Serving Call State Control Function (S-CSCF) performs the following functions:
performs the session control services for the terminal. Within an operator’s network, different S-CSCFs may have different functionality.
maintains session state and has the session control for the registered endpoint's sessions,
acts like a Registrar defined in the RFC2543, i.e. it accepts Register requests and makes its information available through the location server (e.g. HSS),
may also behave as a proxy or as a user agent as defined by RFC 2543,
interacts with services platforms for the support of services,
obtain the address of the destination I-CSCF based on the dialed number or SIP URL,
on behalf of a UE forward the SIP requests or responses to a P-CSCF or an I-CSCF if an I-CSCF is used in the path in the roaming case,
generates charging information,
security issues are currently open in standardization.