Thinwire protocol for connecting personal computers to the Internet
RFC 914

Document Type RFC - Historic (September 1984; No errata)
Last updated 2013-03-02
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Network Working Group                                    David J. Farber
Request for Comments: 914                                   Gary S. Delp
                                                         Thomas M. Conte
                                                  University of Delaware
                                                          September 1984

                          A Thinwire Protocol
                   for connecting personal computers
                            to the INTERNET

Status of this Memo

   This RFC focuses discussion on the particular problems in the
   ARPA-Internet of low speed network interconnection with personal
   computers, and possible methods of solution.  None of the proposed
   solutions in this document are intended as standards for the
   ARPA-Internet.  Rather, it is hoped that a general consensus will
   emerge as to the appropriate solution to the problems, leading
   eventually to the adoption of standards.  Distribution of this memo
   unlimited.

What is the Problem Anyway ?

   As we connect workstations and personal computers to the INTERNET,
   many of the cost/speed communication tradeoffs change.  This has made
   us reconsider the way we juggle the protocol and hardware design
   tradeoffs.  With substantial computing power available in the $3--10K
   range, it is feasible to locate computers at their point of use,
   including in buildings, in our homes, and other places remote from
   the existing high speed connections.  Dedicated 56k baud lines are
   costly, have limited availability, and long lead time for
   installation.  High speed LAN's are not an applicable interconnection
   solution.  These two facts ensure that readily available 1200 / 2400
   baud phone modems over dialed or leased telephone lines will be an
   important part of the interconnection scheme in the near future.
   This paper will consider some of the problems and possibilities
   involved with using a "thin" (less than 9600 baud) data path.  A trio
   of "THINWIRE"  protocols for connecting a personal computer to the
   INTERNET are presented for discussion.

   Although the cost and flexibility of telephone modems is very
   attractive, their low speed produces some major problems.  As an
   example, a minimum TCP/IP Telnet packet (one character) is 41 bytes
   long.  At 1200 baud, the transmission time for such a packet would be
   around 0.3 seconds.  This is equivalent to using a 30 baud line for
   single character transmission.  (Throughout the paper, the assumption
   is made that the transmission speed is limited only by the speed of
   the communication line.  We also assume that the line will act as a
   synchronous link when calculating speed.  In reality, with interrupt,
   computational, and framing overhead, the times could be 10-50%
   worse.)

   In many cases, local echo and line editing can allow acceptable

Farber & Delp & Conte                                           [Page 1]



RFC 914                                                   September 1984
Thinwire Protocol

   Telnet behavior, but many applications will work only with character
   at a time transmission.  In addition, multiple data streams can be
   very useful for fully taking advantage of the personal
   computer/Internet link.  Thus this proposal.

   There are several forms that a solution to this problem can take.
   Three of these are listed below, followed by descriptions of possible
   solutions of each form.

   o    As a non-solution, one can learn to live with the slow
        communication (possibly a reasonable thing to do for background
        file transfer and one-time inquiries to time, date, or
        quote-of-the-day servers).

   o    Using TCP/IP, one can intercept the link level transmissions,
        and try various kinds of compression algorithms.  This provides
        for a symmetrical structure on either side of the "Thinwire".

   o    One could build an "asymmetrical" gateway which takes some of
        the transport and network communication overhead away from both
        the serial link and the personal computer.  The object would be
        to make the PC do the local work, and to make the
        interconnection with the extended network a benefit to the PC
        and not a drain on the facilities of the PC.

   The first form has the advantage of simplicity and ease of
   implementation. The disadvantages have been discussed above.  The
   second form, compression at link level, can be exploited in two ways.

      Thinwire I is a simple robust compressor, which will reduce the 41
      byte minimum TCP/IP Telnet packets to a series of 17 byte update
      packets.  This would improve the effective baud rate from 30 baud
      to 70 baud over a 1200 baud line (for single character packets).

      Thinwire II uses a considerably more complex technique, and takes
      advantage of the storage and processing power on either side of
      the thinwire link.  Thinwire II will compress packets from
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