The subscriber location function, or SLF is an entity within an IP multimedia subsystem

IP Multimedia Subsystem

The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem is an architectural framework for delivering Internet Protocol multimedia services. It was originally designed by the wireless standards body 3rd Generation Partnership Project , as a part of the vision for evolving mobile...

 that provides information about the home subscriber server (HSS) that is associated with a particular user profile. It is generally implemented using a database. If the home domain contains more than one HSS, I-CSCF and S-CSCF will communicate with SLF and find the appropriate HSS based on user profile. CSCF communicates with the SLF using diameter Dx interface and the application server communicates with the SLF using Dh interface.

3GPP specs

They can be downloaded from http://www.3gpp.org/specs/numbering.htm . The list below is a small selection.

• TS 23.228 IMS stage 2
• TS 24.228 Signalling flows for the IMS call control based on SIP and SDP; Stage 3
• TS 29.228 IMS Cx and Dx interfaces : signalling flows and message contents
• TS 29.229 IMS Cx and Dx interfaces based on the Diameter protocol; Protocol details