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

[JR Richardson]

Hi All,

I've been aggressively testing the latest asterisk releases and the new t38
changes.  Mainly focusing on interop with Lucent MAX TNT.  I have the latest
ver 14.0.3 code on a test shelf.  Testing with Asterisk 1.6.1.10, 1.6.0.10.
1.4.27.1, 1.6.1 trunk. No version can establish a t38 session.  I found
something interesting in the TNT docs about the t38 attributes, it is
looking for some specific parameters that are not sent in the invite from
asterisk to the tnt.

Here is what the tnt send to asterisk:
m=image 32730 udptl t38
a=T38FaxMaxDatagram:316
a=T38FaxMaxBuffer:72
a=T38FaxRateManagement:transferredTCF
a=T38FaxUdpEC:t38UDPRedundancy
a=T38FaxVersion:0
a=T38FaxTranscodingJBIG:0
a=T38FaxTranscodingMMR:0
a=T38FaxFillBitRemoval:0
a=T38MaxBitRate:14400

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

The t38 udptl packets never come from the tnt to asterisk even though the
call does switch in the tnt to another dsp supporting t38, like it is trying
to setup a session but does not complete.  So here are the attributes the
tnt is looking for:

a=T38FaxMaxDatagram:316                         ;this value is present but
ignored
a=T38FaxMaxBuffer:72                                ;this value is present
but ignored
a=T38FaxRateManagement:transferredTCF   ;this is present and correct
a=T38FaxUdpEC:t38UDPRedundancy          ;this is present and correct, must
be redundancy, fec is rejected
a=T38FaxVersion:0                                     ;this is present and
correct, any other value is rejected
a=T38FaxTranscodingJBIG:0                        ;this is correct but
missing from asterisk invite
a=T38FaxTranscodingMMR:0                        ;this is correct but missing
from asterisk invite
a=T38FaxFillBitRemoval:0                            ;this is correct but
missing from asterisk invite
a=T38MaxBitRate:14400                              ;this is present and
correct

So i'm guessing the TNT is not setting up the udptl session because it is
not getting these parameters:
a=T38FaxTranscodingJBIG:0                        ;this is correct but
missing from asterisk invite
a=T38FaxTranscodingMMR:0                        ;this is correct but missing
from asterisk invite
a=T38FaxFillBitRemoval:0                            ;this is correct but
missing from asterisk invite
the TNT docs are explicit, these values must in the invite and set to '0'
for t38 to work.

Is there an easy mechanism for me to add these attributed to Asterisk t38
invite or can someone generate a quick patch that adds these in the t38
stack for testing?

Thanks.

JR
-- 
JR Richardson
Engineering for the Masses
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