7.10 Dedicated S2b bearer activation with GTP on S2b

23.4023GPPArchitecture enhancements for non-3GPP accessesRelease 18TS

The dedicated bearer activation procedure for GTP based S2b is depicted in figure 7.10-1.

Figure 7.10-1: Dedicated S2b Bearer Activation 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 assign the EPS 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 PGW 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 ePDG. The Linked EPS Bearer Identity (LBI) is the EPS Bearer Identity of the default bearer.

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 Create 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. The ePDG shall trigger an IKEv2 CREATE_CHILD_SA message, as defined in RFC 7296 [9]. The CREATE_CHILD_SA message shall contain an IKEv2 Notify Payload "TFT" that is a copy of the TFTs received over S2b in step 1. The CREATE_CHILD_SA message shall also contain an IKEv2 Notify Payload "Bearer QoS information".

NOTE 2: One CREATE_CHILD SA exchange results in IPsec SAs for both directions.

4. The UE shall respond with CREATE-CHILD_SA-Response, and shall maintain a binding between the IPsec SA and the applicable TFT and bearer QoS information.

5. The ePDG selects an EPS Bearer Identity, which has not yet been assigned to the UE. The ePDG then stores the EPS Bearer Identity and links the dedicated bearer to the default bearer indicated by the Linked EPS Bearer Identity (LBI). The ePDG uses the uplink packet filter (UL TFT) and/or IPsec SA where applicable, to determine the mapping of uplink traffic flows to the S2b bearer. The ePDG then acknowledges the S2b bearer activation to the PGW by sending a Create Bearer Response (EPS Bearer Identity, ePDG Address for the user plane, ePDG TEID of the user plane, User Location Information) message.

If the ePDG has established a IPsec SA association with the UE for a dedicated S2b bearer, it shall maintain a binding between the IPsec SA and the EPS bearer ID.

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

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, 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 4: 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 dedicated bearer activation procedure are to be specified in TS 23.203 [19]. Steps 1 and 4 are included here only for completeness.

NOTE 5: This procedure does not aim at providing QoS differentiation over untrustred non 3GPP access networks. It is used to establish the same number of bearers on S2b that were or will be established when the UE hands over from/to a 3GPP access.