LTE: Service Reject

·            If the SERVICE REQUEST or EXTENDED SERVICE REQUEST cannot be accepted by the network, then the network shall send SERVICE REJECT message to the UE

·           The MME shall specify an appropriate cause for rejecting the service request from the UE in the IE EMM cause

·            When the EMM cause value is #39 "CS service temporarily not available", the MME shall include a value for timer T3442 in the SERVICE REJECT message (as shown in Example1 below). The UE shall not try to send an EXTENDED SERVICE REQUEST message for MO services to the network, except for MO CS fallback for emergency calls, until timer T3442 expires

·            If the service request for MO services is rejected due to NAS Level Congestion Control, the network shall set the EMM cause value to #22 "congestion" and assign a back-off timer T3346

Reference: 3GPP TS 24.301

Example1: SERVICE REJECT message: Cause#39 “CS service temporarily not available”

Example2: SERVICE REJECT message: Cause#7 “EPS services not allowed”