[asterisk-users] T38 state values

[Joshua C. Colp]

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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