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RN 2002
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Presentation / Author
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Module objectives
After completing this learning element, the participant will be able to:
Theory:
Explain the (E)GPRS main procedures: Mobility management, Session Management and the concept of Temporary Block Flow
Understand the concept behind Routing Area design
List some differences between EGPRS and GPRS
Describe the different identities used on different interfaces
List different categories of MSs
Presentation / Author
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SW and HW Releases
This material describes the Nokia Siemens Network BSS (E)GPRS System with the following Software and Hardware releases:
BSS SW:
BSCi, BSC2i, BSC3i, Flexi BSC
BTS versions:
SGSN
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Functionality - Content
Procedures
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HLR – Home Location Register
TC – Transcoder
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SGSN
Charging & statistics
Border Gateway
Domain Name Server
Makes IP network configuration easier
In GPRS backbone SGSN uses DNS to
get GGSN and SGSN IP addresses
Two DNS servers in the backbone to provide redundancy
Legal Interception Gateway
Chasing criminal activity
LI is required when launching the GPRS service
Presentation / Author
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GPRS implementation
GPRS gives support for Packet Switched services. The introduction of GPRS in basic implementation is limited to Coding Scheme (CS) 1 and 2.
- GPRS capable terminals are required
- GPRS territory is required in BTS
- Packet Control Units (PCUs) need to be implemented in BSCs
- Gb interface to SGSN
- GPRS packet core network
Minimum PCU2 with S11.5 BSC SW (not for Talk family)
Dynamic Abis Pool (DAP)
EDGE capable TRXs and BB (Base Band) units for Metro and UltraSite
FlexiEDGE BTS, UltraSite and MetroSite BTS SW support
Presentation / Author
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Signaling Interface
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EGPRS Implementation
EGPRS can be introduced gradually to the network where the demand is. EGPRS requires:
EGPRS capable MS (supporting GPRS as well)
Network HW readiness/upgrade (BTS and TRX)
Transmission capacity upgrade (Abis and Gb!)
EDGE Dynamic Abis Pool (DAP)
GMSK coverage
8-PSK coverage
EDGE capable TRX,
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(E)GPRS Protocol Architecture
(E)GPRS defines a protocol architecture which allows to transfer IP version 4 or 6 packets from application servers (Host) to Mobile Stations.
L1
L2
IP
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The SNDCP layer works between MS and SGSN.
Main functions:
Option to (de-)compress protocol control information (e.g. TCP/IP header)
Option to (de-)compress data (whole IP packet)
Segmentation/de-segmentation of data to/from LLC layer
Buffering of data fragments in case of LLC acknowledged transfer mode
LLC
SNDCP
IP
TCP/UDP
APP
RLC
MAC
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LLC
SNDCP
IP
TCP/UDP
APP
RLC
MAC
Main functions:
Provision of acknowledged or unacknowledged transfer mode between SGSN and MS
Independent of underlying radio interface protocols
transfer of signalling (GMM, SM or SMS) and SNDCP packets (user data).
Ciphering/deciphering of signalling and user data
Control
Address
FCS
Information
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1-3
1-1520
3
Octets
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RLC
Segmentation/de-segmentation of data from/to LLC layer
MAC
Flagging of PDTCH/PACCH occupancy
LLC
SNDCP
IP
TCP/UDP
APP
RLC
MAC
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and can be splitt into
- Physical Link sublayer (see above)
- Physical RF sublayer (Modulation)
Framing: Placement of data into bursts, frames, radio blocks, etc.
Data (de)coding for maximising the data throughput
CS1 to CS4 or MCS 1 to 9
Detection and correction of errors
Procedures for detecting congestion on the air interface
Procedures for synchronising MS and network
Procedures for monitoring and evaluation the radio link quality
Procedures for cell (re-)selection
Phy. Link
Phy. RF
Normal burst
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SNDCP PDU (SN-PDU)
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Unprotected
usage of Rel 97/98 Reliability Classes QoS parameter 3GPP TS 03.60 (Rel 98)
Precedence Class
Delay Class
Peak throughput Class
Mean throughput Class
A GPRS Subscriber profile describes a service in terms of QoS parameters. The GPRS subscription is stored in the HLR and delivered towards the current SGSN. When a Service is activated the network is requested to provide a bearer with the described characteristics. Correspondingly the network will use Ack or Nack mode on the different interfaces for example.
