In the following diagram below, a SIP endpoint (such as a UA or a SIP Gateway) initiates a session by sending an INVITE message destined for an H.323 endpoint (a GK or GW). Between these entities, the system is positioned to perform interworking. The Oracle Communications Session Border Controller recognizes that the INVITE message is destined for an H.323 device, and returns a 100 Trying message to the SIP endpoint as it attempts to negotiate the H.323 side of the session. This negotiation starts when the Oracle Communications Session Border Controller initiates the RAS process with the H.323 endpoint by sending either an ARQ or an LRQ, allowing the Oracle Communications Session Border Controller to determine if the H.323 endpoint will accept the session.

Once the H.323 endpoint responds with an ACF or LCF, the Oracle Communications Session Border Controller reissues the SIP INVITE on the H.323 side as an H.225 Setup, which is sent with the OLC. Then the H.323 endpoint responds with Proceeding and Alerting messages (which correspond respectively to SIP 183 Progress and 180 Ringing messages). At that point, the H.323 endpoint sends a Connect message that includes the OpenLogicalChannel message (OLC), announcing the logical channel for media flows has been set up. The Oracle Communications Session Border Controller converts the H.323 OLC to a SIP 200 OK. After receiving the 200 OK, the SIP endpoint sends an ACK, confirming that the session has been established. Because there is no H.323 equivalent for the SIP ACK, the Oracle Communications Session Border Controller does not generate a corresponding message on the H.323 side. At this point, the session is fully established and RTP flows between the endpoints.

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 Communications 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 Communications 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 Communications 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 Communications 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 Communications Session Border Controller as a Connect message that includes an OLC. Once the Oracle Communications Session Border Controller sends an ACK to the SIP endpoint, RTP flows between the endpoints.

In the following diagram below, a SIP endpoint (such as a UA or a SIP Gateway) initiates a session by sending an INVITE request destined for an H.323 Slow Start endpoint (a GK or GW). Between these entities, the Oracle Communications Session Border Controller is positioned to perform interworking.

The call flow for this type of translation works fundamentally the same way that the translation does for SIP to Fast Start H.323, with the exception of how the media is established. Media is negotiated through the exchange of TCS and OLC messages after the H.323 Connect and SIP 180 Ringing messages have been sent. The first TCS message is sent from the Oracle Communications Session Border Controller to the H.323 endpoint, and it contains information about media capabilities in SDP. The H.323 endpoint accepts and acknowledges this information with a TCS Ack message. Then the H.323 endpoint sends a second TCS, carrying information about the Gateway’s capabilities, that the Oracle Communications Session Border Controller accepts and acknowledges. The H.323 endpoint and the Oracle Communications Session Border Controller then exchange OLC and OLC Ack messages that establish the operating mode and Gateway capability. Finally, the Oracle Communications Session Border Controller completes the 200 OK/ACK sequence on the SIP side, and RTP flows between the two endpoints.

In the following diagram below, an H.323 endpoint (GW or GK) 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 Communications Session Border Controller is positioned to perform interworking. The H.323 endpoint has completed the RAS process prior to sending the SETUP message.

The call flow for this type of translation works fundamentally the same way that the translation does for H.323 Fast Start to SIP, with the exception of how the media is established. When the Oracle Communications Session Border Controller receives an H.323 message destined for a SIP endpoint, it sends a SIP INVITE message that includes default SDP to that SIP endpoint. The default SDP is constructed using information in the media profiles listed for the IWF configuration; if necessary, this media information is amended later in the sequence. Once the call is set up, the Oracle Communications Session Border Controller negotiates media with the H.323 endpoint through a series of TCS/TCS Ack and OLC/OLC Ack messages that establish the operating mode and Gateway capability.

When the Oracle Communications Session Border Controller completes media negotiation with the H.323 endpoint, it issues a re-INVITE to the SIP endpoint that contains the updated information needed for media transmission. In response, the SIP endpoint sends a 200 OK message that the Oracle Communications Session Border Controller answers with an ACK. Then RTP can flow between the two endpoints.

When a call that requires the IWF terminates from the H.323 side, the Oracle Communications Session Border Controller uses the mapping scheme in the following table to determine the appropriate SIP status.

When a call that requires the IWF terminates from the H.323 side during RAS and generates an error, the Oracle Communications Session Border Controller uses the mapping scheme in the following table to determine the appropriate SIP status.

When a call that requires the IWF terminates from the SIP side, the Oracle Communications Session Border Controller uses the mapping scheme in the following table to determine the appropriate H.323 Release Complete Reason code.

When a call that requires the IWF terminates from the H.323 side and no H.323 Release Complete Reason is specified, the Oracle Communications Session Border Controller maps the Q.850 cause to an H.323 Release Complete Reason using the mapping scheme in the following table. This new H.323 status is then mapped to a SIP status as described in the IWF Termination from SIP table.

The Oracle Communications Session Border Controller uses the following mapping scheme when converting media specifications between H.245 (used in H.323) and SDP (used in SIP).

Media coming into the Oracle Communications Session Border Controller one way exits the system in the corresponding way as specified in the following table. For example, media coming into the Oracle Communications Session Border Controller as H.245 type g711Ulaw64k exits the system as media type PCMU.