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Weird noise during silence on NM-2V w/ 8 FXO ports

I am troubleshooting a buzzing sound that fades in and out at variable rates but is always present. It is only heard on the 7960 end of a call using H323 to all 8 FXO ports of a 2600 router using the NM-2V w/ 2x4 FXO ports. The call manager is v3.3(3) and The phone load on the 7960's is current as of March 11, 2004.

I have verified that VAD and comfort noise are turned off on all calls by checking the config and using the "show call active voice" commands, and that G711 is the codec in use. Jitter and delay are pretty much non existant.

The phone lines have been checked with a digi grabber and with standard analog phones and the weird sound is not heard.

The same phone lines have also been plugged into another 2600 router using a NM-HDA4FXO and the weird sound is not present. The phone lines originally on the NM-HDA4FXO router have been moved to the router with the problem and the problem is heard.

What am I missing??? I suspect an issue with the NM module but fear a replacement might not solve the problem.

Any ideas are appreciated!


Re: Weird noise during silence on NM-2V w/ 8 FXO ports

There have been some issues with either bad code or bad hardware needing code workarounds with the VIC-4FXO. If your trouble is like ours, often unplugging one of the lines from the 4FXO would cause the other 3 to stop experiencing the problem.

Contact TAC and have them reference case F139907 (one of ours) and it should help jumpstart them toward helping you. They should be able to at least give you an engineering release IOS to help.

In case that's not it, I've attached a document on troubleshooting FXO noise problems which documents some of the really nice impedance adjustment and correction tools available in very new code. That might also be the source of the problem.

Community Member

Re: Weird noise during silence on NM-2V w/ 8 FXO ports

Thanks for the headstart on the problem, sounds like it might be either the 4FXO itself or possibly the NLP comfort noise mentioned in the attachment. I will investigate furthur with this additional information. Thanks!

Community Member

Re: Weird noise during silence on NM-2V w/ 8 FXO ports

I have upgraded the router to 12.3(7T) and further diagnosed the problem. The problem occurs when Non-linear processing is enabled. I think it is comfort-noise generated by the router, but is very annoying to the customer. If i use "non-linear mute" it goes away but some form of VAD is present, If the caller on the IP phone stops talking, the line goes completely dead silent until the person on the outside line talks, and clipping occurs (when the VAD kicks in), this happens even when VAD is disabled on the port and dial-peers and "show call active voice" states VAD is off. If I use "no non-linear" then echo becomes a major problem. The only thing I can think of is that this is a problem in the hardware and I will need to replace the hardware with a different solution. sigh....

At this point I will be getting TAC involved. Thanks for the help though!

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