Section: 5.4.2.7 Abnormal cases on the network side
Content: The following abnormal cases can be identified: a) Lower layer failure before the SECURITY MODE COMPLETE or SECURITY MODE REJECT message is received. The network shall abort the security mode control procedure. b) Expiry of timer T3560. The network shall, on the first expiry of the timer T3560, retransmit the SECURITY MODE COMMAND message and shall reset and start timer T3560. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3560, the procedure shall be aborted. c) Collision between security mode control procedure and registration, service request or de-registration procedure not indicating switch off. The network shall abort the security mode control procedure and proceed with the UE initiated procedure. d) Collision between security mode control procedure and other 5GMM procedures than in item c. The network shall progress both procedures. e) Lower layers indication of non-delivered NAS PDU due to handover: If the SECURITY MODE COMMAND message could not be delivered due to an intra AMF handover and the target TA is included in the TAI list, then upon successful completion of the intra AMF handover the AMF shall retransmit the SECURITY MODE COMMAND message. If a failure of the handover procedure is reported by the lower layer and the N1 signalling connection exists, the AMF shall retransmit the SECURITY MODE COMMAND message.