PWG> Re: IFX> Attempt to close on the two Notification specs at the face to face meetings

PWG> Re: IFX> Attempt to close on the two Notification specs at the face to face meetings

PWG> Re: IFX> Attempt to close on the two Notification specs at the face to face meetings

Robert Herriot bob at
Tue Aug 27 05:14:30 EDT 2002


If we agree that we must keep the redirection notion, then I agree (mostly)
with your proposed changes, but not with your reasoning.  However, I still
think that most clients will not implement redirection, so redirection ends
up being effectively proprietary and thus not a concept that should be in a
standard.  Assuming that we will keep redirection, here are my thoughts on
your proposal.

You propose a possible implementation of a printer with a remote
notification server and imply that the existence of this solution somehow
changes the rules.  This implementation may have led you to this solution,
but it is not the essence of your proposal or important to it.

The effect of what your proposed change is that a printer must directly
support ipp-get if it supports event notification. That is, the cannot
return nothing and redirect the client to the real notification server. Your
proposal could have stopped there and said that the redirection uri is

Instead, you added an optional "alternate-target-uri" attribute, which I
think should be called "optimal-target-uri" (as that is what it really is).
The "redirect-uri" has the flaw that the client gets nothing if it doesn't
implement "redirect-uri". With "optimal-target-uri", the client gets event
notifications even if it doesn't implement "optimal-target-uri". Its
implementation is an optimization only -- but perhaps not sufficiently
optimal to be worth the support of anyone.  Once you realize, that
"optimal-target-uri" is just an optimal uri, it need not be just some remote
notification server. It could also be a different uri in the same printer.
It doesn't really matter, but the presence of this attribute tells the
client that there is a better uri to use. If you keep this attribute, I
would leave the language open for the uri to be anywhere a printer wants it
to be.

I also think that in item 3, client support is a "MAY" rather than a
"SHOULD".  It doesn't really matter whether a client supports this
attribute, especially almost no one will implement it.

I also would ask if the "optimal-target-uri" must be different from the
printer-uri. That is, could it always be returned by a printer, even when it
would be the same as the printer uri.  I think that the intention is that a
printer would only return it when there is an optimal uri that is different
from the printer, but that it need not be different (i.e. the client need
not check for this).

Bob Herriot

----- Original Message -----
From: "Hastings, Tom N" <hastings at>
To: <ipp at>; <ifx at>; "Lewis, Harry" <harryl at>
Cc: <pwg at>
Sent: Monday, August 26, 2002 5:25 PM
Subject: RE: IFX> Attempt to close on the two Notification specs at the face
to face meetings

