hopping and so this last one can be neglected, if it is not too aggressive.
6.6 ABIS CONGESTION
As explained in chapters 2.3.2 and 3.1 in B9 Abis TS have a dynamic allocation for PS. Being dynamic, it has
associated a probability of congestion, that increases with the increase of load in the cell. To provide high
EDGE performance, in B9 less extra Abis nibbles are configured for a BTS than in B8.
To detect possible Abis congestion, check first the global transmission indicators and after the Abis specific
indicators.
At transmission (Abis/Ater) level:
o GPRS_transmission_GCH_deficit_time - Cumulated time during which there is a deficit of GCH
resources in the cell.
o GPRS_transmission_GCH_deficit_average - Average number of GCH resources in deficit in the cell.
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At Abis level:
o GPRS_transmission_deficit_extra_and_bonus_time - Cumulated time during which there are extra
and bonus Abis nibbles in deficit in the BTS.
o GPRS_transmission_deficit_extra_and_bonus_average - Average number of extra and bonus Abis
nibbles in deficit in the BTS.
As remark the deficit given by the counter P470, used in the previous indicators, is a "relative" deficit
because it depends on the configuration of two parameters R_AVERAGE_GPRS and R_AVERAGE_EGPRS. The
counter P470 is in the restriction list with the FR 3BKA13FBR181686, the correction was done in MR4 Ed02 - Patch 30CP_00E.
In a critical situation the impact of the Abis congestion should be observed in the TBF establishment
indicators:
o For DL:
• GPRS_DL_TBF_estab_fail_abis_cong - Number of DL establishment failures due to
congestion of Abis.
o For UL:
• GPRS_UL_TBF_estab_fail_abis_cong - Number of UL establishment failures due to
congestion of Abis.
Few parameters can be optimized to decrease congestion in the Abis, however they have end-user
performance impact. For a permanent solution consider a new dimensioning study in the network.
o T_GCH_Inactivity - Timer to postpone the release of the “unused” GCHs of a TRX after TBF
release(s).
• Changeable by operator at BSS level - Min = 1s, Def = 3s, Max = 100s.
• Recommendation for congestion situation:
� Decrease the parameter value for 2s to save transmission resources.
o T_GCH_Inactivity_Last - Timer to postpone the release of the last N_GCH_FAST_PS_ACCESS
“unused” GCHs in a cell, when the last TBF has been released in the cell (launched after
T_GCH_Inactivity).
• Changeable by operator at BSS level - Min = 1s, Def = 20s, Max = 200s.
• Recommendation for congestion situation:
� Decrease the parameter value for 8s to save transmission resources.
6.7 ATER CONGESTION
The Ater congestion or in “high load” situation may impact the end-user performance. The GCHs in deficit
will in first step decrease the TBF throughput and in a second step it may originate TBF establishment
failure.
This degradation can be observed and analyzed by RNO indicators.
At Ater/GPU level:
o GPRS_GPU_Ater_cong_time - Time during which AterMux interface (GICs) for this GPU is congested
(at least one PDCH group impacted). By congestion, in this case is defined as the time during which
the number of used AterMux nibbles is greater than (available Atermux nibbles -
N_ATER_TS_MARGIN_GPU).
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o GPRS_GPU_Ater_cong_percent - Percentage of time during which AterMux interface (GICs) for this
GPU is congested (at least one PDCH group impacted).
o GPRS_transmission_GCH_deficit_ater_nibbles_time - Cumulated time during which there are Ater
nibbles in deficit in the GPU.
o GPRS_transmission_GCH_deficit_ater_nibbles_average - Average number of Ater nibbles which are
in deficit in the GPU.
At DSP level:
o GPRS_DSP_CPU_overload_time - Time during which at least a DSP is in CPU overload state. A DSP is
said overloaded when its CPU load is > =DSP_LOAD_THR2.
o GPRS_DSP_CPU_overload_percent - Percentage of time during which a DSP is in CPU overload state.
o GPRS_GPU_DSP_cong_time - Time during which a DSP enters the congestion state.
o GPRS_GPU_DSP_cong_percent - Percentage of time during which a DSP enters the congestion state.
