IMS Network Element - SLF Overview

IMS Network Element - SLF Overview (for HSS) (Study Note)

Subscription Locator Function (SLF)
- To retrieve the address of the UPSF (HSS) which holds the subscription for a given user
- To query the SLF from I‑CSCF, S‑CSCF or AS
- Response to provide the HSS name towards the I‑CSCF, S‑CSCF or AS

The SLF is accessed via the Dx interface or via the Dh interface.
- The Dx interface is the standard interface between the CSCF and the SLF
- The Dh interface is the standard interface between the AS and the SLF.
- The synchronisation between the SLF and the different HSSs is an O&M issue.
- The SLF may not be required. These interfaces are not required in a single UPSF environment. An example for a single UPSF environment is a server farm architecture.

DX_SLF_Query from
- I‑CSCF receives a REGISTER request from P-SCSCF
- S‑CSCF receives a REGISTER request from I-SCSCF
- I‑CSCF receives a (UE) INVITE request from x-SCSCF
- AS queries the SLF to identify the HSS to access
- SLF determination of unknown user

Further Information: https://docs.google.com/fileview?id=F.0eaba5e5-8ed5-433e-bed4-f0a0d0e657e1