Subject: Re: Taxonomy Term closure needed

From: Joe Touch <[email-masked]>
Date: Fri, 10 Sep 1999 11:33:48 -0700 (PDT)

> > From [email-masked] Thu Sep  9 19:50 EDT 1999
> > 
> > Here's a suggestion for definitions of both forward cache
> > and reverse cache:
> > 
> > A FORWARD CACHE is a cache operating on behalf of a
> > user agent. It is typically outside the control of any
> > content provider.  It is the responsibility of the client or 
> > network operators to deliver requests to the forward cache.
> > Origin servers are typically oblivious to the existence of 
> > forward caches - a forward cache looks just like another client
> > to them, with the exception of a special HTTP request header that 
> > some forward caches insert.
> > 
> > A REVERSE CACHE is the cache operating on behalf of a
> > origin server. It is typically controlled by a content provider.
> > It is the responsibility of the content provider to deliver requests
> > to the reverse cache. Clients are oblivious to the existence of 
> > reverse caches - a reverse cache looks just like the origin server
> > to them, with the exception of a special HTTP response header
> > that some reverse caches insert.
> > 
> > Frank

There is no such thing as "on behalf of" in proxies.
They cache things they get, and serve them to requests they receive.

These definitions are dependent on who pays for it, 
who controls it, etc.

And whether they're oblivious to them or not is
implementation dependent.

The use of forward/reverse still isn't justified.

Joe

---

From: [email-masked]
Date: Fri, 10 Sep 1999 15:32:15 -0700 (PDT)

> The use of forward/reverse still isn't justified.

Unfortunately, the "on behalf of" section of the statement does impact
how a cache works.  For example, the cost (in latency or dollars) to
reach an origin server is likely to be higher for a proxy that acts on
behalf of a campus or organization than for a proxy that acts on behalf
of a content-provider network.  This means that the replacement algorithm
for the proxy acting on behalf of the content-provider network may be
different than the replacement algorithm for the proxy acting on behalf
of a campus.  

I used the term "surrogate" in the IRCACHE BOF to try to capture the
idea that the device acted on behalf of a different network element
(origin server, in this case) and to make clear that there were
operational differences between that model and the model represented
by the current installed base of proxy servers (which acts on behalf
of a group of end-user browsers or other user agents).  While I agree
that from a theoretical point of view they may be the same, they won't
be in implementation or operation; to me, that means they should be
distinguished.

I personally believe that the words "proxy" and "cache" have been
overloaded almost to the point of uselessness.  The taxonomy draft has
to deal with that, and I am coming to the conclusion that the best way
may be to start off with the admission that these terms have been
fuzzied up by sloppy usage.  Give the common definitions, fuzz and
all, then we can get on with more precise definitions which have some
rigor.

			regards,
				Ted Hardie

---

From: Joe Touch <[email-masked]>
Date: Sat, 11 Sep 1999 09:38:15 -0700

> different than the replacement algorithm for the proxy acting on behalf

These are tuning metrics. We're defining what a proxy is,
not who pays for it.

Perhaps I should rephrase - there is no such thing as "intent"
in a taxonomy. (unless we're classifying philosophies :-)

Joe

---

From: [email-masked]
Date: Mon, 13 Sep 1999 11:00:07 -0700 (PDT)

> in a taxonomy. (unless we're classifying philosophies :-)

I think there is a granularity question here, and that we disagree on
the level of granularity required.  The difference between and a proxy
and a surrogate is reflected in operation in a number of ways,
including placement in the network, relationship to other network
elements, and the thresholds used for caching proxying requests; to
me, those aren't just tuning metrics, but important parts of how these
devices act in the network.  You can combine them into a single term,
but I believe doing so forces you then to define derivative terms
which are less clear.

			regards,
				Ted Hardie