Inter-RAT Handover Failure Internal

Inter-RAT Handover Failure

KEY WORDSInter-RAT Handover, RRC_HO_FROM_UTRAN_FAIL,

RRC_HO_FROM_UTRAN_CMD_GSM

DESCRIPTIONIt is new live network. The provider has several live networks, including H_3G, H_2G and

N_2G. Inter-RAT Handover failure which happened from H_3G to N_2G， but handover is successful from H_3G to H_2G.

The signal flow has terminated after “RRC_HO_FROM_UTRAN_CMD_GSM”. UE

release handover session. Failure happened in “RRC_HO_FROM_UTRAN_FAIL”.

ALARMNo

ANALYSIS PROCEDURE

Step 1:

Handover failure happened from H_3G to N_2G，in “RRC_HO_FROM_UTRAN_FAIL”， Failure cause in failure signaling is “ConfigurationUnacceptable: NULL”.

Step 2：According to handover message comes from 2G side：1、Handover from H_3G to H_2G ， the ciphering mode come from 2G BSC is

following. Please see Fig-1 With cipher mode

2023-4-21 华为机密，未经许可不得扩散 第 1 页, 共 4 页

Inter-RAT Handover Failure Internal

Fig-1: With cipher mode

2、Handover from H_3G to N_2G ， the ciphering mode comes from 2G BSC is following. Please see Fig-2 without cipher mode

Fig-2: without cipher mode

According to the analysis above, it could be the problem in cipher mode selection.

SOLUTION1、N_2G equipment is too old, just can support A5/0 that means without cipher

mode. H_2G can support A5/0 and A5/2 that means H_2G equipment can

support both no cipher mode and cipher mode together.

2、Close RNC handover switch followingSET RRCTRLSWITCH:

PROCESSSWITCH=SYS_HO_OUT_CIPHER_SWITCH-1&SYS_HO_CIPHER_CONFIG-0;

3、SYS_HO_OUT_CIPHER_SWITCH. When it is checked, the RNC will add ciphering byte at GSM HANDOVER COMMAND if the GSM system does not

add any cipher information at that message.

4、SYS_HO_CIPHER_CONFIG. When it is checked, the cipher configuration in the added cipher byte in GSM will be A5/1.When it is no checked, the cipher

configuration is A5/0.

2023-4-21 华为机密，未经许可不得扩散 第 2 页, 共 4 页

Inter-RAT Handover Failure Internal

The problem is resolved after two switches was closed,

One is “SYS_HO_OUT_CIPHER_SWITCH” , another one is

“SYS_HO_CIPHER_CONFIG”

2023-4-21 华为机密，未经许可不得扩散 第 3 页, 共 4 页

Inter-RAT Handover Failure Internal

2023-4-21 华为机密，未经许可不得扩散 第 4 页, 共 4 页