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.
• 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 and the related PCC Access Network Information reporting procedure is defined in clause H.4 of TS 23.203. 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.

A UE accessing IMS via untrusted WLAN shall support the following:

• If available, provide the identity of the WLAN AP the UE is currently associated with, and used for IMS signalling at IMS registration, IMS emergency registration, IMS session initiation, SMS over IP, and in any procedure defined in TS 24.229, where access network information is provided.
• If available, provide geographical location coordinates during IMS emergency session setup.
• Provide the cell information (cell-ID) for the most recent seen cell at IMS registration, IMS emergency registration, IMS emergency session initiation, and in any procedure defined in TS 24.229 where access network information is provided. The cell-ID access information shall include additional information describing when the information about the cell-ID was collected and that can be used to calculate the "age" of the information. The information about the cell-ID shall be included in an appropriate field of the SIP request that is distinguished from the information about the access network currently used to transport SIP signalling (i.e. Untrusted WLAN).