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Content for  TS 23.007  Word version:  19.0.0

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31.4 PGW triggered PDN connection restoration  31.4A Combined SGW-C/PGW-C/SMF triggered PDN connection restoration  31.4B PGW triggered PDN connection restoration towards ePDG  31.5 Inter-MME or AMF-MME mobility 

 

31.4  PGW triggered PDN connection restoration  p. 111

The PGW-C/SMF currently supporting a PDN connection, or a new PGW-C/SMF from the same PGW-C/SMF set, may trigger a PDN connection restoration to move the PDN connection to a different PGW-C/SMF as defined in this clause.
This may happen e.g. when a PGW-C/SMF is de-instantiated (scale-in operation), or when a new PGW-C/SMF from the same PGW-C/SMF set is reselected for the PDN connection upon a request from the PCF or the PGW-U/UPF and, more generally, when the PGW-C/SMF supporting a PDN connection is no longer available and a new PGW-C/SMF of the same PGW-C/SMF set needs to send signalling to the SGW or MME, before the MME has triggered a PDN connection restoration.
Reproduction of 3GPP TS 23.007, Fig. 31.4-1: PGW triggered PDN connection restoration
Figure 31.4-1: PGW triggered PDN connection restoration
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Step 1.
The PGW-C/SMF currently supporting the PDN connection or another PGW-C/SMF from the same PGW-C/SMF set determines that the PDN connection needs to be moved to a different PGW-C/SMF, e.g. during a PGW-C/SMF set scale-in operation, or e.g. due to PCF or PGW-U/UPF reselecting an alternative PGW-C/SMF from the same PGW-C/SMF set due to the PGW-C/SMF serving the PDN connection being unavailable and this triggers bearer signalling towards the MME.
Step 2 or 3.
The PGW-C/SMF currently supporting the PDN connection or the new PGW-C/SMF taking over the PDN connection may send an Update Bearer Request for the default bearer towards the SGW immediately or send Create Bearer Request (or a Update Bearer Request or a Delete Bearer Request) when the PGW-C/SMF needs to send this signalling towards the SGW and MME, including the PGW Change Info IE. The SGW shall relay transparently the PGW Change Info IE towards the MME. The PGW Change Info IE shall contain the new S5/S8 PGW IP address for control plane. The PGW-C/SMF may also include the Sender F-TEID for Control Plane IE containing a new S5/S8 PGW F-TEID for control plane. The Create/Update/Delete Bearer Response message shall be sent over S5/S8 using the S5/S8 PGW TEID for control plane received in the Sender F-TEID for Control Plane IE, if any, otherwise using the S5/S8 PGW TEID for control plane earlier assigned to the PDN connection.
Step 4.
Same as step 4 of Figure 31.3-1, with the MME including in the Create Session Request the new S5/S8 PGW-C/SMF IP address received in the PGW Change Info.
Step 5.
Same as step 5 of Figure 31.3-1.
Step 6.
Same as step 6 of Figure 31.3-1.
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31.4A  Combined SGW-C/PGW-C/SMF triggered PDN connection restoration  p. 112

A combined SGW-C/PGW-C/SMF currently supporting a PDN connection, or a new SGW-C/PGW-C/SMF from the same SGW-C/PGW-C/SMF set, may trigger a PDN connection restoration to move the PDN connection to a different SGW-C/PGW-C/SMF as defined in clause 31.4 with the following addition:
  • In step 2, the (new) SGW-C/PGW-C/SMF may include a New S11 SGW-C IP Address IE in the PGW Change Info IE to request the MME to send a Create Session Request message towards the new S11 SGW-C IP address, so to enable to reuse the existing PFCP session and avoid extra signalling towards RAN to update uplink TEID at the user plane function. The (new) SGW-C/PGW-C/SMF may also include the Sender F-TEID for Control Plane IE containing a new S11 SGW-C F-TEID for control plane.
  • In steps 3a and 3b, the Create/Update/Delete Bearer Response message shall be sent over S11 using the new S11 SGW-C TEID for control plane received in the Sender F-TEID for Control Plane IE, if any, otherwise using the S11 SGW-C TEID for control plane earlier assigned to the UE context.
  • In step 4, the MME should send the Create Session Request message towards the SGW as indicated in the New S11 SGW-C IP Address IE in the PGW Change Info IE.
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31.4B  PGW triggered PDN connection restoration towards ePDG  p. 112

