Edge Proxy (EP) resides at the edge of the network in an access Point of Presence (POP). EP serves as the access gateway for Session Initiation Protocol (SIP) clients, and as the egress gateway for messages that leave the network toward these clients. EP maps to the Proxy Call Session Control Function (P-CSCF) of the IP Multimedia Subsystem (IMS) that the Third Generation Partnership Program (3GPP) defines.
EP supports the authentication feature. To authenticate SIP requests from client handsets, EP uses digest authentication as defined in the SIP specification. EP receives the authentication credentials from the Direct Attached Storage (DAS). EP uses Common Object Request Broker Architecture (CORBA) as transport to access the TimesTen Data Authority Server (TTDAS) through the DOS Open Application Programming Interface (DOAPI).
EP sends back a 407 Proxy Authorization Required message that contains a nonce to challenge client requests. The client then uses a cryptographic hash to compute a response. Upon successful authentication, the EP inserts the PAID header into the SIP message and sends the message to the Service Engine (SE).