During S1AP path switch request message, MME releases bearer for QCI 1 with radio network cause 30 and unknown erab id?

Question

What MME shall perform when receiving S1 path switch request (changing tac and lac for the UE) after a NAS tau request. Shall MME respond to UE with TAU reject (which cause code ) or not ?

Answer 1

As per my understanding, nothing like that is mentioned in the specification. I think this is happening in your setup and this could be because of some issues in your software code.

Answer 2

This happens, when UE is in handover state and suppose any party (calling or called party) disconnect the call and MME send the E-RAB release to source eNB, but as source eNB is in Handover processor and it will ignore the E-RAB release request and sent the response as failure, then Target eNB try to switch the path but MME already released the E-RAB so it will reply as Unknown E-RAB ID to target eNB.

Comments

ty ravinder...so it is a normal behaviour or where this should be corrected

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for eNB it's as per 3GPP but in MME we need to enhancement to hold the E-RAB id till HO process get completed.