14 Sep

dog bandwidth

Date: Tue, 14 Sep 93 20:14:09 PDT To: Fun_People Subject: dog bandwidth From: bostic@vangogh.CS.Berkeley.EDU (Keith Bostic) From: Tanenbaum's "Computer Networks", second edition, p.49: Image that you have trained your St. Bernard, Bernie, to carry a box of three floppy disks instead of a flask of brandy. (When your disk fills up, you consider that an emergency.) These floppy disks each contain 250,000 bytes. The dog can travel to your side, wherever you may be, at 18 km/hour. For what range of distances does Bernie have a higher data rate than a 300 bps telephone line? --- [WARNING! Some answers are revealed in the following messages. -psl] --- ______________________________________________________________________________ From: jim@tadpole.com (Jim Thompson) Subject: Re: dog bandwidth Hmm, lets see: speed of Bernie = 5 m/s (1.8 * 10^4 / 3600) speed of modem = 30 bytes/sec seconds to transfer a 'Bernie load' via 300bps modem 750000 bytes / 30 bytes/sec = 25000 seconds distance traveled by Bernie in 25000 seconds: 125000 m seconds to transfer a 'Bernie load' via V.32bis/V.42 modem 750000 bytes / (14400/8) bytes/sec = 416.6 seconds distance traveled by Bernie in 416.6 seconds: 2083 m seconds to transfer a 3.5" PC disk 'Bernie load' via V.32bis/V.42 modem 1.44 * 1024 * 1024 * 3 diskettes = 1509949 bytes 1509949 bytes / (14400/8) bytes/sec = 839 seconds distance traveled by Bernie in 839 seconds: 4195 m Usenet via Bassett hound, anyone? Jim (Please don't embarrass me if I got the math wrong.) ______________________________________________________________________________ From: psl@acm.org (Peter Langston) Subject: Re: Re: dog bandwidth Hmmm.... Gee, Jim, your math is perfect; but you had a couple of typos... > seconds to transfer a 3.5" PC disk 'Bernie load' via V.32bis/V.42 modem > 1.44 * 1024 * 1024 * 3 diskettes = 1509949 bytes > 1509949 bytes / (14400/8) bytes/sec = 839 seconds > distance traveled by Bernie in 839 seconds: 4195 m That probably should have said: 1.44 * 1024 * 1024 * 3 diskettes = 4529848 bytes (approx) 4529848 bytes / (14400/8) bytes/sec = 2516 seconds distance traveled by Bernie in 2516 seconds: 12580 m But that's nothin'. Here's the NeXT version (as Steve J. would have once stated it): seconds to transfer a 'Bernie load' of NeXT Optical disks via 300bps modem 256 * 1024 * 1024 * 3 diskettes = 805306368 bytes 805306368 bytes / (14400/8) bytes/sec = 447392 seconds distance traveled by Bernie in 447392 seconds: 2,236,960 m Note that this is more than one fifth of the way from the Earth's pole to the equator. Go Bernie! -psl

© 1993 Peter Langston