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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.)

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RFC 930 January 1985 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

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RFC 930 January 1985 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.

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RFC 930 January 1985 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.

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