Lecture 3: Applications #1: Intro and Telnet

Telnet NVT

The telnet protocol defines a "Network Virtual Terminal" (NVT) that provides a standard interface to remote systems, regardless of their particular approach to terminal login. A telnet implementation (client or server) maps the semantics of local terminal operation to the NVT before sending data over the connection. Some aspects of the NVT include:

The basic unit of transmission is the "line of text" -- ideal for command-line interfaces.
An NVT text line contains only standard printable US-ASCII characters, terminated by an NVT "newline" indicator.
The NVT "newline" or "line ending" indicator is the two-character sequence: carriage return, decimal 13 followed by linefeed, decimal 10. Traditionally this has been written as <CR><LF>^[3]. A telnet implementation "maps" the "enter" or "return" key to this sequence before sending the line of text over the TCP connection.
The telnet NVT has a few other interesting characterictics: it assigns special meaning to a few other ASCII control codes, permits certain "out of band" commands to be sent to the remote host, and has facilities for "Option Negotiation".

^[3] The "angle brackets" here (ie, < and >) were traditionally used to indicate an ASCII control character. They are now so commonly used in HTML markup (see later) that this older usage is disappearing.

previous | start | next