Reliability Class
GTP Mode
1
Acknowledged
Acknowledged
Protected
Acknowledged
4
Unacknowledged
Unacknowledged
Protected
Unacknowledged
5
Unacknowledged
Unacknowledged
Unacknowledged
For real-time traffic, the QoS profile also requires appropriate settings for delay and throughput.
2
Unacknowledged
Acknowledged
Protected
Acknowledged
3
Unacknowledged
Unacknowledged
Protected
Acknowledged
Non real-time traffic, error-sensitive application that cannot cope with data loss.
Real-time traffic, error-sensitive application that can cope with data loss.
Real-time traffic, error non-sensitive application that can cope with data loss.
Non real-time traffic, error-sensitive application that can cope with infrequent data loss.
Non real-time traffic, error-sensitive application that can cope with data loss, GMM/SM, and SMS.
Presentation / Author
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HLR QoS Profile
HLR parameters define if LLC or RLC protocol work in Ack or NACK mode.
GPRS introduced Rel 97/98 attributes. With UMTS introduction a new set of attributes has been defined in Rel 99, which is common for UMTS and GPRS.
In practice only reliability classes 2 and 3 work today properly from the end user satisfaction perspective and can thus be commercially used.
There are some terminals in the market that can not support the usage of reliability class 2.
SDU error ratio:
Resulting R99 Attribute
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1 TDMA frame = 4.615 ms
= BURST PERIOD
RLC/MAC Blocks
TDMA Bursts
RLC Blocks
4 x TDMA Frames = 4 Bursts = 1 Radio block
12 x RLC/MAC Blocks = 1 x 52 PDCH MultiFrame = 240 ms
12 Radio Blocks / 0.240 s = 50 RLC/MAC Blocks / s
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(E)GPRS Logical Channels
GPRS introduces several new logical channels to the GSM air interface. There are no dedicated signalling channels as in GSM. The PDCH are used for data and signalling.
Packet data traffic channel (PDTCH) is reserved for GPRS packet data transfer. A PDTCH corresponds to the resource allocated to a single MS on one physical channel for user data transmission. In multislot operation, one MS may use multiple PDTCHs in parallel for individual packet transfer. PDTCH are uni-directional as opposed to TCH in GSM.
Packet associated control channel (PACCH) (bi-directional) is a signalling channel dedicated for a certain MS. The signalling information could include acknowledgements, power control, resource assignments, or reassignment messages
Packet timing advance control channel (PTCCH) is used in uplink direction for the transmission of random access bursts to estimate the timing advance for one mobile. In the downlink direction one PTCCH is used to transmit timing advance information to several MSs. PTCCH information is transmitted in positions 12 and 38 of the 52-multiframe structure.
For initiating the data transfer existing GSM Common Channels are used. PBCCH (Packet Broadcast Control Channel) and associated GPRS common channels are not supported.
Presentation / Author
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CCCH
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GMM States
GPRS attach
GPRS detach
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GPRS Mobility Management - GMM States
MS location not known, subscriber is not reachable by the PS core network
IDLE
READY
STANDBY
Packet TX/RX
GPRS Attach
GPRS Detach
MS location known to Routing Area level. MS can be paged DL data transfer.
MS location known to cell level. MS is transmitting or has just been transmitting. MS is capable of receiving point-to-point data.
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GPRS Mobility Management - Mobile States
The GPRS Mobility Management (GMM) is a protocol which manages Security (ciphering, P-TMSI allocation) and GMM States.
State Transition are based on Signaling procedures and timers configured in the SGSN:
GPRS Attach:
The MS makes itself known to the network
The authentication is checked and the location in HLR is updated
Subscriber Information is downloaded from the HLR to the SGSN
State transition Idle to Ready
Normal procedure may take 5 seconds
Session Management (SM):
before any PDP context activation the MS has to be GPRS attached.
If the MS is detached any existing active PDP context is automatically deactivated
Timers controlling state transitions
READY Timer (default 44s)
MOBILE REACHABLE Timer (default about 2 hours – recommendation: bigger than 2x the Periodic Routing Area update timer)
Timer values are configured in the SGSN !
