On Thu, Oct 05, 2006 at 10:53:14AM +0200, raphael Jacquot wrote: > Brian Candler wrote: > > >However on ADSL, you have to add the 15% ATM cell tax. And you would be > >wise > >to add 20% headroom (i.e. so your line is not more than 80% full) > > ATM cell tax is actually 10% as there's 5 header bytes for each 53 bytes > cell,
Only if all cells are filled. On average there will be half a cell empty at the end of each packet. A common case is 1500-byte packets; these will take 32 cells, or 1696 bytes total, giving a tax of 13%. Mix some smaller packets in with that and you get a higher tax. So I tend to work on 15% as a rule of thumb. However it's worse for VoIP as has been pointed out. e.g. if you are sending 60 byte packets (20 IP, 8 UDP, 12 RTP, 20 G729) then they will take two 53-byte cells, so you pay 46 extra bytes to carry 60 bytes of IP; the tax is then 77% (You will also have encapsulation, e.g. PPPoA, but that probably fits in the wasted space without needing another cell) Regards, Brian. _______________________________________________ --Bandwidth and Colocation provided by Easynews.com -- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
