1. HUAWEI TECHNOLOGIES Co., Ltd.
www.huawei.com
HUAWEI Confidential
Call_Setup_Success_Rate
Definition and Troubleshooting
Simple Presentation
Assim Mubder
26-Aprill-2011

2. HUAWEI Technologies Co., Ltd.
Definition and Formula
• 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.
• 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%

3. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup, Digram#1

4. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup. Call Setup establishment passes four steps tell
successful call achieved as below#1:
A——Immediate Assignment Requests (Channel Requests (Circuit Service))-Access
B——Successful Immediate Assignments (Call Setup Indications (Circuit Service))-SD
C——TCH Assignment Requests (Seizure Requests)
D——Completed TCH 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

5. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup, Digram#2

6. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup, Digram#3

7. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup, Clarifications#2
The following description covers the interprocess communication to place a mobile on a
DCCH and have the mobile in communication with the MSC.
1. The mobile accesses the system with a Random Access burst on the BCCH.
2. The RSS passes the request onto the RRSM via the RCI in the form of a Channel
Required message.
3. RRSM asks the CRM to assign a SDCCH channel and the CRM responds.
4. RRSM tells the RSS which DCCH the mobile is to go to and the RSS activates the
channel. When channel activated, the RSS informs the RRSM.
5. The RRSM then tells the mobile via the RSS on an Access Granted Channel,
which DCCH the mobile is to move to.
6. The mobile moves to the DCCH and establishes two way communication with its
allocated BTS. The Mobile forwards CM Service Request, telling the RRSM what
the mobile wants to do. Is it –
responding to a Page from the MSC?
doing a Location Update?
IMSI Deregistration?
wanting to establish a call?
trying to salvage an established call?
7. The RRSM forwards the CM service request up to the SCCP State Machine
(SSM).
8. The SSM then has to request the MSC to handle the call.
RSS: Radio Sub–system
RRSM: Radio Resource State Machine
CRM: Cell Resource Manager
SSM: SCCP State Machine
MTP: Message Transfer Port

8. HUAWEI Technologies Co., Ltd.
Measurement Points of the CSSR through the signaling
process of call setup, Clarifications #3
The following text describes the interprocess communication for the assignment of a
mobile from a DCCH to a traffic channel. This procedure assumes that all authentication
has taken place on the DCCH.
1. The MSC sends a message to the SSM assigning the mobile a terrestrial circuit.
2. The SSM sends an initiate assignment command to the RRSM to assign a channel
to the mobile.
3. The RRSM asks the CRM to assign Traffic a channel. The CRM responds with the
channel.
4. The RRSM then asks the RSS to supply the timing information for the mobile
concerned.
5. The RRSM then tells the RSS to activate the required Traffic Channel.
6. The RRSM then instructs the mobile via the RSS to move onto the new traffic
channel.
7. The mobile now moves to the new traffic channel and establishes signalling links.
8. The RRSM then informs the SSM that mobile is on its new channel and signalling
links have been established, and deactivates the SDCCH channel.
9. The SSM then tells the SM to connect the radio channel to the terrestrial MSC
circuit. The SM responds when complete.
10. The SSM then tells the MSC that the mobile is on the new channel and that the
radio channel has been connected to the MSC channel.
When this procedure is completed, it leaves the mobile on its new traffic channel and
‘talking’ to the MSC.

9. HUAWEI Technologies Co., Ltd.
Influencing Factors
A. Um Interface ((MS<------> BTS))-Air Interface/MS bases
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
B. Abis Interface ((BTS<-----> BSC))-RSL/Cell-Site bases
Channel congestion, transmission problems, improper parameter (including timers)
settings
C. A Interface ((BSC <-----> MSC))-MTL/BSC-bases
Transmission problems (congestion and communication quality)
D. Call Setup Blocking-TCH Blocking
E. Faulty equipments on degraded BSC/site/cell

10. HUAWEI Technologies Co., Ltd.
Analysis Process and Optimization#1
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
Problem handling
completed
Whether the
fault is rectified
No
Yes

11. HUAWEI Technologies Co., Ltd.
Analysis Process and Optimization #2
SN Information 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 e-maps
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.

12. HUAWEI Technologies Co., Ltd.
Investigating Low CSSR by KPIs check
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:

13. HUAWEI Technologies Co., Ltd.
Investigating Low CSSR by KPIs check
Problem
Description
BSC-Level Cell-Level TRX-Level
Immediate Assignment
Success Rate
[BSC Measurement(BSC)]->[Access Measurement
per BSC] ZTR: BSCRPT_RATE_IMM_ASS_SUCC
[Immediate Assignment Measurement per]
RA: CELL_RANDOM_ACCESS_SUCC_RATE
None
SDCCH Drop Rate [BSC Measurement(BSC)]->[Access Measurement
per BSC] ZTR: BSCRPT_RATE_SD_CALL_DROP
[KPI Measurement per Cell]
ZTR: CELL_SD_CALL_DROP
[SDCCH Call Drop Measurement per Cell]
ZTR104B:CELL_SD_CALL_DROP_CALL
None
Assignment Success
Rate
[BSC Measurement(BSC)]->[Access Measurement
per BSC] ZTR: BSCRPT_RATE_ASS_SUCC
[Call Measurement(CALL)]->[Assignment Measurement]
RCA313:CELL_ASS_SUCC_RATE
[KPI Measurement per Cell]
RA333: CELL_CALL_ESTB_SUCC_RATE
RA: CELL_BSS_CALL_ESTB_SUCC_RATE
None

14. HUAWEI Technologies Co., Ltd.
Preventive actions concerning CSSR
• Data base parameters and timers need to be check and audited
periodically on cell/site/BSC bases.
• Sites and BSCs with transmission problems due to outage, MW
problems, all need to be monitored and add redundant RSLs to
sites with togging paths, expand E1 to meet the over utilized sites.
• Alarms and BSS events should be monitored and cleared on daily
bases.
• TCH-Blocking need to be monitored and talked immediately by
soft/ hard actions once observed.
• MSC side should check with core team once a problem observed
on specific region/BSC/LAC.

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HUAWEI Confidential
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