Description of the illustration ''%s''sbsig_ngin

This figure shows a basic call flow of session control, when a session is initiated by a subscriber in an IN supporting SS7 network, where INAP is used. The MSC sends an INAP InitialDP message to Service Controller, which initiates a following SIP session towards the SIP application. The SIP application acts as a back-to-back user agent and sends a SIP Invite message for the second call leg, back to Service Controller. Service Controller responds by sending RequestReportBCSM and Continue messages back to the MSC. The sip application now operates between the two legs of the session, able to act in any IN event, on any of the legs. The figure shows how the SIP application is informed, through Service Controller, when the session is first answered and then disconnected.