Network Working Group Marvin Solomon
Request for Comments: 884 Edward Wimmers
University of Wisconsin - Madison
December 1983
TELNET TERMINAL TYPE OPTION
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.
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 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 WON'T TERMINAL-TYPE
Sender refuses to send 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.)
IAC SB TERMINAL-TYPE IS ... IAC SE
Sender is stating the name of his terminal type. The code for IS
is 0. (See below.)
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3. Default
DON'T TERMINAL-TYPE
WON'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
WILL TERMINAL-TYPE is free to transmit type information, spontan-
eously or in response to a request from the sender of the DO. At
worst, this may lead to transmitting the information twice. 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).
The terminal type information is an NVT ASCII string. Within this
string, upper and lower case are considered equivalent. A few
terminal type names useful in the context of IBM systems are listed
below. It is anticipated that additional names will be added in the
future. The complete list of valid terminal types will be found in
the latest "Assigned Numbers" RFC.
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RFC 884 December 1983
The following is an example of use of the option:
Host1: IAC DO TERMINAL-TYPE
Host2: IAC WILL TERMINAL-TYPE
(Host2 is now free to send status information at any time.
Solicitations from Host1 are NOT necessary. This should not
produce any dangerous race conditions. At worst, two IS's will
be sent.)
Host1 (perhaps): 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 meaning-
ful to both ends of the negotiation. The list of suggestions below
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.
Here are a few terminal types useful in the IBM environment:
