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SiteVELIZY MOBILE COMMUNICATION DIVISION

Originator(s)

A. FREULON

Abis signalling loadB7.2

Domain : Alcatel 900/BSSDivision : PRODUCT DEFINITIONRubric : SYS-TLAType : SYSTEM FUNCTIONAL BLOCKSDistribution Codes Internal : External :

ABSTRACT

This document describes the signalling load on Abis and the simulation model used toestimate the signalling traffic depending on the sub-multiplexing scheme used, if any.

This document applies to B7.2

Approvals

Name

App.

R. MAUGERSYT DPM

J. ACHARDSYT CCM

K. LIBERLOODPM BSC

Name

App.

R. SABELLECKBTS DPM

S. VERETOMC-R DPM


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REVIEWTLAr6#25 08/07/98 TD/SAS/jya/0911.98/Ed.1

B7 E01P2 12/12/2000 Review report in memo MCD/TD/SYT/AFR/00810.2000.

B7.2 Ed02 P1 21/01/2002 Review report in memo MND/TD/SYT/AFR./681.2002

HISTORY

Release B5 : 3BK 11202 0142 DSZZA

Edition Date Author Reason for update

01 in Preparation P1 08/08/96 JY Amaudrut Creation

01 Proposal 1 16/09/96 JY Amaudrut Updated according to the minutes ofreview TLAr5#18, ref :TD/SAS/JYA/1742.96

01 Released 01/10/96 JY Amaudrut Updated according to the minutes ofreview TLAr5#19, ref:

TD/SAS/JYA/1876.96Release B6 : 3BK 11202 0210 DSZZA

Edition Date Author Reason for update

01 Proposal 01 03/04/98 JY Amaudrut Creation- update of scenarii (radio

measurements compression)- 16 kb/s statistical- micro-BTS results

01 Released 09/07/98 JY Amaudrut Updated according to the minutes ofreview TLAr6#25, ref:TD/SAS/jya/0911.98/Ed.1

Release B7.2 : 3BK 11203 059 DSZZAEdition Date Author Reason for update

01 proposal 1 13/07/2000 A. Freulon Creation for B7.2.

- New B7.2 reference call mix (no micro cell /macro cell variant).

- SDCCH load ratio and TCH load ratio areincorporated in the Abis model.

- Impact of B7.2 features TFO, RMS, Abisdynamic.

- Removal of performance figures which have notbeen validated with B7.2 traffic model.

Ed 01 proposal 2 4/12/2000 A. Freulon

-Modification to SDCCH holding time (measuredon a BSS) => new simulation results.

- activation of piggy-backing (to align onimplementation)=> new simulation results.

- MCB configuration 2 FR+ 1 DR added.

- New information for OML

- New information for Abis satellite links.

- Editorial rework (clearer split hypothesis/model/results)


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Ed 01 Released 19/12/2000 A.Freulon

- Updated according to review report for Ed 01proposal 2.

Ed02 Proposal 1 02/01/2002 A. Freulon

Removal of parts related to non-implemented feature(Abis dynamic, 2FR +1 HR MCB configuration)

Ed02 Released 21/01/2002 A. Freulon. Updated according to review report forEdition 1 proposal 2( minor editorial changes, seereview report reference above).

INTERNAL REFERENCED DOCUMENTS

3 BK 10204 0518 DTZZA Abis & Ater dynamic allocation3 BK 10204 0478 DTZZA Tandem Free Operation (TFO)3 BK 10204 0486 DTZZA Radio Measurement Statistics.3 BK 10204 0514 DTZZA Industrialisation of satellite

FUTURE IMPROVEMENTS

SMS signalling load estimate approximated.

FOR INTERNAL USE ONLY

Not applicable


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END OF DOCUMENT


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SYSTEM FUNCTIONAL BLOCK

TABLE OF CONTENTS1

HISTORY 4

REFERENCED DOCUMENTS 4

RELATED DOCUMENTS 4

PREFACE 5

1. SCOPE 7

2. ABIS SIGNALLING LOAD MODEL 82.1 Model for the RSL 82.1.1 Working hypothesis and parameters. 82.1.2 Description of the RSL load model 132.1.3 Layer 2 182.2 Traffic Model for the OML. 202.2.1 O&M traffic rate 202.2.2 O&M traffic flow for Software download. 20

3. TELECOM SIGNALLING FLOW ESTIMATIONS 233.1 Signalling flow per sub channel 233.2 Signalling flow for TRX-oriented procedures. 233.3 Parameters Influence 243.3.1 SDCCH traffic 243.3.2 TCH traffic 273.3.3 BCCH/CCCH traffic 273.3.4 BER 27

3.4 Signallling Flow Estimation For Each TRX Configuration 283.4.1 Nominal traffic (large cells) 283.4.2 Increased traffic (large cells) 283.4.3 Overload 293.4.4 Proportion of I frames on the total flow on the uplink. 293.5 Signallling Flow Estimation For 16 Kbit/S Channel. 313.5.1 Allowed configuration 313.5.2 Simulation results. 313.5.3 Conclusion and recommendations 343.6 Signallling Flow For Statistical Multipexing On 64 Kbit/S Channel. 353.6.1 General 353.6.2 Signalling flow for 1 TRX (FR or DR). 353.6.3 Signalling flow for 2 FR-TRX. 363.6.4 Signalling flow for 4 FR-TRX. 363.6.5 Signalling flow for 2 DR-TRX. 373.6.6 Summary of conclusions and recommendation for MCB 64 Kbit/s 38

4. STATISTICAL DISTRIBUTION OF THE SIGNALLING TRAFFIC 434.1 Distributions of the message lengths 434.1.1 Random flow 434.1.2 Steady flow 444.2 Downlink 444.3 Uplink 444.3.1 Distribution of measurements 444.3.2 Distribution of the SDCCH signalling 46


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4.4 Reception 474.5 Retransmission 47

5. PERFORMANCES ON 64 KBITS/S CHANNELS 485.1 Queue model 48

6. PERFORMANCES ON 16 KBITS/S CHANNELS 52

7. PERFORMANCES ON A 64 KBITS/S AND ON 16KB/S CHANNEL WITH LAPD

STATISTICAL SUB-MULTIPLEXING 557.1 Sub-multiplexing configuration 557.2 TRX and channels Configuration 557.3 Queue model for Lapd sub-multiplexing for BTS G3 557.3.1 at BTS side 567.3.2 at TCU side 567.4 Queue model for Lapd sub-multiplexing for M2M micro-BTS 567.4.1 at BTS side 567.4.2 at TCU side 57

8. PERFORMANCES AND RECOMMENDATIONS 69

8.1 Piggy-backing 698.2 SDCCH spread effect 698.3 TRX position effect 698.4 DElay induced by sub-multiplexing 70

9. GLOSSARY 71

ANNEX A : MESSAGES FLOWS ON ABIS INTERFACE 72

ANNEX B : SYSTEM REACTION TIME 78

ANNEX C : BER 79

ANNEX E : SIMULATION MODEL 84

TABLES2

Table 1: recommended flow to guaranty mean response time for 64 kbit/s. ____________________________8

Table 2: recommended flow to guaranty mean response time for 16kbit/s. ____________________________ 8

Table 3: Available bandwidth on RSL for satellite links.___________________________________________9

Table 4: TRX Full rate configurations ________________________________________________________10

Table 5 TRX dual rate configurations ________________________________________________________10

Table 6: call mix parameters _______________________________________________________________11

Table 7: TCH load _______________________________________________________________________12

Table 8: SDCCH load_____________________________________________________________________12Table 9: comparison of the flows generated by MOC,MOT and LU. ________________________________15

Table 11: BTS software size.________________________________________________________________21

Table 12: Bandwidth usage during SW download (terrestrial)._____________________________________21

Table 13: Available bandwidth for the OML on satellite links._____________________________________22

Table 14: simulation results per channel type. _________________________________________________23

Table 15: simulation results for TRE oriented procedures.________________________________________23

Table 16: Influence of SACCH modify ________________________________________________________24

Table 17: Average SDCCH holding time depending on call mix. ___________________________________24

Table 18: influence of SDCCH holding time on Abis flow. ________________________________________25

Table 19: TRX flow in nominal traffic ________________________________________________________28

Table 20: TRX flow in increased traffic ______________________________________________________29


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Table 21 : TRX flow in cell overload ________________________________________________________29

Table 22: Proportion of I frames on the uplink ________________________________________________29

Table 23: TRX flow on 16K channel, large cell, nominal traffic. ___________________________________31

Table 24: TRX flow on 16K channel, large cell, increased traffic. __________________________________32

Table 25: TRX flow on 16K channel, small cell, nominal traffic. ___________________________________32

