Inter-RAT Handover Success Rate Troubleshooting Guide

Product Name Confidentiality

UMTS Performance INTERNAL

Product VersionTotal 30 pages

R12&R13

Inter-RAT Handover Success Rate Troubleshooting

Guide(For internal use only)

Prepared by Wang Jiaojiao Date 2012-8-7

Reviewed by Date

Reviewed by Date

Approved by Date

Huawei Technologies Co., Ltd.

All rights reserved

Inter-RAT Handover Success Rate Troubleshooting Guide INTERNAL

Contents

Change History......................................................................................3

About This Document...............................................................................4

1 Procedure and Counters.........................................................................41.1 Inter-RAT CS Handovers...................................................................................................................................4

1.1.1 3G-to-2G Handover Procedure.................................................................................................................4

1.1.2 Counters for Failed Handovers.................................................................................................................5

1.2 Inter-RAT PS Handovers...................................................................................................................................6

1.2.1 3G-to-2G Handover Procedure.................................................................................................................6

1.2.2 Counters for Failed Handovers.................................................................................................................7

2 Analysis and Description of Specified Operations..............................................92.1 Determining the Scope and Classifying the Causes..........................................................................................9

2.2 Checking Parameter Settings...........................................................................................................................12

2.3 Checking the Version.......................................................................................................................................13

2.4 Checking the Clock..........................................................................................................................................14

2.5 Checking RF Channels....................................................................................................................................17

2.6 Checking the Resources and Capacity.............................................................................................................17

2.7 Analyzing the Signaling and Drive Test Data..................................................................................................19

2.7.1 Inter-RAT CS handovers.........................................................................................................................19

2.7.2 Inter-RAT PS Handovers........................................................................................................................21

3 Typical Cases....................................................................................26

4 Reference Information.........................................................................29

2012-11-05Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd. of 29


Change History

Date Version Description Reviewer Author

2012-6-26 V0.1 Inter-RAT Handover Success Rate

Troubleshooting Guide

Wang Jiaojiao

2012-8-7 V0.2 Inter-RAT Handover Success Rate

Troubleshooting Guide

Wang Jiaojiao




About This Document

This document describes major factors affecting the 3G-to-2G handover success rate and seven specified operations of inter-RAT handover success rate troubleshooting. It also lists deliverables that need to be fed back by the frontline when reporting inter-RAT handover problems, including the analysis and conclusion of each specified operation.

1 Procedure and Counters

1.1 Inter-RAT CS Handovers

1.1.1 3G-to-2G Handover Procedure

Figure 1-1Figure 1-1 shows the inter-RAT CS handover procedure.




Figure 1-1 Inter-RAT CS handover procedure

As shown at point A in the preceding Figure 1-1, during the outgoing inter-RAT CS handover, when the RNC sends a Handover from UTRAN Command message to the UEs, the IRATHO.AttOutCS counter is measured in the best cell under the SRNC. The counter provides the number of Inter-RAT CS handover attempts.

As shown at point B in the preceding Figure 1-1, during the outgoing inter-RAT CS handover, if the RNC receives an Iu Release Command message with the cause value of "Successful Relocation," "Normal Release," or "Network Optimization" after the RNC sends a Handover from UTRAN Command message, this inter-RAT CS handover succeeds and the IRATHO.SuccOutCS counter is measured in the best cell under the SRNC before the handover. The counter provides the number of successful inter-RAT CS handovers.

1.1.2 Counters for Failed Handovers

Table 1-1 lists the counters that measure failed outgoing inter-RAT CS handovers (the counter ID starting with 1 can be measured only by using OMStar).

Table 1-1 Counters that measure failed outgoing inter-RAT CS handovers

Counter

ID

Counter Name Counter Description

67189756 IRATHO.FailOutCS.CfgUnsupp Number of Failed CS Outgoing Inter-RAT Handovers for Cell (Configuration Unsupported)

67189757 IRATHO.FailOutCS.PhyChFail Number of Failed CS Outgoing




Inter-RAT Handovers for Cell (Physical Channel Failure)

128497 VS.IRATHO.FailOutCS.Other [67189754] – [67189755] – [67189756] – [67189757]

67192660 VS.IRATHO.FailOutCS.NoReply Number of Times that the Timer Waiting for Iu Release Command Expires in CS Outgoing Inter-RAT Handovers for Cell

73394018 VS.IRATHO.FailOutCS.Abort Number of Abnormally Terminated CS Outgoing Inter-RAT Handovers for Cell

Note:

67189754: Number of CS Outgoing Inter-RAT Handover Attempts

67189755: Number of Successful CS Outgoing Inter-RAT Handovers for Cell

67189756: Number of Failed CS Outgoing Inter-RAT Handovers for Cell (Configuration Unsupported)

67189757: Number of Failed CS Outgoing Inter-RAT Handovers for Cell (Physical Channel Failure)

Error: Reference source not foundError: Reference source not found shows the inclusive relationships between some counters.

Figure 1-2 Inclusive relationships between some counters

1.2 Inter-RAT PS Handovers

1.2.1 3G-to-2G Handover Procedure

Figure 1-1Figure 1-1 shows the inter-RAT PS handover procedure.




