Section: 5.3.10.4.2 NAS Security Mode Command procedure
Content: The MME uses the NAS Security Mode Command (SMC) procedure to establish a NAS security association between the UE and MME, in order to protect the further NAS signalling messages. This procedure is also used to make changes in the security association, e.g. to change the security algorithm. Figure 5.3.10.4.2-1: NAS Security Mode Command Procedure 1. The MME sends NAS Security Mode Command (Selected NAS algorithms, eKSI, ME Identity request, UE Security Capability) message to the UE. ME identity request may be included when NAS SMC is combined with ME Identity retrieval (see clause 5.3.10.5). 2. The UE responds NAS with Security Mode Complete (NAS-MAC, ME Identity) message. The UE includes the ME Identity if it was requested in step 1. NOTE: The NAS Security Mode Command procedure is typically executed as part of the Attach procedure (see clause 5.3.2.1) in advance of, or in combination with, executing the ME Identity Check procedure (see clause 5.3.10.5) and in the TAU procedure (see clauses 5.3.3.1 and 5.3.3.2). More details of the procedure are described in TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [41].