Serving CSCF

Serving CSCF

The S-CSCF implementation also communicates with the HSS using Diameter (over the Cx interface) to retrieve authentication vectors, update registration information and download the user profiles as specified in [1]. The S-CSCF can apply the user profile based initial Filter Criteria (iFC) to enforce specific SIP routing rules. It implements support for carrying out the IMS Digest AKA version 1 [2]. Rather than generating authentication vectors it relies on the HSS for this task and compares these values to the ones calculated in the UE.

For fast response times with minimal locking, the registrar of the S-CSCF has a complex structure based on hash-tables. The information that is required to relate a user identity to a physical UE is stored here and used further on for call routing. It also accepts subscriptions to registration state events and notifies the subscribers about changes in the registrar.

Features of the Open Source IMS S-CSCF :

• full Cx interface support (MAR, SAR, PPR, RTR)
• Authentication through AKAv1-MD5, AKAv2-MD5 and MD5
• Service-Route header support
• Path header support
• P-Asserted-Identity header support
• Visited-Network-ID header support
• Download of Service-Profile from HSS
• Initial Filter Criteria triggering
• ISC interface routing towards Application Servers
• "reg" event server with access restrictions
• Dialog statefulness