At transmission (Abis/Ater) level:
o GPRS_transmission_GCH_deficit_time - Cumulated time during which there is a deficit of GCH
resources in the cell.
o GPRS_transmission_GCH_deficit_average - Average number of GCH resources in deficit in the cell.
In a critical situation the impact of the Ater/GPU(GP)/DSP congestion should be observed in the TBF
establishment indicators:
o For DL:
• GPRS_DL_TBF_estab_fail_ater_cong - Number of DL establishment failures due to
congestion of Ater(Mux).
• GPRS_DL_TBF_estab_fail_cpu_cong - Number of DL establishment failures due to CPU
processing power limitations of the GPU.
• GPRS_DL_TBF_estab_fail_dsp_cong - Number of DL establishment failures due to congestion
of DSP.
o For UL:
• GPRS_UL_TBF_estab_fail_ater_cong - Number of DL establishment failures due to
congestion of Ater(Mux).
• GPRS_UL_TBF_estab_fail_cpu_cong - Number of DL establishment failures due to CPU
processing power limitations of the GPU.
• GPRS_UL_TBF_estab_fail_dsp_cong - Number of DL establishment failures due to congestion
of DSP.
If relevant congestion is found in the previous indicators a set of NE recommendation are proposed. In a
first phase, e.g. the congestion is relevant but not critical a few parameter optimizations are proposed,
otherwise a new dimensioning is needed.
The Ater parameter optimizations recommended are:
o N_ATER_TS_MARGIN_GPU - Number of free 64k Ater TSs that are kept “in reserve” in order to be
able to serve some priority requests (first PS traffic) in the cells of the GPU.
• Changeable by operator at BSS level - Min = 0 TS, Def = 2 TS, Max = 10 TS.
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• Parameter impact:
� Increasing the value of this parameter can increase the average number of unused
Ater nibbles in the GPU (only first PS accesses will benefit from the margin, not the
on-going TBF traffic). Remark: if the value is increased there will be more
GPRS_GPU_Ater_Cong_Time, due to the definition of GPRS_GPU_Ater_Cong_Time.
� But on the other hand, a high value will increase the probability of not serving
priority requests in the GPU (cases where several priority requests have to be
served in a short period of time in different cells).
� Setting N_ATER_TS_MARGIN_GPU to 0 can lead to situations where priority requests
cannot be served at all.
• Recommendation for congestion situation:
� The parameter value should be kept at least equal to 2 TS
o Ater_Usage_Threshold - Threshold (percentage of used Ater nibbles, in a GPU) above which the Ater
usage is said “high”.
• Changeable by operator at BSS level - Min = 1%, Def = 70%, Max = 100%.
• Recommendation for congestion situation:
� Decrease the threshold for a more reactive algorithm in case of critical situations.
� Available atermux nibbles - (Available Atermux nibbles * Ater_Usage_Threshold) >
N_ATER_TS_MARGIN_GPU in order to enter in "high load" condition before entering
in congestion.
o GCH_RED_FACTOR_HIGH_ATER_USAGE - Reduction factor of the number of GCHs targeted per PDCH,
when the Ater usage is “high”.
• Changeable by operator at cell level - Min = 0.1, Def = 0.75, Max = 1.
• Parameter impact:
� A low value of GCH_RED_Factor_High_Ater_Usage can be coherent with a high value
of Ater_Usage_Threshold (it will avoid reaching the saturation point of 100% of the
Ater resources used at the same moment in the GPU).
� Reciprocally, a high value of GCH_RED_Factor_High_Ater_Usage can be coherent
with a low value of Ater_Usage_Threshold (it will limit the risks of wasting, i.e. of
not using, Ater resources in the GPU).
• Recommendation for congestion situation:
� In critical situations where the transmission resources are always congested,
decrease the value to reduce the impact of congestion and save resources for new
PS access.
