On Friday 28 May 2004 14:54, Andy Furniss wrote: <snip>
Reading your other post I see your small traffic is ~100b - this would use three cells, so as a temporary kludge you could set your mpu to 159 and see how it goes.
AFAIK the author of the HTB patch is looking into modifying it to do the sums properly for DSL. There isn't one answer though - Eds' formula is fine doing the cells bit, but before this you need to add a ppp overhead to the IP packet length and this varies with pppoa+vc mux/pppoe/bridged pppoe and probably other varieties of dsl implementations.
But there's no tried and true method of determining that information?
You mention at least three methods of mangling PPP with Ethernet/ATM. And the overhead of each kind of setup also would vary depending on the specifics of that setup? (i.e., knowing you have bridged PPPoE doesn't instantly qualify you as having an overhread of 123i.)
Sounds particularly complicated.
But the overhead would be a fixed cost, no? If that is the case you can play whack-a-mole with that until you find a 'good' number. But, as I see it, without a realtime ATM cost scheduler, even if I figure out my true 'overhead' it won't make much difference.
Thoughts, anyone?
You can find it by experementation - if you get a cell count from your modem it's easy.
If you are on BT in the UK using pppoa/vc mux it's 10 (you can't even look that up - the RFC says 9 or 10). ping -s 10 uses 1 cell -s 11 2. 10 data + 20 IP + 8 ICMP = 38, ATM cell data size = 48 so ppp overhead is 10.
Like ED I haven't really looked at the code - but will eventually If it doesn't get done by anyone else first :-)
Andy.
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