Section: Context Request
Content: The new MME/SGSN shall send the Context Request message to the old MME/SGSN on S3/S16/S10 interface as a part of TAU/RAU procedure and UTRAN/GERAN to E-UTRAN/UTRAN (HSPA) SRVCC procedure to get the MM and EPS bearer Contexts for the UE. NOTE 1: During UTRAN/GERAN to E-UTRAN/UTRAN (HSPA) SRVCC procedure as specified in 3GPP TS 23.216[ Single Radio Voice Call Continuity (SRVCC); Stage 2 ]  [43], the GUTI, RAI IE, P-TMSI IE and P-TMSI Signature IE, are not received directly from the UE but from the MSC Server over Sv interface. The new MME shall send the Context Request message to the old AMF on N26 interface as a part of an 5GS to EPS Idle mode Mobility using N26 interface procedure, to get the MM and EPS bearer Contexts for the UE. The new AMF shall send the Context Request message to the old MME on N26 interface as a part of an EPS to 5GS Idle mode registration using N26 interface procedure, to get the MM and EPS bearer Contexts for the UE. If the sending/new node is a MME, it shall include in the Context Request message: - the GUTI IE and Complete TAU 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 and 2.10.2.1.2 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. - the RAI IE and the P-TMSI IE, which are 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 Context 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 TS 23.003[ 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, which is derived from the 5G-GUTI received from UE, and the Complete TAU Request Message IE in the Context Request message, if the AMF receives a mapped GUTI from the UE, that is indication that the old node is an MME, as specified in clause 2.10.2.2.2 of 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. If the receiving/old node is an AMF, it shall construct 5G-GUTI from the GUTI IE (see the mapping relationship between GUTI and 5G-GUTI defined in 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]), and find UE context via this 5G-GUTI. 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 TAU Request Message IE in the Context Request message. The Mapping between temporary and area identities is defined in 3GPP TS 23.003[ Numbering, addressing and identification ]  [2]. 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/AMF 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]. The AMF shall not transmit un-used authentication vectors to an MME and shall discard any un-used authentication vectors received from an MME, regardless of whether the MME and AMF pertain to the same or different serving network domains. Table -1 specifies the presence requirements and conditions of the IEs in the message. Table -1: Information Elements in a Context Request