Table 26: TRX flow on 16K channel, small cell, increased traffic. __________________________________33

Table 27: TRX flow on 16K channel, small cell, TCH congestion __________________________________33Table 28: TRX flow on 16K channel, small cell, increased paging. _________________________________34

Table 29:MCB flow for 2 FR TRX.__________________________________________________________36

Table 30: MCB flow for 2FR-TRX ___________________________________________________________36

Table 31: MCB flow for 4 FR -TRX __________________________________________________________ 36

Table 32: MCB flow for 4 FR-TRX. __________________________________________________________37

Table 33: MCB flow for 2 DR-TRX. __________________________________________________________37

Table 34: MCB flow for 2 DR-TRX __________________________________________________________38

Table 37: summary with MCB signalling load = 40._____________________________________________39

Table 38: summary with MCB signalling load= 48______________________________________________40

02 21/01/02 MCD/TD MCD/TD/SYT

01 19/12/00 MCD/TD MCD/TD/SYT

ED DATE CHANGE NOTE APPRAISAL AUTHORITY ORIGINATOR


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HISTORY

3BK 11202 0142 DSZZA Ed 01 01/10/96 First edition for the B5 release

3BK 11202 0210 DSZZA Ed 01 09/07/98 First edition for the B6 release

3BK 11203 0059 DSZZA Ed 01 19/12/00 First edition for the B7.2 release

3BK 11203 0059 DSZZA Ed 02 21/01/02 Second edition for the B7.2 release

REFERENCED DOCUMENTS

DOCTREE REFERENCES

[1] BSS Telecom Internal Traffic Performances Objectives3BK 11203 0058 DSZZA

[4] layer 3 message dictionary Abis interface3BK 11203 065 DSZZA

[5] layer 3 message dictionary Air interface

3BK 11203 066 DSZZA[6] layer 3 message dictionary A interface3BK 11203 064 DSZZA

[7] Radio measurements data processing3BK 11202 0294 DSZZA

[8] Radio Measurements and Codec Adaptation3BK 11202 0293 DSZZA

[9 ] LapD Management3BK 11202 0335 DSZZA

[10]Abis Signalling Links multiplexing3BK 11202 0330 DSZZA

[11]O&M Abis interface3BK 11203 0059 DSZZA

GSM REFERENCES

[12]Mobile radio interface layer 3 specification(GSM 04.08)ETS 300 557

RELATED DOCUMENTS

[13]Queueing Systems, Volume 2 : Computer ApplicationLeonard Kleinrock

[13]Technical Note: GPRS B7: Overview of the impacts of B7 on BSC performances.

[14] ITU-T G.826 Error Performance parameters and objectives for international, constant bitrate digital path at or above the primary rate.


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PREFACE

This document applies to B7.2. software release of the Alcatel BSS

Tool: The model of the Abis signalling load is implemented with an Excel based tool. Specificstudies can be conducted with this tool.

B7.2 updates: the B7.2 updates impacts only section 1 to 4. Section 5 to 9 (performancesand response time) are the same as B6.2.

Guidelines for a fast reading:

- Most result tables are done with colours, so the electronic document will provide aneasier reading for quantified results.

- The reader only interested in simulation results should go directly to section 3, buthowever check the call mix parameter hypothesis in section 2.1.1.

- Configuration restriction applicable to each multiplexing are in sections 3.5.1, 3.5.3,3.6.6.2.


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RENVFUSIONFORMAT

RENV

RENV

RENV

RENV


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1. SCOPE

The choice of a technical solution for RSL sub-multiplexing implies a perfect knowledge of theperformance required at the Abis interface for the various TRX configurations, including half rate,and for the OMU.

The Abis signalling load presents both a method for load evaluation and specific evaluationsconducted with a set of parameter values. The method remains valid whatever the parametervalues, but the signalling load estimates and following recommendations are based on the Alcateltraffic model for Circuit switched calls. The consequence are:

- If some of the parameters of the Alcatel traffic model change, the results presented inthis document may also need to change.

- The Alcatel traffic model may be pessimistic compared to the traffic model of a particularoperator, and consequently the Abis signalling load may be somehow over-estimated. Itis however the best guaranty that the Abis multiplexing will function correctly within thelimits recommended in this document.

On the basis of an average load of the TRX radio resources (TCH and SDCCH), at several levelsof traffic (nominal, increased, overload) this document establishes the mean Abis LaPD flowobtained with the Alcatel traffic model. It is assumed that the TCH and SDCCH are correctlydimensioned for the Circuit Switched traffic expected, the worst hypothesis is assumed: all TCH

are configured for CS calls1.

These elementary flows (per TRX) are then combined to estimate the Abis signalling load for thestatic and statistical multiplexing, and resulting recommendation for configuration managementare given.

Possible congestion control mechanism which will tend to reduce the flow when this one comesup to the possible maximum allowed by the physical channel are not taken into account by thisstudy.

1 Indeed this assumption is also valid even if there is some GPRS traffic because we have toconsider those RSL which are not affected by the GPRS traffic.


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2. ABIS SIGNALLING LOAD MODEL

2.1 Model for the RSL

2.1.1 Working hypothesis and parameters.

2.1.1.1 Transmission delays in relation with Abis flow.

It is very important that transmission delays on the Abis interface can be guarantied, especially

for the most time sensitive procedures: Random Access/Immediate assignment 2 and handovers.The mean response time in function of the mean Abis flow in Kbit/s is provided in annex D, withseveral hypothesis on BER. Assuming BER < 10E-6, the following table gives the recommendedAbis flow for a 64 Kbit/s channel to obtain a predictable average response time. Correspondingexpectations depending on the traffic level are provided, according to requirements from ref [1]and annex B. Similar requirements for a 16Kbit/s channel are deduced. Note that theseresponse times are only estimation as they do not take into account the statistical distribution of Iframes and UI frames. They however provide a first level of reference which may be seen as

acceptable, because uncertainties due to the possible variations of the the traffic mix parametersare greater. On the down-link, only I-frames are used, so the average delay will be close tothese figures. On the up-link, due to the priority of I-frames over UI-frames the average delayswill be smaller for I-frames and greater for UI-frames.

Abis flowIn Kbit/s

Abis flow in % ofmax throughput

MeanResponse Time

Acceptable withlevel of traffic

64 100% Infinite None

62 97% 100ms Overload60 94% 50ms Increased

50 78% 20ms Nominal

Table 1: recommended flow to guaranty mean response time for 64 kbit/s.

Abis flowIn Kbit/s

Abis flow in % ofmax throughput

MeanResponse Time

Acceptable withlevel of traffic

16 100% Infinite None15.5 97% 100ms Overload

15 94% 50ms Increased

12.5 78% 20ms Nominal

Table 2: recommended flow to guaranty mean response time for 16kbit/s.

2.1.1.2 Restrictions in case of satellite links.

In this case the transmission delay due to the distance with the satellite must be added. Theadded delay is estimated to 250ms (one satellite hop). This delay has an impact on the actually

2 Depending on the value of the parameter TX-integer, the average time between two MS repetitionof the Channel Request message can vary from 366ms to 1145ms. If the Abis delay (and the BSSperformances in general) is such that the Immediate Assignment procedure cannot be completed inthis time interval, the MS will often repeat this procedure, which leads to useless allocation of SDCCHchannels, thus increasing the Abis signalling load and degrading even more the transmission delayand the general performances of the BSS. Hence,a non-respect of the recommended transmissiondelay will cause an important degradation of the QoS.


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available bandwidth depending on the LapD anticipation window and the average messagelength.

The percentage of the bandwidth which can actually be used is given by the following formula,where the processing time in BTS and BSC is considered negligible compared to the satelliteinduced delay.

K_VAL x I_trans_time / ( I_trans_time + sat_delay + RR_Trans_time +sat_delay).

(time actually spent transmitting/ (time transmitting + time waiting for acnowledgment).

K_VAL = LAPD anticipation window (see ref [9 ] for details).I_trans_time is the time of I frame transmission, which depends on the link speed and I framelength.Ack_Trans_time is the time of RR transmission for acknowledment, which depends on the linkspeed and I frame length.Sat-Delay is the delay induced by satellite transmission (one hop), estimated to 250ms.

The following table gives the actual available bandwidth for 16K and 64K channel (without taking

into consideration possible interaction with OML in case of multiplexing), depending on theanticipation window K_val. The average I-frame length on the RSL is estimated to 25 byteswithout the header (so 33 with the header). Only values of K_VAL less or equal to 16 arepossible in Alcatel BSS. The other values are only provided for information.

