uc520 noise on line

Unanswered Question
Mar 5th, 2009

All, I have another issue with noise on a line. This can be either internal calls or internal to external calls, where they hear a sound like "sssshhhhh" (like an ocean sound, but constant). Anyone know how to get rid of something like that? Much appreciated.

I have this problem too.
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Paolo Bevilacqua Fri, 03/06/2009 - 02:19

The phones have their firmware, you can see the level from either router or phone itself, from settings -> device info, or again, accessing the http server at phone's IP address.

davieshuw Fri, 03/06/2009 - 03:26

Hi. i had the same problem on my UC520, I'd forgotten to set the cptone under the voice port

jjoseph01 Fri, 03/06/2009 - 05:25

My apologies beveilacqua, I have a bad habit of taking FW as firewall and not firmware. Again, my apologies. Im looking now, and see the following in the flash for the 524s:


Paolo Bevilacqua Fri, 03/06/2009 - 05:43

Hi, there is a tarfile on CCO, CME area, phone laods 7.0.2, can you check if it contains a newer firmware - I'm not sure.

Paolo Bevilacqua Fri, 03/06/2009 - 06:22

I've downloaded the tarfile and it contains FW 8.1.13 for the 524, you should try that before anything else.

jjoseph01 Fri, 03/06/2009 - 09:36

ok, I just found out from the guy who installed this that there is a 7931 on here also that does the same thing. Not just 524s. Sorry, I didnt know that. I appears that both types of phones, 524s and 7931s are having this issue. Still think it might be a firmware issue?

Paolo Bevilacqua Fri, 03/06/2009 - 09:44

That is quite strange, does it happen for all calls or just sometime? Can you confirm it happens for both internal and external calls.

jjoseph01 Fri, 03/06/2009 - 11:18

Yeah, I called her a few moments ago. She says it happens on all phones, all the time. Both on internal to internal and to internal to external. I setup a ip communicator phone across a vpn and I DONT hear the noise. She says she hears this "crackle" sound, like someone is wadding up paper. It was described to me by the engineer like a "ssshhhhhh" sound.

jjoseph01 Fri, 03/06/2009 - 12:36

I talked to Cisco TAC about this. Im pretty frustrated at their response at this point. They tell me its a QoS issue. I cant hardly believe that since they have 4 ip phones total, and 4 pcs total, all connected to this UC520. Im not sure I believe that, since there is very little traffic going on on the network period.

Nicholas Matthews Fri, 03/06/2009 - 13:06

This is bizarre.

First - I don't know of any bugs on the 524 related to voice quality, and I've done a ton of testing on those phones.

We can play the elimination game here:

IP phone to IP phone means these things are NOT the problem: UC520 (in any form), including voice ports, CP tones, IOS versions, controllers, scripts, or configuration (unless you have MTP configured under the ephones, or this call is hairpinned through a SIP/analog trunk). IP phone to IP phone on a LAN only includes these 3 things: The phone, wiring between the phones and switches, and the switch. The traffic is point to point here. (The more likely explanation is that it doesn't happen.)

2 different phone loads, same problem: This means it is not a firmware issue on either of the phones. (Technically there's an incredibly small chance).

VPN works with communicator: confirms voice port and UC520 again, similar to IP phone to IP phone.

This doesn't leave much. Some possible causes still left:

-Every phone being defective

-Something wrong on the switch leading to packet loss (like QoS)

-Ambient Noise


-Bad Handsets

Some tests to eliminate these:

-Get a packet capture from the back of a phone for a bad audio call, and decode the audio. See if there is packet loss or if it sounds fine. This will clear the switch problems if the audio sounds fine.

-Use a known good phone and see if it has the problem.