Figure 1-1 Inter-RAT PS handover procedure

As shown at point A in the preceding Figure 1-1, during the outgoing inter-RAT PS handover, when the RNC sends a Cell Change Order from UTRAN message, the IRATHO.AttOutPSUTRAN counter is measured in the best cell under the SRNC. The counter provides the number of outgoing inter-RAT PS handover attempts.

As shown at point B in the preceding Figure 1-1, during the outgoing inter-RAT PS handover, if the RNC receives an Iu Release Command message with the cause value of "Normal Release," the IRATHO.SuccOutPSUTRAN counter is measured in the best cell under the SRNC before the handover. The counter provides the number of successful inter-RAT PS handovers.

1.2.2 Counters for Failed Handovers

Table 1-1 lists the counters that measure failed outgoing inter-RAT PS handovers (the counter ID starting with 1 can be measured only by using OMStar).

Table 1-1 Counters that measure failed outgoing inter-RAT PS handovers

Counter

ID


67190476 IRATHO.FailOutPSUTRAN.CfgUnsupp Number of Failed PS Outgoing Inter-RAT Handovers Initiated by RNC (Configuration unsupported)

67190477 IRATHO.FailOutPSUTRAN.PhyChFail Number of Failed PS Outgoing Inter-RAT Handovers Initiated by RNC (Physical Channel Failure)




67192661 IRATHO.FailOutPSUTRAN.NoReply Number of Times that the Timer Waiting for Iu Release Command Expires in PS Outgoing Inter-RAT Handover Initiated by RNC for Cell

128496 VS.IRATHO.FailOutPSUTRAN.Other Number of Failed PS Outgoing Inter-RAT Handovers(except Configuration unsupported and Physical Channel Failure)

73423107 VS.IRATHO.FailOutPS.UEGen Number of Failed Outgoing UMTS-to-GSM PS Handovers due to UE Reselection Back to a UTRAN Cell

73394022 VS.IRATHO.FailOutPS.Abort Number of Abnormally Terminated PS Outgoing Inter-RAT Handovers for Cell

Error: Reference source not foundError: Reference source not found shows the inclusive

relationships between some counters.

Figure 1-2 Inclusive relationships between some counters




2 Analysis and Description of

Specified Operations

2.1 Determining the Scope and Classifying the Causes

Task Description: determine the problem scope and TOP N causes of inter-RAT handover failures

Input: original traffic statistics and PCHR log during busy hours in the morning and evening in the latest one week on the UMTS side

Steps:

1. Use the traffic statistics to analyze whether the inter-RAT handovers fail in the entire network or in TOP N cells.

(1) Exclude the first 20% of TOP N cells with the lowest inter-RAT handover success rate and the first 20% of TOP N cells with the greatest number of handover failures, or exclude the first 20% of TOP N target cells with the greatest number of handover failures. If the handover success rate of the network increases noticeably and reaches the original or target value, the problem occurs in TOP N cells.

(2) Exclude the first 20% of TOP N cells with the lowest inter-RAT handover success rate and the first 20% of TOP N cells with the greatest number of handover failures, or exclude the first 20% of TOP N target cells with the greatest number of handover failures. If the handover success rate does not increase noticeably, the problem occurs in the entire network.

(3) Exclude the first 20% of TOP N cells with the lowest inter-RAT handover success rate and the first 20% of TOP N cells with the greatest number of handover failures, or exclude the first 20% of TOP N target cells with the greatest number of handover failures. If the handover success rate increases but is lower than the original or target value, the problem occurs in both TOP N cells and the entire network.

The counters that need to be queried are as follows (the counter ID starting with 1 can be measured only by using OMStar):

(1) Inter-RAT CS handovers

The counters in Table 2-1 are used to determine the TOP N cells with the lowest inter-RAT handover success rate and TOP N cells with the greatest number of handover failures.




Table 2-1 Counters for Inter-RAT CS handovers

Counter

ID


67189754 IRATHO.AttOutCS Number of CS Outgoing Inter-RAT Handover Attempts

67189755 IRATHO.SuccOutCS Number of Successful CS Outgoing Inter-RAT Handovers for Cell

128475 VS.IRATHO.SuccOutCS.Cell.Rate 67189755/67189754

128505 VS.IRATHO.FailOutCS 67189754-67189755

The counters in Table 2-2 are used to determine the TOP N target cells with the greatest number of handover failures.

Table 2-2 Counters for the inter-RAT CS handover in two neighboring cells

Counter

ID


67183495 VS.IRATHO.AttOutCS.GCell Number of CS Inter-RAT Outgoing Handover Attempts Between Neighboring Cells

67183496 VS.IRATHO.SuccOutCS.GCell Number of Successful CS Inter-RAT Outgoing Handovers Between Neighboring Cells

(2) Inter-RAT PS Handovers

The counters in Table 2-3 are used to determine the TOP N cells with the lowest inter-RAT handover success rate and TOP N cells with the greatest number of handover failures.

