[asterisk-users] digium HW echocancellation - fax tone detection

[Kevin P. Fleming]

On 07/19/2010 11:28 AM, Tim Nelson wrote:
> ----- "Johann Steinwendtner" <steinwendtner at gmx.net> wrote:
>> Hello !
>>
>> I 'm using a TE405P with a HW echocanceller module attached on it.
>> dahdi version is dahdi-linux-complete-2.2.0.2+2.2.0.
>>
>> As far as I know, the fax tone detection is done on the FW board.
>> How can I verify that the echo canceller has been turned off ?
>>
>> When I do a cat /proc/dahdi/1 for span 1 I see still the VPM450 entry
>> near the channel although this was a fax call with CED tone.
>>
>> 	   1 TE4/0/1/1 Clear (In use) (EC: VPM450M)
>>
>> Greping through the source, i see only a CED tone detection
>> entry in:
>>
>> static const struct dahdi_echocan_features vpm450m_ec_features = {
>>          .NLP_automatic = 1,
>>          .CED_tx_detect = 1,
>>          .CED_rx_detect = 1,
>> };
>>
>> Does it mean that CNG tone is not going to be detected ?
>> Does the CED tone detection routine also detect ANSam tone for Super
>> G3 fax ?
>>
> 
> Check your '/var/log/messages' or run 'dmesg'. It should say something like this if the tone is detected and appropriate action taken:
> 
> dahdi: Disabled echo canceller NLP because of CED rx detected on channel 97

Not quite; none of Digium's hardware echocan products report CED tone
detection or NLP enable/disable events, so you'll never see any messages
that indicate whether the tones were detected or whether the NLP was
disabled automatically or not. Those messages are only generated by the
software CED detector in DAHDI, which isn't used if the hardware echocan
can detect CED itself.

To the original poster: all of Digium's hardware echocan products are
compliant with G.165 and G.168 for tone detection and either completely
disabling the LEC or just disabling the NLP portion, depending on which
tone is detected. CED detectors will typically detect ANSam as if it was
CED, which is the way ANSam was designed to operate on echocan units
that don't have specific ANSam detectors.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kfleming at digium.com
Check us out at www.digium.com & www.asterisk.org