[asterisk-users] Asterisk 1.6.1.11 Fax

[Cyprus VoIP]

>> 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.
> 

Hi Kevin,

thank you for your response.

Before posting my question, I analyzed the entire SIP negotiation and it 
was fine. The problem began in the T.38 negotiation itself, after the 
Asterisk's reINVITE. I don't have the old calls traces anymore, but I'll 
make new ones tomorrow and post them here.

Regarding the MaxBitRate, is it possible to increase it to 14400 or is 
9600 the max allowed?

Regards,

Andreas