[Asterisk-Users] Echo Canceling

[Kris Boutilier]

> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com]On Behalf Of Rich
> Adamson
> Sent: Wednesday, October 05, 2005 9:23 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Echo Canceling
> 
> 
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> 
> Identifying why a echo cancel tone is occurring on a normal voice call
> is reasonable, but why would a _local_ echo canceller be needed on a
> four-wire full-duplex digital link?
> 
> If the end-to-end call is digital all the way, there really isn't a need
> for it. So, isn't the issue one of who has responsibility for inserting
> the echo canceller when a 4-wire to 2-wire hybrid is involved? (Obviously,
> its not the originating site since one would have no idea what the 
> destination site is doing.) Or, is there an assumption going on that says
> an echo canceller is always needed on all pstn calls 
> regardless of whether is doing anything or not?
> 

Certainly this is correct if you're only considering the transport network, however it's also possible there are acoustic echos occuring inside the remote parties handset (ie. cheap handsets) or, if they've got you on a speakerphone, acoustic echos from the room itself. We do PRI-IAX-PRI calls between Norstar PBXs (digital path from handset to handset) and were still forced to install hardware echo cancellers facing towards each PBX to supress the acoustic echos introduced when a user went on to handsfree mode. If you consider the enormous number of trashy sets out in the world it becomes more reasonable to simply provision your own echo cancellation system facing the PSTN just incase.

Kris Boutilier
Information Services Coordinator
Sunshine Coast Regional District