Presentation / Author
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Attach Procedure
The GPRS Attach procedure establishes a GMM context between MS and SGSN. There are two types of attach possible:
a normal GPRS Attach, performed by the MS to attach the IMSI for GPRS services only
a combined GPRS Attach, performed by the MS to attach the IMSI for GPRS and non-GPRS services (in case of Gs being implemented)
The Gs interface enables two functions:
Paging Coordination (needed for DTM operation and additionally any MS will not loose CS pagings, while in packet transfer)
Combined Mobility Management (combined attach/Location updates)
The presence of the Gs is indicated to the MS in System Information as Network Mode of Operation (NMO) parameter (sometimes called Network Operation Mode, NOM)
NMO 1: Gs is present
NMO 2: Gs is not present
Gb
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Attach procedure in brief:
MS initiates by sending Attach Request
- If network accepts Attach Request it sends Attach Accept with P-TMSI and RAI
- If network does not accept Attach request it sends Attach Reject
- MS responds for Attach Accept message with Attach Complete (only if P-TMSI changes)
RA-1
HLR
SGSN-1
BSC
LA-1
2a
1
2b
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(3a) SGSN requests triplets from
AC. (First time in PLMN).
(3b) The AC generates the
triplets (RAND, SRES, Kc)
SGSN.
(3f) The SIM calculates SRES’, and
send it to SGSN.
RA-1
HLR/AC
SGSN-1
BSC
LA-1
3a
3b
3f
3c
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(4b) MS sends the IMEI.
(4c) SGSN sends a Check IMEI
message to the EIR.
IMEI ack that will include
the list type where the
IMEI was found (unknown,
white, grey, or black).
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(5a) SGSN sends Update location
message to HLR with
has received the subscriber
an Update Location ack.
received the new P-TMSI.
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Detach Process
GPRS Detach procedure is used for the following two purposes:
a normal GPRS Detach
a combined GPRS Detach (GPRS/IMSI detach, MS originated in case of Gs)
MS is detached either explicitly (by message for example when MS is powered off) or implicitly (upon timer expiry for example when battery runs empty):
Explicit detach: The network or the MS explicitly requests detach.
Implicit detach: The network detaches the MS, without notifying the MS, a configuration-dependent time after the mobile reachable timer expired.
Presentation / Author
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NW initiated detach (here with Gs, MS remains IMSI attached)
HLR
MS
BSS
GGSN
SGSN
MSC/VLR
1. Cancel Location
5. Detach Accept
1. Detach Request
5. Detach Accept
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Routing Area
Routing Area (RA):
One RA is a subset of one, and only one Location Area (LA)
One RA is served by only one SGSN, but one SGSN can serve several RAs
For simplicity, one LA can contain one RA
Too big LA/RA increases the paging traffic, while too small LA/RA increases the signaling for LA/RA Update
Routing Area Identity (RAI) = Location Area Identity (LAI) + Routing Area Code (RAC)
Location
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SGSN
MSC/VLR
Gs
Combined
Combined RA/LA update
Non-GPRS alerts
Identification procedure
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Routing Area
- a normal Routing Area Update
- a combined Routing Area Update (in case of Gs)
- a periodic Routing Area Update
The Routing Area Update is only initiated by the MS once the MS is GPRS attached.
Routing Area Update Accept
Location update request (SDCCH)
Location Update Accept (SDCCH)
MS
BSS
MSC
Location area Update and Routing Area update at LA/RA border (no Gs):
Presentation / Author
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RA Update
New SGSN sends ‘context req’ to old SGSN
Old SGSN sends response and starts tunneling data to new SGSN (if there is any data)
New SGSN sends ‘Update PDP context request’ to GGSN for any active PDP context
New SGSN informs HLR about SGSN change by sending ‘Update location’
HLR provides Subscriber data to SGSN
HLR sends ‘Cancel location’ to old SGSN.
With Gs interface the SGSN would initiate the Location Area update towards the MSS (when the Location Area change took place)
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Session Management - Establishing a PDP Context
The PDP (Packet Data Protocol) Context is mainly designed for two purposes for the terminal.
