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