Telnet Protocol: A Proposed Document
RFC 158

Document Type RFC - Unknown (May 1971; No errata)
Obsoleted by RFC 495
Updated by RFC 318
Updates RFC 139
Last updated 2013-03-02
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Network Working Group                                      T. O'Sullivan
Request for Comments: 158                                       Raytheon
NIC: 6768                                                    19 May 1971

                            TELNET Protocol

   This request for comment is being circulated by the TELNET committee
   to solicit comments, evaluation, and requests for modification of the
   proposed protocol presented here.  Unless comments are received by
   the writer within two weeks of the date of this RFC, they will not be
   considered in the preparation of official TELNET PROTOCOL document.

   The proposed document is the result of the work of the committee.  It
   represents a TELNET protocol felt to be adequate for initial

   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. Response to RFD 110
            Wayne Hathaway, RFC 135 (NIC #6712)

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

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

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

      6. Discussion of TELNET PROTOCOL
            Tom O' Sullivan, RFC 139 (NIC 6717)
         (Although relevant to the obsoleted RFC 137 (NIC 6714) many of
         the examples still hold.  A replacement discussion document RFC
         159 (NIC 6769) will be forthcoming in the near future).

T. O'Sullivan                                                   [Page 1]
RFC 158                     TELNET PROTOCOL                  19 May 1971

                                 TELNET PROTOCOL

                               A Proposed Document

                      T. O'Sullivan for the TELNET Committee

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

T. O'Sullivan                                                   [Page 2]
RFC 158                     TELNET PROTOCOL                  19 May 1971

Telnet Protocol

   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 connection dialogue
      between the processes, e.g., RFC 80 (NIC #5608) #1, as revised by
      subsequent information.

T. O'Sullivan                                                   [Page 3]
RFC 158                     TELNET PROTOCOL                  19 May 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.
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