21 Jan
2007
21 Jan
'07
3:15 a.m.
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)
21 Jan
21 Jan
4:54 a.m.
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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22 Jan
22 Jan
11:26 a.m.
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)
------------------------------------------------------------------------
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Users mailing list
Users(a)openser.org
http://openser.org/cgi-bin/mailman/listinfo/users
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Users(a)openser.org
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23 Jan
23 Jan
2:15 a.m.
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(a)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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3 comments
3 participants
participants (3)
-
Max Gregorian -
Stefano Capitanio -
Stephen Varga