In LTE network when UE initiates re-establishment procedure?

Question

RRC Connection Request message carries "Initial UE identity" which is just 5 bytes long identifier. Why does so many information elements send within the "Re-establish UE-Identity" like C-RNTI, physcellId etc ?

Answer 1

UE initiates re-establishment procedure in following case:

1.)When it detects RLF.
2.)Upon Handover failure.
3.)Upon MobilityFromEutra failure.
4.)Upon Integrity check failure indication from layers.
5.)Upon RRC Reconfiguration failure.