V.1 General

23.2283GPPIP Multimedia Subsystem (IMS)Release 18Stage 2TS

This clause describes the main IP-Connectivity Access Network specific concepts that are used for the provisioning of IMS services over untrusted WLAN access to EPC.

Following specific considerations apply to the case of untrusted WLAN access:

– The Mobility related procedures for untrusted WLAN access to EPC are described in TS 23.402 [82].

– For untrusted WLAN access, ePDG is used to interface the access network and to control relevant PDN connectivity (over S2b) towards a P-GW.

– For untrusted WLAN access, the way the notification of the loss of IP-CAN session for a UE is triggered within an untrusted WLAN is out of scope of 3GPP specifications.

– For untrusted WLAN access, the Reporting of User location information (i.e. UE local IP address and Network Provided WLAN Location Information) in the EPS is defined in clauses 4.5.7.2.8, 7.4.3.1, 7.9.2, 7.10 and 7.11.14 of TS 23.402 [82] and the related PCC Access Network Information reporting procedure is defined in clause H.4 of TS 23.203 [54]. Information flows on how user location information can be further distributed within IMS can be found in Annex R.

– In order to fulfil regulatory requirements, IMS requires in addition to the UE local IP address, the identity of the ePDG to which the UE is connected, and the UE source port (TCP port or UDP port) used by the UE to establish the IKEv2 tunnel with the ePDG.

NOTE 1: The identity of the ePDG is the IP address used in IKEv2 tunnel.

NOTE 2: The P-CSCF has to subscribe to the IP-CAN type changes with PCRF to be notified when IP-CAN type changes to non 3GPP and the ePDG IP address (and other information) is than provided to the P-CSCF.