Not to beat a dead horse but a few more thoughts on bandwidth

[David Farber <dave () farber net>]

Begin forwarded message:

From: "Jonathan M. Smith" <jms () central cis upenn edu>
Date: January 3, 2006 7:08:37 PM EST
To: dave () farber net
Cc: "Jonathan M. Smith" <jms () central cis upenn edu>
Subject: Not to beat a dead horse but a few more thoughts on bandwidth


Dave:
        I really enjoyed that discussion and it brought a few more
thoughts. First, an old rule of thumb in systems design (I may have
learned this from you): accountants care about throughput, users
care about response time. Second, something we thought about in
the Gigabit Testbed effort quite explicitly (e.g., in John Shaffer's
PhD thesis) was the relationship between these two things, which
is roughly that the response time (to get an object) is
propagation time + (object size) / throughput. Third, the
object sizes, due to both Moore's Law (memory sizes are typically
the fastest-rising exponential) and consumer demand (e.g., Mpixels
on digital cameras), are increasing rapidly. The speedups we achieved
with the testbed program achieved usability, as I mentioned in
a previous e-mail on this topic.

The takeaway from the response time relationship however,
is that an increase in throughput
commensurate with increases in memory and object sizes will be
necessary to maintain the present state of affairs, and a trajectory
of even greater throughput improvements will be necessary for
increased usability.
                                                                Best,
                                                                -JMS

------------------------------------------------------------------------ 
-
Jonathan M. Smith
Olga and Alberico Pompa Professor of Engineering and Applied Science
Professor of Computer and Information Science, University of  
Pennsylvania
Levine Hall, 3330 Walnut Street, Philadelphia, PA 19104


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