What is Network Virtual Terminal in TELNET?

TELNET stands for Terminal Network. It follows the approach of client-server. The connection of the local system to the remote system is established in such a way that the local system starts to appear in the remote system. This TCP/IP protocol is used to provide virtual terminal service. Therefore, it allows users to access the services of the remote system and then get back the results to the local system.

Network Virtual Terminal (NVT): 

• NVT (Network Virtual Terminal) is a virtual terminal in TELNET that has a fundamental structure that is shared by many different types of real terminals. 
• TELNET clients and servers send data, commands, and server output using a virtual terminal type called NVT, rather than a variety of terminal types for different operating systems (Network Virtual Terminal) as systems are heterogeneous nowadays. 
• The character set, carriage return, and line termination are all defined by the NVT (Network Virtual Terminal). 
• NVT (Network Virtual Terminal) was created to make communication viable between different types of terminals with different operating systems.

How does NVT work?

It works as follows and is also represented in the above figure:

• The client TELNET converts the characters from the local terminal into NVT format and then sends them to the network.
• Then the server TELNET converts NVT-formatted data and commands into a format that the Remote Computers can understand.

Network Virtual Terminal (NVT) Character Set:

• The Network Virtual Terminal (NVT) primarily employs two sets of characters: one for data and another for control.
• The NVT is an 8-bit character set for data, with the 7 lowest-order bits identical to ASCII and the highest bit set to 0.
• The NVT uses an 8-bit bit character set to communicate control characters between the computers, with the highest-order bit set to 1.
• For sending data and control characters the TELNET makes use of the same connection by just inserting control characters into the data stream.
• Each control character is preceded by the Special Control character, which is popularly known as Interpret as Control, for separating the data characters from the control characters (IAC).