The global transmission parameter optimizations are:
o T_GCH_Inactivity - Timer to postpone the release of the “unused” GCHs of a TRX after TBF
release(s).
• Changeable by operator at BSS level - Min = 1s, Def = 3s, Max = 100s.
• Parameter impact:
� The lower, the faster Ater nibbles are freed when unused (Ater congestion is
reduced).
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� A too low timer value will increase GSL/CPU loads due to numerous GCH releases &
reestablishments. It may also not anticipate traffic resumption on TRXs in an
optimal way (only MSC2 usable at TBF resumption).
• Recommendation for congestion situation:
� Decrease the parameter value for 2s to save transmission resources.
o T_GCH_Inactivity_Last - Timer to postpone the release of the last N_GCH_FAST_PS_ACCESS
“unused” GCHs in a cell, when the last TBF has been released in the cell (launched after
T_GCH_Inactivity).
• Changeable by operator at BSS level - Min = 1s, Def = 20s, Max = 200s.
• Parameter impact:
� The lower the T_GCH_Inactivity_Last vaule will be, the faster Ater nibbles are freed
when unused (Ater congestion is reduced). A too low timer value will however
poorly anticipate traffic resumption on TRXs (higher average duration of TBF
establishments) and increase GSL/CPU loads due to numerous GCH releases &
reestablishments.
• Recommendation for congestion situation:
� Decrease the parameter value for 8s to save transmission resources.
o “Fast initial PS access” feature.
• EN_FAST_INITIAL_GPRS_ACCESS: Changeable by operator at cell level – Def = off.
• N_GCH_FAST_PS_ACCESS: Customizable at MFS level – Min = Def = 1 GCH, Max = 5 GCHs.
• Parameter impact:
� No "fast initial PS access" avoids Ater resource consumption and wastes.
� But "fast initial PS access" guarantees PS traffic in all the cells in which it is
activated (at radio & Abis/Ater levels).
6.8 GSS OPTIMISATION FOR GMM/SM SIGNALLING
From the activation of the PS in a network, the GMM/SM signalling traffic has a high weight in the radio and
transmission resources load. Several optimisations at GSS level are possible, their aim is to reduce both the
RAU and the GPRS Attach procedure.
a) Optimisation by the procedure Suspend/Resume:
The procedure suspend/resume should be activated at BSS (it is activated in default) and at GSS level in
order to avoid that mobiles trigger a RA update procedure at the end of each CS connections, in order to
warn SGSN that they are re-available for PS services.
With Suspend/Resume, this is done directly by the BSS at the end of each CS connections.
b) Optimisation of the procedure GPRS attach:
GPRS attach on demand:
2 modes of Attach at GSS level are possible:
- attach sent at "switch on" of the mobile
- attach "on demand" when the user wants to activate a PDP context
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It is preferable to "force" the configuration of the mobiles towards the second mode in order to avoid all
the GPRS attach procedure not useful as they are not followed by user traffic.
GPRS attach repetitions:
A strong number of GPRS attach can be followed by GPRS attach reject because they are generated by users
having GPRS mobiles but no GPRS subscription. The failure cause "GPRS service not allowed" sent by the GSS
in the GPRS attach reject message should prevent from repeating GPRS attach attempts in such case.
c) Optimisation of the procedure RA update:
The timer T3312 within SGSN manages the periodicity of the sending of RA update request.
In order to avoid a too strong load coming from this procedure, it is preferable to increase the value of this
timer. However, no value can be recommended as it can depend on the GSS vendor implementation.
It has been seen in several networks that this values is set to 54 min, although this value can be increase up
to 3 hours, reducing number of periodic RAU.
