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RE: Scope of CT Guidelines

From: Sullivan, Bryan <BS3131@att.com>
Date: Wed, 24 Oct 2007 01:13:33 -0700
Message-ID: <8080D5B5C113E940BA8A461A91BFFFCD05D93C96@BD01MSXMB015.US.Cingular.Net>
To: <public-bpwg-ct@w3.org>

Here is my initial input. Overall I agree with Jo's proposal that the
initial CT guidelines should focus on a limited scope. To that purpose I
suggest we limit the use cases to the three I mention below. There is
still plenty of variation around that e.g. the available
representations, who selects them, etc.

First, some assumptions: 

1) The focus of the CT guidelines is to enable HTTP-based control of CT
for wired web content usability (which includes compatibility and
effectiveness) by mobile UA.

2) Given user consent for service via a CT proxy for usability purposes,
it's expected that a CT proxy will have no reason to violate a CP or
user agent directive related to the CT service, even if the directive is
incorrect and results in a poor user experience.

3) There are other roles for CT proxies, but they are not covered by
this guideline. They include CT functions related to generic policy
control (e.g. content filtering), content (e.g. ad) insertion,
optimization, etc. For these roles there are cases in which a CT proxy
may violate Content Provider (CP) or user agent directives, thus
negotiation or at least error handling may apply in those cases.

4) For secure services (HTTPS), the CT proxy service would normally be
bypassed for UA invoking TLS tunneling to the CP via the HTTP Connect
method. Alternatively, the CT proxy can rewrite CP URLs as local
resources (recreating the WAP gap!), but this may not be acceptable for
some CP. Thus unless the CT proxy rewrites CP URLs, it can have no role
in CT for secure services.

5) The CT guidelines will focus on CT control and thus assumes at least
one of the CP or UA is CT-aware. The case in which both CP and UA are
CT-unaware will be typical for years to come, but this is
business-as-usual for CT proxies.

6) CT proxies will typically be inserted into the request path by
UA/application configuration or network routing. Non-web UA/applications
will typically be configured to bypass CT proxies. If required,
detection of non-web UA/applications will likely use the same approach
as for CT-unaware UA detection, e.g. UA header filtering.

Re in "Magnus's original contribution"
"The content transformation proxy needs to be able to tell the client
browser...where to find the original content if it has been
transformed.": It seems this would be of no use to the UA unless it can
selectively bypass the CT proxy. As well, the original request URI
should be the same as the location of the original content, unless the
CT proxy is rewriting the URLs.

Re Jo's email:
"in theory at least there are 64 different combinations of aware/capable
component types in the delivery chain": 
I think we should assume the CT proxy is CT-aware. Otherwise all bets
are off; it may ignore the new headers etc that are specified. If you
accept that and my assumption (5), there are only three combinations,
- CT-unaware CP, CT-aware UA
- CT-aware CP, CT-unaware UA
- CT-aware CP, CT-aware UA

Case 3 "Client goes ahead and simulates desktop...this could land the
user in a delay and cost nightmare...": 
UA that attempt to simulate desktops should support advanced HTTP
features such as persistent connections and multiple outstanding
requests. Other than that, I think it should be outside (these) CT
guidelines scope to address optimization. That begins to get into the
policy/value-added-service area, in which as I mentioned before, CP or
UA directives may be violated by the CT proxy.

Best regards,
Bryan Sullivan | AT&T | Service Standards
-----Original Message-----
From: public-bpwg-ct-request@w3.org
[mailto:public-bpwg-ct-request@w3.org] On Behalf Of Jo Rabin
Sent: Tuesday, October 23, 2007 10:12 AM
To: public-bpwg-ct@w3.org
Subject: Scope of CT Guidelines

I thought it worth making a note and stimulating further discussion
following today's productive CT TF call.

I'm worried that if we step into the space of how to do 3 way content
negotiation we will be opening the lid on Pandora's box. 

The starting point, I think, is that there are three types of component,
server, proxy and browser. Each of those can be capable of
transformation. Add to this that each of them will independently also be
aware or unaware of whatever our guidelines state about how to
cooperate. So in theory at least there are 64 different combinations of
aware/capable component types in the delivery chain. That's a bit too
complicated for my taste.

So I wonder if it's worth considering the question of repurposing the
presentation separately from markup and formatting fixups? 

So far as presentation is concerned I think there's a relatively small
set of cases, though each of them undoubtedly has its own complexity.

Case 1.
a) the Server has only a desktop oriented presentation only
b) the browser has mobile presentation only 

A proxy may have a useful role in re-presenting the content.

Note though, that in this case, the server's desktop presentation may
actually be a universal presentation (call my web pages boring but they
are designed to render across all delivery contexts) so in that case the
proxy should not interfere either.

Case 2. 
a) The Server has both a mobile and a desktop experience
b) Client has mobile experience only

Server presents mobile experience. Proxy stays out of the way.

Case 3. 
a) The Server has a desktop oriented presentation only
b) Client can simulate desktop

Client goes ahead and simulates desktop

(There is an argument that says that this could land the user in a delay
and cost nightmare. So is that an argument against the concept of
simulating desktop on a mobile, or is it an argument for saying that
there is a role for transforming proxy to reduce that delay and cost

Also same case as in 1, where the server has a single presentation, but
that presentation is suitable across the board.

Case 4.
a) The server has a choice of presentations
b) The client has a choice of presentations

The user should be able to get either i) the mobile presentation ii) the
simulated desktop presentation. That choice may be triggered by
selection locally to the client or at the server.

Case 5. 

Although this looks like a Web request, in fact it isn't. It's some ad
hoc protocol xmlhttprequest-like thingy.

(Proxy leaves well alone)

I'm assuming that this is a more of less complete list of scenarios
where the presentation is adjusted at most once.

Now I think that we can consider on top of this whether the proxy has a
role adjusting not the presentation, but details of the formatting -
e.g. to tweak the content type header, or to tweak the DOCTYPE to avoid
problems. Possibly to re-render images from one format to another.

To my mind, that is almost certainly enough to do deal with in volume 1
of the guidelines. I think we should leave the door open to later
elaborations that discuss 3 way content negotiation, servers
deliberately delegating formatting or presentation tasks to proxies and
so on. However all that falls firmly in a volume 2.

I'm hoping that by restricting the initial scope we stand a chance of
meeting the proposed timescales for the deliverable, and of addressing
in a timely way the key point of the Task Force's existence - which is
to provide a way for Transforming Proxies to get out of the way of
mobile ready content.  

Hope this makes sense and looking forward to comments.

Received on Wednesday, 24 October 2007 08:14:15 UTC

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