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RE: Messaging Service Layer

From: Anne Thomas Manes <anne@manes.net>
Date: Mon, 17 Feb 2003 16:24:45 -0500
To: "Walden Mathews" <waldenm@optonline.net>
Cc: <www-ws-arch@w3.org>
Message-ID: <ECEDLFLFGIEENIPIEJJPEEKODIAA.anne@manes.net>

Please recognize that the term "transport" has different meaning in
different circumstances. When talking about the OSI 7-layer model,
"transport" refers to level 4, the transport layer (e.g., IP). But when you
pop up out of the network protocol world into the application domain,
"transport" doesn't have such a strict meaning. Many people use the term to
mean "the network protocols that I use to transfer my message" -- which is
equivalent to the entire OSI 7 layer stack. An application's access to this
"transport layer" is through level 7, the application layer. Hence
applications think of level 7 as the "transport layer".

TCP/IP isn't an application layer protocol. It's at levels 5 (TCP) and 4
(IP). An application can't just use TCP/IP. It needs an application-layer
protocol to access the network. Something like HTTP, SMTP, IIOP, etc.

From the network's perspective, SOAP (as with most middleware systems) is an
application. As with any other application, it accesses the network using an
application layer protocol. Unlike other middleware systems, SOAP has been
designed so that it can use any application layer protocol to access the
network. So it can use HTTP, SMTP, IIOP, etc. as its "transport".

We could build an entirely new application layer protocol for SOAP, but why
would we want to? This "transport"-independence is one of its most valuable
features. It's not so much a matter of firewalls. It's that **you don't have
to install a new network protocol to use SOAP.** You can just use what
already there -- e.g., HTTP.

Anne

> -----Original Message-----
> From: Walden Mathews [mailto:waldenm@optonline.net]
> Sent: Monday, February 17, 2003 12:09 PM
> To: Anne Thomas Manes
> Cc: www-ws-arch@w3.org
> Subject: Re: Messaging Service Layer
>
>
> > The topmost level of the OSI stack (Level 7 - the application layer)
> > represents the network layer (application protocol) that
> applications use
> to
> > access the network. HTTP sits in Level 7. That's why we view HTTP as the
> > "transport" layer. It is the OSI Level 7 application protocol
> that we use
> to
> > access the network.
>
> If you want a transport, why don't you use TCP?  Because of firewalls,
> right?
> But since firewalls have to be upgraded to understand what's buried inside
> SOAP
> messages and all that, why not just bite the bullet and decide to
> do things
> right in the first place?  Where, in the space of the WSA, is
> there anything
> remotely echoing this "do it right" sentiment?  The layers of
> bastardization
> are,
> frankly, discouraging.
>
> Walden
>
Received on Monday, 17 February 2003 16:25:03 GMT

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