Call Failure Analysis.pdf

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www.huawei.com

PT. HUAWEI SERVICES

Fact Finding

Call Failure Analysis Reported by HS Optimization Team

Jakarta, 11 November 2012

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The Call Fail Reason can be classified into several reason :

1. Coverage and Interference Problem.

• Coverage Hole and UL Interference.

2. Improper radio and neighbor parameter setting.

• Missing neighbor, wrong setting of neighbor cell, improper setting of Qqualmin and Qrxlevmin.

• Low setting of preamble Power Ramp Step, Low setting for Common Channel.

• Low Setting of Initial SIR Target.

3. Equipment and Interface Problem.

• Abnormality of Equipment Clock/ DSP/CPU, Insufficient RAN Board Resources, Transmission Alarm.

4. Network Element and Interface Resource.

• High Cell Load, High CE Utilization, High IUB,IU CS/PS Utilization.

5. Configuration Inconsistency.

• Inconsistent Number of AAL2PATHs across IU/IUB Interface.

• PATH ID and NSAP Address Configuration Error of AAL2PATH.

A. Call Fail Reason

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The Call Fail Reason can be classified into several reason :

1. Coverage and Interference Problem.

• RRC.FailConnEstab.NoReply

• VS.RAB.FailEstCS.RIPFail

2. Equipment and Interface Problem.

• VS.RRC.Rej.RL.Fail, VS.RRC.Rej.TNL.Fail(Iub problem).

• VS.RAB.FailEstabCS.RNL, VS.RAB.FailEstabCS.TNL.

3. Network Element and Interface Resource.

• VS.RRC.Rej.Power.Cong, VS.RRC.Rej.ULIUBBandCong, VS.RRC.Rej.DLIUBBandCong, VS.RRC.Rej.UL.CE.Cong, VS.RRC.Rej.DL.CE.Cong, VS.RRC.Rej.Code.Cong.

• VS.RAB.FailEstCs.Power.Cong, VS.RAB.FailEstab.CS.DLIUBBand.Cong, VS.RAB.FailEstab.CS.ULIUBBand.Cong, VS.RAB.FailEstCs.ULCE.Cong, VS.RAB.FailEstCs.DLCE.Cong, VS.RAB.FailEstCs.Code.Cong

A. Call Fail Reason Statistic Based

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4. Relocation Problem.

• VS.RAB.FailEstCS.Relo

5. Capability Problem.

• VS.RAB.FailEstCS.Unsp .

6. Setup redirection problem.

• VS.RRC.Rej.Redir.Inter.Att VS.RRC.Reject.Redir.Intrat VS.RRC.Reject.Redir.Service.

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.

B. Call Fail Analysis Flow

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The methodology to analyze Call Drop problem containing several step below:

1. Data Preparation

2. Traffic Analysis.

3. Equipment Analysis.

4. Coverage and Interference Analysis.

5. Signalling Analysis

C. Methodology

• Hourly/Daily Statistic (CS RAB assignment failure per cell, RRC connection reject per cell, Cell TX and RX Power, etc).

• The latest Site Map, Neighbor relation, and cell configuration/parameter data.

• Single subscriber tracing recorded by RNC.

• CHR recorded by RNC.

• Active and History Alarm.

• Data files collected by DT.

C.1 Data Preparation

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• The Traffic analysis is related to CE utilization, IUB,IU Utilization, and Code Utilization. This Information we can get from the Daily/Hourly Statistic.

• The RRC Rejection Cause related to traffic utilization can we get in Raw counter below:

– VS.RRC.Rej.DL/ULIUBBandCong = Iub utilization

– VS.RRC.Rej.Power.Cong = Cell Load

– VS.RRC.Rej.UL.CE.Cong = UL CE utilization

– VS.RRC.Rej.DL.CE.Cong = DL CE utilization

– VS.RRC.Rej.Code.Cong = Code Utilization.

• The RAB Fail Cause related to traffic utilization can we get in Raw counter below:

– VS.RAB.FailEstCs.Power.Cong = Cell Load

– VS.RAB.FailEstCs.ULCE.Cong = UL CE Utilization

– VS.RAB.FailEstCs.DLCE.Cong = DL CE Utilization

– VS.RAB.FailEstCs.Code.Cong = Code Utilization.

– VS.RAB.FailEstab.CS.DL/ULIUBBand.Cong = Iub utilization

C.2 Traffic Analysis

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• The Alarm information of RNC, Node b, MSS, MGW, and Interface(Transmission) can we gather as early diagnosis to reduce time if we found Call Drop problem.

• The History and Active Alarm can help to give quick reference for analyzing the network problem.

• Alarms that affect access failure mainly include transmission alarms of the carrier signaling (E1/T1, SAAL,NCP/CCP, MTP3B, internal IPC and AAL2PATH) and equipment alarms (clock, CPU, DSP, etc.). If such alarms occured, find out the causes and eliminate these alarms thoroughly.

C.3 Equipment Analysis

• The Threshold of CPICH RSCP <=-95 dBm consider as Poor Coverage.

• If the uplink transmit power reaches the maximum before call fail, the call fail is probably due to poor uplink coverage.

• If the downlink transmit power reaches the maximum before call fail and the downlink BLER is weak, the call fail is probably due to poor downlink coverage.

