What happens if eNB didnt receive rrc connection reconfiguration complete message from UE?

Question

During attach procedure, UE sends "Attach Request" along with "RRC Connection Setup Complete", eNodeB sends "Attach Accept" along with "RRC Connection Reconfiguration then why UE does not send "Attach Complete" along with "RRC Connection Reconfiguration Complete" message ? What could be the reason for defining the messages so ?

Answer 1

As per my understanding of specifications, UE runs a timer "T304" when it receives RRC connection reconfiguration (due to mobility). At expiry of timer, UE starts RRC Re-establishment procedure. But in other cases while establishing/modifying/releasing bearer(s) I am not sure that is there any re-transmission of rrc connection reconfiguration happens or not.

Answer 2

there is internal timer at eNB side, Reconfiguration complete timeout.
In case of eNB not receiving response(Reconfiguration Complete) within the timer, It will detect Radio link fail for that UE and inform the same to upper layers to start another timer regarding releasing UE contexts.

Also T304 mentioned in above comment is monitored by UE not eNB, after completion of T304 timer, UE it self declares RLF and starts reestablishment procedure.