Telnet Protocol - a proposed document
RFC 137

Document Type RFC - Unknown (April 1971; No errata)
Updated by RFC 139
Last updated 2013-03-02
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Network Working Group                                   T. C. O'Sullivan
Request for Comments: 137                                       Raytheon
NIC 6714                                                   30 April 1971

                            TELNET Protocol

   This is a request for comment and is being distributed in advance of
   the Atlantic City meetings for review and comment prior to or during
   discussions on TELNET in preparation for issuing an official

   It is also being distributed so that selected installations planning
   to implement early versions of TELNET will have a common basis for
   such implementation.

   The proposed document is the result of the work of the committee.  It
   represents a TELNET protocol felt to be adequate for initial
   implementation.  A few recent suggestions by committee members and
   others have been incorporated where even though not thoroughly
   cleared with all members, the chairman felt that they clarified the
   protocol or would tend to simplify implementation but not
   substantially change the agreed-upon approach.

   Readers are referenced to the following previous releases of

   1. Conventions for Using an IBM 2741 Terminal or a User Console for
      Access to Network Server HOSTS
         Joel Winett, RFC 110 (NIC #5809)

   2. Level III Server Protocol for the Lincoln Laboratory 360/67 HOST
         Joel Winett, RFC 109 (NIC #5808)

   3. First Cut at a Proposed TELNET Protocol
         J. Melvin, D. Watson, RFC 97 (NIC #5740)

   4. ASCII Format for Network Interchange
         V. Cerf, RFC 20 (NIC# 4722)

   Another RFC will be distributed prior to the Atlantic City Meetings
   containing many of the arguments supporting the proposal.

O'Sullivan                                                      [Page 1]
RFC 137                     TELNET Protocol                   April 1971

                            TELNET PROTOCOL

                          A Proposed Document

                T. O'Sullivan for the TELNET Committee

               Will Crowther                 BBN
               Bob Long                      SDC
               John Melvin                   SRI-ARC
               Bob Metcalf                   Harvard
               Ed Meyer                      MAC
               Tom O'Sullivan (Chairman)     Raytheon
               Joel Winett                   MIT-LL

O'Sullivan                                                      [Page 2]
RFC 137                     TELNET Protocol                   April 1971

   TELNET is a third-level protocol, the function of which is to make a
   terminal (or process) at a using site appear to the system or a
   process at a serving site as logically equivalent to a terminal
   "directly" connected to the serving site.  In performing this
   function, the protocol attempts to minimize the amount of information
   each HOST must keep about the characteristics of other HOSTS.


   Protocol Levels (see Figure 1)

      Level 1

         HOST-IMP protocol specified by BBN in NIC 5735, Specifications
         for the Interconnection of a HOST, and an IMP (BBN Report 1822)

      Level 2

         HOST-HOST protocol performed by NCPs as described in Document
         Number 1 (NIC 5413) and subsequent amendments, see RFC 107 (NIC

            One view of the NCP's function is that it takes information
            from the net and routes it to receiving processes via
            mechanisms internal to each HOST; conversely, processes use
            the NCP, via internal system calls, to have information
            routed to other processes in the net (via the other
            processes' NCPs).

      Level 3 (see Figure 2)

         Level 3 is, by definition, the place to which and from which
         the NCP communicates internally in its own host.

            This level may be equivalent to the user process level in
            some systems, but this may not be the case in all systems.
            In using sites, the TELNET process operates at this level.
            In serving sites, the TELNET server operates at this level.

   Initial Connection Protocol (ICP)

      An agreed-upon sequence of level 3 exchanges between two processes
      which is, in general, used to synchronize the dialogue between the
      processes, e.g., RFC 80 (NIC #5608) #1.

O'Sullivan                                                      [Page 3]
RFC 137                     TELNET Protocol                   April 1971

   Serving Site

      The HOST into which the TELNET process is directing the user's
      keyboard input and from which the TELNET process is receiving
      control information and data effecting the user's terminal.  At
      the serving site, a TELNET server is executing.

   Using Site

      The HOST in which the TELNET process is executing.

   Sending Site

      The HOST transmitting data, could be either using site or serving
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