TCH Drop Analysis

KPI Formula

BSC Surabaya2, Semarang, and Bandung2 have same drop reason series as high contributor, that are :

Rank Reason to Drop

1 _TCHDropDistRadLinkFail rate_Nr

2 _TCHDropDistT200 rate_Nr

3 _TCHDropDistInterCellHO rate_Nr

4 _TCHDropDistEquipFail rate_Nr

5 _TCHDropDistHOAccess rate_Nr

While for BSC Yogya have drop reason series as shown below :

Rank Reason to Drop

1 _TCHDropDistRadLinkFail rate_Nr

2 _TCHDropDistRemTranscFail rate_Nr

3 _TCHDropDistT200 rate_Nr

4 _TCHDropDistInterCellHO rate_Nr

5 _TCHDropDistHOAccess rate_Nr

Call Drop Related Events

Can be explained by the following message diagram :

Correlated with Radio Interface Problems Causing : Radio Link Failure , many loss message until T200 expiry, many HO access fail AND any unnecessary DB setting : - RDLNKTO / BS - T200 - T3105 , NY1 - T8

Correlated with Radio Interface Problems Causing : Radio Link Failure , many loss message until T200 expiry, many HO access fail AND HW problems & wrong DB setting might cause Remote Transcoder Failure, that are : - TRACK Modul Failure -> can be detected from BSC fermaint alarm, if this happen, the Remote Transcoder Failure will be distributed on whole sites which access to the broken track - COBA / CU failure - Transmission Flicker - timer setting in DB doesn't meet rule : TTRAU > T8 , TTRAU > T10ensuring that a signaling failure (T8 and T10) is detected before transcoder failure (TSYNC and TTRAU)

TCH Drop with Radio Link Failure Reason

TCH Drop with T200 Expiry Reason

Analysis

TCH Drop Rate = NRFLTCH [1-17] + UNIHIALC + UNIHIRLC TNTCHCL [1,2]

Total TCH Drop Total TCH Loss Connection when HO intracell & HO intercell

Total TCH Connection

TCH Drop with HO Access Failure Reason

Loss Connection when Intercell HO

TCH Drop with Remote Transcoder Failure Reason

expiry, many HO access fail

expiry, many HO access fail

might cause Remote Transcoder Failure, that are :> can be detected from BSC fermaint alarm, if this happen, the Remote Transcoder Failure

will be distributed on whole sites which access to the broken track

TTRAU > T10 , TTRAU = TSYNC => This setting is for ) is detected before transcoder failure (TSYNC and TTRAU)

Every unsuccessful decoding of uplink SACCH message (indicates any radio problems) will lead decrease of S counter in MS by 1. If the S counter reaches 0, the MS regards the dedicated radio connection as failed and stops any further transmission on the dedicated channel, also the BTS cannot correctly decode any uplink SACCH frames anymore because the MS has stopped transmitting them. When the radio link counter in BTS (RDLNKTBS) reaches 0, a CONNECTION FAILURE INDICATION (BTS->BSC) is sent and indicates call drop. S counter in MS and RDLNKTBS should follow the same rule, that is : S = (4 * RDLNKTO)+4

Reccomendation : - Fix any radio problem (interference, coverage, HW&Installation) => can be checked by optimization engineer in area - Increase RDLNKTO from 4 to 6 (RDLNKTBS from 20 to 28

- Radio Analysis include aspects : - Freq interference analysis - Coverage Analysis - HW&Installation Problems - DB setting review - Followed by Radio Optimization based on analysis result

- Radio Analysis include aspects : - Freq interference analysis - Coverage Analysis - HW&Installation Problems - Fermaint Alarm analysis to find broken TRACK/TRAU module possibility - Transmission Alarm - Timer Rule checking within DB - Followed by Optimization based on analysis result

When BTS has sent layer 2 message in acknowledge mode N200+1 times to the MS without receiving layer 2 acknowledgement

Action

When BTS has sent layer 2 message in acknowledge mode N200+1 times to the MS without receiving layer 2 acknowledgement from MS (reasons : any radio problems exist) until T200 timer expired, then the connections are dropped. Messages with acknowledged mode are SABM, DISCONNECT and I-frames. All messages within this acknowledged mode are checked by the LAPDm flow control mechanisms based on sequence numbers that are assigned to each transmitted LAPD message.

Reccomendation : - Fix any radio problem (interference, coverage, HW&Installation) => can be checked by optimization engineer in area - Increase T200 timer for FACCH TCHF, FACCH TCHH, SACCH TCH SAPI0, SACCH TCH SAPI3 from T200 = 29-31-38-90-70-29-168 to T200 = 29-62-76-180-70-29-200

MS doesn't react to PHYS INFO sent by BTS (could be caused by any radio problems), no SABM is received at the BTS until NY1 repetition with period time T3105.

Reccomendation : - Fix any radio problem (interference, coverage, HW&Installation) => can be checked by optimization engineer in area - Check if DB timer meet rule : NY1*T3105 ≥ 2 sec , and (NY1+1)* T3105 << T8 < TTRAU

Loss HO CMD (caused by any radio problems) cause loss connection when intercell HO occurred. Reccomendation : - Fix any radio problem (interference, coverage, HW&Installation) => can be checked by optimization engineer in area - Check T8 setting, must follow rule : T8 < TTRAU, and (NY1+1)* T3105 << T8 < TTRAU - Increase T8 timer for HLFSEC-12 to HLFSEC-14 (T8 determines the time to receive HANDOVER COMPLETE message)

Drop call due to Remote Transcoder Failures might be triggered by : - TRACK/TRAU Module Failure - COBA / CU Failure - Transmission Flicker - Wrong timer setting in DB, doesn't meet rule : TTRAU > T8 , TTRAU > T10, TTRAU = TSYNC => This setting is for ensuring that a signaling failure (T8 and T10) is detected before transcoder failure (TSYNC and TTRAU)

Reccomendation : - Fermaint BSC alarm analysis to detect any TRACK/TRAU broken module - HW check - DB setting review

will lead decrease of S counter in MS , the MS regards the dedicated radio connection as failed and stops any further transmission on

Fermaint Alarm analysis to find broken TRACK/TRAU module possibility

acknowledgement

acknowledgement

=> This setting is for ensuring