Telnet Protocols
RFC 318

Document Type RFC - Unknown (April 1972; No errata)
Updated by RFC 435
Updates RFC 158
Last updated 2013-03-02
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Network Working Group                                         Jon Postel
Request for Comments: 318                                       UCLA-NMC
NIC: 9348                                                  April 3, 1972
References: RFC 139, 158, and NIC 7104

                            Telnet Protocol

   At the October 1971 Network Working Group Meeting, I promised to
   promptly produce a document which clearly and succinctly specified
   and explained the Official Telnet Protocol.  This document fails to
   meet any part of that promise.  This document was not produced
   promptly.  This document is neither clear nor succinct.  There is NO
   Official Telnet Protocol.

   The following pages present my understanding of the ad hoc Telnet
   protocol.  There are some who have serious questions about this
   protocol.  The proposed changes to the protocol are given in Section
   IV.

   Any comments should be promptly directed to me via the Network
   Information Center (Ident = JBP) or by phone (213) 825-2368 or by
   mail.

                              Jon Postel
                              SPADE Group
                              3804 Boelter Hall
                              UCLA
                              Los Angeles, California 90024

Postel                                                          [Page 1]
RFC 318                     Telnet Protocol                   April 1972

I.  DEFINITION OF THE NETWORK VIRTUAL TERMINAL

   The Network Virtual Terminal (NVT) is a bi-directional character
   device.  The characters are represented by 8 bit codes.  The NVT has
   no timing characteristics.  The character codes 0 through 127 are the
   USASCII codes.  (Note all code values are given in decimal.)  The
   codes 128 through 255 are used for special control signals.  The NVT
   is described as having a printer and a keyboard.  The printer
   responds to incoming data and the keyboard produces outgoing data.

The Printer

   The NVT printer has an unspecified carriage width (common values are
   40, 72, 80, 120, 128, 132).  The printer can produce representations
   of all 95 USASCII graphics (codes 32 through 126).  Of the 33 USASCII
   control codes (0 through 31 and 127) the following 8 have specific
   meaning to the NVT printer.

   NAME                  CODE    MEANING

   NULL (NUL)            0       A no operation.

   BELL (BEL)            7       Produces an audible or visible signal.

   Back Space (BS)       8       Backspaces the printer one character
                                 position.

   Horizontal Tab (HT)   9       Moves the printer to next horizontal
                                 tab stop.

   Line Feed (LF)        10      Moves the printer to next line (keeping
                                 the same horizontal position).

   Vertical Tab (VT)     11      Moves the printer to the next vertical
                                 tab stop.

   Form Feed (FF)        12      Moves the printer to the top of the
                                 next page.

   Carriage Return (CR)  13      Moves the printer to the left margin
                                 of the current line.

   The remaining USASCII codes (1 through 6, 14 through 31, and 127) do
   not cause the NVT printer to take any action.

Postel                                                          [Page 2]
RFC 318                     Telnet Protocol                   April 1972

The Keyboard

   The NVT Keyboard has keys or key combinations or key sequences for
   generating all of the 128 USASCII codes.  Note that although there
   are codes which have no effect on the NVT printer, the NVT Keyboard
   is capable of generating these codes.

The End of the Line Convention

   The end of a line of text shall be indicated by the character
   sequence Carriage Return Line Feed (CR, LF).  This convention applies
   to both the sending (Keyboard) and receiving (Printer)  (virtual)
   mechanisms.

Break and Reverse Break

   The Telnet control signals provide a BREAK signal which can be used
   to simulate the use of the break or attention or interrupt button
   found on most terminals.  This signal has no effect on the NVT.  When
   the BREAK Telnet control signal is used from server to user it is
   sometimes called "reverse break".  Such a reverse break has no effect
   on the NVT.

II.  DEFINITION OF TELNET PROTOCOL

   The purpose of Telnet Protocol is to provide a standard method of
   interfacing terminals devices at one site to processes at another
   site.

   The Telnet Protocol is built up from three major substructures, first
   the Initial Connection Protocol (ICP), second the Network Virtual
   Terminal (NVT), and third the Telnet control signals described
   herein.

   Telnet user and server processes follow the ICP to establish
   connections.  The term "Logger" has been associated with the set of
   processes in the serving system which respond to the ICP and perform
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