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Echo with 2651 Routers - Where to start ?

Currently, we are configured with 2 2651 (dual PRI) routers as an intermediary step to our full VOIP rollout.

Employees in the building are using their existing phonesets, plugged into the existing PBX. The PBX interfaces to 1 of the 2651's, which then forwards all calls to the second 2651 which interfaces to the PSTN.

The thought is that with this solution, we can peel off DID's one by one as we roll out.

However, we are seeing some significant echo with this configuration.

Where should we begin to look to resolve this issue. We've turned up the echo-cancellation threshold to 48 (arbitrary) but are still experiencing echo.

Any tips/suggestions welcomed. Thanks.

= K

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Re: Echo with 2651 Routers - Where to start ?

Echo is always caused by the power levels. The best way to get rid of it is to drop the levels on the voice ports.

It depends on who is hearing the echo as to where the level tuning should be done. If we have the following scenario :

user1 ---------VOIP--------user2

and user1 hears echo, then it means the power that user 1 is sending out towards the network is excessive, and for whatever reason (acoustic feedback in handpieces or 2 to 4 wire conversion hybrids) some of the signal is being bounced back.

Therefore, the best thing to do is to reduce the level of user1 before it hits the VOIP network. If this is not possible, then you attenuate the signal on the voice port that user1 interfaces to, so the level of the signal coming into the network is reduced, and any corresponding echo from the far end is reduced accordingly.

On the voice port config of the router at user1, use the command 'input gain -3' to apply a negative gain (attenuation) to the incoming signal. This will drop the signal by 3dB, which is barely perceptible to the human ear but is a half power reduction. This should start to improve things. You may need to try increasing this value by 1 db (to a maximum of -6dB)

You can also try reducing the outgoing signal level at the voice port of user2 so the power sent at the far end is reduced. Use the voice port command 'output attenuation 3dB' to drop the outgoing signal by 3dB.

It may required some fine tuning, but most echo cna generally be tuned out this way.

Refer here for more echo information -

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml

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