LinKspeed

(Kbit/s)

I_trans_time on

RSL (ms)

RR transtime on

RSL (ms)

K_val default and maxvalues

% ofbandwidth

used (Kbit/s)

actual RSLbandwidth

(Kbit/s)

64 4.1 1.0 7 defaultterrestrial

6% 4

64 4.1 1.0 16 default satellite(max allowed)

13% 8

64 4.1 1.0 32 not allowed 26% 1764 4.1 1.0 64 not allowed 52% 33

16 16.5 4.0 7 default terrestrial 22% 4

16 16.5 4.0 16 default satellite(max allowed)

51% 8

16 16.5 4.0 32 not allowed 100% 16

Table 3: Available bandwidth on RSL for satellite links.

2.1.1.3 TRX configurations

The following tables define the full rate and dual-rate TRX configurations which are areconsidered for the simulations. No more than 24 SDCCH per TRX are considered, according toref[1]. The number of SDCCH in a cell has an influence on the CCCH traffic, so for the TRXconfigurations with CCCH, several cases corresponding to the variations of the number ofSDCCH in the cell are considered


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The following notations are used to define each TRX configuration:F = Full rateD = Dual rate.C = BCCH/CCCH combinedB = BCCH/CCCH not combined

S = SDCCHT = TCH

2.1.1.3.1 Full rate

TRX configuration

F= full Rate

BCCH c ombined

or not combined

number of SDCCH in

the cell for the

simulation.

Number of SDCCH on

TRX

Number of TCH on

TRX

F.1C.4S.7T yes 12 4 7

F.1C.12S.6T yes 12 12 6

F.1B.7T3 No 16 0 7

F.1B.8S.6T No 8,16,24 8 6

F.1B.16S.5T No 24,64 16 5

F.1B.24S.4T. No 24,64 24 4

F.8S.7T. not applicable No impact 8 7

F.16S.6T not applicable No impact 16 6F.24S.5T not applicable No impact 24 5

F.8T not applicable No impact 0 8

Table 4: TRX Full rate configurations

2.1.1.3.2 Half rate

TRX configuration

D= full Rate

BCCH c ombined

or not combined

number of SDCCH in

the cell for the

simulation.

Number of SDCCH on

TRX

Number of TCH on

TRX

D.1C.4S.14T yes 12 4 14

D.1C.12S.12T yes 12 12 12

D.1B.14T4 No 16 0 14

D.1B.8S.12T No 8,16,24 8 12

D.1B.16S.10T No 24,64 16 10

D.1B.24S.8T. No 24,64 24 8

D.8S.14T not applicable No impact 8 14

D.16S.12T not applicable No impact 16 12D.24S.10T not applicable No impact 24 10

D.16T not applicable No impact 0 16Table 5 TRX dual rate configurations

3 This configuration is currently not allowed by O&M because of recovery strategy.4 This configuration is currently not allowed by O&M because of recovery strategy.


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2.1.1.4 Traffic model parameters

This document establishes the mean Abis LAPD rate required with the Alcatel traffic model, asdefined in ref [1]. If some of the parameters of the Alcatel traffic model changes, the presentdocument may also need to change. In particular, the Abis signalling load is strongly related tothe SDCCH holding time and to the maximum paging rate on one cell.

Main parameters used in the simulations are recalled hereafter. Note that the Location updaterates and SMS rates are not used because the abis signalling load model is based on SDCCHload ratio (cf 2.1.2.5.8 for justification)..

DT Duration of a TCH connection 50s

DS Duration of a SDCCHconnection 3s

NHO Number of Handover per TCHconnection

3

NPWR Number of Power control perTCH connection

4

PRATE Paging rate on one cell 30/s

TFO_R Ratio of MS-MS calls for TFO 50%

Table 6: call mix parameters

Note: The values of the above parameters have been changed compared to B6.2, in orderto align on the Alcatel traffic model.

2.1.1.5 Other assumptions and parameters.

- no idle time between two consecutive SDCCH or TCH connection,

- Overload Factor on RACH (FOR). The overload on RACH due to unsuccessful channel

required (no SDCCH allocated) is estimated to 25%.

- the call establishment is not OACSU (ringing uses TCH).

- The Mobile Originated Call scenario is used in all cases (maximises layer 3 flow onTCH).

The following parameters are defined (in addition to the call mix parameters):

NS Number of SDCCH in the cell. (input parameter forsimulation)

FOR Overload factor of RACH 25%

BER Abis physical bit error rate 10E-6.

MLOST Number of measurements lost between releaseand establishment 2

Piggy Conditionnal generation of RR (0=yes, 1=no) 0 (active)5

RMS Flag to distinguish load with / without RMS upload 0 or 1

T_BTS_RMS Implementation timer controlling RMS data upload 1s

5 See explanation in section 2.1.3


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2.1.1.6 TCH and SDCCH load in relation with cell size.

The occurrence of scenario depends on the TCH and SDCCH average load, defined respectivelyby the parameter TCH_L (TCH load) and SD_L (SDCCH load).

The TCH and SDCCH load is based on the average Traffic and Signalling Erlangs with the Air

interface blocking rates recommended by Alcatel in ref [1]. It should be noted that for a givenblocking probability, the relative load grows with the number of TCH and SDCCH in the cell. Thisis the so-called trunking effect, expressed mathematically by the Erlang law. See table belowfor values:

Number of TRXin cell

1 2 3 4 5 6 7 8 9 10 11 12 12

(HR)

Number of TCHin cell

7 14 21 28 35 42 49 56 63 70 77 84 168

Cell capacity at2% blocking

2.9 8.2 14.0 20.2 26.4 32.8 39.3 45.9 52.5 59.1 65.8 72.5 154.5

Average TCHload

42% 59% 67% 72% 76% 78% 80% 82% 83% 84% 85% 86% 92%

Table 7: TCH load

Number ofSDCCH

4 8 12 16 24 32 40 48 56 64

Sig. Erlangat 0.5%blocking

0.7 2.7 5.3 8.1 14.2 20.7 27.4 34.2 41.2 48.3

AverageSDCCH

load

18% 34% 44% 51% 59% 65% 68% 71% 74% 75%

Table 8: SDCCH load

The average TCH load and SDCCH load expected on small cells is much lower than on largecells, so the two cases are distinguished.

Note: The TCH load is supposed to be pure CS load (worst case as far as RSL load isconcerned).

Small cells:

Nominal traffic on small cells (maximum 4 TRX FR 6)

TCH average load is 70%SDCCH average load is 50%

Increased traffic on small cells (traffic x1.2)TCH average load is 85%SDCCH average load is 60%

6 The small cell model is used mainly for the statistical 16Kbit/s multiplexing. In this case, theoperator must configure the time slot 0 with an SDCCH time slot (8 sub-channels) on all the TRXs,and consequently the dimensioning of the SDCCH with the SDCCH blocking probability cannot beused. However 8 SDCCH/TRX implies an over-dimensioning of the SDCCH and the expectedSDCCH load is lower than by applying a blocking probability of 0.5%.


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TCH congestionTCH average load is 100%SDCCH average load is 60%

Medium and large cells.

Nominal traffic on medium and large cells:TCH average load is 90%

SDCCH average load is 70% 7

Increased traffic (traffic x1.2)8

TCH average load is 100%SDCCH average load is 85%

Overload (traffic x2)TCH average load is 100%SDCCH average load is 100%

2.1.2 Description of the RSL load model

2.1.2.1 General

The functional scenarios of telecommunication procedures are used, to estimate the signallingtraffic on Abis.First, we define the flow for each procedure , and then we define the occurrence for eachprocedure.Finally the flows generated by each procedures are summed for all channel types and per TRX.

2.1.2.2 Layer 3 flow generated by each procedure

Refer to annex A for the detailed scheme of the exchanges. Because of the possible options inthe network, it is not possible to compute exactly the length of all messages. which aretransmitted transparently by the BSS system. In this case the worst case is assumed. Refer toannex A for the determination of message length.

2.1.2.2.1 BCCH+CCCH related procedure

The flow related to the refreshment of the broadcast information (BCCH INFORMATION) isconsidered negligible.

2.1.2.2.1.1 Successful random access

The random access procedure generates a layer 3 flow of 10 bytes uplink (channel required) and29 bytes downlink (immediate assign cmd), on the Abis LAPD link of the TRXthat handles theBCCH+CCCH.

7This covers up to 48 SDCCH. For 56 and 64 occupation should be 75%. This has not been done inorder to limit the number of simulations. However, because of the granularity of 8 SDCCH, theSDCCH load is an approximation.8For increased traffic and overload the definition is a bit different from ref[1]: The BHCA increased isreflected by the SDCCH load increased, and the TCH holding time is not reduced. The increasedTCH load is considered to take into account the increased uplink flow due to TCH measurements.


