Section: 7.3.1 Forward Relocation Request
Content: A Forward Relocation Request message shall be sent from: - the source MME to the target MME over the S10 interface as part of an S1-based handover relocation procedure; - the source MME to the target SGSN, or from the source SGSN to the target MME over the S3 interface as part of an Inter RAT handover and combined hard handover and SRNS relocation procedures; - the source SGSN to the target SGSN over the S16 interface as part of an SRNS Relocation and PS handover procedures; - the source MME to the target SGSN over the S3 interface as part of an SRVCC from E-UTRAN to UTRAN or GERAN with DTM HO support procedures and from the source SGSN to the target SGSN over the S16 interface as part of SRVCC from UTRAN (HSPA) to UTRAN or GERAN with DTM HO support; - the source MME to the target AMF, or from the source AMF to the target MME over the N26 interface as part of the EPS to 5GS handover and 5GS to EPS handover procedures. - the source AMF to the target MME_SRVCC over the N26 interface as part of the 5G-SRVCC from NG-RAN to UTRAN procedure. A source MME/SGSN which supports CIoT knows whether the target MME/SGSN pool or target AMF (5GS) supports some CIoT optimisations either by using DNS procedures enhanced for DCNs or by local configuration, as specified in clause 5.9 of 3GPP TS 29.303[ Domain Name System Procedures; Stage 3 ]  [32]. A source AMF knows whether the target MME pool supports SGi Non-IP or Ethernet PDN connections either by using DNS procedures enhanced for DCNs or by local configuration, as specified in clause 5.9 and 5.13 of 3GPP TS 29.303[ Domain Name System Procedures; Stage 3 ]  [32]. The target MME/SGSN may forward the Forward Relocation Request to another MME/SGSN in the target MME/SGSN pool which is more suitable to serve the UE, based on the information received in the Forward Relocation Request message, e.g. required CIoT EPS optimisation(s) applicable to the given UE's attachment. NOTE 1: The source MME/SGSN/AMF does not need to know each individual CIoT feature the target MME/SGSN pool or target AMF (5GS) supports. The source MME/SGSN/AMF can behave as if the target MME/SGSN/AMF pool supports all CIoT features when the target MME/SGSN pool is known to support CIoT; the source MME/SGSN/AMF determines then which bearer contexts were successfully transferred as specified in sunclause 7.3.2. NOTE 2: Among the CIoT optimization features, only the support of SCEF Non-IP PDN connection and the support of SGi Non-IP PDN connection are applicable to a SGSN. NOTE 3: 5GS supports Attach without PDU session. 5GS can also support Unstructured and Ethernet PDU session types, which are assimilated to "SGi Non-IP PDN connections" over N26. Forward Relocation procedure across S10 interface (when KASME is taken into use) shall be performed according to the Rules on Concurrent Running of Security Procedures, which are specified in 3GPP TS 33.401[ 3GPP System Architecture Evolution (SAE); Security architecture ]  [12]. When the source MME/SGSN supports one or more of the CIoT optimization features as specified in clause 8.125, the source MME/SGSN shall transfer EPS bearer context(s) for SGi Non-IP PDN connections or for PDN connections to a SCEF only if the target serving node is known to support SGi Non-IP PDN connections or SCEF Non-IP PDN connections respectively, as specified in clause 5.5.1.2.1 and 5.5.2 of 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3]. Likewise, a source AMF shall transfer EPS bearer context(s) for SGi Non-IP PDN connections only if the target MME is known to support SGi Non-IP PDN connections. The source MME/SGSN/AMF shall not proceed with the Forward Relocation Request procedure if the UE does not have any EPS bearer context(s) for SGi IP or Non-IP PDN connections that can be transferred to the target serving node, i.e. under the following conditions: - If the UE is attached to the source MME/SGSN with only the PDN connection(s) of PDN type "non-IP" through the SGW and the PGW, with or without SCEF PDN connections, and the target serving node is known to not support SGi Non-IP PDN Connection (as specified in clause 4.3.17.8.3.3 of 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3] and in clause 5.3.13.8 of 3GPP TS 23 060 [35]); or - If the UE is attached to the source AMF (5GS) with only PDU session(s) of type "Ethernet" or "Unstructured", and the target MME is known to not support SGi Non-IP and Ethernet PDN Connection. The source MME shall transfer the EPS bearer context(s) for the Ethernet PDN connection only if the target serving node is known to support the Ethernet PDN connection, as specified in clause 5.3.3.1 of 3GPP TS 23.401[ General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access ]  [3]. The source MME shall not proceed with the Forward Relocation Request procedure if the UE does not have any EPS bearer context(s) that can be transferred to the target serving node, i.e. under the following conditions: - If the UE is attached to the source MME with only the PDN connection(s) of PDN type "Ethernet" through the SGW and the PGW, and the target serving node is known to not support the Ethernet PDN connection. Table 7.3.1-1 specifies the presence requirements and conditions of the IEs in the message. Table 7.3.1-1: Information Elements in a Forward Relocation Request The PDN Connection grouped IE shall be coded as depicted in Table 7.3.1-2. Table 7.3.1-2: MME/SGSN/AMF UE EPS PDN Connections within Forward Relocation Request The Bearer Context grouped IE shall be coded as depicted in Table 7.3.1-3. Table 7.3.1-3: Bearer Context within MME/SGSN/AMF UE EPS PDN Connections within Forward Relocation Request Table 7.3.1-4: Remote UE Context Connected within MME/SGSN UE EPS PDN Connections within Forward Relocation Request Table 7.3.1-5: MME UE SCEF PDN Connections within Forward Relocation Request Table 7.3.1-6: Subscribed V2X Information within Forward Relocation Request Table 7.3.1-7: PC5 QoS Parameters within Forward Relocation Request Table 7.3.1-8: PGW Change Info with Forward Relocation Request