14 GSM BSS Network KPI Call Setup Time Optimization Manual

8/12/2019 14 GSM BSS Network KPI Call Setup Time Optimization Manual

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GSM BSS Network KPI (Call Setup Time) Optimization Manual INTERNAL

Product Name Confidentiality Level

G3BSC INTERNAL

Product Version Total 27 pages

GSM BSS Network KPI (Call Setup Time)

Optimization Manual

For internal use only

Prepared by Yang Chunjie (ID: 00119951) fromthe GSM&UMTS NetworkPerformance Research Dept.

Date 2008-12-24

Reviewed by Date yyyy-mm-dd

Reviewed by Date yyyy-mm-dd

Approved by Date yyyy-mm-dd

Huawei Technologies Co., Ltd.

PDF created with pdfFactory trial version www.pdffactory.com
http://www.pdffactory.com/http://www.pdffactory.com/


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All rights reserved



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2011-6-28 Huawei Proprietary and Confidential Page 3 of 27

Contents

1 Overview of the Call Setup Time....................... ............................................... 7

1.1 Definition of the Call Setup Time ..................... .................... ..................... .................... .... 7

1.2 Recommended Formulas ................... .................... ..................... ..................... .................. 7

1.3 Signaling Procedure and Measurement Points ................ ..................... .................... .......... 8

2 Influencing Factors............................................................................................ 10

2.1 Procedure Configuration ......................... .................... ........................ ................. ........... 10

2.2 Parameter Settings ................ ........................ .................... ..................... .................... ..... 10

2.3 Routing .......................................................................................................................... 10

2.4 Hardware, Transmission, Coverage, and Interference ...... ...... ...... ...... ..... .... ...... ...... ..... ..... 11

3 Analysis Process and Optimization Method ............................... .................. 12

3.1 Analysis Process ................ ..................... .................... ........................ ..................... ....... 12

3.2 Process Description ............................. .................... ..................... ....................... ........... 13

3.2.1 Procedure Configuration ......................... .................... ..................... .................... .. 13

3.2.2 Parameter Setting ..................... .................... ..................... ..................... ................ 15

3.2.3 Routing.................................................................................................................. 18

3.2.4 Hardware, Transmission, Coverage, and Interference .............................................. 19

4 Test Method ....................................................................................................... 21

5 Optimization Cases ........................................................................................... 22

5.1 Long Call Setup Time Due to Long Period of Assignment Command Delivery ................ 22

5.1.1 Problem Description ................ .................... ..................... ..................... ................ 22

5.1.2 Problem Analysis ..................... .................... ..................... ..................... ................ 22

5.1.3 Suggestion and Summary ........................ .................... ..................... .................... .. 22

5.2 Long Call Setup Time Due to Reporting of Two Classmark Change Messages .... ..... ...... .. 23




5.3 Long Call Setup Time Due to Calling and Called MSs Under Different MSCs ................. 24





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5.4 Long Call Setup Time Due to Inconsistency in Signaling Procedures ............................... 25




6 Information Feedback ....................................................................................... 27



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Revision Record

Date Revision Change Description Author

2008-12-24 V0.3 Draft completed. Yang Chunjie

2009-1-20 V1.0 This document is modifiedaccording to review comments.

Yang Chunjie

References

SN Document Author Date

1 GSM BSS Network KPI

(Call Setup Time) Baseline

Wu Zhen 2007-08-24

2 GSM Call Setup Time(CS) Analysis Report

Zha Shuangliu, LiXiaomeng, Zhang Lida,

and Wu Baishan

2008-10-25



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GSM BSS Network KPI (Call Setup Time)

Optimization Manual

Keywords

Call setup time

Abstract

This document describes the method of optimizing the call setup time.

Acronyms and Abbreviations

MOC Mobile Originated Call

MTC Mobile Terminated Call

PSTN Public Switched Telephony Network

TMSI Temporary Mobile Station Identity



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1 Overview of the Call Setup Time1.1 Definition of the Call Setup Time

The call setup time indicates the mean time from the originating of a call by a

subscriber to the setup of the call. A long call setup time will severely affectthe user experience. Therefore, the call setup time is one of the KPIs that

operators are most concerned about.

