On Monday 11 April 2005 20:01, Chris Bennett wrote: <snip> > The maximum real bandwidth, assuming no waste of data, is 768 * 48 / 53 = > 695. This accounts for the fact that ATM packets are 53 bytes, with bytes > being overhead. So that's the overall rate that I'm working with. Check. > I then set the MPU to 96 (2 * 48) since the minimum ethernet packet (64 > bytes) uses two ATM packets (each having 48 bytes of data). I use 48 > instead of 53 here because we already accounted for the ATM overhead in the > previous calculation. Makes sense. > For the overhead I use 24, since nearly each ethernet packet is going to > end up splitting an ATM packet at some point. Just going with law of > averages (instead of a real world statistical analysis), I'm going with > each ethernet packet wasting (on average) half of an ATM packet. Again > using 48 as the ATM packet size (since we accounted for ATM overhead > already), 48 / 2 = 24. Indeed. > A theoretical comparison of sending 10,000 bytes via various packet would > therefore look like this: > <scary numbers> > Which of course indicates just how much bandwidth small packets waste... Yeah. > So, is this logic crap or what? Should this at least be close to optimum > or did I forget something important or make an erroneous assumption? Those are always the thoughts I had. I never successfully played around with overhead or MPU though. Did you compare results with and without using overhead and mpu settings? <snip> > One thing I wish I could do would be to query the DSL modem to see exactly > how much bandwidth usage it is reporting, but unfortunately my ISP now uses > these crappy new ADSL modems that don't support SNMP :( :( My old SDSL > router did, and I miss that feature a lot, but not enough to buy new ADSL > modems myself. Yeah, my modem provides no useful information either. -- Jason Boxman Perl Programmer / *NIX Systems Administrator Shimberg Center for Affordable Housing | University of Florida http://edseek.com/ - Linux and FOSS stuff _______________________________________________ LARTC mailing list LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
