7.11 S2b bearer modification with GTP on S2b

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

7.11.1 PDN GW initiated bearer modification

The PDN GW initiated bearer modification procedure for a GTP based S2b is depicted in figure 7.11.1-1. This procedure is used to update the TFT for an active default or dedicated S2b bearer, or in cases when one or several of the EPS Bearer QoS parameters QCI, GBR, MBR or ARP are modified (including the QCI or the ARP of the default S2b bearer e.g. due to the HSS Initiated Subscribed QoS Modification procedure, as described in clause 7.11.2).

Figure 7.11.1-1: S2b Bearer Modification Procedure with GTP on S2b

1. If dynamic PCC is deployed, the PCRF sends a PCC decision provision (QoS policy) message to the PDN GW. This corresponds to the initial steps of the PCRF-Initiated IP CAN Session Modification procedure or to the PCRF response in the PCEF initiated IP-CAN Session Modification procedure as defined in TS 23.203 [19], up to the point that the PDN GW requests IP CAN Bearer Signalling. If dynamic PCC is not deployed, the PDN GW may apply local QoS policy. The PCRF may also include a request to provide the User Location Info to the PDN GW.

2. The PDN GW uses this QoS policy to determine that a service data flow shall be aggregated to or removed from an active S2b bearer or that the authorized QoS of a service data flow has changed. The PDN GW generates the TFT and updates the EPS Bearer QoS to match the traffic flow aggregate. The PDN GW then sends the Update Bearer Request (EPS Bearer Identity, EPS Bearer QoS, TFT) message to the ePDG.

Steps 3 and 4 only applies if both the UE, and the ePDG support a separate IPsec SA per dedicated S2b bearer

NOTE 1: If the Update Bearer Request includes a list of EPS Bearers, as defined in TS 29.274 [57], then steps 3 and 4 shall be performed for each dedicated S2b bearer in that list.

3. If either TFTs, and/or bearer QoS information are updated, the ePDG shall trigger an IKEv2 INFORMATIONAL exchange by sending an IKEv2 INFORMATIONAL Request message and shall include the IKEv2 Notify Payload "TFT" and/or "Bearer QoS information" to convey the updated information.

4. The UE shall respond with an empty IKE v2 INFORMATIONAL Response.

5. The ePDG uses the uplink packet filter (UL TFT) to determine the mapping of traffic flows to the S2b bearer and acknowledges the S2b bearer modification to the PGW by sending an Update Bearer Response (EPS Bearer Identity, User Location Information) message.

The User Location Information shall include UE local IP address and optionally UDP or TCP source port number (if NAT is detected). It may also include WLAN Location Information (and its Age) the ePDG may have received from the 3GPP AAA server about the UE. When the PDN GW receives no WLAN Location Information from the ePDG it shall delete any such information it may have stored for the PDN connection.

NOTE 2: The UE local IP address is the source address on the outer header of the IPsec tunnel to the ePDG.

6. If the Bearer modification procedure was triggered by a PCC Decision Provision message from the PCRF, the PDN GW indicates to the PCRF whether the requested PCC decision (QoS policy) could be enforced or not by sending a Provision Ack message allowing the completion of the PCRF-Initiated IP CAN Session Modification procedure or the PCEF initiated IP-CAN Session Modification procedure as defined in TS 23.203 [19], after the completion of IP CAN bearer signalling. If requested by the PCRF, the PDN GW forwards to the PCRF following information extracted from User Location Information it may have received from the ePDG:

– WLAN location information in conjunction with the Age of this information,

– The UE local IP address and optionally UDP or TCP source port number (if NAT is detected).

NOTE 3: The exact signalling of step 1 and 4 (e.g. for local break-out) is outside the scope of this specification. This signalling and its interaction with the bearer activation procedure are to be specified in TS 23.203 [19]. Steps 1 and 4 are included here only for completeness.

7.11.2 HSS Initiated Subscribed QoS Modification

The HSS Initiated Subscribed QoS Modification for a GTP-based S2b is depicted in figure 7.11.2-1. This procedure does not apply to PDN connections for emergency services.

Figure 7.11.2-1: HSS Initiated Subscribed QoS Modification

1. The HSS updates the User Profile as specified in clause 12.2.1.

2. If the QCI and/or ARP and/or subscribed APN-AMBR has been modified and there is a related active PDN connection with the modified QoS Profile, the ePDG sends the Modify Bearer Command (EPS Bearer Identity, EPS Bearer QoS, APN AMBR) message to the PGW. The EPS Bearer Identity identifies the default bearer of the affected PDN connection. The EPS Bearer QoS contains the EPS subscribed QoS profile to be updated.

3. If PCC infrastructure is deployed, the PDN GW informs the PCRF about the updated EPS Bearer QoS. The PCRF sends new updated PCC decision to the PDN GW. This corresponds to the PCEF-initiated IP CAN Session Modification procedure as defined in TS 23.203 [19].

The PCRF may modify the APN-AMBR and the QoS parameters (QCI and ARP) associated with the default bearer in the response to the PDN GW as defined in TS 23.203 [19].

4. The PDN GW modifies the default bearer of each PDN connection corresponding to the APN for which subscribed QoS has been modified. If the subscribed ARP parameter has been changed, the PDN GW shall also modify all dedicated S2 bearers having the previously subscribed ARP value unless superseded by PCRF decision. The PDN GW then sends the Update Bearer Request (EPS Bearer Identity, EPS Bearer QoS, TFT, APN AMBR) message to the ePDG.

5. The ePDG acknowledges the bearer modification to the PDN GW by sending an Update Bearer Response (EPS Bearer Identity) message. If the bearer modification fails the PDN GW deletes the concerned S2b Bearer.

8. The PDN GW indicates to the PCRF whether the requested PCC decision was enforced or not by sending a Provision Ack message.