Media Release for SS-FS Calls

When the Oracle® Enterprise Session Border Controller routes a slow-start to fast-start call, it is possible for the same fast-start call to be routed back through the Oracle® Enterprise Session Border Controller making for a hairpin flow. If it does becomes a hairpin flow, then the Oracle® Enterprise Session Border Controller routes it to its destination as a fast-start to fast-start call. This can result in one-way media if:

The destination of the hairpin call is in the same realm as the originating slow-start to fast-start call
The realm reference in the first bullet item is configured to disable in-realm media management
The called endpoint accepts the proposed fast-start logical channels

The enhancements to the Oracle® Enterprise Session Border Controller’s behavior described in this section show how the Oracle® Enterprise Session Border Controller follows additional procedures when setting up a hairpin flow to avoid one-way media when media release occurs.

For H.323 calls, the Oracle® Enterprise Session Border Controllerestablishes media using the H.245 procedures described in the H.245 ITU-T recommendation: control protocol for multimedia communication. It also uses the Fast Connect procedure defined in the H.323 ITU-T recommendation: packet-based multimedia communication systems.

The latter ITU-T recommendation allows a calling endpoint to send a Setup message that contains a fastStart element, a sequence of OLC structures that describe the calling endpoint’s proposed forward/reverse logical channels. If the called endpoint accepts this proposal, then logical channels are established.

When the Oracle® Enterprise Session Border Controller translates a call originating in slow-start to fast-start, it uses a Fast Connect procedure in the outgoing leg by sending an outgoing Setup that includes a fastStart element with one or more OLC structures. But when the Oracle® Enterprise Session Border Controller constructs this message, it is unaware of whether the call will become hairpinned or if media release will occur. Because it does not yet have this information, the Oracle® Enterprise Session Border Controller sets the Network Address and the TSAP identifier in the OLC structures to the ingress IP address and port of a corresponding media flow allocated for media traveling between the calling and called endpoints. So if the called endpoint accepts the fastStart the Oracle® Enterprise Session Border Controller proposes, the called endpoint would send its media to the Oracle® Enterprise Session Border Controller. After acceptance, the system starts H.245 procedures on the slow-start side of the call to set up logical channels on that side. Then the Oracle® Enterprise Session Border Controller updates the IP address and port of the media flows using OLC and OLCAck messages received from the calling endpoint.

This procedure works well for endpoints that are not in the same realm, or that are in the same realm for which media management is disabled, because each endpoint must send its media through the Oracle® Enterprise Session Border Controller. When the endpoints are in the same realm and when media management is enabled, however, the Oracle® Enterprise Session Border Controller must perform additional steps for media release in slow-start to fast-start calls.

To support media release in slow-start to fast-start calls, the Oracle® Enterprise Session Border Controller performs a hold-and-resume procedure on the fast-start side. After it establishes channels on the slow-start side and if it detects media release being enabled, the Oracle® Enterprise Session Border Controller sends and empty TCS to the fast-start side to put that side on hold. Then the called endpoint closes all the logical channels it previously opened in the Fast Connect procedure and stops transmitting to them. And the Oracle® Enterprise Session Border Controller also closes it logical channels. Once the channels are closed, the Oracle® Enterprise Session Border Controller resumes the call by sending a new, restricted TCS to the fast-start side. The restricted TCS only contains the receive and transmit capabilities of the codecs types that the called endpoint accepted in the Fast Connect procedure, and it forces the called endpoint to re-open logical channels of the same codec types accepted in the Fast Connect procedure. Once it receives and OLC from the called endpoint, the Oracle® Enterprise Session Border Controller sends on OLCAck with the Network Address and TSAP identifier for the logical channel from the calling endpoint. Then the Oracle® Enterprise Session Border Controller re-opens logical channels (of the same codec types that it open in the Fast Connect procedure). If the called endpoint has not changed its Network Address and TSAP identifier for its logical channels, media is re-established after the Oracle® Enterprise Session Border Controller and the called endpoint exit the hold state. The last steps is for the Oracle® Enterprise Session Border Controller to re-sends the full TCS message from the calling to the called endpoint to inform the called endpoint of the full capabilities of the calling endpoint.