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2.1.2.2.1.2 Unsuccessful random access

For the unsuccessful Random Access, a SDCCH may be allocated but no message is sent forthis SDCCH. Only the CCCH traffic (Uplink and downlink) is increased. Several reasons arepossible:1- Ghost RACH: these do not come from a MS but are detected by a BTS because of the

background noise. Ghost RACH have been measured to a maximum 25% (generally 10%).2- Delays of RACH in the BSS which induce repetition by the MS and double SDCCHallocation, Double SDCCH allocation should only occur in case of congestion, and is notconsidered here.

3- Lack of SDCCH and no usage of Immediate Assignment Reject. This case is not consideredhere.

The random access procedure generates a layer 3 flow of 10 bytes uplink (channel req), on theAbis LAPD link of the TRXthat handles the BCCH+CCCH.

2.1.2.2.1.3 Paging

The paging procedure generates a layer 3 flow of 13 bytes downlink (paging cmd), on the AbisLAPD link of the TRXthat handles the BCCH+CCCH.

2.1.2.2.1.4 SMS CB

The maximum downlink SMSCB flow is due to a reload of a cell by the CBC. In this case, up to0.5 Write-Replace requests per second will be sent by the BSC to the BTS (one page message).Each Write-Replace is acknowledged by the BTS by a Report response.A Write-Replace is 108 bytes long, a Report is 19 bytes long.

2.1.2.2.2 SACCH related procedure

The flow related to the refreshment of the broadcast information (SACCH INFORMATION) isconsidered negligible.

2.1.2.2.2.1 MeasurementsOnly measurement without radio measurements data compression are used, in accordance withB6.2 and B7.2 implementation.Measurements are conveyed uplink by a 37 bytes message.

2.1.2.2.2.2 Power control

The MS and BS radio power are controlled by a 6 bytes downlink message (12 in total forMS+BS power).

2.1.2.3 SDCCH related procedure

In the following of this study, only the location updating resulting flow will be taken into account,because this flow maximises the exchanges on SDCCH channels. This implies that the Abissignalling load model is independent of the Alcatel Traffic mix for SMS/call ratio and Locationupdate/call ratio.However the total number of bytes exchanged on SDCCH for each of the three proceduresMobile Originated Call, Mobile Terminating Call, Location Update are very close, as shown byTable 9 below. The number of bytes for SMS cannot be estimated because it depends on themessage content.


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2.1.2.3.1 Dedicated Signalling.

The location updating generates a layer 3 flow of 159 bytes uplink (channel activationACK,location update request, classmark change, authentication response, cipher modecomplete, TMSI reallocation complete, release indication, physical context confirm, RF channelrelease ack) and 261 bytes downlink (channel activation, multiple SACCH Info modify, identity

request, authentication req, encryption command, location update accept, channel release,deactivate SACCH, physical context req, RF channel release) on the Abis LAPD link of theTRXthat handles the SDCCH.This flow assumes that all optional procedures which can be executed during location updatingare actually used by the network. The optional procedures (Identification request, Authentication,Ciphering), depend on the operator options in MSC/VLR , so no general hypothesis can be doneon circumstances under which they would not be used. For SACCH Information modify, the useof this procedure depends on the BSS parameter BSS_SEND_CM_ENQUIRY.

If SACCH Information modify is not used, the downlink flow is reduced by 88 bytes, and 1message.

If other optional procedures are not used the downlink flow is reduced by 63 bytes and 3messages, the uplink flow is reduced by 53 bytes and 3 messages.

This signalling includes the release of the SDCCH channel itself. The scenario "call establishmentgenerates a "similar" flow.

Procedure Uplink bytes at layer3

Downlink bytes at layer 3

Mobile Originated Call 141 249

Mobile Terminated Call 138 261

Location Update 159(=MOC+13%)

261(=MOC+5%)

Table 9: comparison of the flows generated by MOC,MOT and LU.

2.1.2.3.2 TCH and FACCH related procedure

2.1.2.3.2.1 Call establishment

The call establishment procedure generates a layer 3 flow of 89 bytes downlink (channelactivation, alerting, connect) and 59 bytes uplink (channel activation ack, establish ind,assignment complete, connect ack), on the Abis LAPD link of the TRX that handles the TCH.

2.1.2.3.2.2 Call clearing

The call clearing procedure generates a layer 3 flow of 48 bytes downlink (disconnect, releasecomplete, channel release, deactivate SACCH, Physical ctxt req, RF channel release) and 66bytes uplink (disconnect, release, release indication, physical ctxt cnf, RF channel release ack).

2.1.2.3.2.3 Handover

The handover procedure generates a layer 3 flow of 78 bytes downlink (physical ctxt req,handover cmd, RF channel release, channel activation) and 60 bytes uplink (physical ctxt cnf, RFchannel release ack, channel activation ack, handover detection, establish ind, handovercomplete).

2.1.2.3.2.4 Tandem Free Operation

The Tandem Free Operation procedure generates a layer 3 flow of 15 bytes downlink (TFOModify Request) and 15 bytes uplink (Remote Config Report, TFO Report). It is assumed thateach message is sent once for each TFO call.


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2.1.2.4 TRX related procedures

Contrarily to the previous scenario, these are related to one TRX, and not to a specific channel.

2.1.2.4.1 Radio Measurement statisticsOnly the RMS data upload is considered. The influence of other procedures (start RMS, stopRMS) on the Abis signalling load is negligible.The RMS data upload generates a layer 3 flow of 256 bytes uplink (RMS data report), and 0 bytedownlink (no layer 3 acknowledgement).

2.1.2.5


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2.1.2.5 Occurrence of scenarios

The following applies only to terrestrial links. The delays induced by satellite links will inducemuch lower occurrence of scenario. Consequently the Abis signalling load model is only adaptedto terrestrial links. It may be used only as roughely indicative for satellite links.

2.1.2.5.1 Successful random access

The random access rate on the CCCH channel is related to the number of SDCCH in the wholeBTS (assuming SDCCH dimensioning is sufficient).The average duration of a SDCCH is DS (including call establishment), thus the SDCCHestablishment rate is 1/DS*SD_L for one SDCCH The BTS has NS SDCCH channels, so themaximum successful random access on the TRX that handle the BCCH+CCCH isNS/DS*SD_L..

2.1.2.5.2 Unsuccessful random access

We assume the BTS receives several times the maximum usable rate . The unsuccessfulrandom access rate is (FOR*NS/DS*SD_L) (total random access flow : (FOR+1)*NS/DS*SD_L).

2.1.2.5.3 Paging

The maximum Paging rate (PRATE) on one cell from the Alcatel traffic model is assumed.

2.1.2.5.4 SMS CB

The resulting layer 3 flow is 512 bit/s downlink and 144 bits/s uplink.This flow is lower than the flow on SDCCH channels, therefore, we use only SDCCH channels onthe studied configurations.

2.1.2.5.5 Measurements

In mode B, one measurement message is transmitted uplink by the TRXthat handles theSACCH, every 4*D26 s on SACCH/T and 2*D51 s on SACCH/C. The resulting flow isproportional to the TCH occupation ratio TCH_L.

2.1.2.5.6 Power control

1 power control at the channel establishment plus NPWR Power control during a communication,resulting an average (1+ NPWR) / DT TCH_L Power Control /s for one TCH.1 power control at the channel establishment plus NPWR/DT power control during the connection(the power control rate should be the same for SDCCH as for TCH), resulting an average (1/DS+ NPWR/DT)*SD_L Power Control/s for one SDCCH.

2.1.2.5.7 Handover

NHO Handover during a communication, resulting NHO/DT*TCH_L for one TCH.

The handover rate should be the same for SDCCH as for TCH. Let the average handover rate beNHO/DT*SD_L for one SDCCH.

2.1.2.5.8 Dedicated signalling

For the signalling load due to SDCCH we assume the traffic is limited by the air interface and thenetwork response time.

The SDCCH allocation rate rate is 1/DS*SD_L per s and SDCCH. As a simplification, the Abismodel considers that the dedicated signalling load on Abis is independent on the servicerequested (location updating, SMS, SS or call establishment), and uses the Location update forsignalling load computations. See justification in section 2.1.2.3.1.


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This means that the SDCCH load is estimated to the Location Update scenario repeated to themaximum allowed by the SDCCH average load and holding time.

Measurements messages flows are given by the formula : (1/2*D_51) - (MLOST/DS) . (D_51 :multiframe 51 duration, MLOST= number of lost measurements, DS= SDCCH scenario duration)

2.1.2.5.9 Call establishmentThe average call establishment rate be (1/DT)*TCH_L for one TCH.

2.1.2.5.10 Call clearing

Equals to the call establishment rate : (1/DT)*TCH_L for one TCH.

