H.323 Fast Start to SIP

In the diagram below, an H.323 endpoint (a GK or GW) initiates a session by sending a Setup request destined for a SIP endpoint (such as a UA or a SIP Gateway). Between these entities, the Oracle® Enterprise Session Border Controller is positioned to perform interworking. The H.323 endpoint has completed the RAS process prior to sending the SETUP message.

The Oracle® Enterprise Session Border Controller receives the Setup message and then sends a SIP INVITE on the SIP side. The SIP endpoint responds with a 100 Trying; the Oracle® Enterprise Session Border Controller does not resend this message on the H.323 side. Next, the SIP endpoint issues a 180 Ringing message, which the Oracle® Enterprise Session Border Controller reissues to the H.323 endpoint as an Alerting message. The SIP endpoint then sends a 200 OK, retransmitted by the Oracle® Enterprise Session Border Controller as a Connect message that includes an OLC. Once the Oracle® Enterprise Session Border Controller sends an ACK to the SIP endpoint, RTP flows between the endpoints.