Section: 7.3.8 Identification Request
Content: If the UE identifies itself with temporary identity and it has changed SGSN/MME since detach in Attach procedure, the new MME/SGSN shall send an Identification Request message to the old SGSN/MME/AMF over S3, S16, S10 or N26 interface to request IMSI. A new AMF may also send an Identification Request message to the old MME over the N26 interface, during a registration procedure (see clause 4.11.5.2 of 3GPP TS 23.502[ Procedures for the 5G System (5GS) ]  [83]). Table -1 specifies the presence requirements and conditions of the IEs in the message. If the sending/new node is an MME, it shall include in the Identification Request message: - the GUTI IE and Complete Attach Request Message IE, if the GUTI or the indication of mapped or native GUTI received from UE indicates the old node is a MME, as specified in clause 2.8.2.2.2 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. - the RAI P-TMSI, which was derived from the GUTI received from UE, and the P-TMSI Signature that was received intact from the UE, if the GUTI or the indication of mapped or native GUTI indicates the old node is an SGSN as specified in clause 2.8.2.2.2 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. If the sending/new node is an SGSN, it shall include RAI IE, P-TMSI IE and P-TMSI Signature IE in the Identification Request message. If the receiving/old node is an MME, it shall construct GUTI according to the RAI IE, P-TMSI IE and P-TMSI Signature IE (see the mapping relationship between RAI, P-TMSI, P-TMSI signature and GUTI defined in 3GPP TS23.003[ Numbering, addressing and identification ] [2]), and find UE context via this GUTI. If the sending/new node is an AMF, it shall include the GUTI IE and Complete Attach Request Message IE in the Identification Request message. The AMF shall construct the GUTI IE from the old 5G-GUTI received from the UE (mapped from the EPS GUTI by the UE), as specified in clause 2.10.2.2.3 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. The new MME differentiates the type of the old node as specified in clause 2.8.2.2.2 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. If the old node is an SGSN, the GUTI shall be mapped to RAI and P-TMSI by the new MME; if the old node is a MME, the new MME include GUTI IE and Complete Attach Request Message IE in the Identification Request message. The Mapping between temporary and area identities is defined in 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. The GUTI IE shall not coexist with any of the RAI IE, P-TMSI IE and P-TMSI Signature IE in an Identification Request message. If this occurs, the receiving node shall return a corresponding cause value in the response message. The Target PLMN ID IE shall be used in old SGSN/MME in order to decide whether un-used authentication vectors to be distributed to new SGSN/MME or not. Distribution and use of authentication vectors between different serving network domains are specified in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [12]. If the receiving/old node is an AMF, it shall construct the 5G-GUTI from the GUTI IE (see the mapping relationship between GUTI and 5G-GUTI defined in clause 2.10 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]), and find UE context via this 5G-GUTI. Table -1: Information Elements in an Identification Request