[asterisk-dev] Add attributes to Asterisk T38 invite for MAX TNT Interop?

Alex Balashov abalashov at evaristesys.com
Tue Dec 8 19:43:13 CST 2009

Can't comment on the specific issue here, but it is a widely 
acknowledged fact by other users of the TNT with whom I am acquainted 
that its T.38 support is sketchy and interoperability with other 
endpoints extremely problematic.

JR Richardson wrote:

>> JR Richardson wrote:
>>> Here is what Asterisk sends to the tnt:
>>> m=image 20228 udptl t38
>>> a=T38FaxVersion:0
>>> a=T38MaxBitRate:14400
>>> a=T38FaxRateManagement:transferredTCF
>>> a=T38FaxMaxBuffer:0
>>> a=T38FaxMaxDatagram:0
>>> a=T38FaxUdpEC:t38UDPRedundancy
>> That is broken; T38FaxMaxDatagram should never be zero. Something is
>> wrong there.
>> As far as the non-present parameters, they are all optional and it does
>> not matter whether they are present or not, unless the answerer intends
>> to support that particular option/feature. Most T.38 SDP parameters are
>> *not* negotiated, but instead are declarative and indicate what that
>> endpoint wants to receive.
>> --
>> Kevin P. Fleming
> Hmm, ok, I think I buy that as well as Steve's commnet on a=T38FaxMaxBuffer:0.
> I did enable the three questionable parameters in chan_sip.c,
> re-compiled and ran test with same results, so even though all the
> proper attribuets were sent in the invite to the TNT, the TNT did not
> respond with any udptl packets.
> Here is my testing setup:
> PSTN PRI><MAX TNT><SIP><Asterisk><NAT><AC MP203 ATA><Fax machine
> I send fax from the fax machine out to the PSTN, the t38 session is
> started from the fax ATA.
> The invite from the ATA includes:
> a=T38FaxMaxBuffer:1024
> a=T38FaxMaxDatagram:372
> Asterisk ACK the invite back to the ATA and send t38 invite to TNT:
> The invite from Asterisk includes:
> a=T38FaxMaxBuffer:0
> a=T38FaxMaxDatagram:0
> So I'm guessing Asterisk is not reading or storing the parameters
> correctly from the ATA?
> I'll poke around here for a bit, if you have any suggestions, let me know.
> Thanks.
> JR
> --
> JR Richardson
> Engineering for the Masses
> _______________________________________________
> --Bandwidth and Colocation Provided by http://www.api-digital.com--
> asterisk-dev mailing list
> To UNSUBSCRIBE or update options visit:
>    http://lists.digium.com/mailman/listinfo/asterisk-dev

Alex Balashov - Principal
Evariste Systems
Web     : http://www.evaristesys.com/
Tel     : (+1) (678) 954-0670
Direct  : (+1) (678) 954-0671

More information about the asterisk-dev mailing list