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A TABLE OF FIGURES
Figure 2–1: B8 release EGCH vs B9 release M-EGCH........................................................................................ 8 Figure 2–2: M-EGCH and L1-GCH layers location ............................................................................................ 9 Figure 2–3: GCH filling with RLC/MAC PDUs ................................................................................................... 9 Figure 2–4: Abis resources concept in B8...................................................................................................... 11 Figure 2–5: Abis resources concept in B9...................................................................................................... 11 Figure 2–6: Cyclic calculation of the usage of the cell resources ................................................................. 14 Figure 2–7: Cyclic calculation of the average usage of the cell resources .................................................... 15 Figure 2–8: General diagram of the Max_SPDCH_Limit calculation............................................................... 15 Figure 2–9: Detailed diagram of the Max_SPDCH_Limit calculation .............................................................. 17 Figure 2–10: Max_SPDCH_Limit CS and PS zones .......................................................................................... 18 Figure 2–11: PS TS zones – example 1........................................................................................................... 19 Figure 2–12: PS TS zones – example 2........................................................................................................... 19 Figure 2–13: T1 reallocation......................................................................................................................... 21 Figure 2–14: Handling of unused GCHs ......................................................................................................... 25 Figure 2–15: RAE4 diagram........................................................................................................................... 27 Figure 2–16: T3 reallocation - initial MSs allocation. .................................................................................... 33 Figure 2–17: T3 reallocation - final MSs allocation for B9............................................................................. 33 Figure 2–18: T3 reallocation - defragmentation purpose.............................................................................. 34 Figure 2–19: Coding scheme families. .......................................................................................................... 36 Figure 2–20: Trigger of the timer T_max_extended_UL................................................................................ 38 Figure 2–21: Schedule USF............................................................................................................................ 38 Figure 2–22: Expiry of the timer T_max_extended_UL. ................................................................................ 38 Figure 2–23: Restart the uplink TBF. ............................................................................................................. 39 Figure 2–24: NACC. ...................................................................................................................................... 40 Figure 2–25: NACC procedure in NC0 mode.................................................................................................. 40 Figure 2–26: NACC procedure in NC2 mode.................................................................................................. 41 Figure 2–27: Packet (P)SI status. .................................................................................................................. 42 Figure 2–28: Packet SI Status procedure. ..................................................................................................... 42 Figure 2–29: Packet PSI Status procedure. ................................................................................................... 43 Figure 2–30: PS used bandwidth................................................................................................................... 45 Figure 2–31: NC2 cell ranking process – case 1............................................................................................. 45 Figure 2–32: NC2 cell ranking process – case 2............................................................................................. 46 Figure 2–33: DL LLC PDU rerouting feature process. .................................................................................... 46 Figure 3–1: BSS Architecture in B9 release. .................................................................................................. 54 Figure 3–2: BSS Architecture in B9 release with Mx platform. ...................................................................... 54 Figure 3–3: Calculation of the Number of Extra Abis TS. .............................................................................. 56 Figure 3–4: Calculation of the needed GCHs in the Atermux interface......................................................... 57 Figure 3–5: Calculation of the Required_GCH_Traffic by Method 1. ............................................................. 58 Figure 3–6: Measured GCH traffic vs Measured PDCH traffic. ....................................................................... 58 Figure 3–7: Calculation of the Required_GCH_Traffic by Method 2. ............................................................. 59 Figure 3–8: Increase factor........................................................................................................................... 60 Figure 3–9: Transition type........................................................................................................................... 60 Figure 3–10: Method 2 – increase_factor ...................................................................................................... 61 Figure 6–1: Network Architecture. ............................................................................................................... 81 Figure 6–2: Ethereal example - MSS. ............................................................................................................ 82 Figure 6–3: Ethereal example - RWIN. .......................................................................................................... 83 Figure 6–4: Dr. TCP example – TCP parameters ............................................................................................ 83 Figure 6–5: Ethereal example – Time/Sequence graphic 1............................................................................ 84 Figure 6–6: Ethereal example – Time/Sequence graphic 2............................................................................ 84 Figure 6–7: Ethereal example – Time/Sequence graphic 3............................................................................ 85 Figure 6–8: Ethereal example – Time/Sequence graphic 4............................................................................ 85 Figure 6–9: Radio Block structure................................................................................................................. 89 Figure 6–10: RLC block not well decoded ..................................................................................................... 89
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