This section provides information required to troubleshoot inter-RAT handover faults. The information includes fault descriptions, background information, possible causes, and fault handling method and procedure.
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
7.1 Definitions of Inter-RAT Handover Faults
Inter-RAT handover faults are system faults that cause handover initiation failure or handover failure. RAT is short for radio access technology.
7.2 Background Information
This section provides background information about inter-RAT handover faults. The
background information includes counters, handover types, handover procedures, and related formulas.
Related Counters
Inter-RAT Outgoing Handover Measurement (Cell) (HO.IRAT.Out.Cell) For details, see eNodeB Performance Counter Reference.
Handover Types and Procedures
For details, see eRAN Mobility Management in Connected Mode Feature Parameter Description and 3GPP TS 23.401.
Related Formulas
Handover Success Rate Formula
Success rate of handovers from evolved universal terrestrial radio access network (E-UTRAN) to Wideband Code Division Multiple Access (WCDMA) networks
Number of Successful Outgoing Handovers from E-UTRAN to UTRAN/Number of Outgoing Handover Attempts from E-UTRAN to E-UTRAN
Success rate of handovers from E-UTRAN to GSM/EDGE radio access network (GERAN)
Number of Successful Outgoing Handovers from E-UTRAN to GERAN/Number of Outgoing Handover Attempts from E-UTRAN to GERAN
7.3 Troubleshooting Inter-RAT Handovers
This section provides information required to troubleshoot inter-RAT handover faults. The information includes fault descriptions, background information, possible causes, and fault handling method and procedure.
Fault Description
The following are symptoms of inter-RAT handover faults:
l Users file service drop complaints.
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
l The success rate of outgoing inter-RAT handovers is low.
l Signaling message tracing results indicate that handover procedures are incomplete or fail.
Related Information
l UE capability for inter-frequency handover
Monitor the network access signaling procedure on the eNodeB to check whether the UE supports frequency handovers. The information about whether the UE supports inter-frequency handovers can be obtained from the IE Feature group indicators in the
UECapabilityInformation message.
According to 3GPP TS 36.331 B.1 Feature group indicators, the eighth and ninth indicators indicate whether a UE supports packet switched (PS) handovers to GERAN and URTAN, respectively. Table 7-1 lists the eighth and ninth indicators.
Table 7-1 B.1 "Feature group indicators" in 3GPP TS 36.331 In
can only be set to "true" if the UE has set bit number 22 to "true"
9 EUTRA
RRC_CONNECTED to GERAN GSM_Dedicated handover
related to SR-VCC - can only be set to "true" if the UE has set bit number 23 to "true"
If the value of the eighth and ninth indicators is 0, the UE does not support PS handovers.
If the value of the eighth and ninth indicators is 1, the UE supports PS handovers.
l Neighboring cell configuration check
Inter-RAT neighboring cells must be configured before handovers can be performed from evolved universal terrestrial radio access network (E-UTRAN) to UTRAN/GERAN. Use the related commands provided by Huawei to configure inter-RAT neighboring cells.
– Check for missing and redundant neighboring cell configurations.
Check whether the routing area code (RAC) is configured when an external UTRAN cell is added by running the ADD UTRANEXTERNALCELL and whether NoHoFlag is set to Permit Ho when a neighboring relationship is added by running the ADD UTRANNCELL or ADD GERANNCELL command.
– Check handover parameter settings.
Check whether handover threshold parameters are properly set by comparing the settings with the default values or settings for a cell where handovers are normal.
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
The threshold settings can be queried by using the LST
INTERRATHOUTRANGROUP and LST INTERRATHOGERANGROUP commands.
Possible Causes
l The UE does not support inter-RAT handover.
l Inter-RAT handover parameters or evolved packet core (EPC) parameters are incorrectly set, or there are missing neighbor relationships.
l The signal quality is poor. For example, the coverage is poor or there is interference.
Fault Handling
Inter-RAT handover faults are complex and you need to determine whether an inter-RAT handover fault occurs in the entire network or in a cell based on the fault scope and background.
If the fault occurs in the entire network, locate the fault by checking the signaling exchange and parameter settings on the mobility management entity (MME) and serving GPRS support node (SGSN). If the fault occurs in a cell, check the data configuration, frequency, and hardware of the cell.
Figure 7-1 shows the troubleshooting flowchart for inter-RAT handover faults.
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
Figure 7-1 Troubleshooting flowchart for inter-RAT handover faults
Fault Handling Procedure
1. Check whether the UE does not support inter-frequency handover.
Yes: Use a UE that supports packet switched (PS) handover. Go to 2.
No: Go to 3.
2. Check whether the fault is rectified.
Yes: End.
No: Go to 3.
