TCP-on-a-LAN
RFC 872

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RFC 872                                            September 1982
                                                                M82-48

                               TCP-ON-A-LAN

     
     

     

                              M.A. PADLIPSKY
                           THE MITRE CORPORATION
                          Bedford, Massachusetts

     

                                 Abstract
     

     

          The sometimes-held position that the DoD Standard
     Transmission Control Protocol (TCP) and Internet Protocol (IP)
     are inappropriate for use "on" a Local Area Network (LAN) is
     shown to be fallacious.  The paper is a companion piece to
     M82-47, M82-49, M82-50, and M82-51.

                                     i

     
     
     
     
                              "TCP-ON-A-LAN"

                              M. A. Padlipsky

     Thesis

          It is the thesis of this paper that fearing "TCP-on-a-LAN"
     is a Woozle which needs slaying.  To slay the "TCP-on-a-LAN"
     Woozle, we need to know three things:  What's a Woozle?  What's a
     LAN?  What's a TCP?

     Woozles

          The first is rather straightforward [1]:

               One fine winter's day when Piglet was brushing away the
          snow in front of his house, he happened to look up, and
          there was Winnie-the-Pooh.  Pooh was walking round and round
          in a circle, thinking of something else, and when Piglet
          called to him, he just went on walking.
               "Hallo!" said Piglet, "what are you doing?"
               "Hunting," said Pooh.
               "Hunting what?"
               "Tracking something," said Winnie-the-Pooh very
          mysteriously.
               "Tracking what?" said Piglet, coming closer.
               "That's just what I ask myself.  I ask myself, What?"
               "What do you think you'll answer?"
               "I shall have to wait until I catch up with it," said
          Winnie-the-Pooh.  "Now look there."  He pointed to the
          ground in front of him.  "What do you see there?
               "Tracks," said Piglet, "Paw-marks."  he gave a little
          squeak of excitement.  "Oh, Pooh!  Do you think it's a--a--a
          Woozle?"

          Well, they convince each other that it is a Woozle, keep
     "tracking," convince each other that it's a herd of Hostile
     Animals, and get duly terrified before Christopher Robin comes
     along and points out that they were following their own tracks
     all the long.

          In other words, it is our contention that expressed fears
     about the consequences of using a particular protocol named "TCP"
     in a particular environment called a Local Area Net stem from
     misunderstandings of the protocol and the environment, not from
     the technical facts of the situation.

                                     1

     RFC 872                                            September 1982

     LAN's

          The second thing we need to know is somewhat less
     straightforward:  A LAN is, properly speaking [2], a
     communications mechanism (or subnetwork) employing a transmission
     technology suitable for relatively short distances (typically a
     few kilometers) at relatively high bit-per-second rates
     (typically greater than a few hundred kilobits per second) with
     relatively low error rates, which exists primarily to enable
     suitably attached computer systems (or "Hosts") to exchange bits,
     and secondarily, though not necessarily, to allow terminals of
     the teletypewriter and CRT classes to exchange bits with Hosts.
     The Hosts are, at least in principle, heterogeneous; that is,
     they are not merely multiple instances of the same operating
     system.  The Hosts are assumed to communicate by means of layered
     protocols in order to achieve what the ARPANET tradition calls
     "resource sharing" and what the newer ISO tradition calls "Open
     System Interconnection."  Addressing typically can be either
     Host-Host (point-to-point) or "broadcast." (In some environments,
     e.g., Ethernet, interesting advantage can be taken of broadcast
     addressing; in other environments, e.g., LAN's which are
     constituents of ARPA- or ISO-style "internets", broadcast
     addressing is deemed too expensive to implement throughout the
     internet as a whole and so may be ignored in the constituent LAN
     even if available as part of the Host-LAN interface.)

          Note that no assumptions are made about the particular
     transmission medium or the particular topology in play.  LAN
     media can be twisted-pair wires, CATV or other coaxial-type
     cables, optical fibers, or whatever.  However, if the medium is a
     processor-to-processor bus it is likely that the system in
     question is going to turn out to "be" a moderately closely
     coupled distributed processor or a somewhat loosely coupled