On 01/03/2011 06:47 PM, Thomas Rymes wrote:
On Jan 3, 2011, at 3:22 PM, Kevin P. Fleming wrote:
On 01/03/2011 11:26 AM, Tom Rymes wrote:
[snip]
1.) Echo cancellation is automatically disabled upon recognition of a
CNG tone, regardless of the faxdetect setting. This can only be disabled
at compile time.
No. CNG tone is never used to affect the state of an echo canceller. All G.168
compliant echo cancellers will respond to the CED tone (generated by the
answering endpoint) and will reconfigure the echo canceller appropriately. Most
modern ECs will *not* be disabled, but will enter a 'linear' mode where they
can do some echo suppression but not complete cancellation. DAHDI will detect
CED when most software echo cancellers are in use and will disable them (since
none of the available software ECs can go into linear mode). The Digium HPEC
software EC will detect CED on its own and enter linear mode.
OK. Either way, though, the changes to echo cancellation are not affected by
the faxdetect setting, right?
That is correct; the faxdetect setting and the echo canceller behavior
are completely unrelated.
2.) faxdetect=incoming will, upon detection of a CNG tone, send the call
to the fax extension.
If the CNG tone arrives from the network side of the DAHDI channel (the far
endpoint), then yes.
Great. This is the typical usage, I presume, directing fax machines to FFA,
Hylafax, another fax machine, or hangup (if this isn't a fax line).
Is there a time limit to when DAHDI listens for faxes (say the first 10 seconds
of a call?), or might it detect one in the middle of a ten minute call?
I haven't double-checked, but I believe the software DSP will be in
place on the call until it sees a CNG tone, regardless of when that
happens during the call.
3.) faxdetect=outgoing will ??????
The same thing, but if the CNG tone is being sent towards the DAHDI channel
(from the near endpoint). This is rarely used.
[snip]
I figured that must be it. Presumedly you might use this to perform some
activity on an outgoing fax prior to sending it, such as logging something,
etc? Maybe send it to FFA, receive it, and e-mail it to another server that
faxes it out on a local number to save toll calls, etc?
Thanks for the clarification, there's a lot of conflicting info out there.
Feel free to comment on wiki.asterisk.org if any of the information
there led you astray; we'd like to get that to be the most accurate
place for people to find this sort of information.
--
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: [email protected]
Check us out at www.digium.com & www.asterisk.org
--
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