PWG> RE: IFX> Attempt to close on the two Notification specs at the fa ce to face meetings

PWG> RE: IFX> Attempt to close on the two Notification specs at the fa ce to face meetings

PWG> RE: IFX> Attempt to close on the two Notification specs at the fa ce to face meetings

Carl Kugler kugler at
Tue Aug 27 14:34:34 EDT 2002

One reason to have the redirect is to reduce the number of connections 
that the printer has to maintain.  Some printers are very limited in the 
number of simultaneous connections they can support (like, 4).  The relay 
approach would only make that situation worse.


"Hastings, Tom N" <hastings at>
Sent by: owner-pwg at
08/26/2002 06:25 PM

        To:     ipp at, ifx at, Harry Lewis/Boulder/IBM at IBMUS
        cc:     pwg at
        Subject:        PWG> RE: IFX> Attempt to close on the two Notification specs at the fa  ce 
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

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

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

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)?


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.

- 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
(2) The 'ippget' Delivery Method for Event Notifications

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. 


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. If
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




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