The document provides definitions and analysis methods for optimizing the Call Setup Success Rate (CSSR) in GSM networks. It defines the CSSR, lists influencing factors, and describes a three-step analysis and optimization process. The process involves identifying causes of low CSSR related to assignment success rate, immediate assignment success rate, or SDCCH drop rate. An optimization case from Vietnam addresses a difference in core network mechanisms that lowered the CSSR.

1. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
Product Name
Confidentiality Level
G3BSC
INTERNAL
Product Version
INTERNAL
Total 18 pages
GSM BSS Network KPI (Call Setup Success Rate)
Optimization Manual
(For internal use only)
Prepared by
Yang Jixiang, WCDMA&GSM Network
Performance Research Dept.
Reviewed by
Date
Date
Reviewed by
Date
Granted by
Date
Huawei Technologies Co., Ltd.
All rights reserved
2008-06-30

2. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
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Contents
1 Definition of the CSSR...................................................................7
1.1 Definition..................................................................................................................................................................7
1.1 Definition..................................................................................................................................................................7
1.2 Recommended Formula...........................................................................................................................................7
1.2 Recommended Formula...........................................................................................................................................7
1.3 Measurement Point...................................................................................................................................................7
1.3 Measurement Point...................................................................................................................................................7
2 Influencing Factors.......................................................................9
3 Analysis Process and Optimization Method...................................10
3.1 Analysis Process.....................................................................................................................................................10
3.1 Analysis Process.....................................................................................................................................................10
3.2 Process Description...............................................................................................................................................11
3.2 Process Description...............................................................................................................................................11
4 Test Method................................................................................ 13
5 Optimization Cases...................................................................... 14
5.1 Problem Related to the Standardizing of the CSSR in Viettel Project in Vietnam.................................................14
5.1 Problem Related to the Standardizing of the CSSR in Viettel Project in Vietnam.................................................14
6 Information Feedback .................................................................17

3. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
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Figures
Measurement points during the signaling of call setup......................8

4. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
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Revision Record
Change Description
Date
Revision
version
2008-06-30
0. 1
Draft completed
2008-11-01
1.0
Author
Yang Jixiang
Yang Jixiang
References
SN
Document
Author
Data
1
GSM BSS Network KPI (Call Setup Success Rate) Baseline
Wu Zhen
2007-08-21
2
GSM BSS Network KPI (Immediate Assignment Success Rate)
Baseline
Liu Xiuyu
2007-03-10
3
GSM BSS Network KPI (Assignment Success Rate) Baseline
Liu Xiuyu
2007-03-26
4
GSM BSS Network KPI (SDCCH Drop Rate) Baseline
Wu Zhen
2007-09-10
5
Network KPI (Assignment Success Rate) Optimization Manual
Su Shi
2008-03-29
6
GSM BSS Network KPI (Immediate Assignment Success Rate)
Optimization Manual
Wang Fei
7
GSM BSS Network KPI (SDCCH Drop Rate) Optimization
Manual
Du Jian

5. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
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GSM BSS Network KPI (Call Setup Success Rate)
Optimization Manual
Key words: Call Setup Success Rate, Immediate Assignment Success Rate, Assignment
Success Rate, SDCCH Drop Rate
Abstract: This document provides the definition of the Call Setup Success Rate (CSSR) and
the methods of testing and optimizing the CSSR.
Acronyms and abbreviations:
Acronym and Abbreviation
Full Spelling
CSSR
Call Setup Success Rate

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Definition of the CSSR
1.1 Definition
The CSSR indicates the probability of successful calls initiated by the MS. The CSSR is an
important KPI for evaluating the network performance. If this KPI is too low, the subscribers
are not likely to make calls successfully. The user experience is thus affected.
1.2 Recommended Formula
The CSSR can be obtained through traffic measurement and drive tests. The recommended
formula for calculating this KPI is as follows:
CSSR = Successful Assignments/Call-related Requests x 100%
BSS CSSR = Immediate Assignment Success Rate x Assignment Success Rate x (1 - SDCCH
Drop Rate) x 100%
For details on the traffic measurement related to the previous formulas, the three related
counters (Immediate Assignment Success Rate, SDCCH Drop Rate, and Assignment Success
Rate), and the comparison between the counters of Huawei and the counters of other vendors,
refer to the GSM BSS Network KPI (Call Setup Success Rate) Baseline.
This manual takes the traffic measurement of the BSC6000 as an example.
1.3 Measurement Point
The BSS CSSR is a combined KPI. For details on its measurement points, refer to the GSM
BSS Network KPI (Immediate Assignment Success Rate) Baseline, the GSM BSS Network KPI
(Assignment Success Rate) Baseline, and the GSM BSS Network KPI (SDCCH Drop Rate)
Baseline. Figure 1.1 shows the measurement points of the CSSR through the signaling
process of call setup.

