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 From:  Dinesh Nair <dinesh at alphaque dot com>
 To:  sai <sonicsai at gmail dot com>
 Cc:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] voip traffic shaping
 Date:  Thu, 17 Nov 2005 00:55:50 +0800
On 11/15/05 15:04 sai said the following:
> 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 happens usually at the hybrid between the analog and digital circuits. 
if it's a pure VoIP call, then echo is most likely caused by the microphone 
or speaker of the handsets you're using. echo cannot be introduced on the 
wire in a pure VoIP call as the transmit path does not leak into the 
receive path.

however, if you have shaping turned on, any traffic latency caused by the 
traffic shaper could affect the jitter of your voip packets. if you've got 
a jitter buffer or some sort of PLC (packet loss concealment) in your voip 
devices, this could be causing the buzz. try turning off PLC.

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml

-- 
Regards,                           /\_/\   "All dogs go to heaven."
dinesh at alphaque dot com                (0 0)    http://www.alphaque.com/
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