taylor@ecsvax.UUCP (04/19/84)
Some new switching equipment which we are installing has a feature by which the user can enter a two-character ascii sequence to 1) disconnect from the current session, or 2) temporarily disconnect in order to turn echoplex on or off. The sequence is fully definable, and the only restriction is that the first character of each of the sequences must be unique. In order that the character be reproduced in the same fashion on every terminal, the character should probably be a control character for one of the characters 40 through 5f. (This includes the entire 26 character alphabet and a few other characters.) As soon as the first character of the sequence is encountered, it is buffered until the next character is entered. If the next character is the second character of the sequence, the appropriate action is taken. If the second character is not the second character of the defined sequence, both characters are then passed on to the host. The problem is.... HOW DO WE FIND A 2-CHARACTER SEQUENCE THAT NOBODY ELSE USES? For instance, EMACS uses all characters in this range except cntl-\. Escape is also a possibility as the first character, since it is virtually always used in a two-character sequence, but the problem then becomes, what should the second character of the sequence be? At this time, the leading contenders for the world's most innocuous sequences (which could be remembered by users) are: Sequence 1- cntl-\ cntl-\ Sequence 2- escape carriage return sequence 3- escape cntl-\ Has anyone else faced this problem? What were your results? p.s. yes, we can disable this function on a terminal-by terminal basis, but we are striving for as much uniformity as possible in a large network. Thanks! Steve Taylor NC Educational Computing Service !mcnc!ecsvax!taylor (919)-549-0671
emigh@ecsvax.UUCP (04/19/84)
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A scheme of this sort will effectively put a halt to up/down loading of
binary files unless you also looked for a pause before and after the
sequence. I have a Datec-212 Autodial which will disconnect after receiving
three cntl-D's in a row. While this is no problem most of the time, it is
disconcerting to have your line dropped half way through a long session.
A two character sequence will happen much faster (by two orders of magnitude)!
--
Ted H. Emigh North Carolina State University Raleigh NC
USENET: {akgua decvax duke ihnp4 unc}!mcnc!ecsvax!emigh
ARPA: decvax!mcnc!ecsvax!emigh@BERKELEY.ARPAksbszabo@wateng.UUCP (Kevin S. B. Szabo) (04/20/84)
The Sytek LocalNet 20 boxes at Waterloo uses <ESCAPE> <DEL> as the default two character command to enter a modem control mode. (This may have been set by the dept. that installs them). As a user of vi(1) the double buffering of <ESCAPE> <char> is definitely an annoyance. Usually you tend to hit <ESCAPE> twice to make sure it has gotten through or that you are back to command mode. Fortunately we can change it (as you can), and have done so on all terminals that regularly talk to UN*X. I agree that it is difficult to find a two character sequence that nobody else uses. -- Kevin Szabo watmath!wateng!ksbszabo (Elec Eng, U of Waterloo)
thomas@utah-gr.UUCP (Spencer W. Thomas) (05/07/84)
All our Sytek Localnet boxes are set to use <break> as the "escape sequence". They do come from the factory with <esc><rubout> set. This is quite annoying on a DEC-20 with command recognition. On the other hand, you almost never want to send a break. =Spencer
revc@noscvax.UUCP (Bob Van Cleef) (05/09/84)
The problem I have with using the BREAK is the number of terminals/computers that cannot send BREAKs. For example, the Osborne I computer. It cannot send a BREAK through the normal RS-232 port. I like the Sytek's ability to select your option as compared to systems, such as Dialog, that mandate one only. (For Dialog, the last I checked, the only way to interrupt was the BREAK, which my Osborne couldn't send). Bob Van Cleef Computer Sciences Corporation Naval Ocean Systems Center San Diego, CA MILNET revc@nosc UUCP sdcsvax!noscvax!revc CompuServe 71565,533
julian@ecsvax.UUCP (05/14/84)
It would be unfortunate to use any ACSII character, since you run the risk that some file has the sequence, or some device or program would use it. Assuming it is a Unix system, using something like a DEL character may be best of a bad choice, since this is the BREAK character or interrupt character, and no program should use it. Maybe an ESC-DEL would be the sequence to use, if an ASCII is your only choice. An electrical signal, like a BREAK signal of 100ms or more, would be preferred, since this signal should not be produced by any file, whether binary or text. BREAK could be an introducer character for the other functions. Phil Julian ecsvax!julian .