1.2 Recommended FormulasThe call setup time is obtained through drive tests. It refers to the time for an

MS to set up an end-to-end call through radio network equipment. There arethree types of call setup time:

l MS to PSTN: average interval between the transmission of the Channel

Request message from the MS and the MS's reception of the Alertingmessage sent from the MSC

l MS to MS: average interval between the transmission of the Channel

Request message from the calling MS and the calling MS's reception ofthe Alerting message sent from the MSC

l PSTN to MS: average interval between MS's receiving of the pagingmessage from the MSC and sending of the Alerting message from theMS to the MSC

Note that the call setup time is the average setup time of multiple successful

calls. You need to conduct multiple dialing tests.



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1.3 Signaling Procedure and Measurement Points

Figure 1-1Measurement points in an MOC setup procedure (with the earlyassignment procedure as an example)

BTS BSC

Channel RequestChannel Required

Channel Active

Channel Active

ACK

Immediate Assignment Command

SABM

UA

Established

Indication CR

CC

CM Service Accepted

Setup

Call ProceedingAssignment

RequestChannel Active

Channel Active

ACK

Assignment Command

SABM

UA

Established

Indication

Assignment Complete

Assignment

Complete

A

B

MS

Alerting



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Figure 1-2Measurement points in an MTC setup procedure (with the earlyassignment procedure as an example)

MS BTS BSC MSC

Channel Request

Channel Required

Channel Active

Channel Active

ACKImmediate Assignment Command

SABM

UAEstablished

Indication CR

CC

CM Service Accepted

Setup

Call Control

Assignment

RequestChannel Active

Channel Active

ACK

Assignment Command

SABM

UA

Established

Indication

Assignment Complete

Assignment

Complete

Alerting

C

D

paging

Paging CommandPaging Required

In Figure 1-1 and Figure 1-2:

l A is the time when the MS sends a Channel Request message.

l B is the time when the MS receives the Alerting message from the MSC.

l C is the time when the MS receives a paging message.

l D is the time when the MS sends an Alerting message.

In the tests of MS-to-MS or MS-to-PSTN calls, the call setup time is equal to

B minus A; in the tests of PSTN-to-MS calls, the call setup time is equal to D

minus C.



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2Influencing Factors

2.1 Procedure ConfigurationThe setup of either an MOC or an MTC involves many procedures such asauthentication and ciphering mode setting and relates to multiple NEs such asthe MSC, BSC, BTS, and MS. Therefore, the configuration of the call

procedures directly determines the length of the call setup time.

2.2 Parameter SettingsThe call setup time is related to the entire procedure of an MOC or MTC, andtherefore, many parameters can affect the call setup time.

The following are some examples:

l BS-PA-MFRAMS

l Use Imm_Ass Retransmit Parameter

l Max Delay of Imm_Ass Retransmitand Max Transmit Times ofImm_Ass

l Pre-paging function, which is set on the MSC

lImmediate Assignment Opt.

l ECSC, which means early classmark sending control

l Allow Reassign

l Late assignment function, which is set on the MSC

l Assignment command optimization

l Force Queue In Assignment

l T11(s)

2.3 Routing

The network equipment of different manufacturers varies. Therefore, in thecase of interworking between equipment of different manufacturers or changein routing, analysis and handling should be performed, on the basis of drive

test results.



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2.4 Hardware, Transmission, Coverage, andInterference

A problem in hardware, transmission, coverage, or interference may result in

an increase in the call setup time.



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3Analysis Process and OptimizationMethod

3.1 Analysis Process

Figure 3-1Analysis processCall setup time

too long

Collect the testdata

Is it due to a problemin parameter settings?

Is it due to a

problem in routing?

Analyze the problembased on the signaling

and data configurationand take proper measures

Is the problemsolved?