Table 2-3 Counters for inter-RAT PS handovers

Counter

ID


67190411 IRATHO.AttOutPSUTRAN Number of PS Outgoing Inter-RAT Handover Attempts Initiated by RNC for Cell

67190412 IRATHO.SuccOutPSUTRAN Number of Successful PS Outgoing Inter-RAT Handovers




Initiated by RNC for Cell

128481 VS.IRATHO.SuccOutPSUTRAN.Cell.Rate 67190411/67190412

128506 VS.IRATHO.FailOutPSUTRAN.Cell Number of failed PS Outgoing Inter-RAT Handover

The counters in Table 2-4 are used to determine the TOP N target cells with the greatest number of handover failures.

Table 2-4 Counters for the inter-RAT PS handover in two neighboring cells

Counter

ID


67183497 VS.IRATHO.AttOutPSUTRAN.GCell Number of Inter-RAT PS Outgoing Handover Attempts Between Neighboring Cells

67183498 VS.IRATHO.SuccOutPSUTRAN.GCell Number of Successful Inter-RAT PS Outgoing Handovers Between Neighboring Cells

2. Use the traffic statistics to find the TOP N causes of inter-RAT handover failures.

(1) Find the TOP N causes of the increase in the number of inter-RAT handover failures in deteriorating scenarios.

(2) Find the TOP N causes of inter-RAT handover failures in scenarios of existing network optimization, new deployment, and network swapping (cell counters in the original network cannot be obtained).

Refer to 1.1.2 I. Step 11.Table 1-1 and 1.2.2 I. Step 11.Table 1-1 to query the counters that measure failed outgoing inter-RAT handovers.

3. Use the PCHR log to determine whether there are TOP N users and TOP N terminals.

(1) Exclude the first 20% of TOP N users, and if the handover success rate of the network increases noticeably and reaches the original or target value, the problem is caused by TOP N users.

(2) The inter-RAT handover failure rate of the TOP N terminals is twice that of other terminals. Exclude the TOP N terminals, and the handover success rate reaches the expected value.

Obtain user and terminal information by using FMA.

Tools: OMStar, FMA

Output: inter-RAT handover problem scope (the entire network or TOP N cells), TOP N causes, and whether there are TOP N users and TOP N terminals




2.2 Checking Parameter Settings

Task Description: check the parameters related to interoperation, the neighboring cells, the network planning parameters, and the operation logs

Input: configuration scripts of the GSM, UMTS, and core network, parameter mapping table in network swapping scenarios, operation logs of the GSM, UMTS, and core network, and debug log of the UMTS network

Steps:

1. Check interoperation parameters

For the existing and newly deployed networks, check whether the settings of the interoperability-related parameters and switches are consistent with the recommended configurations. If they are inconsistent, find the causes why the parameters are set incorrectly.

For the swapping networks, check whether the settings of the interoperability-related parameters and switches after swapping map the original network correctly. If the mapping is incorrect, find the causes of the incorrect mapping.

2. Check neighboring cells

(1) Check whether there are missing inter-RAT neighboring cells by using the Nastar tool.

(2) Check the 2G/3G parameter consistency. If the UMTS side is configured with external 2G neighboring cells, check whether the configurations of the external 2G neighboring cells are consistent with those on the GSM side. The parameters to be checked include NCC, BCC, and LAC. If the CME tool is deployed, use it for check. If the CME tool is not configured, perform the check manually. Change the parameter settings on the UMTS side to be consistent with the configuration on the GSM side if there is 3G/2G parameter inconsistency.

(3) In network swapping scenarios, check whether the inter-RAT neighboring cells after swapping map the original network correctly. If the mapping is incorrect, add the missing inter-RAT neighboring cells.

(4) If there are TOP N 2G cells, check whether the frequency band of the TOP N 2G cells is E-GSM 900 MHz or GSM 1800 MHz. If yes, check whether the number of neighboring cells configured for the TOP N 2G cells exceeds 18. If the number exceeds 18 and the T309 timer on the UMTS side is set to 5s, change the timer length to 8s.

3. Check network planning parameters

(1) MSC (inter-RAT CS handovers): check whether the MSC is configured with 2G cell information.

(2) SGSN (inter-RAT PS handovers): check whether the LAC/RAC of the UMTS network are registered in the SGSN and check the interface between the SGSNs in 2G/3G inter-SGSN scenarios.

(3) DNS (inter-RAT PS handovers): check whether the LAC/RAC of in GSM and UMTS networks are registered in the DNS in 2G/3G inter-SGSN scenarios.

(4) When the success rate of inter-RAT PS handovers is low and the causes for most handover failures are "Noreply," check whether the IP path of the core network is configured. Check method: use FMA to open the debug log and check whether there is the error code SIG_ERR_TRMP_062C. If yes, the recorded ulPeerIpAddr is the IP address of the missing IP path, which is a decimal value and needs to be converted to an IP address.




4. Check operation logs in abrupt counter change scenarios

Analyze the operation logs of the radio access network and core network before and after the counter change to check whether there are operations which affect the inter-RAT handover counters. If the handover problem is caused by these operations, confirm the purpose of these operations with customers and perform the rollback if possible.

Tools: FMA, Nastar, and CME

Output: check result of parameters (the parameter mapping result in network swapping scenarios), neighboring cells, network planning, and the analysis result of operation logs in abrupt counter change scenarios

2.3 Checking the Version

Task Description: check whether there are known version problems and compare the versions before and after the upgrade to determine whether the target version affects inter-RAT handovers in version upgrade scenarios

Input: release notes of versions

Steps:

1. For the decrease in the inter-RAT handover success rate after the version upgrade of the RNC/NodeB/BSC/BTS:

(1) Check the release notes of the RNC/NodeB/BSC/BTS versions before and after the deterioration of the handover success rate. List the version problems, algorithm changes, and new features. Analyze the possible impact of the version problems and new features.

