[Asterisk-code-review] res_fax: gateway sends T.38 request to both endpoints if V.21 detected (...asterisk[16])

[Alexei Gradinari]

Alexei Gradinari has posted comments on this change. ( https://gerrit.asterisk.org/c/asterisk/+/11422 )

Change subject: res_fax: gateway sends T.38 request to both endpoints if V.21 detected
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Patch Set 4:

(1 comment)

https://gerrit.asterisk.org/#/c/11422/4/res/res_fax.c 
File res/res_fax.c:

https://gerrit.asterisk.org/#/c/11422/4/res/res_fax.c@3050 
PS4, Line 3050: 			if (state_other == T38_STATE_UNKNOWN) {
> That's what I am not understanding, so need clarification. […]
The goal is to switch to T.38 whenever possible.

The SIP endpoint equipment doesn't always detect Fax tone.
For example Cisco SPA adapter has option "FAX Tone Detect Mode" with possible values:
"caller or callee",
"caller only",
"callee only".
Even if the direction of Fax tone matches with this option the adapter stops to detect Fax tone if there is voice packets (fax manual mode).

The scenario when both SIP endpoint supports T.38, but nobody switch to T.38 on fax tone.
In this case the asterisk as T.38 gateway can detect fax tone and can ask both SIP endpoints to switch to T.38.
If both endpoints agree to switch to T.38 then the gateway will step out of the way, allowing transparent T.38 passthrough (ideal scenario).



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Gerrit-Project: asterisk
Gerrit-Branch: 16
Gerrit-Change-Id: I73bb24799bfe1a48adae9c034a2edbae54cc2a39
Gerrit-Change-Number: 11422
Gerrit-PatchSet: 4
Gerrit-Owner: Alexei Gradinari <alex2grad at gmail.com>
Gerrit-Reviewer: Alexei Gradinari <alex2grad at gmail.com>
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