LTE: When does an eNodeB send "UE Context Release Request" message for an UE to MME ?

Question

when mme will change the security keys and send it in ue context modification request message

Answer 1

1. If UEs BUFFER STATUS REPORT IS EMPTY
2. IF UE is coming again and again with RRC integrity failure.
3. In case of x2 handover if source enodeb doesn't get UE context release message from target enodeb before TX2relocoverall timer expires then source enodeb will issue uecontextreleaserequest message to MME

Answer 2

according to 36.413, for following causes eNB can release the UE context “User Inactivity”, “Radio Connection With UE Lost”, “CSG Subscription Expiry”, “CS Fallback triggered”, “Redirection towards 1xRTT”, “Inter-RAT Redirection”, “UE Not Available for PS Service”, for the requested UE-associated logical S1-connection release.

Answer 3

Another simple scenario:
1. UE is attached to eNodeB for quite some time, without uploading or downloading any data
2. Inactivity timer expires at eNB for that particular UE
3. eNodeB sends UE Context Release Request to MME for the UE