2.1.2.5.11 Tandem Free Operation

The average rate of TFO procedure is (1/DT)*TCH_L*TFO_R

2.1.2.5.12 TRX related scenario

2.1.2.5.13 Radio Measurement statistics (RMS)

Radio measurement statistic upload will occur only during a short time, once in a day. Hence, theAbis signalling load generated is an isolated event. While this transfer is ongoing, the occurrenceof data upload messages on one TRX is 1/T_BTS_RMS.

2.1.3 RENVLayer 2

2.1.3.1 Layer 2 protocol.

An 8 bytes frame header is added for each Layer 3 message and an 8 bytes frame is added for

the acknowledgement of each Layer 3 message in the opposite direction, except forMeasurement Results that are carried by the LAPD UI frames. No acknowledgements are usedfor Measurement Results, and the L2 header is 7 bytes long. This is why measurements aresummed in a separated column at layer 3 in Annex A.Both receivers are supposed to be always ready to receive conditions.The layer 2 flow due to the transmission of RR frames (acknowledgements) is added to thetransmitted data flow.

2.1.3.2 Bit Error Rate.

The physical bit error rate on Abis is assumed 10 -6 (Worst case for 2 Megabits/s PCM link)9.With a BER 10-3, the global throughput would increase, and response times would be affecteddue to LAPD retransmission.

2.1.3.3 Inserted bits.

We have taken into account the overload due to the bit transparency algorithm (one 0 insertionevery five consecutive 1). The number of inserted bits is calculated as :NB inserted bits = NB total bits X probability(insertion of one 0 bit) whereprobability(insertion one 0 bit) = (1/2)^5

9 This BER is also valid for Abis on Satellite links, according to ITU recommendation G.826. Wecannot guaranty any performances with satellite links which would not comply with thisrecommendation. .


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2.1.3.4 Piggy-backing:

The LAPD protocol allows a reduction of the acknowledgement flow (RR frame) when the load ofthe physical link increases, because acknowledgements are also included in the opposite Iframes. In our BSS, Piggy-backing is implemented at both ends of the RSL ( c.f. document [9 ]).This reduction is supposed to be optimal (which is the case on a loaded link), so RR Frames are

never sent. The influence of Piggy-backing on the RR flow and response time is studied insection 8.1.

The simulation results presented in this document are with piggy-backing active (no RRframes).


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2.2 Traffic Model for the OML.

Traffic on Abis due to O&M procedures is not taken in account by the simulation model. Onlysome rough estimate of the O&M traffic is done hereafter.

2.2.1 O&M traffic rate

Activation of the O&M scenarios generates Abis load. The O&M functions support the parallelactivation of at most 4 scenarios on the Abis interface, except :

- one file transfer may be activated at a given time per OMU,

- one pending action per SBL,

- one pending fault indication per OMU

Since we do not have a detailed Abis traffic model for O&M, we have made the followingassumptions :

for the downlink, the load is generated by :a BTS downloading (software pre-load can be done while telecom traffic is on-going)

an OMU-CPF (while telecom traffic is on-going)

The remaining O&M traffic on the downlink is due to operator command which do notobey real time constraints (compared to telecom traffic).

For the uplink, the OML load (alarms, response to operator commands) is considerednegligible compared to the RSL load. So it is not taken into account in this document.

Consequently only the O&M traffic corresponding to the Software downloading (worstcase) is taken into account in this document.

The software downloading, unlike the telecom traffic consists of a nearly continuous flow ofmessages during a limited period of time. The OMU response time is very short (a few ms), andwith an anticipation window on the OML with a value greater or equal to 2 (as recommended bydocument [9 ]), then the message rate depends only on the frame length and availablebandwidth.

2.2.2 O&M traffic flow for Software download.

2.2.2.1 Frame length

The O&M traffic flow uses the maximum LapD frame length = 260 octets.

2.2.2.2 Size of the BTS SW.

The duration of the software downloading depends on the BTS software size. The size of thepackage effectively transferred on Abis is taken into account.


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Typical SW size (sizes may differ from one delivery to the other).

Abis SW package for the BTS

Suma (BTS-O&M) 0.9 MBKernel of TRE G3 0.4 MBCiphering TRE G3 0.2 MB

Kernel of TRE G4 0.4 MBCiphering TRE G4 0.2 MBOther files / margin 0.5 MB

Total 2.6 MB

Table 10: BTS software size.

2.2.2.3 Actual OML bandwidth and duration of software download.

Note: In this document we consider only the file transfer time. For a real estimation of the totaldownload time, the configuration and audit time must be added.

Terrestrial links

In this case the LAPD window size is such that the OML can use 100% of the bandwidth.However, in case of statistical multiplexing, the available bandwidth is reduced by the proportiontaken by the telecom signalling. There is no priority mechanism implemented with the statisticalmultiplexing, each LAPD link can send one message at a time (so-called round-robin). Whenthere is some traffic on the RSLs, the proportion of the bandwidth available for each LAPDdepends on the average I frame size and of the number of links multiplexed. The average Iframe size for a RSL is estimated (with LAPD header) to 33 octets. The I-Frame length on theOML for Software downloading is 268 octets. So if there are N (N =1 to 4) RSL multiplexed withthe OML, then the proportion of the bandwidth used by the OML will be: 268 /(268 + Nx 33).From this we deduce the Software downloading time and the remaining bandwidth for the RSLsfor a 2.6 Mbytes software package.

Link speed.Kbits/s

Number ofmux.RSLs

%band-width

for OML

OML actualbandwidth

(Kbit/s)

SWdownload

duration (s)

Samein minutes(rounded)

remainingbandwidth

(Kbit/s)

Averagebandwidth

per RSL

64 0 100% 64 341 6 N.A. N.A

64 1 89% 57 383 7 7 7

64 2 80% 51 425 7 13 6

64 3 73% 47 467 8 17 6

64 4 67% 43 509 9 21 5

16 1 89% 14 1531 26 2 2

Table 11: Bandwidth usage during SW download (terrestrial).

Satellite links

In this case the transmission delay has an impact on the actually available bandwidth dependingon the LapD anticipation window and the average message length.

The percentage of the bandwidth which can actually be used is given by the following formula,where the processing time in BTS and BSC is considered negligible compared to the satelliteinduced delay. The possible multiplexing with one or several RSL is not considered.

K_VAL x I_trans_time / ( I_trans_time + sat_delay + RR_Trans_time +sat_delay).(time actually spent transmitting/ (time transmitting + time waiting for acnowledgment).


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K_VAL = LAPD anticipation window (see ref [9 ] for details).I_trans_time is the time of I frame transmission, which depends on the link speed and I framelength.Ack_Trans_time is the time of RR transmission for acknowledment, which depends on the linkspeed and I frame length.

Sat-Delay is the delay induced by satellite transmission (one hop), estimated to 250ms.

The following table gives the actual available bandwidth for 16K and 64K channel, depending onthe anticipation window K_val. The I-frame length on the OML is 268 octets (with LAPD header).

LinKspeed

(Kbit/s)

I_trans_time on

OML (ms)

RR transtime on

OML (ms)

K_val proposeddefaultvalues

satellite%OML used

actual OMLbandwidth

(Kbit/s)

SW downloadtime in

minutes

64 33.5 1.0 2 13% 8 46

64 33.5 1.0 3 19% 12 31

64 33.5 1.0 4 25% 16 23

64 33.5 1.0 6 38% 24 16

64 33.5 1.0 9 default 56% 36 11

16 134.0 4.0 2 42% 7 55

16 134.0 4.0 3 default 63% 10 37

16 134.0 4.0 4 84% 13 28

Table 12: Available bandwidth for the OML on satellite links.

Note 1: Test conducted in B6.2 has shown an efficient bandwidth of roughly 70% less thanexpected. So the Software download time may be longer by 40% than in the above table.Note 2: For the expected bandwidth to be really used, the application layer above LAPD musthave the same window size (D_LOAD_WIN = K_VAL_OML).

2.2.2.4 Impact of the Software download on the Telecom Signalling.From the previous Table 11, it appears that the sharing of the bandwidth between O&M and RSLfor statistical multiplexing leaves little bandwidth for the RSLs. This remaining bandwidth is notsufficient for nominal traffic on the RSL for most multiplexing schemes (as shown by simulationresults in section 3) . The operator has the choice between two strategies in, case of statisticalmultiplexing:

Either perform the SW download during low traffic periods (presumably at night)

Or accept a disturbance of the telecom signalling during Software download. This shouldmainly affect the establishment of new calls. Established calls would be affected only in thecase where a handover is required.


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3. TELECOM SIGNALLING FLOW ESTIMATIONS

The estimation are derived from the model described in section 2.

3.1 Signalling flow per sub channel

For nominal traffic, TCH load (90%) and SDCCH load (70%) on large cells.

