I-CSCF in IMS Network

I-CSCF refers to "Interrogating Call Session Control Function". It selects the appropriate S-CSCF to handle the user's session. And accordingly, it routes the SIP signalling messages to the selected S-CSCF.

In addition, the I-CSCF serves as the contact point within the IMS network for all inbound SIP signalling traffic from external networks.