What is triggering point of RRC Reconfiguration in case of RRC re-establishment scenario?

Question

HI, in case of initial attach Initial context setup is the triggering point of RRC Reconfiguration. Then, What is triggering point of RRC Reconfiguration in case of RRC re-establishment scenario?

Answer 1

There are two cases when RRC reconfiguration message is exchanged between UE and eNodeB as part of execution of Re-establishment procedure.
1--> RRC connection setup procedure is completed and eNodeB has received Initial Context Setup (ICS) request. As part of Initial context setup procedure, eNodeb establishes AS security. After security activation if radio link failure is detected, UE initiates rrc re-establishment procedure. In this particular case since SRB2 and DRBs informations were not exchanged, eNodeB sends these information to UE in RRC connection re-configuration which actually should have been sent previously but sent as part of re-establishment.

2--> Another case when UE has successfully exchanged RRC connection reconfiguration and after that it detects radio link failure.
Again RRC connection reconfiguration will be exchanged as part of Re-establishment handling.

If I understood your query then above is the answer.

Comments

Hi Harshita,

Thanks for your answer and i agree with your explanation. Here my question is, MME triggers initial context setup to eNB, so that it is the triggering point to eNB to send RRC Connection Reconfiguration to UE.

So what will be triggering point to the eNB from MME in case of Re-establishment? It cant be initial context setup message from MME right ??