End

Yes

Yes

Yes

Yes

No

No

No

Is it due to a problem inprocedure configuration?

No

Optimize the procedureconfiguration and then

verify the optimization

Adjust the parameter

settings and then

verify the adjustment

Is it due to a problem inhardware, transmission,

coverage, or

interference?

Solve the problem

according to the relatedoptimization manual

Yes

No



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3.2 Process Description

3.2.1 Procedure Configuration

During the setup of a call, some procedures are optional, such asauthentication, ciphering mode setting, and TMSI reallocation, and

independent of each other. Therefore, flexible configuration of the proceduresaccording to operators' requirements is applicable.

On the existing networks, ciphering is generally enabled, and authenticationand TMSI reallocation are enabled on a proportion (that is, 10% to 20%) ofMSCs.

Authentication

For a 3G subscriber, during the authentication when the mobile accesses a

GSM network, the MSC sends an authentication message to the mobile. Themessage contains the RAND, AUTN, and RES, and is longer than 23 bytes.

Therefore, the LAPDm needs to divide the message into two and deliver themseparately.

Thus, in a GSM network, a 3G subscriber requires 240 ms to 260 ms morethan a 2G subscriber in terms of the call setup time.

In addition, when the BSC assigns an AMR channel, the AssignmentCommand message will be longer than 23 bytes if the frequency hopping MAis too long. This results in 240 ms to 260 ms more in the call setup time.

Ciphering Mode Setting

During the setup of an MOC, if the ciphering mode setting procedure is not

performed, the MS does not send a Setup message until it receives a CM

Service Accepted message from the MSC; if ciphering is to be enabled,however, the MS can send a Setup message immediately after the cipheringmode setting procedure is performed.

Therefore, for an MOC, the call setup time in the case of ciphering enabled is

generally only 250 ms to 300 ms longer than the call setup time in the case ofciphering not enabled. This is because the MS sends one more message (thatis, the Ciphering Mode Complete message) to the network in the case of

ciphering enabled.

TMSI Reallocation

The TMSI is reallocated according to the settings on the network side after

each operation or several operations on the air interface, such as a call or alocation update.

Classmark Enquiry

The Core Network (CN) can obtain the MS's information about their

multiband and multislot capabilities through the classmark enquiry procedure.



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At the BSS, the cell-oriented parameter ECSCis set. The BSS sends the

parameter through the system information type 3. Once an MS accesses thenetwork, the MS reports Classmark3. According to the protocol, this must beimplemented at MSs that support multiband, multislot, and Voice Group Call

Service (VGCS).

In practice, competitors generally do not enable classmark enquiry in theirCNs but use ECSC. Thus, the LAPDm signaling interaction on the air

interface is reduced, and the call setup time is shortened. Huawei, however,enables classmark enquiry in all its CNs by default. In addition, the classmark

enquiry is not user-configurable. It can be controlled by the related reservedsoftware parameter only.

Therefore, when ECSC is enabled at both competitor's BSS and Huawei BSS,

Huawei CN results in at least 240 ms more than competitor's CN in terms of

the call setup time. For specific cases, see sections 5.2 "Long Call Setup TimeDue to Reporting of Two Classmark Change Messages" and 5.4 "Long Call

Setup Time Due to Inconsistency in Signaling Procedures."

Optimization on I frames at the LAPDm

Before the optimization, Huawei BTS does not support the function of

downlink I frames acknowledging uplink I frames at the LAPDm. That is,

after receiving an uplink I frame from an MS, the BTS immediately sends anRR response message to the MS. During this process, if the BTS receives adownlink I frame from the BSC, the BTS has to postpone the delivery of the

downlink I frame, that is, the BTS sends the downlink I frame in the nextdelivery period. Thus, the delay increases. This problem can be solved afterthe upgrade.

