Enhanced Support for FAX Calls

The Oracle® Enterprise Session Border Controller now supports T.38 fax calls in networks containing elements that do not comply with the ITU-T H.323 Annex D recommendation for how to replace an existing audio stream with a T.38 fax stream. This support applies to signaling that requires interworking between SIP and H.323.

In the standard call model following the ITU-T recommendation, the endpoint detecting the fax tone sends an H.245 RequestMode message to its peer with a T.38 data mode. The receiving endpoint returns a RequestMode Ack by way of acknowledgement, triggering the sending endpoint to close its audio channel and open a T.38 fax channel. The receiving endpoint closes and opens the same channels on its end. T.38 fax streams flow upon the acknowledgement of all relevant channels.

However, certain endpoints close their logical channel before sending the H.245 RequestMode message for T.38, leaving the Oracle® Enterprise Session Border Controller with its audio channel still open and without having attempted to open a T.38 fax channel. To overcome this issue, the Oracle® Enterprise Session Border Controller now checks whether or not audio channels have been closed whenever it receives an H.245 RequestMode message for T.38. If it finds a closed audio channel, the Oracle® Enterprise Session Border Controller checks for the presence of a matching outgoing audio channel. A match causes the Oracle® Enterprise Session Border Controller to close the audio channel and continue with the procedure for converting to T.38 fax.