3. Check whether inter-RAT handover is disabled.
Yes: Run the MOD ENODEBALGOSWITCH:
HoModeSwitch=UtranPsHoSwitch-1; and MOD ENODEBALGOSWITCH:
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
HoModeSwitch=GeranPsHoSwitch-1; commands to enable PS handover to UTRAN and GERAN, respectively. Go to 4.
No: Go to 5.
4. Check whether the fault is rectified.
Yes: End.
No: Go to 5.
5. Check whether neighboring cells are incorrectly configured.
Yes: Correct the neighboring cell configuration. Go to 6.
No: Go to 7.
6. Check whether the fault is rectified.
Yes: End.
No: Go to 7.
7. Check whether EPC parameters are incorrectly configured.
Yes: Ask related personnel to correct the EPC parameter configurations. Go to 8.
No: Go to 9.
If the fault persists, go to 6.
8. Check whether the fault is rectified.
Yes: End.
No: Go to 9.
9. Check whether interference exists and whether the coverage is poor.
If the radio quality is poor, the UE cannot receive the handover command or cannot use the channel assigned by the target cell, causing handover failure. Network planning and optimization engineers can use drive tests to locate coverage problems and use a device or the interference tracing function on the eNodeB to locate interference problems.
Yes: Remove the interference source and adjust the coverage scope. Go to 10.
No: Go to 11.
10. Check whether the fault is rectified.
Yes: End.
No: Go to 9.
11. Contact Huawei technical support.
Typical Cases
l Case 1: In a PS handover from E-UTRAN to UTRAN, the eNodeB did not deliver a PS handover command but delivered a redirection command to the UE.
Fault Description
In a test of PS handover from E-UTRAN to UTRAN in a laboratory at a site, after the UE reported B1 measurement results to the eNodeB, the eNodeB did not deliver a PS handover command but delivered a redirection command.
Fault Diagnosis
The result of tracing the network access procedure found that the UE did not support inter-RAT handover. If a UE does not support inter-inter-RAT handover, the eNodeB will redirect the UE to UTRAN.
Fault Handling
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
The problem was solved after a UE that supports inter-RAT handover was used.
l Case 2: In a test of PS handover from E-UTRAN to UTRAN, the eNodeB did not deliver a PS handover command.
Fault Description
In a test of PS handover from E-UTRAN to UTRAN in a laboratory at a site, after the UE reported B1 measurement results to the eNodeB, the eNodeB did not deliver a PS handover command.
Fault Diagnosis
The result of tracing the network access procedure found that the UE supported inter-RAT handover. The PS handover switch was checked on the eNodeB. The check result indicated that the switch was turned on. Then, the neighboring cell relationships were checked. The check result shows that a RAC was not configured for the neighboring UTRAN cell.
Fault Handling
The problem was resolved after an RAC was added to the neighboring UTRAN cell.
l Case 3: In a test of PS handover from E-UTRAN to UTRAN, the eNodeB sent the MME a PSHO Required message. After two seconds, the eNodeB sent the MME a PSHO Cancel message.
Fault Description
In a test of PS handover from E-UTRAN to UTRAN in a laboratory at a site, the 4G EPC and eNodeB were provided by vendor Y and the 3G core network and radio network controller (RNC) were provided by vendor Z. After handover conditions were met, the eNodeB sent the MME a PSHO Required message. After two seconds, the eNodeB sent the MME a PSHO Cancel message.
Fault Diagnosis
Uu and S1 signaling was traced. The tracing result shows that the eNodeB sent the MME a HO Cancel command after the UE reported B1 measurement results to the MME and the eNodeB sent the MME a HO Required command. The reason why the eNodeB sent the HO Cancel command was that the MME did not respond to the HO Required command.
The length of WaitInterRATSysHoRspTimer configured on the eNodeB was 2 seconds.
The eNodeB did not receive a response from the MME when the timer expired. As a result, the eNodeB sent the Handover Cancel command to cancel the handover. The MME log was checked. The check result shows that the MME received the HO Required command but did not forward the command to the SGSN. The reason why the MME did not forward the command is that the Gn interface was not configured between the MME and the SGSN, and as a result, the MME could not find the SGSN. When the timer expired, the eNodeB sent the UE a PSHO Cancel command.
Fault Handling
The problem was solved after the Gn interface was reconfigured between the MME and SGSN.
Troubleshooting Guide 7 Troubleshooting Inter-RAT Handover Faults
8 Troubleshooting Rate Faults
About This Chapter
This chapter provides definitions of faults related to traffic rates and describes how to
troubleshoot low uplink/downlink UDP/TCP rates and rate fluctuations. UDP is short for User Datagram Protocol, and TCP is short for Transmission Control Protocol.
8.1 Definitions of Rate Faults