> Harry et al,
> In answering Ira's note, a win-win approach occurred to me.  This approach
> will allow a Printer to use a notification server, but won't put any
> on clients.  I called Ira up and he is enthusiastic as well.  He helped me
> flesh out the proposal.  Here is the idea:
> When a Printer implements Get-Notifications using a Notification Server,
> not have the Printer just pass each Get-Notifications request along to the
> Notification Server, which returns the response to the Printer which
> that response to the client.  In protocol terminology, the Printer is
> "relaying" the Get-Notifications request to the notification server.  Yes,
> this are 4 hops, instead of 2, but its transparent to the client.  The
> Notification Server can return to the Printer the "redirect-uri" operation
> attribute as an advisory hint to the client (which the Printer passes back
> to the client) to improve the performance, but clients not knowing about
> that "redirect-uri" operation attribute would simply keep doing subsequent
> Get-Notifications to the Printer.  The down side is that there are 4
> hops, instead of 2, for the client that didn't take the hint and go
> to the Notification Server for subsequent Get-Notifications.  In fact,
> this approach we even eliminate the 'redirection-other-site' status code,
> since the Printer is REQUIRED to return an accurate and up to date
> Get-Notifications response on the first (and all subsequent)
> Get-Notifications returns (by relaying the request to the Notification
> Server).
> Is this a way forward for the IPPGET proposed standard?
> So the changes to the IPPGET document would be as follows:
> 1. Delete the 'redirect-other-site' status code.
> 2. Clarify that the "redirect-uri" operation attribute in the
> Get-Notifications response is just a hint that the Printer returns to
> improve performance when the Printer is implemented using a notification
> server.
> 3. The client conformance section will say that the client SHOULD observe
> "redirect-uri" and try there (in order to improve performance by
> extra hops), but the client doesn't have to.  When going to draft
> if no one has implemented "redirect-uri", we delete it from the standard.
> 4. In order not to get our feature confused with HTTP redirect, lets
> the operation attribute returned from "redirect-uri" to
> "alternate-target-uri", since the client can perform the Get-Notifications
> to either the original Printer or the notification server for those
> that use a notification server.  Our feature is really a "relay", not a
> "redirect".
> Could this win-win proposal be discussed briefly during the PWG Plenary
> tomorrow (Tuesday, August 27) to see if we have consensus there (and we
> discuss it on the mailing list to see if we have consensus there too)?
> Comments?
> Tom and Ira
> P.S. In the future, if we want to generalize the relay mechanism for other
> operations, the same operation attribute can be returned in any response.
> For job operations, we probably would also need to return
> "alternate-job-uri" and "alternate-job-id" operation attributes in
> to the "alternate-target-uri" operation attribute.
> -----Original Message-----
> From: McDonald, Ira [mailto:imcdonald at]
> Sent: Monday, August 26, 2002 14:26
> To: 'Hastings, Tom N'; ipp at; ifx at
> Cc: pwg at
> Subject: RE: IFX> Attempt to close on the two Notification specs at the
> fa ce to fac e meetings
> Hi Tom,
> First - I agree that it would still be good to drop redirect from IPPGET
> and design it IN GENERAL for IPP (any operation response could return
> the redirect), including the fact that while it's nice for
> IPP Clients do NOT need to honor and follow redirects (any more than
> HTTP Clients need to do so - it's a matter of client policy).
> Second - if we publish IPPGET as a Proposed Std RFC (as you suggest)
> and LATER add redirect, we MUST recycle at Proposed Std RFC - it's
> illegal to add ANY new features when moving from Proposed Std to
> Draft Std status - only dropping existing features is legal.
> Cheers,
> - Ira McDonald
>   High North Inc
> -----Original Message-----
> From: Hastings, Tom N [mailto:hastings at]
> Sent: Friday, August 23, 2002 10:54 PM
> To: ipp at; ifx at
> Cc: pwg at
> Subject: IFX> Attempt to close on the two Notification specs at the face
> to fac e meetings
> The IPP WG Last Call period closed July 31 on the two IPP Notification
> that are required for IPP Notification:
> (1) IPP Event Notifications and Subscriptions
> <draft-ietf-ipp-not-spec-09.txt>
> (2) The 'ippget' Delivery Method for Event Notifications
> <draft-ietf-ipp-notify-get-07.txt>
> and Carl-Uno declared that (1) was approved, since there were no comments
> and that (2) achieved consensus to drop the redirection mechanism entirely
> from the IPPGET document.
> However, we have continued discussion about the merits and problems of the
> redirection mechanism because Harry Lewis has been the main objector to
> removing the redirection mechanism from IPPGET.  As a result I have not
> produced a new version of the document and Carl-Uno has not forwarded
> of the documents to Ned Freed, our Area Director.
> <...snip...>
> Process considerations:
> Could we delete the redirection mechanism for now from IPPGET?  Get our
> published as a Proposed standard.  Implement IPPGET and do
> testing.  See if the burden in the Printer of supporting the IPPGET method
> justifies offloading it to a Notification Server using the redirect
> mechanism.  If the implementation experience shows that its not much of a
> burden in the Printer we made the right decision to delete redirection.
> implementation experience shows that having a Notification Server is
> important to off-load the Printer's support of the IPPGET method, then add
> the redirection back into the IPPGET spec before progressing the document
> a Draft standard.  Perhaps in the meantime, IBM can also implement the
> Notification Server and see if it is really a win and that the extra
> administrative effort is worth the benefit to simplifying the Printer
> implementation.
> Comments?
> Tom
> <...snip...>

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