• Poor Coverage could be due to cross feeder, missing neighbor, inconsistency neighbor parameter, neighboring sites down, and node b power amplifier failure.

• UL Interference problem if RTWP is greater than 10 dB from normal value of normal RTWP

value -103 to -107 dBm.

C.4 Coverage and Interference Analysis

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• Radio network signaling includes signaling of four standard interfaces of UU, IU IUB and IUR. When an abnormality occurs in the signaling flow, we can check which part of signaling flow is missing.

• The missing of signaling flow should be correlated to UU,IUB,IU, and IUR interface problem.

• According to single subscriber tracing messages, the call drop is defined as:

1) RRC CONNECTION REQUEST FAILURE

- RNC Fails on receiving UL message of RRC CONNECTION SETUP COMPLETE.

2) RAB ASSIGNMENT REQUEST FAILURE

- CN Fails on receiving UL message of RAB ASSIGNMENT RESPONSE

Check the call drop time and the signaling message before call drop for further analysis.

• The Imsi trace tool with all interface message and monitoring kpi(CPICH RSCP, CPICH ECNO, UL SIR, UL TX PWR, and DL TX CODE POWER) helping us distinguishing Call Fail Reason. The Call Fail related to Air Interface or not related to Air Interface problem.

C.5 Signalling Analysis

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Call Fail Analysis Guide

Using Signalling IMSI

Trace

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• It is Shows details of all calls based on output from Trace Management->Interface Trace Task->UE.

• Provide convenient, PC-based analysis

1. Call Message Event

2. The downlink CPICH RSCP and ECNO Distribution.

3. UL SIR Distribution.

4. UE Tx Power distribution.

5. DL Tx Code Pwr

IMSI Trace on LMT

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Trace Viewer for Post Processing IMSI Trace Log

2 3 4 5

1. Call Message Event

2. The downlink CPICH RSCP and ECNO Distribution.

3. UL SIR Distribution.

4. UE Tx Power distribution.

5. DL TX Code Pwr.

1

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Call Message Event- RncId-Lac-Cell Id Identification

• Filter The Message by RANAP_LOCATION_REPORT/RANAP_INITIAL_UE_MESSAGE message.

• Convert The HEX value into DEC value.

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Call Message Event- Call Fail Identification

• Synchronize the Time of Call Fail.

• Call Fail Message defined as:

1. RRC CONNECTION REQUEST FAILURE

- RNC Fails on receiving UL message of RRC CONNECTION SETUP COMPLETE.

2. RAB ASSIGNMENT REQUEST FAILURE.

- CN Fails on receiving UL message of RAB ASSIGNMENT RESPONSE.

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Call Message Event- RRC.FailConnEstab.NoReply

(RNC does not receive RRC CONNECT SETUP COMPLETE )

• Filter The Message by RRC_RRC_CONNECT_REQUEST, RRC_RRC_CONN_SETUP, and RRC_RRC_CONNECT_SETUP_CMP.

• If No RRC_RRC_CONNECT_SETUP_CMP after RRC_RRC_CONN_SETUP.

• The Serving ECNO is -14 to -13.5 dB.

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Call Message Event- RAB SETUP FAIL(Failure in Radio

Interface prcedure(14))

• Filter The Message by RANAP_RAB_ASSIGNMENT_RESPONSE-raB-FailedList>cause->Disconnect->radioNetwork(14)Failure in Radio Interface Procedure.

• Check All Trace Viewer KPI(RSCP,ECNO,UL SIR, etc) and Alarm Issues.

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• The Breakdown from RF Problem.

• Checking CPICH and RSCP Distribution.

• If RSCP <=-95 dBm Consider as Poor Coverage, Check for missing neighbor and nearby Site problem.

• If ECNO <=-12 dB and RSCP >=-80 dBm consider as DL Interference/Pilot Pollution. Drive Test for verification is needed.

Bad RSCP and ECNO Distribution

Coverage and Interference Analysis

CPICH RSCP and ECNO

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• Checking UL TX PWR Distribution.

• Max UE TX PWR is to 24 dBm.

• If UE TX PWR more than 5 dBm consider as high UE TX PWR.

• High UE TX PWR can be due to Excessive UL Coverage or High UL Interference, Check if any missing neighbor or nearby Site Problem.

High UL TX PWR Distribution


UE TX POWER

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• Checking UL SIR Distribution.

• The SIR Target for this Services is -1.5 dB.

• If The SIR Measured Less than -1.5 dB can be due to Excessive UL Coverage or High UL Interference, Check any missing neighbor or neighbor Site Problem

Bad UL SIR

Distribution


UL SIR

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• Checking DL TX Code Power Distribution.

• The TX CODE POWER MAX Value for this AMR 12.2 is equal to CPICH POWER (example 33dBm) .

• The TX CODE POWER MIN Value for this AMR 12.2 is equal to 18 dBm

• If The TX Code Power Reaching near to CPICH POWER can be due to Poor Coverage/Fringe Cell/DL Interference. Check any missing neighbor or neighbor Site Problem.

High DL TX CODE POWER Distribution


DL TX CODE POWER

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Thank you

Call Failure Analysis.pdf

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