What is it?
The Location Retrieval Function (LRF) is responsible for retrieving the location information of a UE that has initiated an IMS emergency session. This allows emergency responders, for example, to know exactly where you are before they even ask for your emergency!
This function could also be used to retrieve location information for location-based advertisements.
How Does It Work?
When an emergency session is initiated:
1. The P-CSCF identifies the emergency call and forwards the initial emergency INVITE requests to an E-CSCF in the same IMS domain*.
2. The E-CSCF will then look for the appropriate Public Safety Answering Point (PSAP), for example, a police call center, and forward the SIP emergency INVITE to establish a connection.
*During this time, the LRF has already received location information from the E-CSCF