AboutGerry Magill Expertise I am a Software Architect employed by a large multi-national communications company providing VoIP and tradtional TDM communications to Enterprise customers.
Experience <BR><B>Past/Present clients</B><BR>IBM, SBS, Siemens, KPMG, Bank Berlin, Commerzbank<BR>
Expert: Gerry Magill Date: 5/8/2008 Subject: voip "echo"
Question I have a cisco voip system. My users complain occasionally about "echo" I've experienced it myself but its not a standard echo in the sense of like the grand canyon. its a single, delayed, clear, non reverberating bounceback of your own voice. there's no continuing echo where it repeats over and over. I've tried going online to find sound clips of voip echo and they dont sound like mine, they're the "grand canyon" type of echo. I've run QOS reports and all looks fine. we have a PRI going into a voice gateway, then into the network. I can provide many more details if you want.
thanks
Answer First, are you sure it is echo and not speech clipping due to varying delay in your network? Clipping will sometimes be reported as echo by users. Look for some wav file examples of that and see if its more like what you are hearing.
My experience with echo in VoIP networks is that echo is not due to the VoIP design itself, rather it is somewhere where the digital VoIP world meets analog wiring or circuitry.
The most common place to look for this is to ask the end users if they are using head-sets. These are commonly purchased after-market items bought privately by the employees themselves to make their life easier. These devices are analog in nature. They attach to the phone in some way, either by inserting themselves in the wiring of the handset or by sticking to the side of the phone in the form of a microphone/speaker.
These devices work great on traditional phones but are often sources of impedance mis-match on VoIP phones. They also have poorly shielded wiring.
First ask the users if they have such a headset. They might deny it on the phone, so a walk-by is best in my experience. If they have headsets, ask them to remove them and try again. If that was the source of the echo you have your problem. A different brand of headset may solve the issue. Not all are of the same quality.
Also, note that the headset may be on the other parties VoIP phone at the far end. Their own voice is getting echoed back from the far end by that persons headset. If the round-trip delay is above 150ms for a ping, then the user will hear that echo.
Delay is also a source of echo in itself. Most VoIP phones have built in echo cancellers or the gateways do. These echo cancellers do a great job if the window of echo reception is < 150ms. Above that, then their buffers are not large enough to capture the echo and remove it. In VoIP networks, it can be common to have round-trip delays of over 150ms - especially on WAN connections that may not have a guaranteed end-to-end QoS in place by the WAN carrier for voice traffic.
In any voice call, a user actually hears their own voice in their headset, but this is ignored by the brain if the delay is 100-150ms. Your brain has to do this or it would get confused by your own speech resonating inside your head. Once the delay gets too large, your brain cant handle that and this is what is perceived as echo.
Work out what your round trip ping times are at peak times of network traffic or at the times that users complain. You may be surprised at what you find. Many companies have USA to Europe round trip times of 300ms. Fine for data - terrible for voice.
Also check if your users are still using analog phones connected to analog to SIP gateways. Impedance mis-match here can normally be adjusted in the gateway to compensate for wiring.
Let me know if any of the above fit your scenario.
