16.6 Network-initiated bearer modification in WLAN on GTP S2a

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

16.6.1 PDN GW Initiated Bearer Modification

The PDN GW initiated bearer modification procedure for a GTP based S2a is depicted in figure 16.6.1-1. This procedure is used to update the TFT for an active default or dedicated S2a bearer, or in cases when one or several of the S2a bearer QoS parameters QCI, GBR, MBR or ARP are modified (including the QCI or the ARP of the default S2a bearer e.g. due to the HSS Initiated Subscribed QoS Modification procedure, as described in clause 16.6.2).

Figure 16.6.1-1: PDN GW-initiated S2a Bearer Modification Procedure with GTP on S2a

1. If dynamic PCC is deployed, the PCRF sends a PCC decision provision (QoS policy) message to the PDN GW. If the Application Function (e.g. P-CSCF) requests it, the PCRF may also include a request to provide the User Location Information and/or the Time zone. 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.

2. The PDN GW uses this QoS policy to determine that a service data flow shall be aggregated to or removed from an active S2a bearer or that the authorized QoS of a service data flow has changed. The PDN GW generates the TFT and updates the S2a 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 trusted WLAN access network.

Steps 3 only applies in multi-connection mode:

3. The TWAN sends WLCP Bearer Update Request with a list of modified bearers (Bearer ID, TFT, Bearer QoS information) to the UE if multiple WLCP bearers are used between the UE and TWAG. The UE stores and uses the updated TFT or Bearer QoS information for each Bearer Id. The UE acknowledges the WLCP Bearer Update Request by sending WLCP Bearer Update Response.

4. A TWAN specific resource allocation/modification procedure may be executed in this step. The details of this step are out of the scope of 3GPP.

5. The TWAN uses the uplink packet filter (UL TFT) to determine the mapping of traffic flows to the S2a bearer and acknowledges the S2a bearer modification to the PGW by sending an Update Bearer Response (EPS bearer Identity) message. Additionally, the Update Bearer Response includes the current TWAN Identifier as described in clause 16.1.7 and the UE Time Zone.

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 in step1, the PDN GW provides the User Location Information that contains the TWAN identifier and/or UE Time Zone that will be forwarded to the Application Function as defined in TS 23.203 [19].

16.6.2 HSS Initiated Bearer Modification

The HSS Initiated Subscribed QoS Modification for a GTP-based S2a is depicted in figure 16.6.2-1.

Figure 16.6.2-1: 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 trusted WLAN access network sends the Modify Bearer Command (EPS bearer Identity, EPS bearer QoS, APN AMBR) message to the PDN GW. 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 the 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 S2a 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 TWAN.

Steps 5 only applies in multi-connection mode:

5. The TWAN sends WLCP Bearer Update Request with a list of modified bearers (Bearer ID, TFT, Bearer QoS information) to the UE if multiple WLCP bearers are used between the UE and TWAG. The UE stores and uses the updated TFT or Bearer QoS information for each Bearer Id. The UE acknowledges the WLCP Bearer Update Request by sending a WLCP Bearer Update Response.

6. A TWAN specific resource allocation/modification procedure may be executed in this step. The details of this step are out of the scope of 3GPP.

7. The TWAN 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 S2a Bearer.

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