[asterisk-users] T38 state values

David Cunningham
Wed, 23 Mar 2022 22:06:58 -0000

Hi Joshua,

Thanks very much for that information. I guess in that case the 'not
working' scenario has a T38 state of 'T38 was negotiated and is
active',
which doesn't help us find the problem much.

In this case the T38 is passthrough, and in the not working scenario in a
PCAP we see:
PSTN -> Asterisk: 't30ind: cng' packet is received
Asterisk -> ATA: 't30ind: cng' is not sent

Would you have any suggestion on what could prevent the 't30ind: cng'
being
passed through? The Asterisk T38 settings in sip.conf are:

t38pt_udptl = yes
t38_udptl = yes
t38pt_rtp = no
t38pt_tcp = no

Thanks again.


On Fri, 18 Mar 2022 at 21:59, Joshua C. Colp <jcolp at sangoma.com> wrote:

> On Fri, Mar 18, 2022 at 12:27 AM David Cunningham <
> dcunningham at voisonics.com> wrote:
>
>> Hello,
>>
>> We have a problem where one fax ATA connected to Asterisk works, and
>> another ATA with the same model and firmware does not. Both are
configured
>> to use T38.
>>
>> Basically the call comes in to Asterisk which then does a Dial to the
ATA
>> that's registered via SIP, and once that's set up then
there's a re-INVITE
>> from the ATA to switch to T38. The ATA sends a "t30ind:
no-signal" after
>> the 200 OK, and both work up until this point. But then in the working
>> scenario Asterisk sends a "t30ind: cng" back to the ATA, and
in the
>> not-working scenario Asterisk does not send any T38 data at all.
>>
>> We've noticed that in the working scenario when the 200 OK is sent
from
>> Asterisk to the ATA, Asterisk logs:
>>
>> [Mar 17 16:07:50] DEBUG[53838][C-0013e292] chan_sip.c: T38 state
changed
>> to 2 on channel SIP/xx.xx.246.70:5060-0030dde1
>> [Mar 17 16:07:50] DEBUG[6862][C-0013e292] chan_sip.c: T38 state changed
>> to 1 on channel SIP/product-local-bw70-0030ddd9
>>
>> Whereas in the not working scenario it logs:
>>
>> [Mar 17 16:23:05] DEBUG[53838][C-0013e39a] chan_sip.c: T38 state
changed
>> to 3 on channel SIP/product-local-bw70-0030e0a0
>> [Mar 17 16:23:05] DEBUG[24973][C-0013e39a] chan_sip.c: T38 state
changed
>> to 3 on channel SIP/xx.xx.246.70:5060-0030e0a1
>>
>> Notice the difference in the "T38 state changed to" values.
Does anyone
>> know what a value of 1, 2, or 3 means? I tried to find out from the
>> Asterisk source code but it wasn't obvious.
>>
>> Thank you in advance for any tips.
>>
>
> The states you are referring to are chan_sip specific. They are defined
> here[1].
>
> 0 = Disabled
> 1 = We've sent a reinvite to switch to T.38
> 2 = They've sent a reinvite to switch to T38
> 3 = T38 was negotiated and is active
> 4 = T38 negotiation failed/was rejected
>
> [1]
>
https://github.com/asterisk/asterisk/blob/master/channels/sip/include/sip.h#L662
>
> --
> Joshua C. Colp
> Asterisk Technical Lead
> Sangoma Technologies
> Check us out at www.sangoma.com and www.asterisk.org
> --
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--
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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