- Firstly PDP Context is designed to allocate a Packet Data Protocol (PDP) address, either IP version 4 or IP version 6 type of address, to the mobile terminal.
- Secondly it is used to make a logical connection with QoS profiles, the set of QoS attributes negotiated for and utilized by one PDP context, through the GPRS network (from MS to GGSN)
PDP Context Request
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MS
SGSN
GGSN
2. Security Functions (optional)
SM signalling
GTP signalling
PDP Context Activation
This procedure is initiated by the MS (mobile terminated PDP activation currently not implemented). The PDP context Contains QoS and routing information enabling data transfer between MS and GGSN. PDP Context Activation and Deactivation takes about 2 seconds.
Like GMM procedures the messages for SM procedures are exchanged on GPRS resources.
GMM signalling
Presentation / Author
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MS
SGSN
GGSN
2. Security Functions (optional)
SM signalling
GTP signalling
The Deactivation of a PDP context can be initiated by MS (as seen below) or network (in case of inactivity for example). PDPs can only be active as long as the MS is attached. Any kind of detach (with detach procedure or timer expiry in SGSN) will deactivate any active PDP context for a certain UE.
Additionally it is possible to modify QoS parameters related with one active PDP context with PDP context modification procedure. This procedure will be initiated by the SGSN, for example when a MS changes from 3G (where better QoS support is given) to the (E)GPRS network
GMM signalling
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TBF Concept
3GPP 43.064
The temporary block flow (TBF) is active when the MS is in Packet Transfer mode or in DTM State.
The TBF is identified by a Temporary Flow Identifier (TFI) which identifies unidirectional transmission resources on one or several PDCHs. They comprise a number of RLC/MAC blocks, which are used to carry one or several upper layer PDUs or RLC signalling. The TFI is allocated only for the duration of the transmission, i.e. it is temporary.
Radio Resource (RR) States are defined between the MS and PCU
Class A
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DL TBF
Network starts and releases DL TBFs by simply sending an assignment (eg when MS listens to its paging)
FBI (Final Block Indicator) indicates the last block in a DL TBF
The SGSN has to know the cell of the MS and has to provide this information to PCU, so that the DL TBF can be established (the MS has to be in GMM ready state)
Once a UL TBF is running a DL TBFs can be established as concurrent TBF on the PACCH (as RLC signalling on PACCH).
UL TBF
MS requests for (E)GPRS resources on the RACH
Then the MS gets an UL TBF assignment indicating the USF per allocated PDCH, USF granularity, RTSLs and the frequency
When TBF is finished the MS indicates this by starting the countdown procedure (The MS indicates the number of remaining RLC blocks in its buffer)
Once a DL TBF is running an UL TBFs can be established as concurrent TBF on the PACCH (as RLC signalling on PACCH)
BSC/PCU
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Packet Control Ack (for TA)
Packet Polling
AGCH
PDTCH
PACCH
PACCH
Data
PDTCH
MS
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TFI 2
TFI 5
TFI 3
TFI = 2
Several MS may have ongoing DL TBF on the same RTSL. The TFI included in the Downlink RLC Block header indicates which Mobile is the receiver of the Data (or Signalling). There is one RLC/MAC block every 20 ms. Scheduling of Signalling or data for different MS is performed by the PCU.
DL Radio Block
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Channel Request
UL Data or Signaling
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Multiple Mobiles and Uplink Transmission
Maximum of 7 Mobiles can be queued in the Uplink per RTSL (there are 3 bits and one value is reserved for the MSs that have DL TBF to transmit the PACCH)
Mobile transmission is controlled by USF (Uplink State Flag) sent in DL RLC/MAC blocks. The MS is going to send in the next UL block (or next 4 UL Blocks) when it finds its USF value in DL
In standard implementation one MS has to monitor the DL Blocks for each assigned RTSL
With EDA (Extended Dynamic Allocation) the MS will monitor only one DL RTSL and if it finds its USF it can transmit on all assigned UL RTSL in parallel
USF = 1
USF = 2
USF = 3
USF = 3
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USF granularity
There are 2 ways to allocate UL resources to one MS in (E)GPRS:
USF granularity 1 implemented with PCU1 and USF granularity 4 with PCU2:
USF granularity 1
USF granularity 4
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Radio Link Control (RLC)/ Medium Access Control (MAC) Header
Switching between PACCH and Data is managed with the Payload Type field in the RLC/MAC header. The RLC/MAC header is different for UL and DL and for EGPRS. The presented Headers are for GPRS. In case of EDGE there are several header types defined, but the fields are almost the same (with one exception: in GPRS there is no indication about the used CS (CS 1 to 4) but in EGPRS there is an indication of the used MCS (MCS 1 to 9) and PS (Puncturing Scheme 1 to 3).
