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From: ms6b+@andrew.cmu.edu (Marvin Sirbu)
Newsgroups: comp.dcom.telecom
Subject: Re: Prodigy Responds to E-Mail Criticism
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Date: 2 Dec 90 19:34:19 GMT
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X-Telecom-Digest: Volume 10, Issue 861, Message 7 of 12


The Prodigy system is designed like a multi-level memory hierarchy.
Information is stored initially at some nationwide location.  As it is
demanded in a particular city, it is copied to the city node and
cached there.  Thus subsequent reads do not require a transfer from
the national headquarters to the regional node.  (Cacheing is also
done in the PC, but that is irrelevant to the point of this message)

A bboard post, if widely read, will be copied from the national host
to each regional, and then read from the regional many times.  Thus,
every transfer from the national to the regional is "amortized" over
multiple reads.  I infer from the information supplied by Prodigy that
all individually addressed mail goes up to the national host and then
down to the regional for delivery to the recipient.

I also suspect for efficiency, the regionals are designed only to do
object cacheing, independently of the type of object. If so, it would
be a fairly radical change to reimplement mail so that mail objects
with multiple destinations are not replicated at the national host,
but in a two step process that would send one replica to each region
where there are addressees, and the region would then replicate the
object for each addressee. This would require the regionals to do more
than object cacheing: they would have to examine the content of the
object.

If replication does happen at the national level, then, indeed, a
multi-addressed message is much less efficient than a bboard post.


Marvin Sirbu
Carnegie Mellon