Basic GSM TCH Call Drop Analysis

Training goalsTo master definitions of call drop indicators

and relevant countersTo master causes of the three types of call

drop and the corresponding solutionsTo know analysis of call drop and location of

call drop problem with traffic statistics

Contents Indicator definitionHandling of call drop problemCall drop due to radio link faultCall drop due to handover failureCall drop due to LAPD link failure

Indicator definitionTCH call drop rate (excl. HO)

TCH call drop rate (excl. HO) = total of TCH call drops/total of TCH occupancy times (excl. HO) ×100%

TCH call drop rate (incl. HO)TCH call drop rate (incl. HO)=total of TCH call

drops/total of TCH occupancy times (incl. HO)×100%

Traffic call drop rateIndicator definition: traffic volume/number of

TCH call drops*60

Contents Indicator definition Handling of call drop problemCall drop due to radio link faultCall drop due to handover failureCall drop due to LAPD link failure

Flow of handling call drops A cell suffers from high TCH call drop

rate

Analysis of call drop types

Call drop of RF loss

Complete

Call drop of handover failure

Call drop of LAPD

If radio parameters set reasonably?

If interference exists?

Any equipment hardware fault?

Any antenna system fault?

Eliminate antenna

fault

Eliminate equipment

fault

Check& eliminate

interference

Adjust radio

parameters

If radio parameters set reasonably?

If interference exists?

An equipment hardware fault?

Any coverage problem?

Improve coverage

Any hardware fault at BSC?

Any fault with BTS

transmission?

Any hardware fault at BTS?

Eliminate hardware

fault

Eliminate transmission

fault

Eliminate hardware

fault

No

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

Yes

Yes

Locate & analyze call drop with traffic statistics

performance report of BSC level

performance report of cell level

BTS measurement

Cell radio measurement

Performance report of cell level CS basic measurement

Warning statistics

Analysis of common problem

Analysis of specific problem

Warning analysis

Analysis of Traffic statistics

Signaling analysis

Other network optimization methods

Analytical framework 1 2 3 4 5

Problem solvedLocate cell with high call drop rate

Analyze casueConfirm call drop type

Confirm call drops on carrier

From macro to micro view

Count call drops on carrier

Convenient for problem location and analysis

form common to specific

Execution & problem solution

Locate & analyze call drop with traffic statisticsCommon causes for call drops

Unreasonable setting

of handover

parameters

Coverage problem

Equipment hardware

fault

Interference

UL/DL unbalance

Unreasonable settings of

other parameters

Common problem is

analyzed

result in call drop

Contents Indicator definition Handling of call drop problemCall drop due to radio link faultCall drop due to handover failureCall drop due to LAPD link failureTypical cases

Call drop due to radio link failure

UL failure

？？？

DL failure

？？？

Call drop due to radio link failure

MS BTS BSC

Connection Failure Indication

F1

MSC

Clear request

Radio link timeout

Measurement report(SACCH)

Measurement report(SACCH)

Measurement report(SACCH)

Start T3109

Stop T3109Clear Command

RF Channel Release

RF Channel Release ACK

Clear Complete

Call drop due to radio link failure Causes for call drop due to radio link failure & handling

procedures

Weak coverage, poor radio signal; Interference;Unreasonable settings of radio

parameter; Incomplete or wrong adjacent cell

data ;Unreasonable settings of handover

parameters;Congestion in adjacent cell;Equipment hardware fault;Antenna system fault;Subscriber’s fault.

Main causes

Check radio parameters. Adjust

unreasonable settings of radio

parameters;

Check indicators like BER and level of

idle interference band, reduce or

eliminate radio interference ;

Check if coverage problem exists

through DT;

Check and eliminate equipment fault ;

Check antenna system.

Handling procedures

Contents Indicator definitionsHandling of call drop problemCall drop due to radio link faultCall drop due to handover failureCall drop due to LAPD link failure

Call drop due to handover failureClassification of Handover control timer in

BSCT8 expires (inter-BSC handover) T3103 expires (inter-cell handover under one

BSC) T3107 expires (intra-cell handover).

Call drop due to handover failure

Call drop due to intra-cell handover failure

BSCBTS:TRXMS

ASSIGNMENT COMMAND

CHANNEL ACTIVATE

G1

CHANNEL ACTIVATE ACK

SET T3107

T3107 Timeout

MSC

Clear Request

Call drop due to handover failure

Call drop due to intra-BSC handover failure

BSCOld BTS:MS

CHANNEL ACT

H1

CHANNEL ACT ACK

New BTS

SET T3103

T3103 Timeout

MSC

HO_CommandHO_Command

Clear request

Call drop due to handover failure

Call drop due to inter-BSC handover failure

MS New BTSNew BSC

CHL_ACT

MSC

CHL_ACT_ACKHO_REQ_ACK

Old BSCOld BTS

HANDOVER REQUIRED

HANDOVER COMMANDHANDOVER COMMANDHANDOVER COMMAND

SET T8

T8 Timeout

I1

Clear request

Call drop due to handover failure Main causes for call drop due to handover failure & handling procedures

Interference;

Hardware fault;

Unreasonable settings of radio

parameters ;

Inappropriate adjacent cell

relation or wrong adjacent cell

data;

Unreasonable settings of

handover parameters ,which

results in Ping-Pong handover.

Main causes

Check radio parameters, adjust the

unreasonable settings, and add

necessary neighbor relations;

Check indicators like BER and level

of idle interference band, reduce or

eliminate radio interference;

Check equipment hardware,

change panels with problems.

Handling procedures

Contents Indicator definitionsHandling of call drop problemCall drop due to radio link faultCall drop due to handover failureCall drop due to LAPD link failure

Call drop due to LAPD link failure

Call drop due to LAPD link failurePrinciple:

When LAPD link breaks, calls on carriers will be interrupted. BSC

counts after it receives message showing that LAPD link is

broken. Main causes for call drop due to LAPD link failure & handling

procedures

BTS hardware fault

BTS transmission

problem

BSC hardware fault

Main causes

Investigate & eliminate BTS hardware fault;

Investigate & eliminate BTS transmission problem;

Investigate & eliminate BSC hardware fault

Handling procedures

THANKS!!!