Section: 8.2.6.16 EPS NAS message container
Content: The UE operating in the single-registration mode shall include this information element as specified in subclause 5.5.1.3.2 if the UE performs mobility from S1 mode to N1 mode in 5GMM-IDLE mode. The content of this message container is the complete integrity protected TRACKING AREA UPATE REQUEST message, using EPS security context. The UE performing initial registration shall include this information element if a) the UE: 1) was previously registered in S1 mode before entering state EMM-DEREGISTERED; and 2) has received an "interworking without N26 interface not supported" indication from the network; and b) EPS security context and a valid 4G-GUTI are available. The content of this message container is the complete integrity protected ATTACH REQUEST message, using EPS security context.