we have deployed a VoIP network with 2821 MGCP gateways running 12.3(14)T7 IOS and CCM 4.1(3). Since the deployment the users experience an intermittent echo on the IP phone side.
I have gone through the troubleshooting exercise starting by checking the PRI trunks, making test calls, but the echo was so intermittent and so hard to replicate that we almost ended up by a conclusion that it's simply not there...
But I couldn't rest until I had some facts in my hand to see what the hell is going on there. So I wrote an expect script repeating the "sh call active voice ..." command every 2 seconds, put the IP phone into the 1kHz generator mode and captured the signal levels on the gateway.
What I got was a constant -15dB line of the Output signal, almost constant -67dB line of the Input signal level and quite interesting line of the ERLlevel. It was -30dB almost all the time, but intermittantly the gateway decided to drop the level to -6dB for a moment.
I was curious and did the same test using different GW with different IOS and I got straight ERLlevel line. As straight as it could possibly be.
(You can have a look into the attached picture.)
My question is - what the hell is going on with the first gateway, could that cause the intermittent echo and shouldn't the ERLlevel graph be straight?
Thanks to whoever takes the time to drop me a couple of line of what he thinks!!!
yes, the line levels should be level in an environment that is stablized. perhaps there is noise of some sort. could be generated by the hardware due to some issue. what is your tail coverage?
if you can attempt to up or downgrade IOS and test again.
i would say yes, that with an unpredictable ERL, then echo is possible intermittently.
Thanks for your opinion Greg. Upgrading or downgrading the IOS will probably be the ultimate solution in the end, because we have similar behavior on a couple of the gateways with a common denominator - the IOS.
I am just not absolutely certain what the ERLlevel that the router shows in the "sh call active ..." is suppose to mean. The descriptions I found on the CCO are quite vague and contacting TAC (due to the nature of the issue) could be fruitless.
by digging through this newsgroup i found a post about an interesting bug: CSCsb68986
Upgrading the 12.4 fixed the echo at my customer's site, after I had done everything possible to troubleshoot it (out att and all the other stuff).
Hi Dragi, thanks for your post. I actually found another threat concerning the 12.4 IOS that describes this type of echo too, which deters me from upgrading... The guy fixed it by upgrading to 12.4(6)T2.
Can I please ask what exact version did you use in your fix?
Hi Dragi, thanks a lot. The issue is currently on hold at the client side, because the impact to the users is really minimal. So in the interim I'm currently collecting info about a 12.4 image I will need to upgrade to in a couple of weeks time and your input is appreciated.
Hi guys, I did the same test with my 3825 in 12.3(11)T10 code and I am having the same issue. The ERL value just all of a sudden dropped to "6". Can any Cisco guy take a look at it or anyone found a solution already?
Did you ever get a sample expect script? Mirek, can you post the script you used for us please? I've been playing around with ciscocmd, cygwin and expect and I can get single commands to work, but not sure how you loop it to repeat the show commands, such as what we are trying to accomplish by automating the show voice commands to check the signal levels every couple of seconds.
By the way, nice Excel file!