[asterisk-users] Digium FFA + Gafachi T38 outgoing issues

[Kevin P. Fleming]

On 10/08/2011 05:21 AM, Steve Underwood wrote:
> On 10/08/2011 04:04 AM, Kevin P. Fleming wrote:
>> On 10/07/2011 02:20 PM, James Sharp wrote:
>>> On 10/07/2011 12:27 AM, Nasir Iqbal wrote:
>>>> Check firewall and NAT settings!
>>>>
>>>> Monitoring sip and media flow from asterisk cli can help, use "sip set
>>>> debug on", "rtp set debug on" and "udptl set debug on"
>>>>
>>>
>>> No NAT involved and I shut off IPTables. Still no luck. Debug shows the
>>> SIP invite, RTP frames going in & out, the SIP reinvite, and then UDPTL
>>> frames coming in until timeout.
>>>
>>> See the entire transaction at http://pastebin.ca/2087758
>>
>> Thanks for that; it helps.
>>
>> First, we can see that Gafachi's T.38 implementation still has some
>> breakage in it (although the problems are ones that Asterisk has been
>> taught to deal with). In its 200 OK to the T.38 re-INVITE, it has
>> "a=T38FaxRateManagement:transferredTCFlocalTCF"; this is not valid
>> (the valid values for this are 'transferredTCF' and 'localTCF'). In
>> addition, even though Asterisk sent "a=T38FaxUdpEC:t38UDPRedundancy",
>> Gafachi replied with "a=T38FaxUdpEC:t38UDPFEC". For T.38 version 0
>> (which is in use here), the only valid response was either what
>> Asterisk sent, or no T38FaxUdpEC value at all.
> t38UDPFEC is perfectly valid for version 0 of T.38. It works badly, so
> it makes no sense to use it, but it is valid.

Yes, it's a valid option in an offer, but it's not a valid option in 
answer unless that's the value that was in the offer; in all T.38 
recommendations until the most recent, the answer must include either 
the same T38FaxUdpEC value as the offer did, or no value at all. The 
most recent version allows the answer to include a different value from 
the offer, because it was always reasonable, just not allowed by the 
recommendation.

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