[asterisk-users] Asterisk 1.6.1.11 Fax

[Kevin P. Fleming]

Cyprus VoIP wrote:

> We're trying to receive faxes on the Asterisk server, but for the time 
> being T.38 negotiation fails.
> 
> The SDP that the Asterisk reINVITE sends contains these lines:
> ----------------------
> m=image 4968 udptl t38
> a=T38FaxVersion:0
> a=T38MaxBitRate:9600
> a=T38FaxFillBitRemoval
> a=T38FaxTranscodingMMR
> a=T38FaxTranscodingJBIG
> a=T38FaxRateManagement:transferredTCF
> a=T38FaxMaxDatagram:1400
> a=T38FaxUdpEC:t38UDPRedundancy
> ----------------------
> 
> The MaxDatagram and MaxBitRate are definitely not what they should be, 
> and maybe other parameters are also wrong. I would like to have 400 and 
> 14400 respectively.

There is no point in having a smaller T38FaxMaxDatagram value;
Asterisk's FAX applications can handle larger packets than 400 bytes, so
 Asterisk is telling the sending endpoint that it can send them if it
wishes to do so.

As far as the T38MaxBitRate, that is only a suggestion in the
negotiation, and rarely has any effect on the negotiation process or on
the resulting FAX transmission.

As before, you've provided only a very small amount of information, not
enough to be able to help you determine what is wrong. Nothing in that
SDP offer indicate any problems of any kind. In addition, you haven't
indicated which FAX applications in Asterisk you are using (app_fax or
res_fax), which could also have an impact on the T.38 negotiation process.

If you'd like people to be able to help you debug problems, you need to
provide enough information for them to do so; most of us are not
clairvoyant, telepathic or omniscient. In any situation where T.38
negotiation is failing, that means a 'sip set debug on' log trace that
shows the entire T.38 negotiation transaction, ideally with 'core set
debug 10' and 'core set verbose 10' as well so we can see all the
actions that Asterisk and the FAX application took during the
negotiation process.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kpfleming at digium.com
Check us out at www.digium.com & www.asterisk.org