Telnet

The initial purpose of Telnet was to allow users to connect and control machines remotely. The Telnet protocol uses a plaintext TCP connection to transmit and receive data—so when SSH, which uses encrypted and secure connections, was introduced, administrators switched from Telnet to SSH. Telnet is now rarely used to remotely access a UNIX machine, but can still be used for troubleshooting TCP/IP networks and services.

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