(2) Check whether there are known version problems which affect inter-RAT handovers after the upgrade. If the versions have known problems, upgrade the versions or change parameter settings to solve the problem.

(3) Compare the configuration files of the RNC/NodeB/BSC/BTS before and after the upgrade. List the differences in parameter settings and analyze possible impacts.

2. For the swapping or newly deployed networks, check whether there are known version problems which affect inter-RAT handovers after the upgrade. If the versions have known problems, upgrade the versions or change parameter settings to solve the problem.

3. The known version problems which affect inter-RAT handovers detected currently are as follows:




(1) Base station bug causes UEs to mistakenly regard all 0 data as the FCCH only in inter-RAT PS handover scenarios and the involved versions are BTS3900V100R003C00SPC350 and earlier in SRAN5.0, BTS3900V100R004C00SPC130 and earlier in SRAN6.0, BTS3000V100R012C00SPC042 and earlier in GBSS12.0, and BTS3000V100R013C00SPC019 and earlier in GBSS13.0.

Check method:

a. Check whether the TRX channel attribute in the 2G configuration scripts is set to combined BCCH (CBCCH).

b. Check whether the TRX boards configured on the GSM side are of the following types: MRRU V2, MRFU V1, MRFU V2, MRFUd, MRFUe, RRU3928, RRU3929, and MRFU V3.

Solution: Upgrade the BTS version to BTS3900V100R004C00SPC150 and later or BTS3900V100R003C00SPC360 and later accordingly.

(2) If the RNC version is earlier than R13SPH558, when the CIO configuration in external 2G neighboring cells is not 0, the CIO sent by the RNC is changed (inconsistent with the actual configuration).Check method: run the LST UEXT2GCELL/ADD UEXT2GCELL command to determine whether there are external 2G neighboring cells where the CIO configuration is not 0.

Solution: upgrade the RNC version to R13SPH558 or later or set the CIO value to 0 and the CIOOFFSET value to the original CIO value.

Tools: Beyond Compare, OMSTAR

Output: version check result

Reference Document: none

2.4 Checking the Clock

Task Description: check whether the 2G/3G clock is abnormal

Input: 2G/3G alarms

Steps:

1. Check whether there are 2G/3G clock alarms.

2. If there are no 2G/3G clock alarms, check whether the 2G/3G clock has a micro frequency offset which does not reach the clock alarm threshold. Perform the following steps to obtain the 2G/3G clock information.

(1) Check the BSC/RNC clock quality.

Run the DSP CLK command on the BSC and RNC respectively. Check the clock quality every one minute on the BSC and RNC for 10 times and feed back the execution result.




(2) Query the DA values of the 2G/3G base stations.

Right-click GTMU on the 2G device panel and choose Query Board Information. Feed back the screenshot, as shown in the following figure.

(3) Query the NodeB clock.

After logging in to the NodeB on the LMT, run the DSP CLKDA command to query the initial DA, current DA, and center DA values, as shown in the following part.

%%/*30532*/DSP CLKDA:SN=7;%%

RETCODE = 0 Operation succeeded.

Display Clock DA

Cabinet No. = 0

Subrack No. = 0

Slot No. = 7

Initial DA = 31546

Center DA = 31460

Current DA = 31443

(Number of results = 1)

After logging in to the NodeB on the LMT, run the LST CLKRECORD command to query the recorded values of the current DA and center DA, as shown in the following part.




%%/*30003*/LST CLKRECORD:SN=7;%%

RETCODE = 0 Operation succeeded.

List Clock Record

Time PLL Status Current DA Center DA

2012-05-22 09:40:58 Locked 31443 31460

2012-05-22 09:11:01 Locked 31444 31460

2012-05-22 08:41:04 Locked 31445 31460

2012-05-22 08:11:07 Locked 31446 31460

2012-05-22 07:41:11 Locked 31445 31460

2012-05-22 07:11:14 Locked 31447 31460

2012-05-22 06:41:17 Locked 31443 31460

2012-05-22 06:11:20 Locked 31442 31460

(4) Perform the clock test.

After logging in to the BSC on the LMT, click Clock Test on the monitor tab page to perform the GBTS clock test, as shown in the follow figure.

