RFC 764 (rfc764) - Page 1 of 15

Telnet Protocol specification

IEN 148                                                        J. Postel
RFC 764                                                              ISI
                                                               June 1980

                     TELNET PROTOCOL SPECIFICATION


INTRODUCTION

   The purpose of the TELNET Protocol is to provide a fairly general,
   bi-directional, eight-bit byte oriented communications facility.  Its
   primary goal is to allow a standard method of interfacing terminal
   devices and terminal-oriented processes to each other.  It is
   envisioned that the protocol may also be used for terminal-terminal
   communication ("linking") and process-process communication
   (distributed computation).

GENERAL CONSIDERATIONS

   A TELNET connection is a Transmission Control Protocol (TCP)
   connection used to transmit data with interspersed TELNET control
   information.  TCP and the connection establishment procedure are
   documentented in the ARPA Internet Protocol Handbook.

   The TELNET Protocol is built upon three main ideas:  first, the
   concept of a "Network Virtual Terminal"; second, the principle of
   negotiated options; and third, a symmetric view of terminals and
   processes.

   1.  When a TELNET connection is first established, each end is
   assumed to originate and terminate at a "Network Virtual Terminal",
   or NVT.  An NVT is an imaginary device which provides a standard,
   network-wide, intermediate representation of a canonical terminal.
   This eliminates the need for "server" and "user" Hosts* to keep
   information about the characteristics of each other's terminals and
   terminal handling conventions.  All Hosts, both user and server, map
   their local device characteristics and conventions so as to appear to
   be dealing with an NVT over the network, and each can assume a
   similar mapping by the other party.  The NVT is intended to strike a
   balance between being overly restricted (not providing Hosts a rich
   enough vocabulary for mapping into their local character sets), and
   being overly inclusive (penalizing users with modest terminals).

      *NOTE:  The "user" Host is the Host to which the physical terminal
      is normally attached, and the "server" host is the Host which is
      normally providing some service.  As an alternate point of view,
      applicable even in terminal-to-terminal or process-to-process
      communications, the "user" Host is the Host which initiated the
      communication.






Postel