The PGW-C/SMF currently supporting a PDN connection, or a new PGW-C/SMF from the same PGW-C/SMF set, may trigger a PDN connection restoration to move the PDN connection to a different PGW-C/SMF as defined in this clause.
This may happen e.g. when a PGW-C/SMF is de-instantiated (scale-in operation), or when a new PGW-C/SMF from the same PGW-C/SMF set is reselected for the PDN connection upon a request from the PCF or the PGW-U/UPF and, more generally, when the PGW-C/SMF supporting a PDN connection is no longer available and a new PGW-C/SMF of the same PGW-C/SMF set needs to send signalling to the ePDG, before the ePDG has triggered a PDN connection restoration.
Reproduction of 3GPP TS 23.007, Fig. 31.4B-1: PGW triggered PDN connection restoration towards ePDG
Figure 31.4B-1: PGW triggered PDN connection restoration towards ePDG
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Step 1.
The PGW-C/SMF currently supporting the PDN connection or another PGW-C/SMF from the same PGW-C/SMF set determines that the PDN connection needs to be moved to a different PGW-C/SMF, e.g. during a PGW-C/SMF set scale-in operation, or e.g. due to PCF or PGW-U/UPF reselecting an alternative PGW-C/SMF from the same PGW-C/SMF set due to the PGW-C/SMF serving the PDN connection being unavailable and this triggers bearer signalling towards the ePDG.
Step 2 or 3.
The PGW-C/SMF currently supporting the PDN connection or the new PGW-C/SMF taking over the PDN connection may send an Update Bearer Request for the default bearer towards the ePDG immediately or send Create Bearer Request (or a Update Bearer Request or a Delete Bearer Request) when the PGW-C/SMF needs to send this signalling towards the ePDG, including the PGW Change Info IE. The PGW Change Info IE shall contain the new S2b PGW IP address for control plane. The PGW-C/SMF may also include the Sender F-TEID for Control Plane IE containing a new S2b PGW F-TEID for control plane. The Create/Update/Delete Bearer Response message shall be sent over S2b using the new S2b PGW TEID for control plane received in the Sender F-TEID for Control Plane IE, if any, otherwise using the S2b PGW TEID for control plane earlier assigned to the PDN connection.
Step 4.
Same as step 4 of Figure 31.3A-1, with the ePDG including in the Create Session Request the new S5/S8 PGW-C/SMF IP address received in the PGW Change Info.
Step 5.
Same as step 5 of Figure 31.3A-1.
Step 6.
Same as step 6 of Figure 31.3A-1.
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31.5  Inter-MME or AMF-MME mobility  p. 113

During inter-MME mobility, the source MME shall transfer the PGW Change Info to the target MME, if available.
During an inter-MME mobility procedure, if the PDN connection is pending to be restored at the source MME, i.e. when the source MME has started the PDN connection restoration procedure (see clauses 31.4 and 31.3) for one or more PDN connections but not yet for this PDN connection, or when the source MME has sent the Create Session Request towards the new PGW-C/SMF but it has not yet received the Create Session Response message, the source MME shall set the Pending PDN connection Restoration Indication in the MME/SGSN/AMF UE EPS PDN Connections IE to "1" to request the target MME to perform the PDN connection restoration instead of contacting the PGW-C/SMF identified in the "PGW S5/S8 IP Address for Control Plane or PMIP" IE. In addition, the source MME shall include the New PGW-C/SMF IP Address and the New PGW Node Name IEs when available, e.g. when the PDN connection was requested to be moved to a specific new PGW-C/SMF during a PGW triggered PDN connection restoration procedure, or when the source MME has selected an alternative PGW-C/SMF and sent the Create Session request message to the new PGW-C/SMF to restore the PDN connection but it had not received the Create Session Response yet.
During a 5GS to EPS mobility procedure (See also clauses 4.11.1.2.1 and 4.11.1.3.2 of TS 23.502), the PGW Change Info shall be populated as part of the MME/SGSN/AMF UE EPS PDN Connections IE from the source AMF to the target MME, if available. For a Home-routed PDU session or a PDU session with an I-SMF, the (H-)SMF may pass the PGW Change Info in the EpsPdnCnxInfo to the V/I-SMF prior to the 5GS to EPS mobility procedure, to enable the V/I-SMF to include the PGW Change Info in the EpsPdnCnxContainer as part of the SmContextRetrievedData. For a non-roaming PDU session without I-SMF, the PGW-C/SMF may include the PGW Change Info directly in the EpsPdnCnxContainer.
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