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From: mmorse@Z.NSF.GOV ("Michael H. Morse")
Newsgroups: comp.protocols.tcp-ip
Subject: Escape sequences over Telnet/TCP
Message-ID: <9105031255.AA10231@z.nsf.gov>
Date: 3 May 91 12:54:59 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 47


   We have a public information system (a bulletin board) that anyone
on the Internet can log on to.  The user interface is full screen
and makes use of cursor control keys, function keys, and keypad
functions such as pageup/pagedn.  It also uses the Escape key to mean
"exit this function."

   Like curses, we use a timer to distinguish between an
escape-sequence and the escape-key.  Dispite dire warnings, we have
found that this works across the Internet for *most* people.  The
reason it works, from my inspection of packets, is that, most of the
time, Telnet/TCP puts the entire escape sequence into a single packet,
so no matter how long it spends traversing the network, our timer
works.

   We have recently run into a system that seem to purposely break the
escape sequence up.  First it sends a packet with just the Escape
character, then it sends a packet with the remainder of the escape
sequence.  Obviously, a lot of the time this doesn't work on our
system, as the timer runs out before the rest of the escape sequence
arrives.  I assume it is doing this on purpose because it *always*
puts an escape in a single packet, but other packets sometimes contain
multiple characters.

   My question is:  How common is this?  Where did this "feature" come
from?  Are more or fewer systems going to behave like this in the
future?  Any information from folks familiar with this area would be
appreciated.  Is the feature implemented in Telnet or in TCP?  I would
think that most Telnet/TCP implementations would want to put closely
typed characters into a single packet to save overhead, and what could
be more closely typed than an escape sequence?

   Thanks in advance.

--Mike

p.s.  Please don't flame me for the choice of using the Escape
key.  I understand the technical limitations, and the fact that
there is probably nothing in the TCP/IP specs that guarantee that the
entire escape sequence should arrive together.

-- 

Michael Morse                           Internet: mmorse@note.nsf.gov
National Science Foundation               BITNET: mmorse@NSF
1800 G St. N.W. Room 401               Telephone: (202) 357-7659
Washington, D.C.  20550                      FAX: (202) 357-7663