The Call Session Control function (CSCF) is the heart of the IMS architecture and is used to process SIP (Session Initiation Protocol) signaling. The main function of the CSCF is to provide session control for terminals and applications using the IMS network.
Session control includes:
- The secure routing of the SIP messages.
- Monitoring of the SIP sessions.
- Communicating with the policy architecture to support media authorization.
It has also the responsibility for interacting with the HSS. As below shown in Figure CSCF can play three different roles:
- Serving – Call Session Control Function (S-CSCF).
- Interrogating – Call Session Control Function (I-CSCF).
- Proxy-Call Session Control Function (P-CSCF).