Tools: none

Output: clock check result

2.5 Checking RF Channels

Task Description: analyze and determine whether there are RF channel problems in target cells of handovers




Input: original traffic statistics in the latest one week on the GSM side

Steps:

1. Check whether there is uplink interference in TOP N target cells if inter-RAT handover failures occur in TOP N target cells. Analyze the interference band analysis and measurement in the traffic statistics of TOP N 2G cells. The higher the interference band level, the greater the interference strength. Calculate the ratio of 2G cells in interference bands 4 and 5 to all 2G cells and determine whether there are strong interference cells. The 2G counters that need to be queried are TRX.CH.IN.INTFR1.AVR.NUM.SD, TRX.CH.IN.INTFR2.AVR.NUM.SD, TRX.CH.IN.INTFR3.AVR.NUM.SD, TRX.CH.IN.INTFR4.AVR.NUM.SD, and TRX.CH.IN.INTFR5.AVR.NUM.SD. Calculate the ratio of interference bands 4 and 5 to all interference bands and if the ratio exceeds 10%, the cell has strong interference. Eliminate the interference on the GSM side if TOP N 2G cells have strong interference. If the interference on the GSM side cannot be eliminated, adjust CIOOFFSET of the TOP N 2G cells on the UMTS side by running the MOD U2GNCELL command to avoid handing over UEs to the TOP N 2G cells.2. Check whether the uplink and downlink levels are unbalanced (the uplink level is weak) in TOP N target cells if inter-RAT handover failures occur in TOP N target cells. The 2G counters that need to be queried are TRX.BALANCE.LEV.1, TRX.BALANCE.LEV.2, TRX.BALANCE.LEV.3, TRX.BALANCE.LEV.4, TRX.BALANCE.LEV.5, TRX.BALANCE.LEV.6, TRX.BALANCE.LEV.7, TRX.BALANCE.LEV.8, TRX.BALANCE.LEV.9, TRX.BALANCE.LEV.10, and TRX.BALANCE.LEV.11. Calculate the proportion of TRX.BALANCE.LEV.10 and TRX.BALANCE.LEV.11 in all the balance levels. If the ratio exceeds 30%, the uplink and downlink levels are unbalanced in the cell (the uplink is weak). If the uplink and downlink levels in TOP N 2G cells are unbalanced, troubleshoot the problem on the GSM side.

3. Check whether there are RF channel faults in TOP N 2G cells if inter-RAT handover failures occur in TOP N target cells. For details, see the GSM X document Detection and Troubleshooting of GSM RF Tunnel Faults: Principle + Tools + Cases + Deliverables.

4. In network swapping scenarios, check whether the network coverage changes before and after the network swapping.

Tool: OMStar

Output: TOP N cells with strong interference and unbalanced uplink and downlink levels, 2G cells with RF channel faults, and cells with the coverage change after the network swapping


2.6 Checking the Resources and Capacity

Task Description: determine whether resource congestion occurs in TOP N target cells with the greatest number of handover failures

Input: original 2G/3G traffic statistics in the last week

Steps:

Analyze 3G traffic statistics per hour to locate TOP N 2G cells with the greatest number of handover failures. Query 2G traffic statistics of TOP N 2G cells in the corresponding periods to determine whether resource congestion occurs. The 2G traffic statistics that need to be queried are as follows:




(1) Inter-RAT CS handovers

Counter ID Counter Name Counter Description

1278087448CELL.KPI.TCH.CONGESTION.RATE

K3045: Congestion Rate on TCH (All Channels Busy)

1278087426CELL.KPI.TCH.CONG.SIG

K3021: Failed TCH Seizures due to Busy TCH (Signaling Channel)

1278087431CELL.KPI.TCH.ASS.CONG.TRAF

K3011A: Failed TCH Seizures due to Busy TCH (Traffic Channel)

1278087435CELL.KPI.TCH.HO.CONGEST.TRAF

K3011B: Failed TCH Seizures in TCH Handovers due to Busy TCH (Traffic Channel)

(2) Inter-RAT PS Handovers

Counter ID Counter Name Counter Description

1278476438CELL.RATE.SD.CONG

RR370: Congestion Rate on SDCCH per CELL (due to Busy)

1278087420CELL.KPI.SD.CONGEST

K3001: Failed SDCCH Seizures due to Busy SDCCH

1278070435CELL.DISC.CH.REQ.LOC.UPDATE

L3189E: Discarded Channel Requests (Location Updating)

1278070428 CELL.FCTRL.PAGING.MSG.DEL.PCH.QUE

L3188L: Paging Messages Discarded from the PCH Queue

1279173419 UP.GPRS.TBF.ESTB.FAIL.NO.CHAN.RES

A9003: Number of Failed Uplink GPRS TBF Establishments due to No Channel

1279174419 DOWN.GPRS.TBF.ESTB.FAIL.NO.CHAN.RES

A9103: Number of Failed Downlink GPRS TBF Establishments due to No Channel

1279175419 UP.EGPRS.TBF.ESTB.FAIL.NO.CHAN.RES

A9203: Number of Failed Uplink EGPRS TBF Establishments due to No Channel

1279176419 DOWN.EGPRS.TBF.ESTB.FAIL.NO.CHAN.RES

A9303: Number of Failed Downlink EGPRS TBF Establishments due to No Channel

73415210 VS.XPU.CPULOAD.MEAN AR9780: Average CPU Usage of the XPU

1279369424

(FR transmission)

BC.TRAN.UP.UTILIZATION.RATE RL9608: Uplink bandwidth usage of the BC

1279369426

(FR transmission)

BC.TRAN.DOWN.UTILIZATION.RATE

RL9610: Downlink bandwidth usage of the BC




Tool: OMStar

Output: 2G cells with resource congestion


2.7 Analyzing the Signaling and Drive Test Data

Task Description: analyze the traced signaling and drive test logs to find the root cause of inter-RAT handover failures

Input: 2G/3G traced signaling, drive test logs, and core network traced signaling

Output: signaling file of the BSC/RNC, drive test logs, and traced signaling file of the core network

2.7.1 Inter-RAT CS handovers

1. 3G Signaling Analysis

(1) For TOP three 3G cells with the greatest number of handover failures, trace and analyze the IOS signaling. Compare the signaling procedures and information elements between successful handovers and failed handovers during the period from call setup to handover completion. Find and analyze their difference. In addition, check events 2D/2F during the signaling tracing and signal levels in target cells reported by the UEs. Determine whether the target threshold of the inter-RAT CS handover is consistent with the configured value.

