SPA-3000 Echo on Line1-UK PSTN calls, firmware 2.0.10Gwf

[descore]

Hi,

I wanted to create a thread to get all information on the notorious SPA-3000 PSTN Echo problems in one place.

Just had first VoIP argument w/wife due to echo on PSTN->Line1 calls.

I'm using VoIP for all outbound calls now, and the sound quality is really good, so my only problem is when we get incoming calls on the PSTN line, but I observe the same behaviour when I dial out from Line1 to PSTN.

I've seen a number of topics dealing with this, but none provide an answer that helped me, and none of the suggestions helped in my case.

What I tried first is try to play with the SPA to PSTN and PSTN to SPA gain values and the Echo Cancellation settings, all on the PSTN line tab (there are no problems whatsoever with VOIP calls so I don't see why I should mess with the FXS port gain etc. under regional settings).

Last I tried looking at FXO Port Impedance. I couldn't find much about what it's supposed to be in the manual but after some Googling I came up with this (from http://www.eusso.com/FAQ03/VoIP/faq_voip.htm):

tel_id   Line characteristic
-------  -------------------
     1    600 ohms
     2    900 ohms
     3    220+820//115nF (Germany)
     4    200+680//100nF (China)
     5    370+620//310nF (UK)
     6    180+910//150nF (France)
     7    270+750//150nF (Sweden)
     8    120+820//110nF (Norway)
     9    150+830//72nF  (Belgium)
    10    400+500//330nF (Denmark)

So, since I'm in the UK I've set it to 370+620/310nF. It would be nice if this table or similar was included in the Sipura docs.

With the correct impedance setting the echo issue is much better (I hear a tiny bit of echo just when I answer the phone but then it goes away).

So I wanted to share this info for others who are trying to deal with this problem.

Right now I want to increase outgoing gain a bit, to make my voice sound louder in the remote end. If I manage to do this without reintroducing the echo problem, I am satisfied with this solution.

However, I am a bit disappointed that Sipura, with their outstanding reputation in the VoIP community, is having problems with something as basic as this (I mean, this is really the core functionality of the SPA-3000). To find out how widespread this is, I've created a poll.

Please reply to this thread with your experiences, and any tips that might be useful.

Descore

[descore]

Found some more info on Line Impedance here http://akson.sgh.waw.pl/~chopin/ios1...#xtocid1887488:

Use the impedance command to specify the terminating impedance of an FXO voice-port interface. The impedance value selected needs to match the specifications from the specific telephony system to which it is connected. Different countries often have different standards for impedance. CO switches in the United States are predominantly 600r. PBXs in the United States are normally either 600r or 900c.

If the impedance is set incorrectly (if there is an impedance mismatch), there will be a significant amount of echo generated (which could be masked if the echo-cancel command has been enabled). In addition, gains might not work correctly if there is an impedance mismatch.

Configuring the impedance on a voice port will change the impedance on both voice ports of a VPM card. This voice port must be shut down and then opened for the new value to take effect.

[dboyce]

Hello,

What are your thoughts on my earlier comments, as the problem may be at the FXS port?

In the UK BT states that their lines (Exchange Port & Cables) will present an impedance of 300+1000||220nF and Terminal devices should have an impedance of 370+620||310nF

From the SPAs settings, in the case of say the PSTN Tab / FXO port Impedance, does this control the actual impedance of the SPAs FXO port, or is it for me to select the impedance of my line as provided by my telco? I.e. if the former then I should select 370+620||310nF (i.e. the SPA FXO port is a terminal device to BTs PSTN line and should present an impedance of 370+620||310nF), but if the latter I should select 320+1050||230nF being closest match to the Telco

[descore]

Hi,

Well I have two thoughts on that..

1) Telephones are generally built to be quite tolerant of different line characteristics. I have used phones bought in several different countries, generally with good results. My guess is that many phones auto-adapt to the line they are on, although I don't know how this is done.

2) For the FXO port setting on SPA-3000, I believe that the logic is that you have to describe the line the SPA will connect to, not actually set the impedance of the FXO port. Understanding the configuration like that, the range of available choices make sense. Also the same logic for the FXS port, basically specify the FXO line standard for the country you are in (or where your phones are from).

I'm not sure about this, but it works quite well in my setup.

Descore

[oasis-k]

I'm using Sipura 3000 in the UK too - I just opened the box today, configured the user/proxy info, changed the codec to G711a and tested it.

I get the same echo problem on the PSTN line so I will try to solve it along the lines you indicate.

But I notice you get good VoIP outgoing calls. I get adequate voice quality to UK mobiles, but I got lousy quality on a call to a 0870 call center number - broken voice, and in the beginning a nasty click-click sound. I've noticed call centers are particularly challenging to VoIP - calling them with all sorts of softphones is also a problem (UK based call centers not in INdia).

I obviously need to test it and work with it much more, but I was wondering if you had made any changes to the default config to get such good quality VoIP calls.

cheers

[oasis-k]

Following up on David's comments about the FXO/FXS ports and impedance. First off, thanks for the helpful numbers from BT!

Logically (I suppose), the FXS port should be set to emulate the BT line since it is providing the voltage (tone), and the FXO port should be set to emulate the terminal since it accepts the voltage from BT. However, as you point out - there is no 300+1000||220nF value in the SPA FXS settings, but there is a 370+620||310nF value for the FXO port (which is also available for the FXS).

I've set the impedance to 370+620||310nF on both FXO and FXS and the echo problem has now gone completely. I also reduced the FXS input/output gain from the -3 default to -1.

PSTN incoming works fine now, so thanks to those who contributed to this thread.

cheers

[dboyce]

I am currently using the same settings (370+620||310nF) for both without echo problems, and I am running both the in and out gain on the PSTN Line at +10 (it sorted out a long term problem with very quiet BT DECT phones).

Here is the link to the BT doc if you have a little time on your hands.

http://<a href="http://www.sinet.bt....51v4p1.pdf</a>

[sk3-403]

I've never had any such problems with my SPA-3000, andI've been using it for months....

[oasis-k]

Thanks for the link to the bt doc - very interesting.

re: sk3's comment.
No problems with echo on incoming PSTN. And you're using the default fxs/fxo settings on the spa3k right?

[sk3-403]

Yep, it seems to work absolutely fine...

Give me a call to test it if you like, the PSTN line number is +44 1634 261266
(Home number)

I have it set to forward to my IP phone at work.