Telnet

Telnet is an application designed for reliable communication between two hosts to support user interaction with a remote system. It is one of the oldest IP protocols and from it several other protocols were developed. A telnet server listens for connections on TCP port 23. When a connection is opened from a telnet client to a server, the client attempts to connect to the remote machine using TCP on port 23 and uses a local port above 1023. The remote server will then provide services over that TCP connection. The client sends in ASCII text data and the server responds according to it's design. Telnet is the most basic of all TCP based protocols. When the client receives input from the user, it forwards that information to the telnet server. The client normally will send in the user data one ASCII character at a time unless the NAGLE algorithm is in use.

NAGLE ALGORITHM

The NAGLE algorithm makes telnet more efficient. Rather than wrap up every single character in a complete IP datagram, the whole input buffer of the keyboard or computer is sent at once or stored and sent as a group of characters once the return key is pressed on the keyboard (an end of line is detected on standard input by the telnet client).

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