To reduce signalling latency and achieve a better load balancing among PGW-C/SMFs in a Set, an PGW-C/SMF, MME, ePDG supporting S2b over GTPv2 and UPF may support the procedures specified in this clause. These procedures enable an SMF/PGW-C to request MME/ePDG supporting S2b over GTPv2/UPF to move PDN connections and PFCP sessions associated with certain FQ-CSIDs (when partial failure handling is supported), Group IDs or PGW-C/SMF IP Addresses, to (another) PGW-C/SMF(s) in the set, without causing massing signalling. The requirements specified in this clause shall apply in addition to the previous requirements specified in clause 31.

To optimize the resource utilization for PDN connection(s) and/or PFCP session(s), e.g. to meet different traffic requirements for different APNs/DNNs and/or DCNs/Network Slices, and also to facilitate moving a (sub)set of PDN connections/PFCP sessions among a PGW-C/SMF set, e.g. for a partial or complete PGW-C/SMF failure or a scale-in operation, a PGW-C/SMF in a PGW-C/SMF Set may:

• allocate a globally unique Group Id in the PGW Change Info IE in the Create Session Response message for a PDN connection during a PDN connection creation procedure and mobility procedure moved from 5GC without N26, or in the Modify Bearer Response for a PDN connection moved from 5GC with N26, and update the Group Id associated to the PDN connection, if necessary, in subsequent Create/Update/Delete Bearer Request messages (see also TS 29.274);
• allocate a globally unique Group Id in the PFCP Session Establishment Request message for a PFCP session during a PFCP session establishment procedure and update the Group Id, if necessary, in subsequent PFCP Session Modification Request messages (see also clause 5.22 of TS 29.244).

Alternatively, if partial failure handling is supported and deployed, the PGW-C/SMF may assign an FQ-CSID to a PDN connection and/or a PFCP session as specified in clause 23. Subsequently, e.g. when a partial or a complete failure takes place affecting all PDN connections and PFCP sessions which are sharing either the same FQ-CSID or the same Group ID (see clause 31.6.1), a PGW-C/SMF in a PGW-C/SMF Set may trigger the restoration procedure for those affected PDN connections/PFCP sessions as specified in clauses 31.6.3 and 31.6.4.

When there is a need to change the PGW-C/SMF controlling certain PDN connections, e.g. when a partial or complete PGW-C/SMF failure takes place, in order to trigger the MME(s) to re-establish the PDN connections that need to be taken over by a different PGW-C/SMF (e.g. PDN connections affected by the partial or complete failure), a PGW-C/SMF (either the one which experienced the partial failure or is shutting down, or another one in the same set) may trigger the PGW triggered PDN connection restoration procedure specified in clause 31.4 towards the MME or in clause 31.4A towards the ePDG, with the following additional requirements:

• in steps 2a or 2b, the PGW Change Info IE shall additionally include one or more PGW-C/SMF FQ-CSID(s) or one or more Group ID(s) or one or more PGW-C Control Plane IP Address(es), to request the MME/ePDG to re-establish all the PDN connections associated with the PGW-C/SMF FQ-CSID(s) or Group ID(s), or having their PGW S5/S8/ S2a/S2b F-TEID containing one of the PGW-C Control Plane IP Address(es), towards the new S5/S8/S2b PGW IP address for control plane. The PGW-C/SMF may instruct the MME/ePDG to move sessions associated with different PGW-C/SMF FQ-CSIDs, Group Ids or PGW-C/SMF Control Plane IP addresses to different PGW-C/SMF addresses.

When there is a need to change the combined SGW/PGW-C/SMF controlling certain PDN connections, e.g. when a partial or complete SGW/PGW-C/SMF failure takes place, in order to trigger the MME(s) to re-establish the PDN connections that need to be taken over by a different combined SGW/PGW-C/SMF (e.g. PDN connections affected by the partial or complete failure), a combined SGW/PGW-C/SMF (either the one which experienced the partial failure or is shutting down, or another one in the same set) may trigger the Combined SGW-C/PGW-C/SMF triggered PDN connection restoration procedure specified in clause 31.4A, with the following additional requirements:

• in steps 2a or 2b, the PGW Change Info IE shall additionally include one or more PGW-C/SMF FQ-CSID(s) or one or more Group ID(s) or one or more PGW-C Control Plane IP Address(es), to request the MME to re-establish all the PDN connections associated with the PGW-C/SMF FQ-CSID(s) or Group ID(s), or having their PGW S5/S8/ S2a/S2b F-TEID containing one of the PGW-C Control Plane IP Address(es), towards the new S5/S8 PGW IP address and the new S11 SGW-C IP Address IE for control plane. The combined SGW/PGW-C/SMF may instruct the MME to move sessions associated with different PGW-C/SMF FQ-CSIDs, Group Ids or PGW-C/SMF Control Plane IP addresses to different PGW-C/SMF addresses.

When there is a need to change the PGW-C/SMF controlling certain PFCP sessions, e.g. when a partial or complete failure takes place, the PGW-C/SMF (either the PGW-C/SMF serving the PFCP sessions or another PGW-C/SMF in the same Set taking over the control of the PFCP sessions) may send a PFCP Session Set Modification Request message to the PGW-U/UPF(s) to request the PGW-U/UPF(s) to send subsequent PFCP Session Report Request messages to the alternative PGW-C/SMF (as indicated in the Alternative SMF IP Address IE) for the PFCP sessions which are associated with the FQ-CSID(s) or Group ID(s), or which have their CP F-SEID containing one of the PGW-C/SMF IP Address(es) as shown in Figure 31.6.4-1. The PGW-C/SMF may instruct the UP function to move sessions associated with different PGW-C/SMF FQ-CSID(s), Group Ids or PGW-C/SMF IP addresses, to different PGW-C/SMF addresses.