With the optimization, the BTS can acknowledge uplink I frames by downlinkI frames. That is, after receiving an uplink I frame from an MS, the BTS doesnot send an RR frame immediately. Instead, the BTS waits a period of time

and checks whether it receives a downlink I frame. If the BTS receives adownlink I frame during this period, it acknowledges the uplink frame by thedownlink I frame. Thus, the delay is decreased by one delivery period.



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Figure 3-2 shows the effect of the optimization.

Figure 3-2Optimization on I frames at the LAPDm

The optimization can be achieved by BTS upgrade only. It is incorporated into

V300R008C11B337 of the BTS. During the optimization on the call setuptime on site, the optimization on I frames can be considered.

3.2.2 Parameter Setting

The main parameters that affect the call setup time are as follows:

l BS-PA-MFRAMS

This parameter specifies the number of multi-frames used as a unit of thepaging sub-channel.

If this parameter is set to a high value, the average paging delay is great.

Thus, the MS-to-MS call setup time and the PSTN-to-MS call setup timeare prolonged.

l Use Imm_Ass Retransmit Parameter

If this parameter is set to Yes, the BSC sends the immediate assignmentretransmission parameter to the BTS. Otherwise, the BSC does not sendthe immediate assignment retransmission parameter to the BTS.

The immediate assignment retransmission function can help increase the

call completion rate of MSs but may increase the access delay of MSsand the load of the BSC.

It is recommended that this function be disabled.

l Max Delay of Imm_Ass Retransmitand Max Transmit Times ofImm_Ass



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These two parameters specify the maximum delay of the immediate

assignment retransmission and the maximum number of immediateassignment retransmissions respectively.

When the network quality is poor, an immediate assignment messagemay need to be retransmitted. If these parameters are set to high values,

the average call setup time may be prolonged.

l Pre-paging function

This parameter is set on the MSC.

If the pre-paging function is enabled, the MSC pages the called partyas soon as the MSC receives the Setup message from the callingparty.

If this function is not enabled, the MSC pages the called party as soonas the MSC sends the Call Proceeding message.

Therefore, for MS-to-MS calls, the call setup time can be shortened if the

pre-paging function is enabled.

It is recommended that this function be enabled.

l Immediate Assignment Opt.

The channel activation and immediate assignment commands are sent atthe same time to accelerate the signaling processing, thus improving theresponse speed of the network.

It is recommended that this function be enabled.

l ECSC

This parameter specifies whether the MSs in a cell use early classmarksending.

If this parameter is set to Yes, after a successful immediate

assignment, the MS sends additional classmark information to thenetwork as early as possible.

For dual-band MSs, if this parameter is set to No, the MSC sends aClassmark Request message after the MS reports an Establish

Indication message. The MS then reports the Classmark Updatemessage. The access delay of the MS is affected.

l Allow Reassign

If this parameter is set to Yes, the BSC initiates a reassignment whenreceiving an assignment failure message over the Um interface. Thishelps increase the call completion rate and improve the QoS of the

network. The successful reassignment, however, results in an increase inthe access delay of MSs and the load of the BSC.


l Late assignment procedure

This parameter is set on the MSC. With the late assignment function, theassignment command is sent after alerting. This can shorten the call

setup time. In the late assignment procedure, however, the reception ofthe Alerting message does not necessarily indicate the establishment of acall. Therefore, the call setup time is not measured in the late assignmentprocedure.



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l Assignment command optimization

If frequency hopping is enabled at Huawei BTS, the ARFCNs in the

assignment command are delivered in the form of CA+MA by default,

which may result in the assignment command longer than 23 bytes. Then,the message is divided into two I frames at the LAPDm, which aredelivered separately. Thus, the delay is increased by about 230 msbecause of the addition of a delivery period.

To shorten the call setup time, the ARFCNs can be delivered in the formof frequency list so that the assignment command can be delivered in oneI frame.

On live networks, the frequency list mode is recommended. Table 3-1describes how to set this parameter.

Table 3-1Setting of the assignment command optimization parameterParameter Setting Decrease in

the Delay

Assignment

commandoptimizationparameter

Bit 1 of the

cell-orientedreserved parameter1 is 1, that is, the

parameter value is65535.

