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Cisco Bug: CSCuj95866 - S4-SGSN: IRAT From LTE to UMTS with RAU - idle mode at LTE fails.

Last Modified

Feb 06, 2017

Products (1)

  • Cisco ASR 5000 Series

Known Affected Releases

15.0(14)

Description (partial)

Symptom:
S4-SGSN: IRAT From LTE to UMTS with RAU - idle mode at LTE fails.

Conditions:
When we try to do Handover from LTE to UMTS with RAU , SGSN is taking the new configured S interfaces(S4/S3/S12) to register the SPGW and for creating the bearer.

Key Observations from the logs :

- RAU is recieivng at SGSN when we shut LTE signal and MME/SGSN context transfer through S3 is also good.
- After RAU reaches the SGSN , SGSN does a DNS query and it is responding with the correct S3 Ip( In our case S11 Loopback at MME)
- Right after this we are receiving an ISD from HLR , and it is giving the Wildcard APN(*) to the SGSN.
- SGSN is generating Delete session Request  and UE is detaching.

After this procedure UE does a fresh attach in the SGSN (3G) through S interfaces.
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