Telnet terminal type option

Network Working Group                                     Marvin Solomon
Request for Comments: 930                                 Edward Wimmers
Supersedes: RFC 884                    University of Wisconsin - Madison
                                                            January 1985

                      TELNET TERMINAL TYPE OPTION


Status of This Memo

   This RFC specifies a standard for the ARPA Internet community.  Hosts
   on the ARPA Internet that exchange terminal type information within
   the Telnet protocol are expected to adopt and implement this
   standard.  Distribution of this memo is unlimited.

   This standard supersedes RFC 884.  The only change is to specify that
   the TERMINAL-TYPE IS sub-negotiation should be sent only in response
   to the TERMINAL-TYPE SEND sub-negotiation.  See below for further
   explanation.

1. Command Name and Code

   TERMINAL-TYPE    24

2. Command Meanings

   IAC WILL TERMINAL-TYPE

      Sender is willing to send terminal type information in a
      subsequent sub-negotiation

   IAC WON'T TERMINAL-TYPE

      Sender refuses to send terminal type information

   IAC DO TERMINAL-TYPE

      Sender is willing to receive terminal type information in a
      subsequent sub-negotiation

   IAC DON'T TERMINAL-TYPE

      Sender refuses to accept terminal type information

   IAC SB TERMINAL-TYPE SEND IAC SE

      Sender requests receiver to transmit his (the receiver's) terminal
      type. The code for SEND is 1. (See below.)

Telnet Terminal Type Option


   IAC SB TERMINAL-TYPE IS ... IAC SE

      Sender is stating the name of his terminal type. The code for IS
      is 0. (See below.)

3. Default

   WON'T TERMINAL-TYPE

      Terminal type information will not be exchanged.

   DON'T TERMINAL-TYPE

      Terminal type information will not be exchanged.

4. Motivation for the Option

   This option allows a telnet server to determine the type of terminal
   connected to a user telnet program.  The transmission of such
   information does not immediately imply any change of processing.
   However, the information may be passed to a process, which may alter
   the data it sends to suit the particular characteristics of the
   terminal. For example, some operating systems have a terminal driver
   that accepts a code indicating the type of terminal being driven.
   Using the TERMINAL TYPE and BINARY options, a telnet server program
   on such a system could arrange to have terminals driven as if they
   were directly connected, including such special functions as cursor
   addressing, multiple colors, etc., not included in the Network
   Virtual Terminal specification.  This option fits into the normal
   structure of TELNET options by deferring the actual transfer of
   status information to the SB command.

5. Description of the Option

   WILL and DO are used only to obtain and grant permission for future
   discussion. The actual exchange of status information occurs within
   option subcommands (IAC SB TERMINAL-TYPE...).

   Once the two hosts have exchanged a WILL and a DO, the sender of the
   DO TERMINAL-TYPE is free to request type information.  Only the
   sender of the DO may send requests (IAC SB TERMINAL-TYPE SEND IAC SE)
   and only the sender of the WILL may transmit actual type information
   (within an IAC SB TERMINAL-TYPE IS ... IAC SE command).  Terminal
   type information may not be sent spontaneously, but only in response
   to a request.

   The terminal type information is an NVT ASCII string.  Within this

Telnet Terminal Type Option


   string, upper and lower case are considered equivalent.  The complete
   list of valid terminal type names can be found in the latest
   "Assigned Numbers" RFC.

   The following is an example of use of the option:

      Host1: IAC DO TERMINAL-TYPE

      Host2: IAC WILL TERMINAL-TYPE

         (Host1 is now free to request status information at any time.)

      Host1: IAC SB TERMINAL-TYPE SEND IAC SE

      Host2: IAC SB TERMINAL-TYPE IS IBM-3278-2 IAC SE

6.  Implementation Suggestions

   The "terminal type" information may be any NVT ASCII string
   meaningful to both ends of the negotiation.  The list of terminal
   type names in "Assigned Numbers" is intended to minimize confusion
   caused by alternative "spellings" of the terminal type.  For example,
   confusion would arise if one party were to call a terminal
   "IBM3278-2" while the other called it "IBM-3278/2".  There is no
   negative acknowledgement for a terminal type that is not understood,
   but certain other options (such as switching to BINARY mode) may be
   refused if a valid terminal type name has not been specified.  In
   some cases, a particular terminal may be known by more than one name,
   for example a specific type and a more generic type.  In such cases,
   the sender of the TERMINAL-TYPE IS command should reply to successive
   TERMINAL-TYPE SEND commands with the various names, from most to
   least specific.  In this way, a telnet server that does not
   understand the first response can prompt for alternatives.  However,
   it should cease sending TERMINAL-TYPE SEND commands after receiving
   the same response two consecutive times.  Similarly, a sender should
   indicate it has sent all available names by repeating the last one
   sent.  Note that TERMINAL-TYPE IS must only be sent in response to a
   request (TERMINAL-TYPE SEND), because a host that sent TERMINAL-TYPE
   IS and then received TERMINAL-TYPE SEND couldn't determine whether
   the other host was requesting a second option or the TERMINAL-TYPE
   SEND and the TERMINAL-TYPE IS crossed in midstream.

   The type "UNKNOWN" should be used if the type of the terminal is
   unknown or unlikely to be recognized by the other party.

Telnet Terminal Type Option


   The complete and up-to-date list of terminal type names will be
   maintained in the "Assigned Numbers".  The maximum length of a
   terminal type name is 40 characters.