An I-CSCF (Interrogating-CSCF) is a SIP proxy, which provides a service locator function. Its major functions include:
- Registration: Assigning a S-CSCF to a user performing SIP registration
- Session Flows: Routing a SIP request received from another network to the S-CSCF, or routing intra-domain SIP requests between users on different S-CSCFs.
- Charging and Resource utilization
Acts as a Topology Hiding Internetwork Gateway: A case of I-CSCF, which hides the configuration, capacity, and topology of the network from the outside. The P-CSCF forwards the SIP messages received from the User Equipment to the Interrogating Call Session Control Function (I-CSCF) and/or the Serving Call Session Control Function (S-CSCF), depending on the type of message and procedure. The I-CSCF provides a contact point within an operator's network allowing subscribers of that network operator, and roaming subscribers, to register. Once registered, the S-CSCF maintains session state for all IMS services.
OSIMS ICSCF component is based on Open IMS Core.