Telnet window size option (RFC1073)
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
Status of this Memo
Network Working Group D. Waitzman
Request For Comments: 1073 BBN STC
Telnet Window Size Option
Status of this Memo
This RFC describes a proposed Telnet option to allow a client to
convey window size to a Telnet server. Distribution of this memo is
1. Command Name and Option Code
Name = NAWS (Negotiate About Window Size)
Code = 31
2. Command Meanings
IAC WILL NAWS
Sent by the Telnet client to suggest that NAWS be used.
IAC WON'T NAWS
Sent by the Telnet client to refuse to use NAWS.
IAC DO NAWS
Sent by the Telnet server to suggest that NAWS be used.
IAC DON'T NAWS
Sent by the Telnet server to refuse to use NAWS.
IAC SB NAWS <16-bit value> <16-bit value> IAC SE
Sent by the Telnet client to inform the Telnet server of the
window width and height.
The window size information is conveyed via this option from the
Telnet client to the Telnet server. The information is advisory.
The server may accept the option, but not use the information that is
The client and server negotiate sending the window size information
using the standard Telnet WILL/DO/DON'T/WON'T mechanism. If the
client and server agree, the client may then send a subnegotiation to
convey the window size. If the client's window size is later changed
(for instance, the window size is altered by the user), the client
may again send the subnegotiation. Because certain operating
systems, on which a server may be executing, may not allow the window
size information to be updated, the server may send a DON'T NAWS to
the client to forbid further subnegotiation after it was initially
accepted. A negotiation loop will not form following these rules.
The subnegotiation consists of two values, the width and the height
of the window in characters. The values are each sent as two bytes,
in the Internet standard byte and bit order. This allows a maximum
window width or height of 65535 characters. A value equal to zero is
acceptable for the width (or height), and means that no character
width (or height) is being sent. In this case, the width (or height)
that will be assumed by the Telnet server is operating system
specific (it will probably be based upon the terminal type
information that may have been sent using the TERMINAL TYPE Telnet
The syntax for the subnegotiation is:
IAC SB NAWS WIDTH ...