PSTN Echo

[bsdaiwa]

I have an OBi 200 with the OBiLine attached to handle my PSTN line. My problem is I have an echo on the line. The party on the other end of a call cannot hear the echo but I can and it is rather pronounced. The echo occurs on boty inbound and outbound PSTN calls. Can anyone give me advice on how to cancel the echo? The echo does not occur on the VOIP (SIP) lines.
Thanks

I should add that I am in Brasil (Brazil).

[drgeoff]

Is the echo on all your PSTN calls or only to one number or small subset of numbers you call through the OBiLINE?

Echo can be introduced at many points between you and the other end of a call.  Some is usually deliberately introduced by your own handset.  https://en.wikipedia.org/wiki/Sidetone.  You don't perceive this as echo because it is not delayed.

The annoyance of an echo depends on its level (relative to the wanted speech from the other end) and its delay.  More level and/or more delay means greater annoyance.

Delayed echo is generally introduced at places outside your local setup.  Thus being outside your realm of control you cannot eliminate it.  Some things you can do to mitigate it are:

1.  Decrease the signal level that you send.  This reduces the echo level in two ways.  Firstly it reduces the absolute level of the echo signal that comes back to you.  Secondly, a lower level from you typically encourages the distant speaker to speak more loudly.  So the relative echo level you hear is improved by a double whammy.

2.  Decrease the delay in the send and receive paths of your own equipment.  Things such as reducing jitter buffers and using a PCM codec (G.711) instead of others which have more algorithmic delay.

http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/spa3102-voice-gateway-router/108731-pqa-108731.html was written with the Sipura/Linksys/Cisco SP3102 in mind but is generally applicable also to the OBiLINE and OBi110.

[bsdaiwa]

Thank you for the input. I made the following change and that seems to have cured the problem. I went to Physical Interfaces > Line > Port Settings > ACImpedance and set it to Global. That seems to have fixed the problem since I don't have an echo on PSTN calls. I have no idea what "Global" means, I have not been able to find an explanation in the OBi manual.

This issue only occurred when I used the PSTN line, it did not occur when I used GV or CallCentric, based on that I eliminated the handset as the problem.

Thank you drgeoff, will keep the link for future reference.

[bsdaiwa]

Can anyone tell me what the "Global" setting means in the Physical Interfaces > Line > Port Settings > ACImpedance setting? I can't seem to find any explanation in the OBi manual.

[Lavarock7]

I don't know if this is applicanle, but I found this refering to the Obiline:

I hope this added info helps make your purchasing decision.

Echo solution:
If you experience echo during POTS use, here is the solution:
1: Login to your "OBi Dashboard."
1.5: MAKE SURE THAT YOU HAVE THE LATEST FIRMWARE INSTALLED.
2: Choose your device and then scroll to the bottom of the screen & click on "OBi Expert Configuration" then "Enter OBi Expert".
3: Now choose "Physical Interfaces" then "Line".
4: Scroll to "Port Settings" and edit parameter "ACImpedance"
5: In my case, "270+(750||150nF) and 275+(780||150nF)" was my solution.

Depending on the region you are in the world, the "ACImpedance" will have to be adjusted accordingly to your telephone network.

Cisco compiled a global list of AC Impedance settings, caller ID info, etc in order to "fine tune" your system for your country of use:
Preform a internet search using the following term without the quotes: "44705-SPA400Configuration_060109.pdf"

[bsdaiwa]

Thanks Lavarock7, I had seen that post and it was helpful. I am in Brazil now and have been able to reduce the echo but still haven't been able to completely eliminate it by playing around with the ACImpedance settings. My dilemma is what is the setting entitled Global, all the other settings show the impedance but this one is not explained and shows nothing but the title "Global". It seems to solve the problem but I would like to know what it represents because one of the other settings may be closer to eliminating the problem.

[drgeoff]

Those AC impedances listed in the Cisco document or elsewhere are merely nominal system design figures.  No actual phone line will precisely have the impedance that the relevant telco network is designed around. The telco does NOT tweak each POTS line to make it come within some tolerance of the design figure. If you want the best impedance match to a particular POTS line, you have no real alternative but to try most of the available settings.

[bsdaiwa]

Thaks to all for there input and guidance but I am still left with the unanswered question of "what is the setting entitled Global, all the other settings show the impedance but this one is not explained and shows nothing but the title "Global".
When you use the down arrow in the Value settings for ACImpedance you are given a list of settings starting with 600 then 900 and so on until you see at the bottom of the list the setting entitled Global. What I would like to know is what is that setting is that all of the above or 600+900+200.........what does it mean?