(2) If there are TOP N users with the greatest number of handover failures, trace and analyze the signaling of single UEs for the TOP three users. If all the handovers of the user fail, analyze whether the failed signaling procedure is abnormal. If some handovers of the user succeed, compare the signaling procedures and information elements between successful handovers and failed handovers during the period from call setup to handover completion. Find and analyze their difference.

2. Joint Analysis of 2G/3G Signaling

(1) Locate TOP three pairs of neighboring cells with the greatest number of handover failures based on the traffic statistics of neighboring cells.

(2) Trace the signaling over the Uu interface (Measurement Control, Handover from UTRAN Command, and Handover from UTRAN Fail) and over the Iu-CS interface (Relocation Required, Relocation Command, Relocation Cancel, Relocation Cancel Ack, and Iu Release Command) of 3G cells.

(3) Trace the CS signaling of 2G cells over the Abis and A interfaces.

(4) Use FMA to open the Uu interface signaling and the Iu interface signaling respectively. Filter the Uu interface signaling to obtain the Handover from UTRAN Fail message and record the user IDs of every handover failure. Find all the corresponding signaling over the Uu and Iu interfaces based on the user ID. Query the NCC, BCC, and BCCH frequency of the target handover cell from the Handover from UTRAN Command message to locate the 2G target cell. Find the handover-reference value from the Relocation Command message over the Iu interface, as shown in the following figure.




(5) Determine whether the signaling of the target 2G cell located in (4) has been traced. If yes, query the 2G signaling over the Abis interface before and after the handover (the 2G and 3G clocks may be different). Query the handover-reference value from the Channel Activation message and find the number consistent with the handover-reference value in (4) so one handover of the same user is confirmed. Use the Call Trace function to obtain all the signaling of this handover recorded over the Abis interface. Query the signaling and find the point where the handover of this UE fails on the GSM side during the signaling procedure.



Y

N

N

Trace the signaling over the Abis and Gb interfaces and obtain the 3G PCHR in that period.

Based on the PCHR analysis, find the CI, UE TMSI, and delivering time of Cell Change Order from UTRAN

message of the target cell with handover failures.

Find and analyze the signaling over the Abis interface of the UE based on the UE TMSI.

Is location area update of the UE complete?

Y

Obtain the TLLI of the UE from the GPRS Suspension Request message. Find and analyze the signaling over the Gb

interface of the UE based on the TLLI.

Find and analyze the failure causes.

NAnalyze the PCHR and check whether handover failures occur due to Noreply and ping-pong

reselections.


3. Analysis of Drive Test Logs

(1) If specified operation 1 finds that there are TOP N terminals, perform the drive test or lab simulation test for the TOP N terminals to obtain the UE log. Analyze the UE log to determine whether the handover procedure is abnormal.

(2) If specified operation 1 finds that there are TOP N pairs of neighboring cells, perform the drive test for the TOP three cells when failure causes cannot be found by tracing signaling on the network side. Analyze in detail the UE logs of the handover failure obtained from drive tests and find the point where the handover fails during the procedure. In addition, analyze whether the signal strength and quality of 2G cells are abnormal, which causes handover failures.

2.7.2 Inter-RAT PS Handovers

1. 3G Signaling Analysis

(1) For TOP three 3G cells with the greatest number of handover failures, trace and analyze the IOS signaling. Compare the signaling procedures and information elements between successful handovers and failed handovers during the period from call setup to handover completion. Find and analyze their difference. In addition, check events 2D/2F during the signaling tracing and signal levels in target cells reported by the UEs. Determine whether the target threshold of the inter-RAT PS handover is consistent with the configured value.

(2) If there are TOP N users with the greatest number of handover failures, trace and analyze the signaling of single UEs for the TOP three users. If all the handovers of the user fail, analyze whether the failed signaling procedure is abnormal. If some handovers of the user succeed, compare the signaling procedures and information elements between successful handovers and failed handovers during the period from call setup to handover completion. Find and analyze their difference.

2. 3G PCHR and 2G Signaling Analysis (Only in Other Failure Scenarios)

The analysis procedure is as follows:




Note:

(1) Based on specified operation 1, find TOP three 2G cells with the greatest number of inter-RAT PS handover failures and trace the signaling over the CS Abis and PS Gb interfaces of the TOP three 2G cells.

(2) Use the PCHR to find handover failures due to Noreply and ping-pong reselections and find the CI, UE TMSI, and delivering time of Cell Change Order from UTRAN message of the target cell with handover failures.