Complete description can be found in 3GPP 43.064.
Abbreviations:
SI Stalled indication
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E
BSN
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Bit-No
USF
S/P
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MAC
header
RLC
header
BSN
PI
spare
PFI
E
BSN - Block Sequence Number= RLC block number TFI - Temporary Flow Indicator Countdown value - used to calculate number of remaining RLC blocks TLLI Temporary Logical Link Identifier (identity of MS)
Presentation / Author
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(E)GPRS Identities
IMSI or P-TMSI
Temporary Flow Identifier (TFI) allocated by PCU as long of TBF is running
The MS has independent TFI for UL and DL TBFs
Temporary Logical Link Identifier (TLLI) in UL is chosen by MS (based on P-TMSI or random TLLI in case of MS has no P-TMSI, then MS has to do the attach procedure)
TLLI is carried in the RLC protocol to PCU in UL TBF and forwarded to the SGSN in BSSGP protocol. There are 2 ways to transfer the TLLI,
It can be part of the RLC header in case of one phase access type
It can be transferred as part of RLC control message (Packet Resource Request) for other access types
TLLI is carried in BSSGP protocol by SGSN to PCU in DL TBF and PCU can check if there is already UL TBF running or an assignment has to be sent
MS
BTS
BSC
SGSN
TC
PCU
MSC
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RA 1
BSC 3
RA 3
In basic implementation one Packet Processing Unit (PAPU) could serve one (or several) RA.
The Large RA Support feature now allows more than one PAPU to serve one RA/NSE (Network Service Entity) by making it possible to define PAPU groups with several PAPUs.
Together with the High Capacity PAPU this feature offers a possibility of enhancing capacity within a certain RA or NSE as the number of subscribers increases.
With HCPAPU (High Capacity PAPU) max. 60 000 subscribers in one RA.
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(Can not be attached in CS and PS core)
Class B Packet and Speech (not at same time)
(can be attached in CS and PS core, but can only make call or sent data)
Class A Packet and Speech at the same time
(support for Dual Transfer Mode [DTM] is given)
(E)GPRS Mobile Terminal Classes
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Multislot Classes 1-12
- Max 4 DL or 4 UL TSL (not at same time)
- Up to 5 TSL shared between UL and DL
- Minimum 1 TSL for frequency change
- 2-4 TSL freq. change
(not at same time)
High Multislot Classes 30-45 (3GPP Rel-5)
- Max 5 downlink or 5 uplink (6 shared)
- Max 6 downlink or 6 uplink (7 shared)
Type 2
1 TSL for Frequency Change
DL
UL
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(E)GPRS Multislot Classes - Dual carrier
Example: Multislot class 12, Dual carrier, with DL (8 TSL) plus UL (1 TSL) TBFs
A key part of the evolution of EDGE is the utilization of more than one radio frequency carrier. This overcomes the inherent limitation of the narrow channel bandwidth of GSM. Using two carriers enables the reception of twice as many radio blocks simultaneously or, alternatively, the original number of radio blocks can be divided between the two carriers enabling a bigger flexibility, resulting in trunking gain.
Downlink dual carrier (DLDC) is only for DL and EGPRS, not GPRS!
requires optional support of MS (3GPP Rel 7)
existing Multislot classes are used (MS indicates additionally support for DLDC)
requires re-dimensioning of EGPRS resources
doubles downlink peak throughput up to 1184 kbps (but not for all Multi-slot classes*)
One of the carriers can be the BCCH carrier and the other on a TCH/TRX with frequency hopping
Neighbour cell
measurements (Rx)
* Release 7 defines MS with max 12 TSL in DL
IDLE
IDLE
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