In addition to the architecture described in clause 5.1 above, the P-CSCF may have an interface to an LRF which may contain a CLF as described below in Figure C.1. For more information on the CLF refer to ETSI ES 282 004 [18].

For fixed broadband access, the UE may know its own network location or geographical location. If the UE knows its location, it shall insert the location information in the SIP INVITE request when establishing the emergency IMS session. As an alternative, if the UE is not able to determine its own location, the UE should try to request its location from the access network, if the UE supports such functionality. The access network may know the location of the access point where the UE is connected to. In this case, the UE should request the location information from the access network according to clause 7.6. The UE shall insert the location information received as a response to the location query, if any, in the emergency SIP INVITE request. This location information may be network based, e.g. line identification, or geographical location information. If the UE does not know its location and is unable to obtain its location from the access network, the UE should have a means to indicate in the emergency SIP INVITE that its location is unknown. If the UE does not provide location information, the P-CSCF may request location information from the LRF as described in clause 7.6 and insert the location information in the received INVITE request. The IMS network may also request location information from the LRF in the case that verification of the location information provided by the UE is required. After such verification, the IMS network may insert the location information received from the LRF or override the location information received from the UE before routing the request to the PSAP. Alternatively, subject to operator policy, the S-CSCF may receive from the HSS a reference location of the user at registration and insert it in the INVITE request, when network-provided location information is not already present. The reference location (e.g. line identification) is determined by the operator as part of the user profile.

In addition to clause 7.6, the following applies for a fixed broadband access:

• When the UE is requesting to retrieve the location information from IP-CAN, the UE may use the DHCP option for coordinate-based geographic location of the client as specified by IETF in RFC 3825 and the DHCP option that allows hosts to learn their civic location via DHCP, as specified in RFC 4676. This DHCP option shall not be used by an UE on an IP-CAN using 3GPP RAT.
• The line identifier used by the UE with fixed broadband access may be authenticated by the IMS core.