Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!ames!ucbcad!ucbvax!CRYS.WISC.EDU!solomon From: solomon@CRYS.WISC.EDU.UUCP Newsgroups: mod.protocols.tcp-ip Subject: Submission for mod-protocols-tcp-ip Message-ID: <8703261719.AA12871@crys.wisc.edu> Date: Thu, 26-Mar-87 12:19:24 EST Article-I.D.: crys.8703261719.AA12871 Posted: Thu Mar 26 12:19:24 1987 Date-Received: Sat, 28-Mar-87 05:11:26 EST Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The ARPA Internet Lines: 42 Approved: tcp-ip@sri-nic.arpa Path: crystal!solomon From: solomon@crys.WISC.EDU (Marvin Solomon) Newsgroups: mod.protocols.tcp-ip Subject: Re: Station wagon full of bits Summary: There's more to data communication than bits/second. Message-ID: <291@crys.WISC.EDU> Date: 26 Mar 87 17:19:24 GMT References: Organization: U of Wisconsin CS Dept Lines: 31 Vint Cerf has pointed out one pitfall in trying to use a single number to compare very different technologies: One must consider not only bandwidth, but also latency. But all the discussion on this topic so far has failed to note that the information-carrying capacity of a station wagon full of tapes (or a knapsack full of CS's, or whatever) and a 56Kbps leased line have different dimensions! Vint's "Johnny Appleseed" has units capacity*velocity = bits*length/time, whereas a communications line is measured in bits/time. Thus, to compare the two, one has to mention the distance. The problem we are considering was posed by Jon Bentley in his delightful Programming Pearls column, "The Back of the Envelope" in the March 1984 issue of "Communications of the ACM": At what distances can a courier on a bicycle with a reel of magnetic tape be a more rapid carrier of information than a 56-kilobaud [sic] telephone line? Than a 1200-baud line? [op cit, p. 182] The answers (based on considerably more realistic estimates about magnetic tape than have been bandied about in this forum, by the way) are, respectively, 20 miles and the distance the cyclist can travel in a week. The point is that a communication line can beat ANY bulk transfer over sufficiently long distances. Of course, we can effectively cut off discussion at (say) the diameter of the earth. To summarize: The advantages of networking are both low latency and distance-independence. -- Marvin Solomon Computer Sciences Department University of Wisconsin, Madison WI solomon@gjetost.wisc.edu or seismo!uwvax!solomon