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Internet Printing Protocol scenarios for XP

From: Anderson, William L <WAnderson@crt.xerox.com>
Date: Tue, 16 Jan 2001 10:51:24 -0500
Message-ID: <BF85F885643CD21188230008C756293502E1E99B@crte128-2.wrc.xerox.com>
To: "'xml-dist-app@w3.org'" <xml-dist-app@w3.org>
One of my colleagues at Xerox has raised two scenario based concerns with
the current XP req'ts. Briefly the concerns arise from trying to implement
the Internet Printing Protocol (IPP) over HTTP and they are due to the fact
that the client and server roles are fixed in HTTP, with all invocation of
requests coming from the client side. There were two scenarios where this
didn't work well for IPP:

1) Initiation of security services usually need to come from the server side
as a challenge; initiating it from the client is possible with a new spec
from the IETF, but it not commonly implemented in products yet. There is
also a desire to invoke security services, based on particular operation
types requested by the client during an HTTP session, but this violates the
current IETF model for invocation of security services.

2) When you want to return notifications to the client side from the server,
which can happen minutes or even hours after the original print job request
was made, or be triggered by the printer running out of some resource, such
as paper, ink, etc.
To solve the problem, we either had to:
	a) have the client poll the server frequently for notifications, or
	b) use another HTTP session, with the client and server roles
reversed (but people usually don't like to have HTTP servers in work
stations for security reasons), or
	c) use a totally different protocol, like SMTP to send back
notifications.

If HTTP servers had been able to also issue requests back to HTTP clients,
we would not have had these problems.

It is important that there are not restrictions in XP that prevent it from
supporting the scenarios described above.

My understanding is that implementing these scenarios is at the application
level and is above the level of XP. Is this correct?

Bill Anderson
Xerox Corp.
Received on Tuesday, 16 January 2001 10:50:58 GMT

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