Product Name
Confidentiality Level
G3BSC
CONFIDENTIAL
Product Version
Total 17 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
Contents 1 Definition of the CSSR...................................................................6 1.1 Definition..................................................................................................................................................................6 1.1 Definition..................................................................................................................................................................6 1.2 Recommended Formula...........................................................................................................................................6 1.2 Recommended Formula...........................................................................................................................................6 1.3 Measurement Point...................................................................................................................................................6 1.3 Measurement Point...................................................................................................................................................6
2 Influencing Factors.......................................................................8 3 Analysis Process and Optimization Method.....................................9 3.1 Analysis Process.......................................................................................................................................................9 3.1 Analysis Process.......................................................................................................................................................9 3.2 Process Description..............................................................................................................................................10 3.2 Process Description..............................................................................................................................................10
4 Test Method................................................................................12 5 Optimization Cases......................................................................13 5.1 Problem Related to the Standardizing of the CSSR in Viettel Project in Vietnam.................................................13 5.1 Problem Related to the Standardizing of the CSSR in Viettel Project in Vietnam.................................................13
6 Information Feedback .................................................................16
Figures Measurement points during the signaling of call setup......................7
Revision Record Change Description
Date
Revision version
2008-06-30
0.1
Draft completed
Author 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
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
1
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. 1.1 shows the measurement points of the CSSR through the signaling process of call setup.
Figure 1.1 Measurement points during the signaling of call setup
Note: The measurement points illustrated in 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
2
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.
3
Analysis Process and Optimization Method
3.1 Analysis Process Problem handling started
When the fault is related to Immediate Assignment Success Rate, SDCCH Drop Rate or Assignment Success Rate
Immediate Assignment Success Rate optimized
SDCCH Drop Rate optimized
Assignment Success Rate optimized
No
Whether the fault is rectified Yes Problem handling completed
3.2
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
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.
4
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.
5
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.
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.
[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.
6
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
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.
SN
Informati on
Remarks
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.
