asterisk users - Mar 2022 - T38 state values

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.

-- 
David Cunningham, Voisonics Limited
http://voisonics.com/
USA: +1 213 221 1092
New Zealand: +64 (0)28 2558 3782
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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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