CSCF (Call Session Control Function)
General term for a functional entity within a IMS core network that can act as Proxy CSCF (P-CSCF), Serving CSCF (S-CSCF), or Emergency CSCF (E-CSCF).
E-CSCF (Emergency Call Session Control Function)
The E-CSCF is the entity in the IMS core network that handles certain aspects of emergency sessions, e.g. routing of emergency requests to the correct emergency center or PSAP.
P-CSCF (Proxy Call Session Control Function)
The P-CSCF is the first contact point for the user equipment (UE) within the IMS core network. For an IMS-based emergency call, the P-CSCF detects the emergency call and forwards it to an E-CSCF.
The S-CSCF is the entity in the IMS core network that handles the session states.