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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.
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All rights reserved
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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
5.2.1 Problem Description ................ .................... ..................... ..................... ................ 23
5.2.2 Problem Analysis ..................... .................... ..................... ..................... ................ 23
5.2.3 Suggestion and Summary ........................ .................... ..................... .................... .. 24
5.3 Long Call Setup Time Due to Calling and Called MSs Under Different MSCs ................. 24
5.3.1 Problem Description ................ .................... ..................... ..................... ................ 24
5.3.2 Problem Analysis ..................... .................... ..................... ..................... ................ 24
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5.3.3 Suggestion and Summary ........................ .................... ..................... .................... .. 24
5.4 Long Call Setup Time Due to Inconsistency in Signaling Procedures ............................... 25
5.4.1 Problem Description ................ .................... ..................... ..................... ................ 25
5.4.2 Problem Analysis ..................... .................... ..................... ..................... ................ 25
5.4.3 Suggestion and Summary ........................ .................... ..................... .................... .. 26
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.
It is recommended that this function be disabled.
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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It is recommended that this function be disabled.
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.
5.2.2 Problem Analysis
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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5.2.3 Suggestion and Summary
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.
5.3.2 Problem Analysis
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.
5.3.3 Suggestion and Summary
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.
5.4.2 Problem Analysis
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
5.4.3 Suggestion and Summary
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