(3) Query the signaling over the 2G Abis interface around the delivering time of Cell Change Order from UTRAN for each handover failure and find the Establish Indication message. Use the UE TMSI obtained in (2) to determine whether the message is the 2G signaling of UEs with the greatest number of handover failures. The TMSI in the Establish Indication message can be queried in two ways. In one way, open the message to query the information elements, as shown in the following figure.

In the other way, query directly the last eight bits of the corresponding message content, as shown in the following figure.

The first way is more difficult than the second way.




(4) Use the Call Trace function to obtain the signaling of the UE over the Abis interface. Check whether the location area update on the GSM side is complete. If yes, perform the subsequent operations. If no, find the causes of the location area update failure.

(5) Obtain the TLLI number from the GPRS Suspension Request message over the Abis interface. Note: The signaling review tool cannot parse the content of the message. The type of this message is Data Indication which has multiple messages. The TLLI number can be obtained only by opening the message.




(6) Find the signaling of the UE over the Gb interface based on the parsed TLLI number in the Report Condition column. Obtain the Routing Area Update Request message first to find the UE quickly. Then, use the Call Trace function to find the signaling of the UE over the Gb interface. Note: The TLLI number over the Gb interface has one bit difference from the TLLI number obtained in (5) so if the most bits are the same, they are the TLLIs from one UE.




(7) Query the signaling of the UE over the Gb interface and check whether the routing area update of the UE is complete. If no, record the failure causes (for example, the routing area update is rejected and there is no response to the routing area update and ask the SGSN side for assistance. If yes, this handover failure is caused by the untimely release or incorrect release cause on the SGSN side.

3. Signaling Analysis of Single UEs in the Core Network (Only in Other Failure Scenarios)

Signaling analysis of single UEs in the core network applies to the following two scenarios:

(1) Huawei provides the SGSN equipment but not the equipment in the GSM network and the 2G signaling cannot be traced and analyzed.

(2) Huawei provides the SGSN equipment and the GSM network equipment. However, 3G PCHR and 2G signaling analysis show that the handover failure of the UEs to the GSM network is caused by no response of the routing area update. Check whether the SGSN receives the routing area update request and whether the SGSN internal processing is normal.

Analysis method:

(1) Find the IMSIs of TOP N UEs with the greatest number of handover failures due to Noreply or ping-pong reselections based on specified operation 1 and trace the signaling of a single UE on the SGSN and UMTS sides simultaneously.

(2) Analyze the signaling of a single UE on the UMTS side and find the handover failure time. Query the SGSN signaling at the corresponding time and analyze whether the SGSN receives the routing area update request of the UE on the GSM side. If no, packet loss occurs over the Gb interface. Then, check whether the transmission over the Gb interface is normal and whether there is congestion. If yes, check whether the SGSN internal processing is normal.

4. Analysis of Drive Test Logs (in Physical Channel Failure Scenarios)

Because the physical channel failure occurs during the air interface access, the 2G signaling cannot be traced to analyze the point where the handover fails in the procedure and drive test logs need to be used to analyze the failure causes. Analysis method:

(1) The frontline personnel perform the drive test in TOP N cells with inter-RAT PS handover physical channel failures. Obtain drive test logs of the handover failure and trace a single UE on the RNC side.

(2) Analyze the drive test data and find the root cause of inter-RAT PS handover failures.

Tools: FMA, Probe/TEMS, and signaling review tools used for the GSM network and core network

Output: root cause of inter-RAT handover failures




3 Typical Cases

Table 3-1 Typical cases

Problem Type

Problem Description Cause Description Solution

Parameter check

The success rate of inter-RAT PS handovers is low and the traffic statistics show that the causes for most handover failures are "Other".

Incorrect parameter settings of the core network cause internal problems. Though the UE has completed the handover on the GSM side, the Iu Release Command message sent by the SGSN still carries the release cause of "non-standard," which causes handover failures on the UMTS side.

Change the software parameter settings of the core network. SET SOFTPARAOFBIT: DT=BYTE, PARANUM=58, VALUE=VALUE_1, POSITION=4;

After the Nokia GSM network is swapped, the success rate of inter-RAT PS handovers on the UMTS side decreases and the number of "Noreply" causes increases among the failure causes.

The minimum signal receive level of PS RACH is –105 dBm and that of CS RACH is –109 dBm. Due to the high PS RACH threshold, the low-level UEs that are handed over to the GSM network are rejected, increasing the number of PS handover failures due to Noreply.

Change the minimum signal receive level of PS RACH to –109 dBm.

After the rehoming of nine sites, the success rate of inter-RAT PS handovers decreases by 9% and the causes for these 9% handover failures are "Other."

The cells which are cut over to the new RNC are configured with the new LAC and RAC, which are not registered with the SGSN. As a result, the routing area update of the UEs on the GSM side is rejected.

Register the new LAC and RAC with the SGSN.

After the GSM and UMTS networks are cut over from co-SGSN to inter-SGSN, the success rate of inter-RAT PS handovers on the UMTS side decreases and the causes for these incremental handover failures are "Other."

Due to the SGSN parameter settings, the SGSN on the UMTS side does not release the Iu connection immediately after receiving the Cancel Location message replied by the HLR. Instead, the SGSN startsT3 timer and releases the Iu connection only after the T3 timer expires. During this period, the UEs are handed over back to the UMTS or the RNC waits until Iu Release Command times out. This is counted as a inter-RAT PS handover failure.

