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OpenSIPS IMS - Community Edition - S-CSCF

The Serving Call Session Control Function (S-CSCF) handles the UE registrations, manages users authentication, SIP sessions routing and external service integration.

The S-CSCF interacts with I-CSCF for registrations and server assignement, and with P-CSCF and AS (application servers) for calls routing.

Interfaces

The S-CSCF implements the following interfaces:

  • Mw - (defined in 3GPP TS 24.229) describes the SIP messages exchanged between the S-CSCF and I-CSCF, as well as with different AS (application servers).
  • Cx - (defined in 3GPP TS 29.228) - Diameter interface between the S-CSCF and the IMS HSS. Supported Diameter commands are:
    • MAR - Multimedia-Auth-Request sent by the S-CSCF to request security information for a particular user.
    • MAA - Multimedia-Auth-Answer containing information used for digest/AKA authentication

Configuration

The S-CSCF can be configured through the environment variables defined here.

Additionally, the S-CSCF must have a dial plan provisioned in the MySQL scscf database dialplan table to handle call routing effectively. The required fields in the database are:

  • dpid - dialplan ID, needs to be set to 1
  • match_op - matching operator - 0 if a string match is used, 1 if regex
  • match_exp - the regular expression used to match the dialled number
  • repl_exp - the way the dialled number should be handled. Currently supported values:
    • USER: if the dialplan is a user, the call is routed back to a user, if registered
    • SERVICE: the call is sent to an internal service - currently not handled
    • APPLICATION: the call is sent to an Application Server - currently not handled