CA+MA No

Bit 1 of the

cell-orientedreserved parameter

1 is 0, that is, theparameter value is

65533.

Bit 2 of reserved

parameter 1 is 0, thatis, the parameter valueis 65529.

Frequency list

with thevariable bit mapcoding scheme

About200 ms

Bit 2 of reservedparameter 1 is 1, thatis, the parameter valueis 65533.

Frequency listwith the bit map0 codingscheme

The assignment command optimization is incorporated into BSC6000V900R008C11B168SP11 and later releases.

For specific cases, see chapter 5 "Optimization Cases."

l Force Queue In Assignment

When this parameter is set to Yes, the BSC puts an assignmentrequest message into the assignment request message queue if noTCH is available for assignment, or the BSC assigns a TCH to theMS if the TCH is available for assignment.

If this parameter is set to No, the value of queuing allowed indicatorin the assignment request message is 0, which means that the



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assignment request message cannot be put into the assignment

request message queue. Then, the channel request is rejected when noTCH is available for assignment.

The default value of this parameter is No.

l

T11(s)This parameter specifies the length of the timer that is started to wait fora channel requested by an assignment request message. When the BSCreceives an assignment request but no channel is available forassignment, the BSC starts the queuing procedure and this timer. If thechannel request is accepted before the timer expires, the timer stops. Ifthe timer expires, the channel assignment fails.

When queuing is enabled, a high value of this parameter directly leads toa long call setup time.

3.2.3 Routing

On live networks, when swapping is performed, the BSC and MSC are

re-deployed and thus the call routing changes. Therefore, the setup time ofinter-MSC calls is affected. In this case, tests should be conducted, and theanalysis should be performed on the basis of the test results obtained before

and after the swapping.

For a specific case, see section 5.3 "Long Call Setup Time Due to Calling and

Called MSs Under Different MSCs."

Table 3-2 lists the example values of delay during an MS-to-MS call made inthe lab. On live networks, the delay values are related to the actual situations.

The data in Table 3-2 is provided only for reference.

Table 3-2Example values of delay during an MS-to-MS call made in the labSignaling of an Outgoing MS-to-MS Call (Authentication,Ciphering, and TMSI Reallocation Enabled, Whereas ClassmarkEnquiry Disabled)

Relative Delay(Unit: s)

Channel Request (UL) -> Immediate Assignment (DL) 00.050

Immediate Assignment (DL) -> SABM-CMD (UL) 00.132

SABM-CMD (UL) -> Authentication Request (DL) 00.708

Authentication Request (DL) -> Authentication Response (UL) 00.125

Authentication Response (UL) -> Ciphering Mode Command (DL) 00.564

Ciphering Mode Command (DL) -> Ciphering Mode Complete (UL) 00.000

Ciphering Mode Complete (UL) -> Setup (DL) 00.005

Setup (UL) -> TMSI Reallocation Command (DL) 00.458

TMSI Reallocation Command (DL) -> TMSI Reallocation Complete (UL) 00.001



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Signaling of an Outgoing MS-to-MS Call (Authentication,Ciphering, and TMSI Reallocation Enabled, Whereas ClassmarkEnquiry Disabled)

Relative Delay(Unit: s)

TMSI Reallocation Complete (UL) -> Call Proceeding (DL) 00.466

Call Proceeding (DL) -> Assignment Command (DL) 00.466

Assignment Command (DL) -> Assignment Complete (UL) 00.011

Assignment Complete (UL) -> SABM-CMD (UL) 00.039

SABM-CMD (UL) -> Alerting (DL) 04.797

Total delay 07.822

The versions of NEs used in the test are as follows:

l

CN: G9MSC90 MSOFTX3000V100R003l BSC: V900R008C01B051

l BTS: V3.03R002.20011015

3.2.4 Hardware, Transmission, Coverage, andInterference

If a TRX or combiner is faulty or if an RF cable is incorrectly connected,

seizing the SDCCH or TCH becomes difficult, and thus the call setup timeincreases.

