ip phone users are hearing their own echo on some incoming calls. the calls come in via a h.323 vg200 gateway from a telco t-1 circuit. i've tried putting on the input gain -3 and attenuation 3 commands. where can i go from here ? what is causing the echo?
I am having similar intermittant problems.
H.323 on a Cisco 3640 to ISDN PRI's.
I am in the process of trying the advice in "http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Ddisplay_messages%26mode%3Dnew%26location%3D.ee6fc61%2F9" . . . we'll see. The router is running 12.1(5)T7 and the conditions mentioned in the above link are identical to mine.
Any additional advice on how to cut echo in this config?
What I have found is that if users are hearing themselves, the signal is "too hot" going into the IP network. I would look at the output attenuation and input gains to find the comfort zone. REMEMBER....START FROM 0!!!!! The biggest mistake I've done is entering these commands and making more work for myself. Enable comfort noise (if you turned it off) to help with cut-off words at the beginning of a conversation. I've had to go as high as 6db in order to get the right sound. If you're lucky enough to carry a T-bird analyzer in your tool bag, you can get the CO db settings from there. But if you're like me and don't have access to a 50k piece of equiment, then its trial and error.
we have had same issue. echoing passing thru a DT24 behind the PBX. opened a TAC case and they did a bugtrack on it. got a new load for the DT24. but you might lookup the bugtrack info. unfortunatly this has not resolved the problem. thanks marc r smith
D00303010019 - Load for Bug Fix CSCdv19745
The best document that I have found so far on echoes
This document does an excellent job of describing why echoes occur and what you can do about them. We have 6608 digital gateways and we get echoes on some calls. Here's what we have done so far with no noticeable success:
1. Adjusted Audio Signal Adjustment into IP Network up to minus6db
2. Adjusted Audio Signal Adjustment from IP Network up to minus6db
3. Had the local Telco provider measure signal strength on T1's
We adjusted the audio signal 1db at a time and only one signal adjustment at a time, either into or from the IP network. We did this over several weeks, with no noticeable change to the echoes. We ended up removing the adjustments due to complaints above volume of the voice. The above document states that the audio signal adjustments only mask the problem and it does not fix the problem.
Here's our next step:
1. Educate the users about the cause of echoes and the difference between persistent echoes and echoes that are cancelled by the hardware.
2. Ask users to report persistent echoes that last the entire call. We want the user to report the "Caller" phone number, date and time of call, type of echo (loud or long delay), and if a headset or speaker phone was used during the call.
3. We created a team that includes local Phone Company system engineer, internal Telco service provider, Cisco system engineer, and us (VoIP boys). The purpose of the team is to take the reported echoes and determine what we can do to correct the problem. Then hopefully start making an impact on the number of reported echoes.
Based on the document, echoes will always be problem as long as there are analog tail circuits involved in the call. So, it appears my best option in the short term is to educate the users about the problem and then make a reasonable (cost effective) effort to remove echoes that we can control.
we have the VERY same problem-echo on the ip phones-across a DT24+ getting a telco t-1 trunk feed from a pstn into a vg200 h.323. working with cisco on a P2 basis. tried changing the load on the DT24, tried the new load with the bug fix for the DT D00303010019 but it didnt resolve anything. now we are doing sniffer captures. and cisco is looking at them. when i find something i will post or write me direct.
I've had the same problems for 5 months with a VG200 and a NM-HDV-1T1-24E. I'm connecting to the PSTN with an ISDN PRI. I've sent sniffer files, debugs, and configs to TAC and we've tried a few things. On the controller T1 try the various "cablelength short" commands, and on the voice-port try the "output att 6" and "echo-cancel cov 32". These seem to cancel the echo through most of the call except the beginning. Some calls have the echo throughout the call. We also used a debug command that showed the incoming level of the call, but I can't remember the command for the life of me. I'll keep looking. Does your CLEC claim that they can not change the level at which they send signals to your VG200/DT-24?
We found that if the echo is heard on the PSTN side, then if you lower the volume level on the IP phone the echo disappear. But I have to say that we are experiencing echo rarely, but when the problem occurs it is solved by lowering the volume level. For a test try phone calls with the volume level cranked up and lower it gradually to see the effect.
We have had this at 6 out of 8 VG200 installs. The other 2 could just be that the customer has not really complained about it at this point. We have solved this at 1 site with many changes and tries of the echo cancellation, input gain and output attenuation. The same settings don't work everywhere and that customer has been echo free (at least no complaints) for a week now. We also a site with echo on the Catalyst 4000 GWY module with the same problem/settings. Some sites are solved, some are not. TAC is engaged on all of them and even Cisco engineers dispatched to assist with this and similar results.
Ironically 2 out of 2 Catalyst 6500 8-port PRI modules we have installed have no echo with no change to the default settings.
Just luck? I am guessing a more efficient echo canceller exists in the Cat6500 blade or something to that affect. Both Cat6500 customers love the system and no complaints about echo.
The 6608 blade has an echo canceller tail circuit length measured at 29ms using the G.711 codec, 16ms using G.729. If you configure the echo-cancel coverage to 32ms on the VG200 and 4604 module the ecan function should perform the same as the 6608 blade. I am thinking that the customer using the 6608 has circuits with better telco side echo cancellation, or there were other problems occuring at the other sites.
I have seen some results with the following:
1- Make sure your cable length on the T1 controller is set correctly. It defaults to long and should probably be set to short.
2- Try 12.2.1c IOS. This cleared all of the echo problems on my VG200 with a PRI. Of course I lost some of my call progress tones again, but was worth it to get rid of the echo.
If you are using CCM version 3.1 or higher the problem is probably in your phone loads and not the gateway. We were having the same problem and noticed that the echo was only occuring on the ip phone. We also noticed that we could get the echos between ip to ip phone calls. By changing the phone load from a 3.1 version to a previous version (P003D310) from 3.0(8), our users have given good feedback and have not had any complaints. So until Cisco fixes the phone load to pre 3.1 levels for a quick fix use a phone load before 3.1.