[asterisk-users] Re: Bandwidth requirements

[Benny Amorsen]

>>>>> "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