Hearing an echo when answering a call


GXP2170 with on UCM 6510.

I have, from time to time, experienced an echo of myself when making or answering a SIP call. It often disappears and has never persisted long enough for me to be concerned about it.

I now have a new site where the receptionist is hearing this occasionally on an ongoing basis. So I now need top dig a little deeper and find a resolution.

Can anyone shed some light on why this happens and how it can be resolved?


SIp or analog or?

Echo is either acoustic or from the telephone line (hybrid, line, near, far, etc.). Echo occurs at the analog level so it is not possible for SIP, being digital, to cause echo. It would be akin to getting your computer monitor to display two pictures, which in the analog television days was possible when the signal paths of a given TV station was reflected in some manner (building, cut in a cable) which allowed the signal to be received at the same reception point but at two different times and at two different signal levels.

So, if not acoustic, then it is somewhere in the analog realm where the SIP provider or, a path along the way, is reflecting back excess energy. Echo cancelers and suppressors can be effective, but alas you will likely have to contact the provider with some details about the given calls as I doubt there is much that you can do unless, using analog lines and then you can play the TX-RX and impedance settings. This is where the impedance matching comes into play when using the FXO ports of a SIP gateway.


This is a totally SIP install. It happens when a call is answered/made on the 2170 from/to the UCM6510 from/to a SIP trunk.

So you are saying this is not in the 2170 itself (its settings, etc.) nor the UCM, but is something happening at the ITSP’s level?

I should point out it is only happening on this phone, and that I use the same ITSP and have not had this happen to me or any of my other users of this particular ITSP (other than the rare occurrence).


No, I am saying it is at the analog level and it conceivably could be the handset or the analog transition in the A/D / D/A conversion or even an acoustic echo in the handset. As you only indicated - “I now have a new site where the receptionist is hearing this occasionally on an ongoing basis” with no other pertinent details until your latest, there was little to suggest.

Given that it occurs only occasionally, presumably never happens on extension to extension calls, and there are no settings in the phone or the UCM given their SIP nature to try, unless it is acoustic echo, that leaves the provider as the next in line. I am not faulting the provider as they likely get their feeds from a major who has the interconnect, but they can still look.

I suppose you could try moving the phone or even letting the receptionist use your phone as maybe there is a difference in how the firmware controls the analog circuitry as I do not know if the same FW is in your 2170.


Thanks for the clarification.

And yes, I have little to go on either. I will be back in Toronto next week and I plan to stop in and further investigate.

I am thinking that it is a hardware issue, since it is happening so frequently.


Unlikely, but possible I suppose. If so frequently, do a transfer, move phone change firmware or sub phone, that will isolate.

BTW, have looked for Nortel on-hold. I have not found and see where others were looking, but the site that reported had it is no longer up. Maybe someone else has.


Does the receptionist use a Headset?

Does the echo happen during the first 10 seconds of the call and then go away or is it throughout the call?


No she does not.

Yes it comes and then goes away after the other party talks.


If you answered the calls do you hear the same - point incoming calls to your handset and then from your mobile/cell ring the number and see if you hear the same echo to start then hear if it disappears.

If it does then the issue you are facing is an upstream provider echo cancellation issue, if it does it 100% of the time for the first part of the call then it is definitely a provider issue and not your hardware.

Ordinarily with echo cancellation - the first 10 seconds of the call the echo cancellers perform a train functionality where it tries to match the call characteristics and mitigate noise/disparaging networks (analogue/primary rate/basic rate ISDN to SIP)

This might be what you are experiencing…



Interesting. But it does not happen on every call, just a lot of them.

If this is the issue, what do you suggest?


If the issue is noise from the calling parties line - then there is nothing you can do as it is the callers problem.



is not a solution, but try to change the codec only for testing, remember that when he had done it to me, changing the codec the echo disappeared.


Catch packet and see if you can find echo there.
It can be incoming echo not related to UCM/GXP at all (usually is not related).
Check what numbers generate this echo (maybe they are all landline ?).
If you receive echo from ITSP sent them this info, maybe one of their device is wrong configured ?


All good ideas. I will have to investigate further.


drostoker the biggest problem is the randomness of the echo being heard over the sip trunk…

Only other thing that I can think of is perhaps congestion over the visp links and perhaps trans-coding from g729 to g711 ulaw or even it might prove to be a link with a g711 alaw to g711 ulaw trans-coding issue.


The GXP2170 is set to use the following Codecs in order:

  • G.722
  • PCMU
  • H.264

The VoIP trunk, with voip,ms, is set to use PCMU

At voip,ms, the trunk is set to use G.711U & G.729a

I believe the problem is mostly happening on inbound calls to the receptionist. Inbound call are routed to a Ring Group which right now only has the receptionist extension on it.


David, maybe using mirroring to be able to run a wireshark packet capture to the receptionist handset ip

Leave it sit and when reception logs the time of an echo call to pause the wireshark and read it at the time logged. hopefully you will be able to identify the issue


I am remote from the site - in Ottawa while the site is in Toronto (4.5 hours or so drive away).

I am going to remote in and try to get a capture from the UCM. GS tech support is going to look at it and see what they see.

I am finding this thread very educational. Thanks to everyone for their support!


According to Grandstream the echo is being caused from the ITSP (voip.ms) system side.

Grandstream is suggesting moving from PCMU to G.729 as it is more compressed.

I have several systems all configured the same with voip.ms and have not had this problem before. I opened a ticket with voip.ms and am waiting to see what they have to say.

I’m waiting to hear back from voip.ms before making any further changes.


I would just add G729a on the SIP trunk and see if the issue disappears to be honest.