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Figure 1.1 Measurement points during the signaling of call setup
Note: The measurement points illustrated in Figure 1.1 are as follows:
A——Immediate Assignment Requests (Channel Requests (Circuit Service))
B——Successful Immediate Assignments (Call Setup Indications (Circuit Service))
C——Assignment Requests (Seizure Requests)
D——Completed Assignments (Successful TCH Seizures)
The following formula shows the relations between the CSSR and Immediate Assignment
Success Rate, SDCCH Drop Rate, and Assignment Success Rate.
BSS CSSR = Successful Assignments/Call-related Requests
= D/A
= B/A x C/B x D/C
= B/A x (1-(B-C)/B) x D/C
= Immediate Assignment Success Rate x (1 - SDCCH Drop Rate) x Assignment Success Rate

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Influencing Factors
The CSSR is a combined KPI. For details on the factors that influence the CSSR, refer to the
Network KPI (Assignment Success Rate) Optimization Manual, the GSM BSS Network KPI
(Immediate Assignment Success Rate) Optimization Manual, and the GSM BSS Network KPI
(SDCCH Drop Rate) Optimization Manual. This section provides a simple classification of
the factors that influence the CSSR. The following table describes the key factors.
Um
Interface
Intra-network interference and inter-network interference, improper
parameter (including timers) settings, coverage problems, mobile phone
problems, antenna problems, hardware (including repeaters and jumpers)
failure
Abis
Interface
Channel congestion, transmission problems, improper parameter (including
timers) settings
A Interface
Transmission problems (congestion and communication quality)
Based on the preceding information, you can check whether the problem is related to the Um
interface, Abis interface, or A interface.
For more details, refer to the manuals mentioned earlier.

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Analysis Process and
Optimization Method
3.1 Analysis Process

10. GSM BSS Network KPI (Call Setup Success Rate) Optimization Manual
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Process Description
The process of analyzing the CSSR is as follows:
1. Find out the causes of a low CSSR.(Check whether a low CSSR is caused by Immediate
Assignment Success Rate problems, SDCCH Drop Rate problems, or Assignment Success
Rate problems.)
A. Conditions for checking whether a low CSSR is caused by Immediate Assignment
Success Rate problems.
[Call Measurement(CALL)]->[Immediate Assignment Measurement] RA303G: Immediate
Assignment Success Rate. RA303G is used to measure the immediate assignment success rate
of a cell. If the immediate assignment success rate is low in a cell, optimize the related
configurations of the cell by referring to the GSM BSS Network KPI (Immediate Assignment
Success Rate) Optimization Manual.
B. Conditions for checking whether a low CSSR is caused by SDCCH Drop Rate
problems.
[Call Measurement(CALL)]-> [SDCCH Call Drop Measurement] ZTR104B: SDCCH Drop
Rate. ZTR104B is used to measure the SDCCH drop rate of a cell. If the SDCCH drop rate is
low in a cell, optimize the related configurations of the cell by referring to the Network KPI
(SDCCH Drop Rate) Optimization Manual.
C. Conditions for checking whether a low CSSR is caused by Assignment Success Rate
problems.
[Call Measurement(CALL)]-> [Assignment Measurement] RCA313: TCH Assignment
Success Rate. RCA313 is used to measure the TCH assignment success rate of a cell. If the
TCH assignment success rate is low in a cell, optimize the related configurations of the cell by
referring to the Network KPI (Assignment Success Rate) Optimization Manual.
The following table describes the related counters.
Problem
Descripti
on
BSC-Level
Cell-Level
TRXLevel
Immediate
Assignment
Success Rate
[BSC Measurement(BSC)]>[Access Measurement per
BSC] ZTR110A:
BSCRPT_RATE_IMM_ASS_S
UCC
[Immediate Assignment Measurement per]
None
SDCCH
Drop Rate
[BSC Measurement(BSC)]>[Access Measurement per
BSC] ZTR104A:
BSCRPT_RATE_SD_CALL_D
ROP
[KPI Measurement per Cell]
RA303G:
CELL_RANDOM_ACCESS_SUCC_RATE
ZTR104C: CELL_SD_CALL_DROP
[SDCCH Call Drop Measurement per Cell]
ZTR104B:CELL_SD_CALL_DROP_CALL
None

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Problem
Descripti
on
BSC-Level
Cell-Level
TRXLevel
Assignment
Success Rate
[BSC Measurement(BSC)]>[Access Measurement per
BSC] ZTR102A:
BSCRPT_RATE_ASS_SUCC
[Call Measurement(CALL)]->[Assignment
Measurement]
None
RCA313:CELL_ASS_SUCC_RATE
[KPI Measurement per Cell]
RA333:
CELL_CALL_ESTB_SUCC_RATE
RA33A:
CELL_BSS_CALL_ESTB_SUCC_RATE
2. Optimize the related configurations of the cell by referring to the related optimization
manual. Evaluate the optimization result. If the problem is not solved, repeat step 2.
3. If a symptom, which is not described in the optimization manual, occurs, send the
information described in Chapter 6 to the WCDMA&GSM Network Performance Research
Department. The engineers concerned will then assist you in locating the problem and
analyzing the fault.

