What are reasons for which UE will send rrc connection reconfiguration failure message at initial attach procedure?

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

RRC connection reconfiguration send during initial attach procedure for DRB establishment and SRB2 configuration.during attach procedure MME send 'Initial context setup request' msg to enb, E-RAB setup list is information element of initial context setup request.so,enb send rrc connection reconfiguration msg to ue and ask to establish the DRB according to E-RAB setup list.if ue will unable to establish a DRB according to E-RAB set up list then ue will send rrc connection reconfiguration reject msg.

one more reason may be,rrc connection reconfiguration complete msg send after AS security activation.so,if AS security is not activated due to any reason then ue will send rrc connection reconfiguration reject message.