Expert Echo Reduction

[justin.cohen]

I have a few customers experiencing various amounts of echo, after reviewing the ver common "Troubleshooting echo problems between ip phones and Cisco IOS Gateways" document, I am looking for some thoughts from users.

I have a user now who is complaining of various levels of echo.

When calling a loopback number I get these readings from the gateway

NoiseLevel=-70

ACOMLevel=53

OutSignalLevel=-18

InSignalLevel=-72

InfoActivity=2

ERLLevel=4

EchoCancellerMaxReflector=3

this would tend to tell me we need adjust some gain levels. Thoughts?

(Currently the settings are input gain -3 and output attenuation 3 and 32ms of coverage)

Thoughts?

[8r-schumann]

I am not sure that this is enough information. Are you using an IP phone? If so use the tone generator in the 7960 so send a test -15db tone. You can then use that consitant to figure out if the outbound or inbound needs to be adjusted.

[justin.cohen]

7960 set, the reading you see above were done during a call to a loopback with the tone being sent.

for some reason the inbound wasn't showing the -15 though, so i'm questioning the loopback number I used but it's the only one available.

[dgahm]

If you set your cancellers for 64ms of coverage you will fix most if not all your problems. If 32 is your max setting you will need to upgrade to 12.3.4T or 12.2.15ZJ IOS for the enhanced 168 cancellation.

[justin.cohen]

64 has been tried.

My concern is that the echo is too loud, and being seen as voice by the canceller.

Additional echo canceller ms will not help if it's all being seen as voice anyway.

[scott-crosby]

To troubleshoot this properly remove the output attenuation and input gain commands and “shut”, “no shut” the voice port in question.

Next setup an IP Phone to generate the test tone, this test tone only works with G.711 calls.

1. **# to unlock the phone

2. place a call (if you don’t the next command will reboot the phone)

3. **3 to turn on the tone generator feature

4. place a call out the voice port in question to the destination in question

5. while the call is up on the IP phone hit the “?” button twice and press the tone button to generate the test tone

6. after finishing the test call, reboot the phone to kill the tone gererator

Then do a “show call active voice” again and check the settings.

Check these three lines again.

OutputSignalLevel =

InSignalLevel =

ERLLevel =

The difference between the IN and Output levels need to be greater than 6 dB and the ERL needs to also be greater than 6dB. If they aren’t you need to adjust the input gain and the output attenuation settings on the voice port until 6 dB or greater is achieved to get the ECAN to differentiate the echo from the main signal.

Remember every time you adjust the ECAN, gain or output settings “shut”, “no shut” the port to make the settings take effect.

--Scott

[scott-crosby]

By the way, the full procedure is in the "troubleshooting Cisco IPT" book.

--Scott