12.1 The NVT Protocol

NVT is an acronym for Network Virtual Terminal. NVT is a subset of the Telnet protocol, i.e., it is as if the Telnet protocol consists of two layers: the lower layer called NVT and the upper layer called the main Telnet protocol. The NVT protocol deals with data presentation, i.e., it provides answers to questions such as into which byte should the letter A be transformed in order to be interpreted as A again at the other end of the network connection, or which Telnet protocol command should be generated when the well-known Ctrl + C (^C) combination of characters is keyed in for abnormal termination of a program run from the console.

It is precisely the NVT protocol that is used (to a limited extent) for data presentation in a number of other protocols such as FTP, POP3, SMTP, NNTP, HTTP, etc. Multipurpose Internet Mail Extension (MIME) is basically an extension of this philosophy. This is also the reason why the NVT protocol is discussed in such detail. It is a...