Section: 5.4.3.7 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 T3460 The network shall, on the first expiry of the timer T3460, retransmit the SECURITY MODE COMMAND message and shall reset and start timer T3460. This retransmission is repeated four times, i.e. on the fifth expiry of timer T3460, the procedure shall be aborted. NOTE: If the SECURITY MODE COMMAND message was sent to create a mapped EPS security context during inter-system change from A/Gb mode to S1 mode or Iu mode to S1 mode, then the network does not generate new values for the nonceMME and the nonceUE, but includes the same values in the SECURITY MODE COMMAND message (see the clause 7.2.4.4 in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [19]). c) Collision between security mode control procedure and attach, service request, tracking area updating procedure or detach 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 EMM 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 MME handover and the target TA is included in the TAI list, then upon successful completion of the intra MME handover the MME shall retransmit the SECURITY MODE COMMAND message. If a failure of the handover procedure is reported by the lower layer and the S1 signalling connection exists, the MME shall retransmit the SECURITY MODE COMMAND message.