Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!gatech!gitpyr!robert
From: robert@gitpyr.gatech.EDU (Robert Viduya)
Newsgroups: comp.dcom.lans
Subject: Re: can you recommend an escape sequence?
Message-ID: <2765@gitpyr.gatech.EDU>
Date: Fri, 5-Dec-86 11:18:54 EST
Article-I.D.: gitpyr.2765
Posted: Fri Dec  5 11:18:54 1986
Date-Received: Sat, 6-Dec-86 03:13:04 EST
References: <1420@PUCC.BITNET>
Reply-To: robert@gitpyr.UUCP (Robert Viduya)
Organization: Office of Computing Services, Georgia Tech
Lines: 39

>IRWIN@PUCC.BITNET (IRWIN@PUCC.BITNET, <1420@PUCC.BITNET>):
> At Princeton we are building a campus-wide network which will support
> a variety of different devices.  We are in search of a good
> escape sequence which we can reserve for the use of the internet.
> Users currently type ESCAPE DELETE to get the network, but this sequence
> is used by some software.  We are considering Control-X Control-A, and
> would like to hear from others who have faced this situation.  What
> sequence did you choose?  Does anyone have a favorite piece of software
> or hardware that already makes use of the sequence Control-X Control-A?

Well, the Kermit protocol uses Control-A as a Start-Of-Packet indicator and
specifies that any character may precede it.

At GaTech, our campus-wide network uses the sequence Control-O
Control-L Control-L as a hold (i.e., pause the virtual circuit and drop
into a network control prompt) and Control-O Control-K Control-L as a
disconnect (hangup).  I'm not sure why those particular sequences were
chosen, but I do know that a three character sequence was chosen over a
two character sequences mainly to decrease the chances of that sequence
from occurring in various communication protocols.  One could easily
argue that a four character or five character sequence would decrease
the chances even more, but one has to draw a line somewhere.  Anyway,
the user can set the sequence to anything he wants to at any time,
although network software limits it to a maximum of four characters.
Alternatively, each port can be configured to use a BREAK instead of a
sequence of characters as either hold or disconnect (I've got BREAK set
as my hold sequence and no disconnect sequence).  In my opinion, BREAK
seems to be the best choice mainly because it is an "out-of-band"
signal (similar to RTS/CTS being "out-of-band" flow control signals).
Most host based software treat BREAK as being "fragile" and provide
ways of signalling a BREAK through other characters.


				robert
-- 
Robert Viduya					     robert@pyr.ocs.gatech.edu
Office of Computing Services					(404) 894-4660
Georgia Institute of Technology
Atlanta, Georgia	30332