Faults such as poor transmission quality, instability of transport links,insufficiency of resources, or bit errors on the Abis and A interfaces may lead

to an increase in the error rate on the links, which results in more messageretransmissions between switches. Thus, the message transfer delay increasesand congestion may occur on the links. In severe cases, routes changefrequently, which leads to instability and congestion on the links. If thepreceding problem occurs during call setup, the call setup time increases.

The problem can be identified from traffic statistics. Table 3-3 lists thetransmission-related alarms at the BSC.

Table 3-3Transmission-related alarms at the BSCAlarm ID Alarm Name

1000 LAPD OML Fault

11270 LAPD Alarm

11278 E1 Local Alarm

11280 E1 Remote Alarm



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Alarm ID Alarm Name

20081 Loss of E1/T1 Signals (LOS)

20082 Loss of E1/T1 Frames (LOF)

Coverage or interference problems can be identified from the traffic statisticsor KPIs. For example, the interference information can be obtained on the

basis of the interference band distribution in the traffic measurement results. Ifa large proportion of interference levels belong to interference bands 3!5, youcan infer that there is strong interference in the uplink. To obtain the downlink

interference information, you can perform drive tests or analyze the trafficmeasurement results that are related to receive quality. Strong interferenceaffects the call drop rate on TCH, the TCH assignment success rate, and the

SDCCH setup success rate, thus affecting the call setup time.

The interference elimination can be classified into intra-network interference

elimination and inter-network interference elimination. For details aboutinterference elimination, see the G-Guide to Eliminating Interference.

If a coverage problem exists, you can solve the problem by using the methods

such as adjusting the tilt of the antenna, increasing the transmit power, addingrepeaters, and changing the combining mode. For details, see the GSM BSS

Network Performance KPI (Coverage) Optimization Manual.



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4 Test MethodThe call setup time is one of drive test KPIs. It can be obtained from theresults of call quality tests or drive tests for calls between MSs or between MSand PSTN.

The method is to perform a short MOC test. During the test, the intervalbetween two calls is 5s, each call lasts 10s, and the interval between a call

failure and the next call attempt is 30s. The recommended number of callsduring the test is 100. The number of calls can be changed as required. Duringthe test, the signaling on the Um and A interfaces needs to be traced.

If a value of call setup time is abnormal, analyze the signaling to checkwhether the abnormal value is due to failure of the first paging. If the

abnormal value is due to failure of the first paging, do not take this value intomeasurement of the call setup time. Otherwise, take this value into themeasurement. Check the signaling on the A interface. If the MSC sends twoPaging messages for one call, you can infer that the first paging for the call

fails.



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5 Optimization Cases5.1 Long Call Setup Time Due to Long Period of

Assignment Command Delivery5.1.1 Problem Description

After swapping of Ericsson equipment for Huawei equipment at a site, the callsetup time became longer. It was found that the delivery of an assignment

command from Huawei equipment took two or three periods whereas thatfrom Ericsson equipment generally took only one period.

5.1.2 Problem Analysis

In frequency hopping mode, the BSC6000 currently delivers the ARFCNs inCA+MA form through the assignment command. CA uses the TV format andits length is fixedly 17 bytes, and MA uses the TLV format and its length is

3!10 bytes. If an AMR channel is to be assigned (coded in TLV format in thecommand), the length of the assignment command increases by 4!8 bytes.

Thus, the assignment command is longer than 23 bytes. Therefore, at theLAPDm, the assignment command is divided for delivery. Before the

swapping, however, the ARFCNs are delivered in the form of frequency list,which uses the TLV format, and therefore in most cases, the assignmentcommand can be delivered with one frame.

5.1.3 Suggestion and Summary

When setting the assignment command optimization parameter, which isavailable only when frequency hopping is enabled in a cell, at the BSC, note

that:

l If this parameter is set to CA+MA, the original Huawei ARFCN deliveryform is retained.

l If this parameter is set to Frequency List, the coded ARFCNs for

frequency hopping will be delivered in the form of frequency list.