Change the software parameter settings so that the SGSN releases the Iu connection immediately after receiving the Cancel Location message. SET SOFTPARAOFBIT: DT=DWORD, PARANUM=59, VALUE=VALUE_1, POSITION=3;




After the core network swapping, the number of inter-RAT PS handovers increases sharply.

Before the core network swapping, for UEs which initiate an Attach/RAU procedure, the NSN SGSN starts a 10s timer and automatically releases the Iu connection after the timer expires if the UEs carry follow-on request; the NSN SGSN releases the Iu connection immediately if the UEs do not carry the follow-on request. After the core network swapping, the Huawei SGSN does not automatically release the Iu connection so that the online duration of single signaling service increases and the probability of initiating inter-RAT handovers increases accordingly, which causes the sharp increase in the number of handovers.

Change the timer for the Huawei　SGSN to a 10s timer that automatically releases the Iu connection.SET PROCR: RELIU=YES;SET PMMTMR: IURLSTMR=10

Note: The Iu connection release of the NSN SGSN cannot be achieved only by changing the parameter settings of the Huawei SGSN because the Iu connection release mechanisms of the Huawei SGSN are different for the UEs which carry the PDP context and the UEs which do not carry the PDP context.

After the EFD feature is enabled on the UMTS side, the success rate of inter-RAT PS handovers decreases.

1. After some terminals report the SRCI message, the network side transits the terminals to the CELL-PCH state and then initiates the inter-RAT handover in the CELL-DCH state. The compatibility problem occurs and the terminals report the CCO failure because configurations are not supported.2. After some terminals report the SRCI message, the network side sends the CCO message, but the terminals do not attempt to hand over to the GSM networks. As a result, the handover fails due to Noreply.

　

In the new UMTS sites, the success rate of inter-RAT PS handovers is low and the causes for most handover failures are "Noreply."

On the UMTS side, missing configurations of IP paths to the GGSN causes the L2 setup failure and handover failure after the timer expires during the context interaction.

Add the missing IP path.

After the UMTS network swapping, the success rate of inter-RAT CS handovers decreases and the number of handover attempts decreases to 20% of the number before the swapping.

After the swapping, the NCC/BCC of 2G cells configured on the UMTS side is inconsistent with the configuration on the GSM side so that the UEs cannot detect valid neighboring cells.

Change the NCC/BCC of 2G cells configured on the UMTS side to be consistent with the configuration on the GSM side.




Version check

After the Nokia GSM network is swapped, the success rate of inter-RAT PS handovers on the UMTS side decreases and the causes for most handover failures are the physical channel failure.

The onsite MRRU V2 module is configured with a CBCCH. When SDCCH and SACCH in the CBCCH are unoccupied, all 0 data is sent at the non-coding time. Then the UEs mistakenly regard this all 0 frame as the FCCH so that they cannot detect the SCH. As a result, the PS handover fails due to the physical channel failure. This problem is caused by the product defect.

Upgrade the BTS version to BTS3900V100R004C00SPC150 and later or BTS3900V100R003C00SPC360 and later accordingly.

The success rate of inter-RAT CS handovers in existing networks is lower than the expected value.

The RNC version is earlier than V900R013SPH558. Due to the product defect, when the CIO configuration in external 2G neighboring cells is not 0, the CIO sent by the RNC is changed (inconsistent with the actual configuration), which causes the low threshold of the handover to some 2G cells and therefore the handover fails.

Upgrade the RNC version to V900R013SPH558 and later or set the CIO value to 0 and the CIOOFFSET value to the original CIO value.

Clock check

According to the lab test of operator D in country G, some UEs cannot initiate CS handovers to the GSM network.

When the UEs are required to parse and confirm the BSIC of 2G cells, they cannot send the measurement report so that the handover cannot be initiated. The cause is that there is a frequency offset in the BSC clock but it does not reach the clock alarm threshold. The BTS locks the BSC clock so the frequency in 1800 MHz cells is offset by about 890 Hz over the Um interface. However, some terminals have a high requirement for the frequency offset so that when the network requires these UEs to parse and confirm the BSIC of 2G cells, the Um interface cannot be synchronized.

Change the DA value of the BTS clock to the factory default.

RF channel check

The success rate of 3G inter-RAT CS handovers in existing networks is lower than the expected value.

Strong interference in TOP N 2G cells causes handover failures.

Eliminate the interference source in the GSM network.

Resource and capacity check

After the GSM/UMTS network swapping, the success rate of inter-RAT PS handovers is lower than the expected value and the success rate is low only during busy hours.

After the GSM network swapping, the CPU is overloaded heavily during busy hours so that the number of discarded channel requests increases sharply, which is indicated by the increase in the physical channel failures of the inter-RAT PS handover on the UMTS side. In addition, the TBF congestion is severe during busy hours so that the TBF setup success rate is low, which is indicated by the increase in the Other failures of inter-RAT PS handovers.

Expand the capacity of the GSM network.




4 Reference Information

(This part is for the materials that don't need to be familiar with at ordinary times but may be required in use for reference.)



Inter-RAT Handover Success Rate Troubleshooting Guide

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