Section: 5.4.3 Security mode control procedure 5.4.3.1 General
Content: The purpose of the NAS security mode control procedure is to take an EPS security context into use, and initialise and start NAS signalling security between the UE and the MME with the corresponding EPS NAS keys and EPS security algorithms. Furthermore, the network may also initiate the security mode control procedure in the following cases: - in order to change the NAS security algorithms for a current EPS security context already in use; - in order to change the value of uplink NAS COUNT used in the latest SECURITY MODE COMPLETE message as described in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [19], clause 7.2.9.2; and - in order to request the UE radio capability ID from the UE. For restrictions concerning the concurrent running of a security mode control procedure with other security related procedures in the AS or inside the core network see 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [19], clause .