OpenSIPS IMS - Community Edition - I-CSCF

The Interrogating - Call Session Control Function (I-CSCF) handles SIP signaling for session control and facilitates secure interactions between the home network and external networks.

The I-CSCF receives messages from the P-CSCF and determines the assigned S-CSCF for a particular user by querying the HSS.

Interfaces

The I-CSCF implements the following interfaces:

• Mw - (defined in 3GPP TS 24.229) describes the SIP messages exchanged internally between the CSCF sub-components - in particular, the I-CSCF uses the SIP Mw interface to communicate with P-CSCF and S-CSCF.
• Cx - (defined in 3GPP TS 29.228) - Diameter interface between the I-CSCF and the IMS HSS. Supported Diameter commands are:
  • UAR - User-Authorization-Request sent to HSS in order to request the authorization of the registration of a multimedia user alocate resources
  • UAA - User-Authorization-Answer received from HSS containing the S-CSCF instance that should handle the multimedia user

Configuration

The I-CSCF can be configured through the environment variables defined here.