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Test Method
The CSSR is one of the traffic measurement KPIs. It is evaluated through the counters related
to Call Measurement(CALL).
The CSSR, as a KPI, has a great impact on customer service. Therefore, it must be traced in
routine network optimization. If a cell has a low CSSR (below 95%), the cell is classified as a
faulty cell.
You must then locate the problem and analyze the fault by referring to the analysis process.
Analysis mainly refers to the traffic measurement analysis. You can also use signaling tracing
and the specified drive tests for troubleshooting.
The purpose of designated drive tests is to trace the signaling on the Um interface and on the
Aibs interface in different scenarios. Thus, the signaling process can be comprehensively
analyzed and the problem can be located easily.

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Optimization Cases
Only one case is provided in this section. For more cases, refer to the Network KPI
(Assignment Success Rate) Optimization Manual, the GSM BSS Network KPI (Immediate
Assignment Success Rate) Optimization Manual, and the GSM BSS Network KPI (SDCCH
Drop Rate) Optimization Manual.
5.1 Problem Related to the Standardizing of
the CSSR in Viettel Project in Vietnam
[Problem Description]
The CSSR after swapping is low compared with the CSSR before swapping. After
optimization, the CSSR increases to 99.2%, which is 0.3% lower than the standard value,
which is the value before swapping.
[Problem Analysis]
1. Analyze the CSSR-related counters: Immediate Assignment Success Rate, Assignment
Success Rate, and SDCCH Drop Rate. The result shows that Assignment Success Rate is
0.45% lower than that before swapping (Assignment Success Rate before swapping is 99.87%
and after swapping is 99.42%), and SDCCH Drop Rate is 0.175 lower than that before
swapping (SDCCH Drop Rate before swapping is 0.355% and after swapping is 0.180%) The
initial conclusion is that a low Assignment Success Rate (ASR) leads to a decrease in the
CSSR.

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2. Further analysis shows that the number of failed assignments due to call clearing performed
by the MSC takes up 78.19% of the total failures. The result shows that call clearing
performed by the MSC decreases TCH Assignment Success Rate on the live network.
3. Signaling analysis shows that signaling exceptions exist in the network. In the channel
assignment procedure, the MSC, on receiving the setup message, sends a Disconnect message
to clear the call before a channel is assigned.
4. The Viettel project in Vietnam adopts the Huawei core network equipment. The MSC, on
receiving the setup message, sends a Disconnect message to clear the call before a channel is
assigned in fast channel assignment procedure. This can be solved by setting the software
parameter P173 on the core network.
[Problem Location]
The working mechanism of Huawei core network differs from that of peer vendor`s
equipment. To improve the parallel processing capability of the system, the MSC sends a
Disconnect message to clear a call after receiving the setup message and before a channel is
assigned to the call.

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[Solution]
Based on the actual requirements and after negotiation with the customer, you must enable
P173 (call clearing and suspension function). To enable p173, perform the following
operation.
P173: The fourth bit (**** **** ***X ****) specifies whether the call clearing and
suspension function is enabled.
= 0: Enabling the call clearing and suspension function
= 1: Disabling the call clearing and suspension function
Conclusion: The call clearing and suspension function helps to improve the CSSR. This
function, however, prolongs the clearing time; therefore, more number of SDCCHs and TCHs
are occupied. As a result, counters such as SDCCH Congestion rate and TCH Congestion
Rate may be affected.

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Information Feedback
If the CSSR is too low, send the data described in the following table to the WCDMA&GSM
Network Performance Research Department.
SN
Informati
on
Remarks
Purpose
1
Software
version
Software versions of the BSC and BTS
Check whether the software version is
defective.
2
Data
configuration
table
Configuration files of the BSC, in *.dat
format
Check the network optimization
parameters and power configuration.
3
Alarm
information
Alarm information related to hardware,
clock, and transmission (self-check)
Check whether such alarms exist in the
faulty cell. Such alarms should be
cleared.
4
Traffic
measurement
<Immediate Assignment
Measurement><Assignment
Measurement><SDCCH Call Drop
Measurement per Cell><KPI
Measurement per Cell>
Observe the traffic measurement result
and check for congestion or
interference problems.
5
Signaling
RSL signaling tracing of fault
occurrence time in the faulty cell
Search for the cause of call setup
failure.
6
Drive test
data
*.log (*.CELL) files or *.ant files
Observe the drive test data and check
for interference or coverage problems
7
Network
planning data
Engineering parameter tables and emaps
Network planning data facilitates the
checking of the geographical
information by the NASTAR tool.
8
Optimization
Report
The optimization report provides the
optimization projects described in this
manual and implemented on site. The
report also provides the optimization
measures, which are not described in
this manual but implemented on site.
The optimization report serves as a
reference for future network planning.

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Informati
on
Remarks
INTERNAL
Purpose
The operations described in items 5 and 6 in the preceding table should be performed
simultaneously. That is, when performing drive tests, you must trace the RSL signaling of the
corresponding cell. Before the drive tests, you must also synchronize the PC time used for
drive tests with the BSC time.