TELNET: the mother of all (application) protocols

摘要

Telnet's true value is not the abstraction of how-to-wire-terminals-to-hosts (standardizing connections); instead, it's the abstraction of terminals (standardizing endpoints). Telnet's application-level semantics are captured in its external interface, the Network Virtual Terminal. Its internal interfaces have close ties to TCP transport facilities, an option negotiation scheme, and symmetric treatment of client and server roles. Notice that none of these three internal functions has any bearing on remote-login, the most popular application of Telnet. Instead, in considering Telnet against the taxonomic criteria set forth previously, we need to separate Telnet from the services it can access. That helps highlight the enduring lessons of Telnet for future seventh-layer protocol designers.