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RE: T is for Transfer

From: Joseph Hui <jhui@digisle.net>
Date: Thu, 28 Mar 2002 13:51:55 -0800
Message-ID: <C153D39717E5F444B81E7B85018A460B081B2797@ex-sj-5.digisle.com>
To: "Mark Baker" <distobj@acm.org>
Cc: "Appleton Pete M" <PMAppleton@bemis.com>, <highland.m.mountain@intel.com>, <xml-dist-app@w3.org>
> From: Mark Baker [mailto:distobj@acm.org]
[snip]
> BTW, what do you mean by "application-level payloads"?
E.g. SOAP messages, XML messages, ...
Note that HTTP messages can be seen as application-level payloads
as well.  Such payload's PDU is usually per-message, though
sometimes the boundaries are murky, like in the case of HTML text.

In contrast, TCP packets are transport-level payload for 
network-level protocols like IP, where the PDU is per-packet.

Cheers,

Joe Hui
Exodus, a Cable & Wireless service
===============================================

> Does HTTP not
> already carry these?  It is an application protocol, in the OSI sense
> of the term.
> 
> > HTTP is not a transport protocol by design; but it doesn't 
> stop people
> > from seeing it as one creatively, often for its "port-80 firewall
> > friendliness."  I'd be quite comfortable to design an application
> > protocol that specifies HTTP as its transport where in-band data
> > (e.g. HTML content) are carried in HTTP bodies, and out-of-band
> > data ( e.g. application-specific content signals) are embedded
> > in HTTP extended headers.
> 
> I think the main reason that people want to use HTTP as a transport
> protocol is that they don't understand how they can achieve their
> goals by using it as an application protocol.  i.e. they don't
> understand what the HTTP methods, particular POST, mean.
> 
> Let me explain ...
> 
> If I wrote up a purchase order on a piece of paper, and walked up to
> a stranger on the street and handed it to them, they could either
> say "ok, I'll take care of it", or "what the heck is this"?  This
> is what POST does.  Of course, "I'll take care of it" can mean many
> things; if the person shreds paper, then that will yield a different
> result than if the person works at the purchasing department 
> of Walmart.
> That's why it always helps to know what type of person they are.  On
> the Web, I might find that out through several means such as;
> 
> <a href="http://strange-person.org" 
> rel="http://walmart.com/purchaser">
> 
> or
> 
> HEAD http://strange-person.org
> response;
> Resource-Type: http://walmart.com/purchaser
> 
> or
> 
> <http://strange-person.org> rdf:type <http://walmart.com/purchaser>
> 
> etc..
> 
> MB
> -- 
> Mark Baker, Chief Science Officer, Planetfred, Inc.
> Ottawa, Ontario, CANADA.      mbaker@planetfred.com
> http://www.markbaker.ca   http://www.planetfred.com
> 
Received on Thursday, 28 March 2002 16:51:59 GMT

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