Date: Mon, 18 Jun 2001 12:51:47 -0700
From: Mark Nottingham <mnot(_at_)akamai(_dot_)com>
Organization: Akamai Technologies
User-Agent: Mozilla/5.0 (X11; U; Linux 2.4.5 i686; en-US; rv:0.9.1)
Subject: RE: WG Review: Open Pluggable Edge Services (opes)
ALthough I've raised these concerns in the past, it seems appropriate to
OPES wants to interpose an intermeidiary processing model into HTTP (and
possibly other application-layer protocols), to allow services to be
applied to messages as they pass through.
While there are many scenarios where this is useful (especially when
there is knowledge and consent from either or both endpoints),
there are others where it is dangerous (where there is no such knowledge
or consent). In such solutions, the only thing an intermediary can do is
to use heuristics to determine how to interpose services.
As such, the OPES goals break end-to-end transparency at the
application layer. As a result, (using HTTP as an example, because it
seems the first target of OPES), the publisher loses control over a
resource once it leaves their server. It then becomes impossible to
makes statements about that resource (e.g., P3P, Semantic Web, legal
status of a resource, etc.).
I suppose this would be fine if there was an active need for client- or
server-driven OPES vectoring in the market (e.g., integration of OPES
into the browser, or into content delivery networks, etc.). However, I
see no market for OPES in the CDN world, despite ICAP's existence for
more than two years, and nothing on the client side. Instead, the only
ICAP services to date seem to be targetted at ISPs (e.g., virus
scanning, content transformation, ad insertion, etc.).
While nothing stops intermediaries from doing this now, it's another
thing, IMHO, to encourage these practices by standardizing them. HTTP
(perhaps unfortunately) does not preclude transformation of messages by
intermediaries, so OPES has authority to do what it wants to with the
protocol. My problem is that it provides considerable power to
intermediaries, before there are mechanisms (trust, etc.) in place to
mitigate its effects.
Mark Nottingham, Research Scientist
Akamai Technologies (San Mateo, CA USA)
Michael W. Condry
Director, Network Edge Technology