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)
>
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