[asterisk-users] Question about echo cancelation

[Olivier]

2008/10/11 Eric ManxPower Wieling <eric at fnords.org>

>
> <snip>
> Where did you hear that media gateways "filter one-way only"?
>
> Hi ,

Reading over this reply, it seems to me that having EC working in one
direction is not a so well known fact.

Could we say :
1. EC working in one direction is the general case but some of us were not
aware of that (I was not, for instance)
2. or this is not so widespread use and some private architectures involve
EC working in both directions ?


For instance, what about Cisco Call Manager ?

Reading this
http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080149a1f.shtmland
specifically reading "IP Phone user hears echo" paragraph, I can't say
which direction(s) is (are) involved (as article don't mention which voice
is echoed).


Another interesting thing to note in this paper is the "solution is to use a
load ID on the IP phone, which includes echo suppression on the handset and
headset" (PSTN phone user  hears echo).
Does it imply echo cancelling is mostly done inside phones ?
In an IP phone, is it more cost effective to use 2-wires connections (which
produces echo) AND echo cancellation systems to suppress echo than to use
4-wires connections which don't produce echo in the first place ?
Does it also imply that Cisco IP phones use 2-wires connections ?


Cheers
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