Subject: Re: [Ieprep] VoIP demo in Atlanta

From: [email-masked]
Date: Wed, 27 Nov 2002 12:35:22 EST

In a message dated 11/27/2002 6:45:08 AM Eastern Standard Time, 
[email-masked] writes:

> Dave Oran, who knows a fair bit about the internals of the IP phone that
> Bill was using for the demos, said that the particular IP phone that was 
> used
> for the demo always adds substantial implementation-specific FEC beneath the
> G.711 codec output and above UDP.  That is, this FEC is a normal property 
> of that
> particular IP phone in its default configuration.  

[MAP] Interesting addition to the the whole notion of VoIP. G.711 takes 
exactly 64 kbit/s in circuit mode. It has been generally said that it takes 
80 kbit/s over IP because of the overhead (similar to what the IETF liked to 
call "Cell Tax" when talking about ATM). If an FEC needs to be added to 
tolerate the commonly occurring packet loss ratio, what does this add to the 
required bandwidth? I would suspect at least another 10-15 kbit/s if it can 
tolerate a 40% packet loss ratio.

Perhaps Dave would like to tell us exactly what bandwidth this phone uses.

Mike Pierce
Artel