[asterisk-users] Re: Bandwidth requirements

[Matthew Crocker]

True but you need to look at the actual speed of a DSL line.  a 1.5m/ 
384k DSL line is actually 1.7m/467k  so a chunk of that ATM cell tax  
is already factored into the speed you buy from your DSL provider.   
If you get an integrated DSL modem/router like a Zoom X5 you can see  
the actual speed of the link.



On Oct 5, 2006, at 9:31 AM, Benny Amorsen wrote:

>>>>>> "rJ" == raphael Jacquot <sxpert at sxpert.org> writes:
>
> rJ> ATM cell tax is actually 10% as there's 5 header bytes for each 53
> rJ> bytes cell,
>
> For VoIP the cell tax is much larger. In the example, each RTP packet
> contains 20 useful bytes and 40 bytes IP overhead. 60 bytes doesn't
> fit in one cell, so you end up with 106 bytes at the ATM layer to
> transport 20 bytes of G.729. The ATM-caused overhead is thus 46 bytes
> per voice packet, thereby making the needed bandwidth 77% larger.
>
> All in all VoIP over ADSL adds 430% overhead, when using G.729 and
> 20ms packets. Lovely, isn't it?
>
>
> /Benny
>
>
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--
Matthew S. Crocker
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Crocker Communications, Inc.
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PO BOX 710
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