LTE: Reestablishment Procedure for RLF

Question

To send reestablishment request UE will follow rach procedure and will be getting another C-RNTI,So EnodeB has to send reestablishment(SRB1 configuration) over a same generated C-RNTI.Then what about the context with respect to previous C-RNTI ?

Answer 1

An eNodeB maintains UE old context including old C-RNTI as parameters.
After the RLF when UE triggers RRC Re-establishment Request message to eNodeB, it verifies the received IEs with the stored one.

Though C-RNTI term seems in the context the MAC layer but RRC layer or eNodeB application maintains UE context based on the C-RNTI as well. RRC layer or eNodeB application may need to find UE Context based on the C-RNTI in case of re-establishment procedure.

Comments

Over a newly generated C-RNTI UE is able to receive RRCReestablishment with srb1 configuration and EnodeB is also able to receive complete from UE over same C-RNTI but next EnodeB is trying to send srb2 configuration over a same C-RNTI, UE is not able to receive that configuration,What can be the problem???

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But, how does eNB come to know the new C-RNTI which it has sent?

Answer 2

In case of rrc conn reestablishment, UE performs contention base rach.UE will get temp crnti in rar then UE will send rrc connection reestablishment using temp crnti. If UE gets rrc reestablishment complete then UE make temp crnti to crnti. In this scenario, eNB have UE context with old crnti. UE sends old crnti in rrc reestablishment with PCI and short mac-i so that rrc(enb)can identify the UE context. If enb rrc is able to identify the ue context Then rrc update ue context from old crnti to new crnti.