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TELNET tips The Telnet protocol has been implemented on a variety of systems. Each is different, so specific commands depend on your version. However, all versions function similarly, so there are a few general guidelines to follow. The one common element across the disparate environments of the Internet is the TCP/IP software protocol suite, the basis of communications. Telnet, the terminal-handler portion of the TCP/IP protocol suite, is the cornerstone of this striking communications technology. Telnet handles the remote login to another Internet host, so it is useful to know something about the way it works. Telnet operates in a client/server environment in which one host (the computer you are using, running Client (User) Telnet) negotiates opening a session on another computer (the remote host, running Server Telnet). During the behind-the-scenes negotiation process, the two computers agree on the parameters governing the session. One of the first things they settle is the terminal type to be used -- in general, a line-by-line network virtual terminal, for simplicity's sake. Virtual terminal, in this context, refers to a set of terminal characteristics and sequences that both sides of a network connection agree to use to transmit data from terminals across the network, regardless of the terminal used. Finding Telnet Commands Try typing "help" or "?" at the Telnet prompt to get a list of the commands available in your Telnet software. Using Local versus Remote Commands Once you have established a remote session, all commands you type will be sent to the Server Telnet on the remote host for execution. If you want a Telnet command issued in the remote environment to be acted on locally by your client Telnet, on most systems you would normally precede the command with an escape sequence (a predetermined character or combination of characters that signal your Telnet software to execute the command that follows locally). For example, in NCSA Telnet for pc-compatible microcomputers, the F10 key is the escape character that alerts Telnet to execute locally the next command you type (to turn local echo on or off, or to toggle capture on or off, etc.). The Telnet escape sequence by itself followed by [cr] returns you temporarily to your local operating environment. On UNIX systems, the escape sequence is usually the control key (CNTL) and left bracket ([) pressed simultaneously. Logging On TELNET [host] or TELNET [cr] followed by OPEN [host] at the prompt. The basic command set is simple. You also need to know either the machine domain name or the machine Internet address (a series of numbers). The numbers will always work; the names will work if they are in a software table available to your version of Telnet. IBM systems that use TN3270 may require you to type a carriage return, "DIAL VTAM," or just "VTAM" in response to the first prompt from the remote system. Logging Off LOGOFF or LOGOUT (also try QUIT, END, EXIT, STOP, etc.) CLOSE, prefixed by the escape sequence. ABORT, prefixed by the escape sequence--use as a last resort! To exit the remote system, first try that system's logoff command. To determine what the appropriate logoff command is, check the menus, help, and welcome screens when you first log on. Oftentimes, the logoff information is listed there but not always easy to retrieve later. Logging off the remote system may return you to your primary operating environment (all the way out of Telnet), or you may be left in Telnet. If so, type "quit". But some information systems have no graceful exit for remote users. In that case, you have two options --- CLOSE or ABORT. CLOSE should be your next choice after LOGOFF. If you are unable to CLOSE the connection normally (e.g., if your remote session is hung), try the Telnet ABORT command to drop your connection locally. ABORT will return control to you in your local environment, but it may not properly terminate your session on the remote machine. Since this can leave the port on the remote machine busy for an indefinite period even though you are no longer using it, ABORT should be used only as a last resort. In either case, you can also try escaping back to your local environment and then issuing the termination commands. If one method doesn't work, try the other. Other commands may allow you to control your communications environment. Investigate the help systems both in your local Telnet and on the remote system at the outset. Using the BREAK Key Don't be hasty with the Break key. Too many Breaks may cause your Telnet session to be dropped! There is no standard BREAK key across versions of Telnet and in remote information systems. Telnet is based on the concept of a network virtual terminal, in which the control functions (breaks, etc.) are communicated with characters regardless of terminal type (rather than line conditions, used in the terminal server environment). Your local Telnet receives your break and sends out a character sequence which is reinterpreted on the other end, hopefully as the break you intended. Your Break may not always be understood by the remote system, so you should try HELP or ? when you begin (at the Telnet prompt) to determine what your version of Telnet uses as BREAK. Tips: In UNIX, CNTL-C may work for BREAK. In the Mac environment, BREAK may be a click down menu option or a character combination. In NCSA Telnet (a popular PC version), BREAK is F10 followed by a lower case letter "b". Using the Backspace Key The backspace character may not be recognized by the remote system. Investigate in your local Telnet how to set an erasing backspace. Type ? at the Telnet prompt, or SET ? for a list of possibilities. Adjusting the Settings to your Needs Most Telnet programs have the ability to SET or TOGGLE many of these settings on and off. Erasable backspace, local echo, carriage return interpretation ([cr] or [cr][lf] -- i.e., carriage return or carriage return with line feed), and the escape character you use to return to the local environment are things that you can usually SET or TOGGLE at the Telnet prompt. Type ? and use Telnet's internal help system to change a setting. Using Function Keys Remember that special function keys are local implementations and have no significance in a remote session. Function keys such as INSERT, DELETE, ERASE END-OF-FIELD, PF, and PA keys may not be recognized in the remote environment. Even though function keys and control key combinations may have significance on the remote system, they may vary from those on your local system.