Hi,
Does anyone know if OpenSER supports T.38 for Fax over IP? Or has anyone managed to get it to work?
I did some quick tests and what I got was the destination Fax machine rang, but the fax message did not arrive. I don't think the destination fax picked up.
Setup was:
Fax (PC modem) -> IP Gateway -> OpenSER -> PSTN -> Fax machine
Is it possible the Fax tones are not being properly generated by OpenSER, and so not being recognised by the Fax machine? (For reference, the Gateway used is advertised as supporting T.38)
Max,
OpenSER does not get involved with the media stream, it just handles call setup and therefore does not generate FAX tones. It is up to the UAs to negotiate CODEC used for the call. In the example you provided of the call path, both the IP gateway and the PSTN gateway would have to support the T.38 specification. If one side does not support T.38 they will most likely use a normal voice CODEC to handle the FAX tones and FAX tones do not do well when compressed with voice CODECs.
Steve
Max Gregorian wrote:
Hi,
Does anyone know if OpenSER supports T.38 for Fax over IP? Or has anyone managed to get it to work?
I did some quick tests and what I got was the destination Fax machine rang, but the fax message did not arrive. I don't think the destination fax picked up.
Setup was:
Fax (PC modem) -> IP Gateway -> OpenSER -> PSTN -> Fax machine
Is it possible the Fax tones are not being properly generated by OpenSER, and so not being recognised by the Fax machine? (For reference, the Gateway used is advertised as supporting T.38)
Users mailing list Users@openser.org http://openser.org/cgi-bin/mailman/listinfo/users
Hi,
yes, there are a lot of problems using T.38 between two different UAs implementations (like your IP GW and your PSTN GW), but the SIP Proxy is not involved. We have achieved better fax results using "pass-through" technique (with non-compressed codec G.711), but this is valid only if your IP network has a very low packet-loss rate...
regards, Stefano
Stephen Varga ha scritto:
Max,
OpenSER does not get involved with the media stream, it just handles call setup and therefore does not generate FAX tones. It is up to the UAs to negotiate CODEC used for the call. In the example you provided of the call path, both the IP gateway and the PSTN gateway would have to support the T.38 specification. If one side does not support T.38 they will most likely use a normal voice CODEC to handle the FAX tones and FAX tones do not do well when compressed with voice CODECs.
Steve
Max Gregorian wrote:
Hi,
Does anyone know if OpenSER supports T.38 for Fax over IP? Or has anyone managed to get it to work?
I did some quick tests and what I got was the destination Fax machine rang, but the fax message did not arrive. I don't think the destination fax picked up.
Setup was:
Fax (PC modem) -> IP Gateway -> OpenSER -> PSTN -> Fax machine
Is it possible the Fax tones are not being properly generated by OpenSER, and so not being recognised by the Fax machine? (For reference, the Gateway used is advertised as supporting T.38)
Users mailing list Users@openser.org http://openser.org/cgi-bin/mailman/listinfo/users
Users mailing list Users@openser.org http://openser.org/cgi-bin/mailman/listinfo/users
Yes, i'm beginning to think the gateway isn't really doing what it's supposed to be doing.
I read about the uncompressed codec thing somewhere, but what threw me was some of the signalling I was getting back which made me wonder whether I needed any special configuration on Openser.
I guess a "488 Media Not Supported" error back after the intial INVITE-100 Trying, when using PCMU or PCMA (as suggested by the device manufacturer) probably means that T.38 (auto detection) has not been fully implemented/supported yet on that Gateway.
When I added other codecs in Fax pass-through mode, it seemed to default (negotiate) to G.729 but the destination Fax machine rings, although it does not connect because the Gateway was not responding to the reinvites - which confirms what you just said.
On Openser I saw the re-INVITE come in with T.38 in the SDP then other INVITEs but with G.729 so it seemed to be trying both audio and Fax. Quite clearly G.729 will not work and is not meant to work anyway.
I will re-test with other gateways that support T.38 (and other codecs) and see if I will have any success.
Thanks for replies.
(I guess you learn something new everyday.)
On 21/01/07, Stephen Varga varga@zbzoom.net wrote:
Max,
OpenSER does not get involved with the media stream, it just handles call setup and therefore does not generate FAX tones. It is up to the UAs to negotiate CODEC used for the call. In the example you provided of the call path, both the IP gateway and the PSTN gateway would have to support the T.38 specification. If one side does not support T.38 they will most likely use a normal voice CODEC to handle the FAX tones and FAX tones do not do well when compressed with voice CODECs.
Steve
Max Gregorian wrote:
Hi,
Does anyone know if OpenSER supports T.38 for Fax over IP? Or has anyone managed to get it to work?
I did some quick tests and what I got was the destination Fax machine rang, but the fax message did not arrive. I don't think the destination fax picked up.
Setup was:
Fax (PC modem) -> IP Gateway -> OpenSER -> PSTN -> Fax machine
Is it possible the Fax tones are not being properly generated by
OpenSER,
and so not being recognised by the Fax machine? (For reference, the Gateway used is advertised as supporting T.38)
Users mailing list Users@openser.org http://openser.org/cgi-bin/mailman/listinfo/users
-
Max Gregorian -
Stefano Capitanio -
Stephen Varga