On 05/11/2012 12:23 PM, Worley, Dale R (Dale) wrote: > What I've seen in practice is that the initial INVITE offers G.711. > Once the fax handshake tone is recognized, the gateway device > re-INVITEs, changing the one m= line to type "image" with the various > "a=T38..." attributes. If the receiving device supports T.38, it > responds 200 to the re-INVITE. If the receiving device does not > support T.38, it responds 488 Not Acceptable Here, conveniently leaving > the media configuration unchanged, with G.711 available as a codec.
Yep; this is by *far* the preferred way to handle the G.711-to-T.38 transition. The only problem area I've seen with gateway devices that do this is those that offer to receive UDPTL media on the *same* port they were previously receiving G.711 media. This is RFC compliant, if the device is capable of distinguishing the two types of media it could receive on that port, but of course in practice they never are, and if they receive G.711 media after they believe they have 'switched' to T.38, hilarity ensues. -- Kevin P. Fleming Digium, Inc. | Director of Software Technologies Jabber: kflem...@digium.com | SIP: kpflem...@digium.com | Skype: kpfleming 445 Jan Davis Drive NW - Huntsville, AL 35806 - USA Check us out at www.digium.com & www.asterisk.org _______________________________________________ Sip-implementors mailing list Sip-implementors@lists.cs.columbia.edu https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
