jbash@cisco.com (07/25/90)
> Hello people! > > I have three questions as follows: > > 1. In the MIL-STD 1782, Telnet have commands such as SE, NOP, DM, BRK, IP, > AO, AYT, EC, EL, GA, SB, WILL, WON'T, DO, DON'T, and IAC. How I can use > these commands? MIL-STD says, first we need to issue "Interpret as command" > (IAC) and then type command code to enter the above commands. With that, > still I can't understand. How I can do that in Telnet session? > > [ similar for FTP and SMTP ] You're suffering from the same misconception in all three cases. The MIL-STD documents and the Internet RFCs define protocols for communication between application programs, not between the user and the application. If you run a TELNET program on your local machine, that program may send commands to the remote machine. Normally, it will try to automatically negotiate TELNET options that reflect the attributes of your local terminal using WILL, WONT, DO, and DONT. If you hit the break key, it may automatically send a BRK. It's not intended that you, as a user, be able to send these commands. If, for instance, you were to send option negotiation commands that changed the way the remote program thought the link was configured, while the local program wasn't informed, you could render the connection completely nonfunctional. The local application _may_ allow you to directly send some of the protocol commands. For example, BSD TELNET allows you to send a BRK command from its control mode, and BSD FTP actually allows you to send any protocol command with its "quote" command... although you risk confusing the computers if you do this without knowing all the possible effects. The local application is not _required_ to let you do this. In fact, because it _is_ required to make sure the commands come in acceptable sequences, it could be argued that it should avoid letting you send arbitrary commands. All the standards you reference refer to communication between computers, not to communication between a computer and its user. The user interface is left up to the application developer, and any resemblance to the underlying protocol is a coincedence. -- J. Bashinski Release Engineering, cisco Systems