Fun_People Archive
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