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Therefore, the assignment command will be delivered in one period, thusshortening the call setup time.

5.2 Long Call Setup Time Due to Reporting ofTwo Classmark Change Messages

5.2.1 Problem Description

After swapping for Huawei equipment at a si te, the call setup time becamelonger.


When Huawei CN is used, an additional Classmark Change message isreported during the call setup procedure if ECSCis set to Yes. The reason is

that the classmark enquiry procedure is enabled by default in Huawei CN.Figure 5-1 shows the difference in the signaling procedure before and after the

swapping.

Figure 5-1Classmark enquiry procedure enabled after the swapping



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To avoid the preceding problem, set ECSCto Yesand CM Update OptimizeTypeto 2, or coordinate with the CN to disable classmark enquiry at the CN.

5.3 Long Call Setup Time Due to Calling andCalled MSs Under Different MSCs

5.3.1 Problem Description

After swapping of some BSC in country R, the drive test results indicated thatthe call setup time was about 3,000 ms longer than that before the swapping.

The call setup time is one of the acceptance check items of the project. It

refers to the delay between sending of the Channel Request message and

reception of the Alerting message.


As indicated by the parameter check result, the parameters in the network areinherited from the previous network. Therefore, the parameters related to thecall setup time remain unchanged.

As indicated by the call signaling on the TEMS, the duration of the cipheringmode setting procedure after the swapping is the same as that before the

swapping.

Compared with the signaling messages before the swapping, the signaling

messages after the swapping include another two Progress messages, whichare present between the Assignment Complete message and the Connect

message. The description in the progress messages is "Call is not end-to-endPLMN/ISDN, further call progress information may be available in-band." Asindicated by messages traced at the CN, after the swapping, though the callednumber under the test is the same as that before the swapping, the test call isan inter-MSC one. That is because the calling MS is controlled by Huawei

MSC whereas the called number remains under its original MSC.


During the drive test on site after the swapping, the called number was the

same as that before the swapping, but the fact that the calling MS and the

called number were under different MSCs was not noticed. Therefore, whenchecking consistency between test conditions before and after swapping, pay

attention to such hidden changes.



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5.4 Long Call Setup Time Due to Inconsistency inSignaling Procedures

5.4.1 Problem DescriptionAfter swapping for Huawei equipment at a si te, the call setup time becamelonger.


The comparison between the call setup signaling procedures before swapping

and those after swapping should be performed. If the call setup after swappingincludes more procedures than that before swapping, remove them. Take theGP swapping in Bengal as an example. Figure 5-2 shows the difference

between the signaling procedures before and after the swapping.

Figure 5-2GPRS suspension procedure enabled after the swapping

As shown in Figure 5-2, the difference between the signaling procedures was

the presence of a GPRS suspension procedure in the test after the swapping.The presence of this procedure is related to whether the MS in the test has

performed GPRS attach.

According to 3GPP TS 44.108, as shown in Figure 5-3, the MS sends a GPRSSuspension Request message to suspend PS services, regardless of whether

the MS has any PS service in progress.



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Figure 5-3GPRS suspension procedure described in the protocol


For CS call setup time test, the GPRS suspension procedure should beremoved. To remove this procedure, change the related setting of the mobile.

The following are two examples:

l On a NOKIA N73 mobile, set Tools> Settings> Connection> Packetdata> Packetdataconn> Whenneeded.

l On a Sony Ericsson K790 mobile, set Settings> Connectivity> Datacommunication> Preferredservice> CSonly.

The GPRS suspension procedure is always present in the test after swapping.If this procedure is not or seldom present in the test before swapping, this

procedure can be removed to reduce the delay.



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6 Information FeedbackThe following information is required:

l Data configuration file in .dat format

l Log files and comparison data obtained from drive testsl Settings on the MSC, such as pre-paging and late assignment

14 GSM BSS Network KPI Call Setup Time Optimization Manual

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