[asterisk-dev] [Code Review] Fax Gateway Implementation T30<->T38

[Kevin P. Fleming]

On 04/14/2011 12:47 PM, Pavel Selivanov wrote:
> 05.04.2011 23:33, Klaus Darilion wrote:
>>> disable echo cancellation. Echo cancellers that are G.168 compliant
>>> detect CED tones generated by *called* FAX terminals and take action
>>> themselves to reconfigure properly so as to not interfere with a FAX
>>> transaction.
>> One more note: the faxdetect code (triggered by CNG) does *NOT*
>> What about the software echo cancellers in DAHDI, are they G.168
>> compliant?
> dahdi (dahdi-base.c) is searching for CNG tone, unless you disable it
> (in dahdi_config.h).
> Once CNG is detected - dahdi will switch echo canceller of.

No, this is not correct. DAHDI can report detection of CNG tones if an 
echocan (usually a hardware echocan) reports them, but it does *not* 
setup a CNG detector.

DAHDI *does* setup a CED detector and react to detection of CED when 
appropriate. In addition, in current DAHDI releases, it does not 'switch 
the echocan off', instead it tells the echocan to switch into 'FAX' 
mode; the exact effects that result are dependent on how the echocan 
implements that operation.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
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