Re: SUPDUP protocol


Barry Margolin (barmar@think.com)
9 Oct 87 00:50:07 GMT


In article <266223.871008.PAP4@AI.AI.MIT.EDU> PAP4@AI.AI.MIT.EDU ("Philip A. Prindeville") writes:
>I have a hard time imagining BITBLTing across the Internet at 56kps (and
>less). Now if we had T1 or T3... In any case, such bitmap transfers
>would be slower than waiting for the remote host to do your editing for
>you... And gobble much more bandwidth.

How often would you have to transfer huge bitmaps? About the only
time would be when you dump a screen to a file or printer. Most of
the time the units that window systems operate on are much higher
level, such as characters, lines, polygons, and windows.

Assuming that packet transmission cost is the same regardless of the
packet size, SUPDUP and windowing protocols can have about the same
network cost. In SUPDUP, each keystroke results in a tiny packet (one
TCP octet) being sent from the user's machine to the remote machine,
and a similar packet being returned. In X, it results in a keystroke
event packet, and an output packet being returned; X has its own
headers and stuff, so these packets are larger than the corresponding
SUPDUP packets, but they are still just one packet each way. This
requires that applications use X efficientl; for example, it has the
ability to transmit an event when a key is pressed and when it is
released, but it can be told not to bother sending the KeyUp.
Similarly, mouse tracking is usually done in the local host, not in
the remote; an event is generated when when a mouse button is pressed,
when boundaries are crossed, etc., unless the application really needs
to see all mouse motion.

---
Barry Margolin
Thinking Machines Corp.

barmar@think.com seismo!think!barmar



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