> >with more than 15 voip phones working at the same time I get 
> some echo 
> >and buzzing sounds when shaping is turned on. Any ideas as 
> to why echo 
> >happens in voip networks?

Echo can occur for all sorts of reasons. In a straight IP-IP scenario it's
most likely caused by too great a latency between endpoints (itself a
symptom of insufficient bandwidth much of the time). If you have multiple IP
phones and you aren't running a local gateway (asterisk/SER/etc.) then
unless you have a very high-bandwidth connection you're going to suffer.

Rather than spend money on a faster connection, you'd be better off running
a gateway locally and consider persuading the IP clients (be they
hardphones, softphones or ATAs) to work with a less bandwidth-heavy codec.

FWIW, with IAX trunking you should be able to run between 10 and 15
concurrent calls over a 256/256 connection.

Regards,

Chris
-- 
C.M. Bagnall, Director, Minotaur I.T. Limited
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