-Don't use headsets

You can use part of this post to decode the G.711 audio stream:



Paolo Bevilacqua Fri, 03/06/2009 - 13:55

Nick detailed various possibilities, I always like to take shortcuts, can you have the 7931 make an external call and check, that will eliminate the 524s from equation.

jjoseph01 Fri, 03/06/2009 - 15:18

Yeah, it will be on Monday, as they are gone now for the weekend. Thanks all, Ill get back with you.

jjoseph01 Wed, 03/11/2009 - 11:44

All, my apologies on this one. I have talked to the customer again today on this issue. It turns out the customer did not tell me the truth on all of the symptoms. It turns out that the only time they hear the noise is when they are on a PSTN call, NOT INTERNAL calls. Again, I apologize for wasting everyones time, Im as frustrated as you guys are. They told me on 2 different occasions what has been stated, then today they told me something different. I questioned them on it and they act like "oh well". Thanks for everyones input. I say its the phone company's issue.

jjoseph01 Mon, 03/16/2009 - 16:15

ok, I finally have a grip on what the issue REALLY is. I drove up there to this location, an hour away, to find out exactly what the deal is. Here is what I found:

All phones, not just one type of phone, have this issue. The issue is the sound of "white noise", is what I know it as. Its relatively loud when the call out/in from/to the PSTN takes place. No, it doesnt happen at all internally, but every call to the PSTN, or from the PSTN, has this sound. Whats odd is that when I put my analog phone directly to the PSTN (by unplugging it from the uc520 and plugging it directly to the anl phone), I do NOT hear the white noise sound. I even took an extra uc520 we had laying around with me, put it in place, and still the same issue. There is this document out there about troubleshooting sounds like static, crackling, popping, etc. They mention VAD, of which Im not sure I know what that is exactly. Cisco TAC mentions firmware still. I cant hardly believe that, since its on all types of phones, plus the analog phone when connected to the FXS port. I upgraded the IOS today, with no success in fixing it.

Anyone know anything about either getting rid of the "white noise" or turning down the volume of it? Much appreciation to all for helping. Id ALMOST give a reward to get this issue past me.

jjoseph01 Mon, 03/16/2009 - 20:33

Ok, I have to admit, its a little over my head, but I can understand the tests and will do this. Thanks, Ill let you know.

Nicholas Matthews Mon, 03/16/2009 - 21:27

If you want to prove it's not the firmware of the phones, do the last step provided in my post above. Decode the audio stream and listen to it (it's fun! I swear!).

Otherwise you will need to inspect the FXO line - ask the TAC engineer to get a PCM capture and you may want to run an impedance test on the line.

Place a call, and put both sides on mute. Then use this exec command:

test voice port 0/1/0 thl verbose


jjoseph01 Fri, 03/20/2009 - 07:44

ok, I did this test. Any setting just made things worse or stayed somewhat the same. Also, I did the packet capture and listened to the audio. In the audio from the capture, you can not hear the white noise at all. Weird.

jjoseph01 Fri, 03/20/2009 - 09:51

Yeah, it does happen on both the 524 phone and the 7931 phones. I went up there an tested these myself to verify, since I kept getting inaccurate information from the customer. But, here is the funny thing, it also happens when I plug an analog phone into the FXS port as well. Thats why I thought it might not be a firmware issue. Recap on some things Ive done:

1. Upgraded the IOS to cme7.x

2. put the config on another uc520

3. took a 524 phone of mine and put it on my uc520 with thier config

4. done the voice line tests as recommended by bevilacqua (cool tests by the way)

5. done the packet capture off the uc500, and listed to the audio (which does not produce the sound)

6. put the analog phone on the FXS port (I do hear the white noise on it)

7. Ive tried the max conf x gain command (hmmmm. I just thought maybe I should run that number down to something like 2 and give it a shot) Any thought on that?

slongewa Wed, 03/25/2009 - 09:34

Were you ever able to resolve this issue? I'm running into a similar issue with one of my uc520s and was wondering if you had been able to resolve it yet.



Nicholas Matthews Fri, 03/20/2009 - 12:27

If you don't hear it in the packet capture that leads to a phone problem.

Troubleshoot the endpoint, unless you've got a codec negotiation failure (like using g711ulaw instead of g711alaw).


jjoseph01 Wed, 03/25/2009 - 12:29

No, I have not resolved this yet. I still have to take the time to go out and load the new firmware. Still not resolved yet.

slongewa Fri, 04/03/2009 - 13:10

I recently resolved a situation like this by turning off VAD and muting the non-linear processing running on the FXO ports.

no vad

non-linear mute



Joe Del Sat, 11/07/2009 - 13:55

I see a few messages indicating to turn-off VAD - I am a little confused, as I thought VAD is off by default.


Paolo Bevilacqua Sat, 11/07/2009 - 19:29

vad is a voip dial-peer command and does not apply to cme and fxo.

I have indicated before the guide to optimize impedence on fxo that can be source of noise.


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