16.5 Dedicated bearer activation in WLAN on GTP S2a

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

The dedicated bearer activation procedure for GTP based S2a is depicted in figure 16.5-1.

Figure 16.5-1: Dedicated S2a Bearer Activation 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 Info 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 assign the S2a bearer QoS, i.e., it assigns the values to the bearer level QoS parameters QCI, ARP, GBR and MBR. If this dedicated bearer is created as part of the handover from 3GPP access with GTP-based S5/S8, then the PDN GW applies the Charging ID already in use for the corresponding dedicated bearer while the UE was in 3GPP access (i.e. bearer with the same QCI and ARP as in 3GPP access). Otherwise, the PDN GW generates a new Charging ID for the dedicated bearer. The PDN GW sends a Create Bearer Request message (IMSI, EPS bearer QoS, TFT, PDN GW Address for the user plane, PDN GW TEID of the user plane, Charging Id, LBI) to the trusted WLAN access network. The Linked EPS bearer Identity (LBI) is the EPS bearer Identity of the default bearer.

Steps 3 only applies in multi-connection mode:

3. The TWAN sends WLCP message Bearer Creation Request (PDN connection ID, Bearer ID, TFT, Bearer QoS information, User plane connection ID) to the UE if UE is capable of multiple WLCP bearers per PDN connection. The user plane connection ID is assigned by the TWAG and shall be unique among all WLCP bearers for that UE. The UE stores the information on the new WLCP bearer and responds with WLCP Bearer Creation Response to the TWAN. For uplink packets that match bearer TFT according to same principles as for 3GPP access, the UE applies Bearer QoS and send packet on that bearer i.e. on the user plane connection ID (MAC address) associated with the bearer. 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.

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 selects an EPS bearer Identity, which has not yet been assigned to the UE. The TWAN then stores the EPS bearer Identity and links the dedicated bearer to the default bearer indicated by the Linked Bearer Identity (LBI). The TWAN uses the uplink packet filter (UL TFT) to determine the mapping of uplink traffic flows to the S2a bearer. The TWAN then acknowledges the S2a bearer activation to the PGW by sending a Create Bearer Response (EPS bearer Identity, TWAN Address for the user plane, TWAN TEID of the user plane) message. Additionally, the Create Bearer Response includes the current TWAN Identifier as described in clause 16.1.7 and the UE Time Zone.

6. If the dedicated bearer activation 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, 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 step 1, 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].