IFX Mail Archive: RE: PWG> RE: IFX> Attempt to close on t

IFX Mail Archive: RE: PWG> RE: IFX> Attempt to close on t

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

From: Hastings, Tom N (hastings@cp10.es.xerox.com)
Date: Tue Aug 27 2002 - 18:15:59 EDT

  • Next message: Carl: "RE: IPP> Re: IFX> Attempt to close on the two Notification specs at the face to face meetings"

    I called Carl and his use case for using a separate Notification Server was
    for a number Printers that supported only a limited number of connections,
    say 4 as in a number of IPP printer network cards, and a large corporation
    with many clients (10,000). Off-loading these persistent connections to a
    big Notification Server seems important if a large number of clients might
    be using Event Wait Mode to get events for submitted jobs. If the job queue
    gets backed up on a Printer the number of such clients could be large, i.e.,
    the number of jobs in the queue.
    So this argument further justifies keeping the "optimal-target-uri" in the
    spec and perhaps increasing the client conformance from SHOULD to MUST, but
    certainly not watering it down to MAY.
    Following on with the strategies of a Printer with limited connections, such
    as might be used for an IPPFAX implementation, we have:
    Such a Printer can decide to terminate Event Wait Mode at any time,
    including in the first response, by returning the "notify-get-interval"
    operation attribute. And the client MUST disconnect and retry. So if the
    client conforms and disconnects, then the Printer's connection becomes free
    immediately, and the Printer doesn't have to remember the connection.
    Its only the case where the Printer decides to terminate Event Wait Mode,
    but the client is non-conforming and doesn't disconnect, that the Printer
    would have to disconnect (but have to remember the connection for 4 minutes
    according to TCP rules, thereby tying up the connection for that length of
    From the IPPGET spec:
    However, the Printer MAY decide to terminate Event Wait Mode at any time,
    including in the first response. In this case the Printer MUST return the
    "notify-get-interval" operation attribute. This attribute indicates that
    the Printer wishes to leave Event Wait Mode and the number of seconds in the
    future that the Notification Recipient client SHOULD try the
    Get-Notifications operation again. The Notification Recipient client MUST
    accept this response and MUST disconnect. If the Notification Recipient
    client does not disconnect, the Printer SHOULD do so.<?xml:namespace prefix
    = o ns = "urn:schemas-microsoft-com:office:office" />

    So this response would also contain the "optimal-target-uri". In this case,
    the Printer would NOT have had to relay the Get-Notifications to the
    Notification Server. Then the client MUST disconnect and then
    MUST/SHOULD/MAY (TBD) retry the Get-Notifications on the returned URI (which
    could be anywhere, including the original target).
    Tom and Carl

     -----Original Message-----
    From: Carl Kugler [mailto:kugler@us.ibm.com]
    Sent: Tuesday, August 27, 2002 14:12
    To: Hastings, Tom N
    Cc: ipp@pwg.org
    Subject: RE: PWG> RE: IFX> Attempt to close on the two Notification specs at
    the face to face meetings

    A Printer dropping the connection doesn't help much. If a TCP server closes
    the connection, then according to TCP protocol it must remember the
    connection for two times max TTL, or 4 minutes. In most implementations, a
    connection in TIME_WAIT consumes the same resources as an ESTABLISHED


            "Hastings, Tom N" <hastings@cp10.es.xerox.com>

    08/27/2002 01:48 PM

            To: Carl Kugler/Boulder/IBM@IBMUS
            cc: ipp@pwg.org
            Subject: RE: PWG> RE: IFX> Attempt to close on the two
    Notification specs at the face to face meetings

    Good point that there are really two reasons why a Printer might want to use
    a notification server:
    1. off-load notification from the Printer to the Notification Server (e.g.,
    the Server maintains the Subscription objects and searches them when the
    Printer sends an event to the Notification Server)
    2. (new) reduce the number of IPPGET connections that the Printer has to
    maintain simultaneously.
    So a printer with limited connections would want the clients to go directly
    to the Server. However, the Printer can drop an IPPGET connection anytime,
    right? So perhaps we should add to the explanation about why a client
    SHOULD go directly to the alternate-target-uri notification server, in order
    to avoid having the IPPGET connection terminated.
    Or are you saying that we need to REQUIRE the client to use the
    "alternate-target-uri"? I'm hoping not, so that we can get the IPPGET
    document agreed to.
    -----Original Message-----
    From: Carl Kugler [mailto:kugler@us.ibm.com]
    Sent: Tuesday, August 27, 2002 11:35
    To: Hastings, Tom N
    Cc: Harry Lewis
    Subject: Re: PWG> RE: IFX> Attempt to close on the two Notification specs at
    the fa ce to face meetings

    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@cp10.es.xerox.com>
    Sent by: owner-pwg@pwg.org

    08/26/2002 06:25 PM

           To: ipp@pwg.org, ifx@pwg.org, Harry Lewis/Boulder/IBM@IBMUS
           cc: pwg@pwg.org
           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 burden
    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, why
    not have the Printer just pass each Get-Notifications request along to the
    Notification Server, which returns the response to the Printer which returns
    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 network
    hops, instead of 2, for the client that didn't take the hint and go directly
    to the Notification Server for subsequent Get-Notifications. In fact, with
    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 eliminating
    extra hops), but the client doesn't have to. When going to draft standard,
    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 change
    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 Printers
    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 will
    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 addition
    to the "alternate-target-uri" operation attribute.

    -----Original Message-----
    From: McDonald, Ira [mailto:imcdonald@sharplabs.com]
    Sent: Monday, August 26, 2002 14:26
    To: 'Hastings, Tom N'; ipp@pwg.org; ifx@pwg.org
    Cc: pwg@pwg.org
    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 interoperability
    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@cp10.es.xerox.com]
    Sent: Friday, August 23, 2002 10:54 PM
    To: ipp@pwg.org; ifx@pwg.org
    Cc: pwg@pwg.org
    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 specs
    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 yet
    produced a new version of the document and Carl-Uno has not forwarded either
    of the documents to Ned Freed, our Area Director.


    Process considerations:

    Could we delete the redirection mechanism for now from IPPGET? Get our RFC
    published as a Proposed standard. Implement IPPGET and do interoperability
    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 to
    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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