Downlink Uplink

Sub Channels bit/s I

frame/s

bit/s I+UI

frame/s

CCCH combined (for 4 SDCCH) 5,576 30.93 2,215 1.17

CCCH combined (for 12 SDCCH) 6,300 32.80 2,685 3.50

CCCH not comb. (for 8 SDCCH) 5,938 31.87 2,450 2.33





SDCCH+SACCH/C

(one sub-channel)

742 2.79 857 3.53

CBCH 479 0.50 111 0.00

TCH+SACCH/T 95 0.46 760 2.38

Table 13: simulation results per channel type.

3.2 Signalling flow for TRX-oriented procedures.

Flows corresponding to procedures at TRX level are provided hereafter. They are independent ofthe TRX load. In case of RSL multiplexing, the RMS upload may go on in parallel on the TRXwhich are multiplexed together, hence the RMS upload flow is multiplied in case of RSLmultiplexing and becomes significant. However the RMS data upload should occur not more thanonce a day, and with lasts only about 10 seconds (transfer of a 2K octets per TRX with the flowindicated below).

RMS data upload flow Abis dynamic flow

Downlink bit/s Uplink bit/s Downlink bit/s Uplink bit/s

0 2 183 462 198

Table 14: simulation results for TRE oriented procedures.

With Abis dynamic active, a reduction of CS traffic on the TCH shall be considered to account forGPRS traffic.


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3.3 Parameters Influence

For a given TRX configuration (F1B8S), we studied the influence of the input parameters on theresulting flow. The parameters which have a significant influence are the SDCCH holdingtime and the paging rate.

3.3.1 SDCCH trafficTwo assumptions are considered: an increase of the total exchanged length, and an increase (ordecrease) of the duration of the scenario. power control

Increase of this traffic is due to the duration of a call (see previous chapter), and the numberof power control during a call.- an increase of about 100% of the number of power control will produce a 1,5% increase ofthe downlink throughput (negligible influence).

handoverFlow due to handover scenario may be consider as negligible, therefore, possible increase ofthis traffic due to an increase of the total length of the bytes exchanged has no influence.

SACCH modify optionThis is the only Location update option which depends on a BSS parameter. We study theinfluence of this option on the Abis flow (the influence is on the downlink only). The activationof this option adds a flow of roughly 1.5 Kbit/s for each SDCCH time slot (8 sub-channels).The other simulation results presented in this study are done with this option being activated.

flow for 8SDCCH

Abis flow in bit/s with standardSDCCH holding time (3s)

SACCH modif yes No

DL overload 8,485 6,373

DL nominal 5,940 4,461

Table 15: Influence of SACCH modify

SDCCH holding time:

The SDCCH holding time has been measured with Alcatel test-bed for the procedures whichuses the SDCCH. The average SDCCH holding time is deduced depending on the traffic mixparameters. The simulations presented in this document have been conducted with the worstcase: No location update, no SMS (=> SDCCH holding time = 3s). However when high SDCCHtraffic is due to SMS or Location Updates, a longer SDCCH holding time could be used.

Procedure MOC MTC LU Imsiattach

Imsidetach

SMS

SDCCH

averageHT

SDCCH HT per procedure 3300 2850 4400 2970 2565 6500

%Acatel mix (LU +SMS) 0.6 0.4 4 0.1 0.1 1 4480

% No LU, noSMS

0.6 0.4 0 0.1 0.1 0 3061

% No LU, with SMS 0.6 0.4 0 0.1 0.1 1 4624

% with LU, no SMS 0.6 0.4 4 0.1 0.1 0 4091

Table 16: Average SDCCH holding time depending on call mix.


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The following table gives the mean signalling flow related to 8 SDCCH (one time slot), duringoverload (100% load) and in nominal traffic (70% load). The values corresponding to Alcateltraffic mix is shown in bold. Values are also plotted below the table. This parameter has thegreater influence on the Abis flow related to SDCCH. It should be noted that for longer values ofthe SDCCH holding time, the uplink flow becomes more important. This is due to the fact that theradio measurement flow is independent of the SDCCH holding time.

Abis Flow for 8 SDCCH Abis flow in bit/s with variable SDCCH holding time (in s)

2 2.5 3 3.5 4 4.5 5

DL overload (100%) 12,457 10,074 8,485 7,351 6,499 5,837 5,308

UL overload (100%) 11,581 10,584 9,919 9,445 9,089 8,812 8,590

DL nominal (70%) 8,720 7,052 5,940 5,145 4,550 4,086 3,715

UL nominal (70%) 8,107 7,409 6,944 6,611 6,362 6,168 6,013

Table 17: influence of SDCCH holding time on Abis flow.

Figure 1: influence of SDCCH holding time (nominal).

T h r o u g h p u t f o r 8 S D C C H i n n o m i n a l t r a f f i c

0

5 , 0 0 0

1 0 , 0 0 0

1 5 , 0 0 0

2 2 . 5 3 3 . 5 4 4 . 5 5

S D C C H h o l d i n g t i m e ( s )

b

i

t

s

/

s

d o w n l i n k

u p l i n k


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Figure 2: influence of SDCCH holding time (overload).

Assignment reject sent by the BSCnot studied.

T h r o u g h p u t f o r 8 S D C C H i n o v e r l o a d

0

5 , 0 0 0

1 0 , 0 0 0

1 5 , 0 0 0

2 2 . 5 3 3 . 5 4 4 . 5 5

S D C C H h o l d i n g t i m e ( s )

b

i

t

s

/

s

d o w n l i n k

u p l i n k


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3.3.2 TCH traffic

TCH holding time:

A decrease of the duration has a low influence 10 on the resulting uplink and downlink flows.- with a 50 s duration, the downlink flows gets an increase of 2,5%, the uplink flows

gets even a lower increase.

Call establishment message length:we can study an increase of the total exchanged bytes.- an increase of 100 % of the exchanged bytes will produce a 0,1 % increase of the

uplink throughput (negligible). Call release, handover message length:

their influence is the same as for the call establishment scenario.

3.3.3 BCCH/CCCH traffic

pagingThe paging flow has a strong influence on the resulting throughput.The Abis flow due to paging is increased proportionally to the increased Paging rate.

Roughly the downlink Abis signalling flow is increased by 1 Kbit/s each time a flowof 6 Paging/s is added.

random accessWith the previous assumptions, the successful random access is considered to be maximum.We may study the influence of the overload factor of RACH.

- with an overload factor of 2 (instead of 1), there is an increase of 3,4% of the uplinkthroughput

3.3.4 BER

Refer to Annex D for charts. In this study a BER < 10E-6 is assumed which guaranties thatnearly the maximum channel throughput is reachable (64 Kbit/s on an Abis time slot).

10 This low influence is a consequence of the model used for the Abis traffic, which does notestablish a relation between the TCH holding time and the SDCCH load. In the reality, a reduction ofthe TCH holding time induces an increase of the SDCCH load. If the number of SDCCH is notincreased by the operator to cope with this extra load, then the Abis load for a given TRXconfiguration increases.


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3.4 Signallling Flow Estimation For Each TRX Configuration

The following tables give the expected Abis flow for several TRX configurations and level oftraffic. RMS upload is not taken into account. The level of traffic (nominal, increased, overload)are defined in section 2.1.1.6. The notations for TRX configurations are defined in section2.1.1.3.

RSL sub-multiplexing is not considered here. When no multiplexing is used, all allowed TRXconfigurations have enough throughput to offer satisfactory performances, even in case ofoverload.

