What is I-CSCF (Interrogating call session control function)?

Interrogating call session control function empowers requests to be routed to the right Serving Call State Control Function. The I-CSCF is answerable for ahead routing of SIP messages to the appropriate Serving CSCF for a given user. It is a vital component in the IMS roaming technique. The I-CSCF cross examines the HSS to get the address of the relevant S-CSCF to process the SIP starting request.