Thanks for the info Rich looks like I'll have to wait for the new FXO module. The impedence in the UK is zcomplex(2) which looks a long way away from a straight 600 ohms.
Here is the list of zcomplex impedences Zcomplex(1) = 150 nF // 750 ohms + 270 ohms ( European harmonized, France Telecom & Telefonica ) Zcomplex(2) =230 nF // 1050 ohms + 320 ohms ( British Telecom plc ) Zcomplex(3) = 115 nF // 820 ohms + 220 ohms ( Deutsche Telekom AG ) Zcomplex(4) = 310 nF // 620 ohms + 370 ohms ( Telecom New Zealand ) Zcomplex(5) =47 nF // 510 ohms + 150 ohms ( Russian Telecom ) ----- Original Message ----- From: "Rich Adamson" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, June 25, 2004 2:32 PM Subject: RE: [Asterisk-Users] X101P on a UK BT line ---- txgain issue > > > I do get echo, lots of it, I am waiting until the new patch they > > > are all on about on the list gets into a stable release, then I > > > will upgrade and see if that does the trick. > > Not likely the patch will get applied to the Stable release since its > been stated several times that's all but dead. > > > The patch didn't seem to work for me. > > > > > I am told that some of the echo may be to do with a mismatch in the > > > impedance with the BT line. > > There are at least several sources of echo, which have been noted > several times in the past six months or so: > a. echo can in * not functioning correctly in some circumstances (patch) > b. mismatched x100p -> pstn line > c. pstn line problems (eg, imbalance between tip/ring and ground) > d. 2-wire to 4-wire conversion along the end-to-end voice path > > Any single pstn line could have one or more of those happening. > > > Problem is do we really want BT messing with gain there end and impedance > > cos it might mess our ADSL lines up =) I know im on the limits. > > The telco isn't going to mess with changing impedance on their stuff > as that would require re-engineering their entire outside plant (cables), > line interfaces within the CO, etc. You couldn't pay them enough > money to do it. Its also highly unlikely they have any technician > adjustable transmission level adjustments on ordinary pstn CO line > interfaces, as those are engineered to 'standards', and manufacturing > engineers typically don't want support technicians to muck with > those for lots of very valid reasons. > > I'm in the US and don't have any real clue what the UK standards are > for impedance, transmission levels, etc. (It would be somewhat > interesting to here from someone who knows for sure what those are.) > > The x100p card (from digium) uses the Silicon Labs ( www.silabs.com ) > 3012 chip to interface with the pstn line, the 3021 chip to interface > the 3012 (analog-to-digital converter) to the Tigerjet PCI controller. > The 3012 is responsible for matching pstn line impedance. The spec > sheets at their site tend to suggest the 3012 was built to interface > to 600 ohm pstn lines and is not adjustable/setable to other values. > If the UK pstn lines are not 600 ohm impedance, then its unlikely the > x100p is going to properly match up with UK lines from an impedance > matching perspective. However, imedance mismatches have to be rather > dramatic to cause a lot of echo. > > The tdm fxo module uses the 3019 and 3050 chipset, where the 3019 pstn > line interface chip has many different pstn line impedance settings > including 600, 900, 270, 220, 370, 320, 275, 120, 350, etc, ohms. > Have no clue which countries use which settings, but obviously > Silicon Labs intended this chip set to operate in different countries, > whereas the 3012 spec sheet doesn't seem to support those objectives. > > So, backing into exactly what is causing the echo in the three UK > cases noted yesterday on this list... > - not likely to be "d" (2-wire to 4-wire conversion along the > end-to-end voice path) as that would impact all telco users, > not just * users. > - item "c" (pstn line problems) can contribute to echo depending > upon how bad the pstn line actually happens to be. Most telco's > have the equipment to measure line quality, however most will > stop at the cable entrance to your home/business, leaving you to > guess at what's happening inside. > - item "b" (mismatched x100p -> pstn line) can contribute, but without > knowing the exact specs (and probably more info from Silicon Labs), > its impossible to guess at this one. > - item "a" (echo can in *) is still a very real possibility, and Mark > is about the only person I know of that has the knowledge of the > spec's and * to weight in on this one. > > One of the methods that I used to help determine whether my tdm echo > was a pstn line or * issue was to eval echo on three different pstn > lines using the exact same physical * port (x100p). If the lines > are clean from an analog phone perspective (eg, no hum, no noise) and > the lines cause equal echo when used with *, then its highly likely the > issue is either "a" or "b". If the answers to "b" rule out impedance > mismatches, then "a" is likely. Why? Your not likely to have multiple > pstn lines with exactly the same fault. (Could happen but not likely.) > > Second, if your pstn line is also a DSL line with appropriate filters, > the DSL line is far more critical of pstn imperfections then is the > * interface to the analog pstn line. In the majority of cases, a poor > pstn line will cause significantly more DSL problems and probably a > total DSL failure way before the pstn analog path is impacted. > > Third, I obtained a Mediatrix 1204 sip gateway to displace the x100p's > to eliminate the echo. It worked fine (zero echo) on all three lines, > essentially proving the pstn lines were not the issue causing echo. > After that test, there was nothing left other then * echo can functions > (which turned out to be the case with my tdm fxo _and_ CO operation, > and resulted in this recent patch). > > Given that Mark has been successful at eliminating 95%+ of the echo > on the tdm fxo module, it proves the algorithm in use within * is > very reasonable. The algorithm is not sensitive to which "country" > it happens to be running in, but "how" that algorithm is applied to > UK pstn lines is suspicious. > > I'd suggest someone in the UK with echo problem go through the > logic above to rule out as many items as possible, and then try to > coordinate some of Mark's time (in advance) to help resolve the last > item. Do that via opening a Bug report, include as much factual > detail as possible, and be ready on the IRC channel. > > Rich > > > _______________________________________________ > Asterisk-Users mailing list > [EMAIL PROTECTED] > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users > _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users