3.4.1 Nominal traffic (large cells)

SDCCH average load 70%

TCH average load 90%

TRX FULL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

TRX DUAL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

F1C4S 12 9,938 11,435 D1C4S 12 10,606 16,758

F1C12S 12 15,782 17,528 D1C12S 12 16,355 22,091

F1B11 16 7,330 8,243 D1B 16 7,998 13,566F1B8S 16 13,174 14,336 D1B8S 16 13,747 18,899

F1B16S 24 19,743 20,899 D1B16S 24 20,220 24,701

F1B16S 64 23,362 23,248 D1B16S 64 23,840 27,050

F1B24S 24 25,587 26,992 D1B24S 24 25,969 30,034

F1B24S 64 29,207 29,341 D1B24S 64 29,589 32,383

F8S any 6,608 12,177 D8S any 7,276 17,500

F16S any 12,452 18,270 D16S any 13,025 22,833

F24S any 18,296 24,363 D24S any 18,774 28,166

F8T any 763 6,084 D16T any 1,527 12,167

Table 18: TRX flow in nominal traffic

3.4.2 Increased traffic (large cells)



TRX FULL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

TRX DUAL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

F1C4S 12 10,881 12,939 D1C4S 12 11,623 18,853

F1C12S 12 17,988 20,471 D1C12S 12 18,624 25,540

F1B 16 7,714 9,035 D1B 16 8,457 14,950

F1B8S 16 14,821 16,567 D1B8S 16 15,457 21,637

F1B16S 24 22,807 24,670 D1B16S 24 23,337 28,895

F1B16S 64 27,202 27,522 D1B16S 64 27,732 31,747

F1B24S 24 29,913 32,202 D1B24S 24 30,337 35,582

F1B24S 64 34,309 35,054 D1B24S 64 34,733 38,434

F8S any 7,955 14,292 D8S any 8,697 20,206

F16S any 15,061 21,824 D16S any 15,698 26,893

F24S any 22,168 29,356 D24S any 22,698 33,580

F8T any 848 6,760 D16T any 1,697 13,519

11 This configuration is currently not allowed by O&M because of recovery strategy.


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Table 19: TRX flow in increased traffic

3.4.3 Overload



TRX FULL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

TRX DUAL

RATE

SDCCH

in cell

Downlink

bit/s

Uplink

bit/s

F1C4S 12 11,750 13,861 D1C4S 12 12,493 19,776

F1C12S 12 20,130 22,935 D1C12S 12 20,766 28,005

F1B 16 8,025 9,237 D1B 16 8,767 15,151

F1B8S 16 16,404 18,311 D1B8S 16 17,040 23,381

F1B16S 24 25,818 28,057 D1B16S 24 26,348 32,281

F1B16S 64 30,989 31,412 D1B16S 64 31,519 35,637

F1B24S 24 34,197 37,131 D1B24S 24 34,621 40,511

F1B24S 64 39,368 40,486 D1B24S 64 39,792 43,866

F8S any 9,228 15,834 D8S any 9,970 21,749

F16S any 17,607 24,908 D16S any 18,243 29,978

F24S any 25,986 33,983 D24S any 26,517 38,208

F8T any 848 6,760 D16T any 1,697 13,519

Table 20 : TRX flow in cell overload

3.4.4 Proportion of I frames on the total flow on the uplink.

One can see from the above results that the uplink flow is greater than the downlink flow12.However, most of the uplink flow is made from radio measurements which are carried by UI(unacknowledged) frames. The table below gives the ratio of the flow corresponding to I frame on

the total flow for the uplink, depending on the TRX configuration. This ratio varies between 7%and 36% for a FR TRX. The same study on a DR TRX give a ratio between 8% and 32%.

UplinkTRX FULL

RATE

SDCCH

in cellbit/s Bit/s (I only) % I uplink

F1C4S 12 11,435 2,170 19%

F1C12S 12 17,528 4,581 26%

F1B 16 8,243 1,114 14%

F1B8S 16 14,336 3,525 25%

F1B16S 24 20,899 6,287 30%

F1B16S 64 23,248 8,039 35%

F1B24S 24 26,992 8,699 32%

F1B24S 64 29,341 10,450 36%

F8S any 12,177 2,815 23%

F16S any 18,270 5,227 29%

F24S any 24,363 7,638 31%

F8T any 6,084 404 7%

max => 36%

min => 7%

Table 21: Proportion of I frames on the uplink

12 With our traffic model. With very high level of paging, this will not remain true.


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3.5 Signallling Flow Estimation For 16 Kbit/S Channel.

This section is valid both for static multiplexing at 64 Kbit/s (=4x16) and for statisticalmultiplexing on a 16Kbit/s channel. For a more accurate result with statistical multiplexing, theO&M load should also be taken into account (see section 2.2).

3.5.1 Allowed configuration

Results from section 3.4 on Dual Rate TRX showed that 16 Kbit/s channels cannot be used, sothey are not reported here.

The following Full Rate TRX configurations are allowed on 16K channels (see section 2.1.1.3 fornotations).

F1C4S, F1B8SF8S,F8T (only static multiplexing, not allowed with statistical)They appear in bold characters in the simulation results.

The following TRX configurations are not allowed on 16K channelsF1C12S, F1B16S, F1B24SF16S, F24S, F1BSome of these configurations are however considered for simulations.

3.5.2 Simulation results.

The shading and colour in the result tables has the following meaning. The performancesexpectations are derived from Table 2 in section 2.1.1.1. Note that RMS upload should not lastmore than 10s.

11,956 Abis flow is below 12.5 Kbit/s. Good performances are expected.

13,898 Abis flow in the range [12.5 Kbit/s15 Kbit/s]. The performances are not verygood, but no severe problems are expected.

15,273 The Abis flow is greater than 15 Kbit/s. The performances are poor, andcongestion is likely to occur.

3.5.2.1 Nominal traffic (large cells)



TRX and cellconfiguration

TCH

number

bit/s

Downlink

bit/s

Uplink

bit/s

Uplink +RMS

upload

F1B8S (24 SD cell) 6 13,898 14,806 16,988

F1B8S (64 SD cell) 6 17,518 17,154 19,337

F1B16S 5 19,743 20,899 23,082

F8S 7 6,608 12,177 14,360

F16S 6 12,452 18,270 20,453

F8T 8 763 6,084 8,266

Table 22: TRX flow on 16K channel, large cell, nominal traffic.


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3.5.2.2 Increased traffic (large cells)



TRX and cell

configuration

TCH

number

bit/s

Downlink

bit/s

UplinkF1B8S (24 SD cell) 6 15,700 17,138

F1B8S (64 SD cell) 6 20,096 19,990

F1B16S 5 22,807 24,670

F1B24S 4 29,913 32,202

F8S 7 7,955 14,292

F16S 6 15,061 21,824

F8T 8 848 6,760

Table 23: TRX flow on 16K channel, large cell, increased traffic.

3.5.2.3 Nominal traffic (small cells).

SD_L SDCCH average load 50%TCH_L TCH average load 70%


TCH

number

bit/s

Downlink

bit/s

Uplink

bit/s

Uplink

+ RMS upload

F1C4S 7 8,631 9,050 11,233

F1C12S 6 12,799 13,311 15,494

F1B8S (8SD cell) 6 10,678 10,885 13,067

F1B8S (16SD cell) 6 10,936 11,053 13,235

F1B8S (24 SD cell) 6 11,453 11,388 13,571F1B16S 5 15,622 15,649 17,832

F8S 7 4,762 8,993 11,176

F16S 6 8,931 13,254 15,437

F8T 8 594 4,732 6,914

Table 24: TRX flow on 16K channel, small cell, nominal traffic.


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3.5.2.4 Increased traffic ( small cells)



TCH

number

bit/s

downlink

bit/s

uplink

bit/s

uplink + RMS

upload

F1C4S 7 9,321 10,536 12,719

F1C12S 6 14,322 15,667 17,849

F1B8S (8SD cell) 6 11,777 12,742 14,925

F1B8S (16SD cell) 6 12,087 12,944 15,126

F1B8S (24 SD cell) 6 12,708 13,346 15,529

F1B16S 5 17,709 18,477 20,659

F8S 7 5,722 10,876 13,059

F16S 6 10,723 16,007 18,190

F8T 8 721 5,746 7,928

Table 25: TRX flow on 16K channel, small cell, increased traffic.

3.5.2.5 TCH congestion (small cells)




TCH

number

bit/s

Downlink

bit/s

Uplink

bit/s

uplink

+ RMS upload

F1C4S 7 9,433 11,423 13,606

F1C12S 6 14,418 16,427 18,610

F1B8S (8SD cell) 6 11,872 13,503 15,685

F1B8S (16SD cell) 6 12,183 13,704 15,887

F1B8S (24 SD cell) 6 12,803 14,107 16,289

F1B16S 5 17,788 19,111 21,293

F8S 7 5,833 11,764 13,946

F16S 6 10,819 16,768 18,950

F8T 8 848 6,760 8,942

Table 26: TRX flow on 16K channel, small cell, TCH congestion


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3.5.2.6 Increased Paging (small cells) in nominal traffic.


TRX and cellconfiguration,TCHnumber bit/sDownlink

30 paging/s

bit/sdownlink

40 paging/s

bit/sdownlink

50 paging/s

bit/suplink

F1C4S 7 8,631 10,376 12,125 9,710

F1C12S 6 12,799 14,544 16,293 13,971

F1B8S (8SD cell) 6 10,678 12,423 14,172 11,545

F1B8S (16SD cell) 6 10,936 12,682 14,430 11,713

F1B8S (24 SD cell) 6 11,453 13,199 14,947 12,048

F1B16S 5 15,622 17,367 19,116 16,309

F8S 7 4,762 4,762 4,762 8,993

F16S 6 8,931 8,931 8,931 13,254

F8T 8 594 594 594 4,732

Table 27: TRX flow on 16K channel, small cell, increased paging.

