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RE: HTTP Asynchronous Client Notifications (draft paper)

From: Frank DeRose <frankd@tibco.com>
Date: Fri, 4 May 2001 18:53:04 -0700
To: <eamon.otuathail@clipcode.com>, <xml-dist-app@w3.org>
IMHO, building event notification on top of HTTP is a really bad idea.

Think about the implications of using Technique 3 in your paper
(Delay-until-event, "never-ending-request") to do publish/subscribe with
wide fanout (1 publisher -> n subscribers, where n is very large).

HTTP (or rather, TCP, the usual underlying transport) is a
connection-oriented, point-to-point protocol.

So, first of all, you will consume resources just keeping the connections
open; as you noted in your paper, long-lived connections can get terminated
after an appropriate interval, so they will constantly need to get
reestablished (by whom?), with all the attendant round-trips.

Secondly, every time a publisher publishes a message, it will have have to
multiplex it into n point-to-point messages.

In this scenario, the network is quickly overwhelmed.

The right way to deliver events is through a multicast transport. Of course,
picking the right multicast transport and turning it into a standard that is
widely accepted, satisfies all security considerations, and has support in
standard software components (like browsers) is a major political
undertaking. But, paying the price up front is vastly preferable to trying
to graft event notification onto HTTP.

Frank DeRose
TIBCO Software Inc.
3165 Porter Dr
Palo Alto, CA 94303
650-846-5570 (vox)
650-846-1267 (fax)

> -----Original Message-----
> From: xml-dist-app-request@w3.org [mailto:xml-dist-app-request@w3.org]On
> Behalf Of Eamon O'Tuathail
> Sent: Sunday, April 22, 2001 2:32 PM
> To: xml-dist-app@w3.org
> Subject: HTTP Asynchronous Client Notifications (draft paper)
> One of the interesting challenges with SOAP and the XML Protocol is how to
> transport events and other asynchronous notifications from components that
> reside on an HTTP origin server to a client.
> There is a draft discussion paper that examines a range of techniques at:
>   http://www.clipcode.com/peer/index.htm
> and a summary diagram is at:
>   http://www.clipcode.com/peer/http_async_client_notifications.png
> I would be interested in hearing (a) if there are any other techniques in
> use, and (b) if anyone has had positive / negative experiences with any of
> these techniques?
> Eamon O'Tuathail
> Clipcode.com
> mailto:eamon.otuathail@clipcode.com
> http://www.clipcode.com
Received on Friday, 4 May 2001 21:54:48 UTC

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