<div dir="ltr"><br><br><div class="gmail_quote">2008/10/11 Eric ManxPower Wieling <span dir="ltr"><<a href="mailto:eric@fnords.org">eric@fnords.org</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d"><br>
<br>
Olivier wrote:<br>
> 2008/10/10 Eric ManxPower Wieling <<a href="mailto:eric@fnords.org">eric@fnords.org</a>><br>
><br>
>> All calls with a 2-wire analog piece have echo. You cannot perceive the<br>
>> echo because it happens so fast on non-VoIP connections. On VoIP calls<br>
>> you have significant extra latency while causes you you to perceive the<br>
>> echo.<br>
><br>
> Do you mean "generated locally" or "generated distantly" ?<br>
><br>
> I understand that VoIP extra latency sometrimes renders perceivable what was<br>
> unperceivable before.<br>
> What suprises me is to hear that media getways "filter one-way only" : as<br>
> 2-wires analog devices produce echo, and every phone has 2-wires analog<br>
> audio, in every call you've got at least 2 sources of echo : one in each<br>
> endpoint.<br>
<br>
</div>Where did you hear that media gateways "filter one-way only"?</blockquote><div><br>From a media gateway vendor (mentioning its own products capabilities).<br>That's the main reason I opened this thread as it surprised me a bit ...<br>
</div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><br>
<br>
Any 2-wire analog leg will be a source of echo. Many, many, many calls<br>
do not have a 2-wire leg.</blockquote><div>Even in handset audio circuit ?<br>I was thinking that any handset is a potential echo source due to this audio circuit ...<br>Do you agree ?<br> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Think cell/mobile or endpoints with PRI or T-1.<br>
<div class="Ih2E3d"><br>
><br>
>> Echo must be removed before the call is converted to VoIP -- in<br>
>> your case the Media Gateway is the device that must remove echo.<br>
><br>
><br>
> So, if Alice is hearing its own voice,<br>
> 1. where does it most probably come from ?<br>
> 2. where should it be removed ?<br>
<br>
> For both, I would reply :<br>
> 1. it most probably comes from Bob's phone (as other devices in-between are<br>
> digital so voice can't leak from there),<br>
> 2. Alice voice echo should canceled at every location: Bob's PBX, PSTN<br>
> network (ISDN in the case I had in mind) and Alice's Media gateway<br>
<br>
</div>If you (Alice) are hearing echo then the echo canceling can be done any<br>
time after it leaves Bob's 2-wire circuit but before the audio is<br>
converted to VoIP on your end.<br>
<br>
Telcos echo cancel cell/mobile phone calls (also a high latency path)<br>
and long distance calls, but almost never do EC on local calls. This<br>
is why you seldom get echo when calling a mobile phone or a long<br>
distance number -- you mostly get it on local calls.</blockquote><div><br>That's what I thought after reading white papers here and there <br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
<font color="#888888"><br>
--<br>
Consulting and design services for LAN, WAN, voice and data. Based near<br>
Birmingham, AL. Now accepting clients worldwide. Contact me for Tellabs<br>
echo canceling systems. Also see <a href="http://www.fnords.org/skillslist.html" target="_blank">http://www.fnords.org/skillslist.html</a><br>
</font><div><div></div><div class="Wj3C7c"><br>
_______________________________________________<br>
-- Bandwidth and Colocation Provided by <a href="http://www.api-digital.com" target="_blank">http://www.api-digital.com</a> --<br>
<br>
asterisk-users mailing list<br>
To UNSUBSCRIBE or update options visit:<br>
<a href="http://lists.digium.com/mailman/listinfo/asterisk-users" target="_blank">http://lists.digium.com/mailman/listinfo/asterisk-users</a><br>
</div></div></blockquote></div><br></div>