The protocol developed for the ARPANET to allow users on one host computer to connect to the time-sharing resources of another host. The TELNET protocol specifies a standard terminal type, the network virtual terminal (NVT), including its character set (a modified form of ASCII) and standard control sequences for terminal functions such as ‘move to the next line’. Standard control sequences are also defined for host functions such as ‘interrupt process’. It is the responsibility of the programs at each end of the TELNET connection to perform a suitable mapping between the NVT’s character set and control functions, and the conventions of the local system. Many of the parameters of the NVT can be modified through option negotiation, in which both ends of the TELNET connection must agree to a proposed change before it can take place.

The name TELNET is also used for similar protocols in networks other than the ARPANET.