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Three flavors of CSCFs
- Proxy CSCF (P-CSCF) - Entry point to IMS for devices
- Interrogating CSCF (I-CSCF) - Entry point to IMS from other networks
- Serving CSCF (S-CSCF) - Session control entity for endpoint devices
P-CSCF (Proxy-CSCF):
- Entry point to IMS from any access network
- Performs integrity protection
- Local outbound stateful proxy for all SIP requests/responses, ensuring all signalling is sent via the home network
- Includes a Policy Decision Function (PDF) that authorizes bearer resources
I-CSCF (Interrogating-CSCF):
- First contact point in home network
- Selects assigned S-CSCF
- Performs network hiding (THIG)
S-CSCF (Serving-CSCF):
- Stateful proxy that provides session control
- Performs subscriber authentication
- Acts as SIP registrar
- Invokes the AS’ (Application Servers) based on IFC (Initial Filter Criteria)
Further Information: https://docs.google.com/fileview?id=F.8b4bc0e6-cb99-415b-8848-165f3b548ba6
