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"? Any 2-wire analog leg will be a source of echo. Many, many, many calls do not have a 2-wire leg. 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. -- 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
