TELNET TCP/IP terminal simulation Protocol

TELNET: TCP/IP Terminal Emulation Protocol
TELNET is a terminal simulation protocol in a TCP/IP environment. It establishes a connection between the server and the client over TCP. After the connection, the TELNET server and the client enter the negotiation stage to determine the options.) Select both parties to support the connection operation, and each connection system can negotiate the new options or re-negotiate the old options at any time ). Generally, TELNET serves as many options as possible at any end to maximize system performance.

Once a TELNET connection is established, both ends of the connection can be initiated or interrupted in the network virtual terminal NVT. NVT is a hypothetical device that represents the standard, generic, and intermediate representation of a standard terminal, this avoids the need for "servers" and "users" to maintain information such as terminal and terminal processing examples. The principle of negotiable options is based on this fact: Any host wants to provide other available services on NVT, and any user has excellent terminal devices and needs high-quality services.

Once a TELNET connection is established, the optional requests between the two Parties will be sent back and forth as each party wants to obtain as many services as possible from the other party. In addition, these optional requests can also be used to dynamically modify connection features to adapt to changing local environments.

Over the past 20 years, TELNET is a multi-function simulator. Option enables TELNET to transmit binary data, support for byte macros, simulation graphics terminals, and transfer information to support centralized terminal management.

The TELNET command uses ASCII text. The TELNET command is as follows:

Commands Code No. DecHex Description data     All terminal input/output data. End subNeg 240 FO End of option subnegotiation command. No Operation 241 F1 No operation command. Data Mark 242 F2 End of urgent data stream. Break 243 F3 Operator pressed the Break key or the Attention key. Int process 244 F4 Interrupt current process. Abort output 245 F5 Cancel output from current process. You there? 246 F6 Request acknowledgment. Erase char 247 F7 Request that operator erase the previous character. Erase line 248 F8 Request that operator erase the previous line. Go ahead! 249 F9 End of input for half-duplex connections. SubNegotiate 250 FA Begin option subnegotiation. Will Use 251 FB Agreement to use the specified option. Won’t Use 252 FC Reject the proposed option. Start use 253 FD Request to start using specified option. Stop Use 254 FE Demand to stop using specified option. IAC 255 FF Interpret as command.

Defined in RFC854

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