Echo - Comcast Voice

[ITFelix]

Hi,

I've got a problem at two locations with Comcast Digital voice (eMTA with POTS handoff). There is echo on all calls when using SIP phones. Yealink, Grandstream, Cisco, doesn't matter the type. Phone system is a Xorcom with 8 FXO, 8 FXS, Asterisk 11.x Oslec on or off doesn't make a difference. Added an Astribank with hardware echo cancellation, same issue. I've tried a Sangoma Vega 50 SIP to FXO gateway, same issue.

Analog phones on an FXS port are fine, no echo at all. Calls between SIP phones are fine. No packet loss, fragments, or other issues on the managed switches.

Tried current 32bit and 64bit FreePBX distros on a spare laptop using the Sangoma Vega 50, same issue.

Tried a basic 3CX install on another box with the Sangoma Vega for kicks, same issue.

If you connect an analog phone directly to the Comcast eMTA, there is no echo. Tried shielded RJ-11 cables, reversed tip/ring, blah, blah, blah.

Any ideas? I have this same issues at two locations 6 miles apart with the same carrier.

Thank you

 

[busster]

Had this problem years ago, back when they were zap not dahdi trunks. The lines from the provider were "too hot". Had to adjust the gain on the lines using zaptel configuration files. I am assuming dahdi has something similar.

If I remember correctly, there was a configuration utility to help you identify the issue.

My guess is there is a high loop current from Comcast's device, causing the echo on whatever device you connect to.

Have you asked Comcast to replace their equipment? Check the loop current? I believe the specs are broad, like 26ma to 120ma, but the higher the loop current, the more likely the echo.

Clowns to the left of me, jokers to the right, here I am, stuck in the middle with you.

 

[ITFelix]

Thanks for the info. I'm registering 38-39ma at the Comcast eMTA. DAHDI fxotune returns all zeros so it thinks everything is wonderful. Same echo on the Sangoma VEGA gateway with hardware echo cancellation built-in at 16, 32, 64, and 128 taps. Same problem with DAHDI and Digium licensed HPEC.

Comcast replaced the eMTA already. This site recommends staying under 35ma.

http://www.sandman.com/echobull.html#Step4

Any other thoughts?

 

[busster]

I would try and drop the line current to see if this resolves anything.

Might be a cheesy, but if you brought in two or three new boxes of cable, daisy chained them together and put your tester on the end, this should have dropped the line current. Test behind the two/three boxes of cable. If echo is gone, then at least you know the problem. Go buy some resisters and put them in line, hidden within an old biscuit jack.

Clowns to the left of me, jokers to the right, here I am, stuck in the middle with you.

 

[busster]

Sandman also sells a modular loop current regulator which keeps the line at 25ma no matter what.

http://www.sandman.com/loop.html#LoopCurrentRegulator

Clowns to the left of me, jokers to the right, here I am, stuck in the middle with you.

 

[ITFelix]

I purchased the current regulator, same issues remain. It did indeed bring the line down to 25ma

 

[ITFelix]

So I purchased the Echo Stopper from Sandman, it changes slightly but still there.... I also added 3000' of cable for fun with no perceivable changed. Finally, I connected an analog phone to the Comcast eMTA and listening very carefully the echo can be heard. VoIP latency seems to be amplifying it. Crazy.