Call Setup Success Rate Definition and Troubleshooting

HUAWEI TECHNOLOGIES Co., Ltd.

www.huawei.com

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Call_Setup_Success_RateDefinition and Troubleshooting

Simple Presentation

Assim Mubder

26-Aprill-2011

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%


Measurement Points of the CSSR through the signaling

process of call setup, Digram#1



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



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



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.


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


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


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.

2Data configuration table

Configuration files of the BSC, in *.dat formatCheck the network optimization parameters and power configuration.

3 Alarm informationAlarm information related to hardware, clock, and transmission (self-check)

Check whether such alarms exist in the faulty cell. Such alarms should be cleared.

4Traffic 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 SignalingRSL 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 filesObserve the drive test data and check for interference or coverage problems

7Network planning data

Engineering parameter tables and e-mapsNetwork planning data facilitates the checking of the geographical information by the NASTAR tool.

8Optimization 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.


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:


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


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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Call Setup Success Rate Definition and Troubleshooting

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