Note: an added Paging flow of 6 Paging messages per second roughly adds 1 Kbit/s to thedown-link flow (cf section 3.3.3).

3.5.3 Conclusion and recommendations

In addition to the above configuration restrictions, the following recommendation should befollowed:

The channel at 16 Kbit/s should not be used where the average SDCCH load is expectedto be higher than 60% (large cells). The obligation to configure 8 SDCCH/TRX forstatistical 16Kbit/s will tend to limit the average SDCCH load in this case.

The Channel at 16 Kbit/s should not be used on large cells where the CCCH load may betoo high on configuration 1B.8S (even with nominal traffic).

The bandwidth needed for the OML in case of software download may disturb thetelecom traffic (see section 2.2 )

To offer a better resistance to performances degradation, the TX-integer parameter maybe set so that the Channel Request repetition by the MS is spread on the longest timeinterval as possible.


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3.6 Signallling Flow For Statistical Multipexing On 64 Kbit/S Channel.

3.6.1 General

The sub-multiplexing allows the OMU and the TRX belonging to the same BTS to share one

64Kbit/s Abis Time Slots. The group of LapD channels which are multiplexed statistically on a64Kbit/s time slot is called MCB (Multiplexed Channel Block). Each MCB configuration is studiedhereafter.

The multiplexed configurations foreseen for LapD signalling on one Abis TS on a 64 Kbit/schannel are:

- 2, or 4 RSL

- 1, 2, or 4 RSL + 1 OML

For more information on this multiplexing scheme, refer to document [10].

In this section only the RSL flow is estimated. The interaction with the O&M signalling isstudied in section 2.2.

To each MCB configuration a signalling load is computed with the following formula. This ismeant to be used as a simple mean to discriminate acceptable and non acceptable MCBconfigurations.

MCB signalling load = Number of SDCCH sub-channels in MCB+ 4 x Number of combined BCCH in MCB+ 8 x Number of non-combined BCCH in MCB.

The shading and colour in the result tables is as follows:

49,875 Abis flow is below 50 Kbit/s. Good performances are expected (cf section2.1.1.1).

54,623 Abis flow in the range [50Kbit/s60Kbit/s]. The performances are not very good, butno severe problems are expected. (cf section2.1.1.1).

62,261 The Abis flow is greater than 60Kbit/s. The performances are poor, and congestion islikely to occur.

In the following two types of cells are studied:

Very large cells: the CCCH flow is computed with 64 SDCCH in the cell. It is assumed thatin this case it is not possible to have two TRX with BCCH on the same MCB

Large cells: the CCCH flow is computed with 32 SDCCH in the cell. It is assumed that in thiscase it is possible to have two TRX with BCCH on the same MCB

The same level of traffic, as defined in section 2.1.1.6, are used for both cell types.

3.6.2 Signalling flow for 1 TRX (FR or DR).

This case is already studied in section 3.4 for the RSL aspects (FR and HR). The interaction withthe O&M is described in section 2.2.This MCB configuration can cope with any traffic level for DR and FR TRX.


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3.6.3 Signalling flow for 2 FR-TRX.

Very large cells (64 SDCCH).The following results corresponds to very large cell simulations. The CCCH flow has beenobtained with 64 SDCCH in the cell, which corresponds to a cell with at least 8 TRX. The TCHand SDCCH load for each level of traffic are defined in section 2.1.1.6.

MCB values (added for all the RSLs) Nominal traffic Increased traffic Overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

32 1 11 40 35,815 41,518 45,883 42,264 49,345 48,596 56,321

40 1 10 48 41,659 47,611 51,976 49,370 56,877 56,975 65,395

Table 28:MCB flow for 2 FR TRX.

large cells (32 SDCCH).The following results corresponds to large cell simulations. The CCCH flow has been obtainedwith 32 SDCCH in the cell, which corresponds to a cell with up to 8 TRX. The TCH and SDCCH

load for each level of traffic are defined in section 2.1.1.6.

MCB values (added for all the RSLs) Nominal traffic Increased traffic Overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

24 1 12 32 27,074 33,546 37,911 31,641 39,532 36,080 44,562

24 2 11 40 35,089 36,644 41,009 40,265 42,949 45,325 48,381

32 1 11 40 32,919 39,639 44,004 38,747 47,064 44,459 53,636

32 2 10 48 40,933 42,737 47,103 47,372 50,481 53,704 57,456

Table 29: MCB flow for 2FR-TRX

Conclusion: This multiplexing scheme is valid for large cells in nominal traffic with MCB load upto 48. Some degradation of performances may occur during RMS upload or with increasedtraffic. Congestion on the Abis can occur in case of cell overload. For MCB load = 40, there is nocongestion problem at all.

3.6.4 Signalling flow for 4 FR-TRX.


MCB values (added for all the RSLs) Nominal Increased Overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

16 1 29 24 25,653 41,499 50,229 29,747 47,801 33,534 51,691

24 1 28 32 31,497 47,592 56,322 36,854 55,333 41,913 60,765

32 1 27 40 37,342 53,685 62,416 43,960 62,865 50,292 69,840

40 1 26 48 43,186 59,779 68,509 51,067 70,397 58,672 78,914

Table 30: MCB flow for 4 FR -TRX


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large cells (32 SDCCH).The following results corresponds to large cell simulations. The CCCH flow has been obtainedwith 32 SDCCH in the cell, which corresponds to a cell with up to 8 TRX. The TCH and SDCCHload for each level of traffic are defined in section 2.1.1.6.

MCB values (added for all the RSLs) Nominal Increased Overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

24 1 28 32 28,601 45,713 54,443 33,337 53,051 37,776 58,081

24 2 27 40 36,616 48,812 57,542 41,962 56,468 47,021 61,900

32 1 27 40 34,446 51,806 60,537 40,444 60,583 46,155 67,155

24 3 26 48 44,630 51,910 60,640 50,586 59,884 56,266 65,720

32 2 26 48 42,460 54,905 63,635 49,068 64,000 55,400 70,975

40 1 26 48 40,290 57,900 66,630 47,550 68,115 54,535 76,230

Table 31: MCB flow for 4 FR-TRX.

Conclusion: This multiplexing scheme is valid for large cells in nominal traffic with MCB load upto 40. Some congestion may occur during RMS upload or with increased traffic. Congestion onthe Abis can occur in case of cell overload.

3.6.5 Signalling flow for 2 DR-TRX.


MCB values (added for all the RSLs) Nominal Increased overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

24 1 24 32 31,115 44,550 48,915 36,429 51,953 41,489 57,386

24 2 22 40 41,930 48,767 53,132 48,464 56,806 54,765 63,044

32 1 22 40 36,864 49,883 54,248 43,430 58,640 49,762 65,615

32 2 20 48 47,679 54,100 58,465 55,465 63,493 63,038 71,274

40 1 20 48 42,613 55,216 59,581 50,430 65,327 58,036 73,844

Table 32: MCB flow for 2 DR-TRX.


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Large cells (32 SDCCH).The following results corresponds to large cell simulations. The CCCH flow has been obtainedwith 32 SDCCH in the cell, which corresponds to a cell with up to 8 TRX. The TCH and SDCCHload for each level of traffic are defined in section 2.1.1.6.

MCB values (added for all the RSLs) Nominal Increased overload

Number of

SDCCH

Number

of BCCH

Number

of TCH

Signalling

load

DL flow

bit/s

UL flow

bit/s

UL flow

bit/s

+ RMS

DL flow

bit/s

UL flow

bit/s

DL flow

bit/s

UL flow

bit/s

24 1 24 32 28,220 42,671 47,036 32,913 49,671 37,352 54,701

24 2 22 40 36,139 45,009 49,374 41,431 52,243 46,491 57,676

32 1 22 40 33,968 48,004 52,369 39,914 56,358 45,625 62,931

32 2 20 48 41,888 50,342 54,707 48,432 58,930 54,764 65,905

40 1 20 48 39,717 53,337 57,702 46,914 63,045 53,899 71,160

Table 33: MCB flow for 2 DR-TRX

Conclusion: This multiplexing scheme is valid for large cells in nominal traffic with MCB load up

to 48. Some degradation of performances may occur during RMS upload or with increasedtraffic. Congestion on the Abis can occur in case of cell overload. For MCB load = 40,congestion occurs only in case of cell overload.

RENV

SEQARABERENV

SEQARABE

3.6.6 Summary of conclusions and recommendation for MCB 64 Kbit/s

3.6.6.1 Results summary

The following tables summarise the previous results with MCB signalling load 40 and 48. Itprovides the maximum Abis flow (rounded) which can be expected with the variousconfigurations and level of traffic (as defined in section 2.1.1.6).


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