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        INTERNET-DRAFT                                  Robert Herriot (editor)
        <draft-ietf-ipp-notify-get-01.txt>                          Xerox Corp.
                                                                    Carl Kugler
                                                                     IBM, Corp.
                                                                    Harry Lewis
                                                                     IBM, Corp.
                                                              November 16, 2000
                           Internet Printing Protocol (IPP):
                  The 'ippget' Delivery Method for Event Notifications
        
            Copyright (C) The Internet Society (2000). All Rights Reserved.
        
        Status of this Memo:
        
        This document is an Internet-Draft and is in full conformance with all
        provisions of Section 10 of [rfc2026].  Internet-Drafts are working
        documents of the Internet Engineering Task Force (IETF), its areas, and
        its working groups.  Note that other groups may also distribute working
        documents as Internet-Drafts.
        
        Internet-Drafts are draft documents valid for a maximum of six months
        and may be updated, replaced, or obsoleted by other documents at any
        time.  It is inappropriate to use Internet-Drafts as reference material
        or to cite them other than as "work in progress".
        
        The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
        
        The list of Internet-Draft Shadow Directories can be accessed as
        http://www.ietf.org/shadow.html.
        
        
        Abstract
        
        The notification extension document [ipp-ntfy] defines operations that
        a client can perform in order to create Subscription Objects in a
        Printer and carry out other operations on them. A Subscription Object
        represents a Subscription abstraction. The Subscription Object
        specifies that when one of the specified Events occurs, the Printer
        sends an asynchronous Event Notification to the specified Notification
        Recipient via the specified Delivery Method (i.e., protocol).
        
        The notification extension document [ipp-ntfy] specifies that each
        Delivery Method is defined in another document. This document is one
        such document, and it specifies the 'ippget' delivery method.
        
        The 'ippget' Delivery Method is a 'pull and push' Delivery Method. That
        is, the Printer saves Event Notification for a period of time and
        expects the Notification Recipient to fetch the Event Notifications
        (the pull part). The Printer continues to send Event Notifications to
        
        
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        the Notification Recipient as Events occur (the push part) if the
        client has selected the option to wait for additional Event
        Notifications.
        
        When a Printer supports this Delivery Method, it holds each Event
        Notification for an amount of time, called the Event Notification Lease
        Time.
        
        When a Notification Recipient wants to receive Event Notifications, it
        performs an IPP operation called 'Get-Notifications', which this
        document defines. This operation causes the Printer to return all Event
        Notifications held for the Notification Recipient. If the Notification
        Recipient has selected the option to wait for additional Event
        Notifications, the Printer continues sending Event Notifications to the
        Notification Recipient as additional Events occur.
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
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        The basic set of IPP documents includes:
        
          Design Goals for an Internet Printing Protocol [RFC2567]
          Rationale for the Structure and Model and Protocol for the Internet
             Printing Protocol [RFC2568]
          Internet Printing Protocol/1.1: Model and Semantics [RFC2911]
          Internet Printing Protocol/1.1: Encoding and Transport [RFC2910]
          Internet Printing Protocol/1.1: Implementer's Guide [ipp-iig]
          Mapping between LPD and IPP Protocols [RFC2569]
          Internet Printing Protocol/1.0 & 1.1: IPP Event Notification
             Specification [ipp-ntfy]
        
        The "Design Goals for an Internet Printing Protocol" document takes a
        broad look at distributed printing functionality, and it enumerates
        real-life scenarios that help to clarify the features that need to be
        included in a printing protocol for the Internet.  It identifies
        requirements for three types of users: end users, operators, and
        administrators.  It calls out a subset of end user requirements that
        are satisfied in IPP/1.0.  A few OPTIONAL operator operations have been
        added to IPP/1.1.
        
        The "Rationale for the Structure and Model and Protocol for the
        Internet Printing Protocol" document describes IPP from a high level
        view, defines a roadmap for the various documents that form the suite
        of IPP specification documents, and gives background and rationale for
        the IETF working group's major decisions.
        
        The "Internet Printing Protocol/1.1: Model and Semantics" document
        describes a simplified model with abstract objects, their attributes,
        and their operations that are independent of encoding and transport.
        It introduces a Printer and a Job object.  The Job object optionally
        supports multiple documents per Job.  It also addresses security,
        internationalization, and directory issues.
        
        The "Internet Printing Protocol/1.1: Encoding and Transport" document
        is a formal mapping of the abstract operations and attributes defined
        in the model document onto HTTP/1.1 [RFC2616].  It defines the encoding
        rules for a new Internet MIME media type called "application/ipp".
        This document also defines the rules for transporting over HTTP a
        message body whose Content-Type is "application/ipp".  This document
        defines a new scheme named 'ippget' for identifying IPP printers and
        jobs.
        
        The "Internet Printing Protocol/1.1: Implementer's Guide" document
        gives insight and advice to implementers of IPP clients and IPP
        objects.  It is intended to help them understand IPP/1.1 and some of
        the considerations that may assist them in the design of their client
        and/or IPP object implementations.  For example, a typical order of
        
        
        
        
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        processing requests is given, including error checking.  Motivation for
        some of the specification decisions is also included.
        
        The "Mapping between LPD and IPP Protocols" document gives some advice
        to implementers of gateways between IPP and LPD (Line Printer Daemon)
        implementations.
        
        
        The "Event Notification Specification" document describes an extension
        to the IPP/1.0, IPP/1.1, and future versions. This extension allows a
        client to subscribe to printing related Events. Subscriptions are
        modeled as Subscription Objects.  The Subscription Object specifies
        that when one of the specified Event occurs, the Printer sends an
        asynchronous Event Notification to the specified Notification Recipient
        via the specified Delivery Method (i.e., protocol).  A client
        associates Subscription Objects with a particular Job by performing the
        Create-Job-Subscriptions operation or by submitting a Job with
        subscription information.  A client associates Subscription Objects
        with the Printer by performing a Create-Printer-Subscriptions
        operation.  Four other operations are defined for Subscription Objects:
        Get-Subscriptions-Attributes, Get-Subscriptions, Renew-Subscription,
        and Cancel-Subscription.
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
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                                   Table of Contents
        
        
        1  Introduction......................................................7
        
        2  Terminology.......................................................7
        
        3  Model and Operation...............................................8
        
        4  General Information...............................................9
        
        5  Get-Notifications operation......................................11
         5.1  Get-Notifications Request.....................................12
         5.2  Get-Notifications Response....................................13
        
        6  Subscription Template Attributes.................................18
         6.1  Subscription Template Attribute Conformance...................18
         6.2  Additional Information about Subscription Template Attributes.18
           6.2.1 notify-recipient-uri (uri).................................18
         6.3  Subscription Description Attribute Conformance................19
        
        7  Additional Printer Description Attributes........................19
         7.1  Printer Description Attribute Conformance.....................19
         7.2  New Values for Existing Printer Description Attributes........19
           7.2.1 notify-schemes-supported (1setOf uriScheme)................19
           7.2.2 operations-supported (1setOf type2 enum)...................19
         7.3  begin-to-expire-time-interval (integer(0:MAX))................20
        
        8  New Status Codes.................................................20
         8.1  redirection-other-site (0x300)................................20
        
        9  Encoding.........................................................20
        
        10 Conformance Requirements.........................................21
        
        11 IANA Considerations..............................................21
        
        12 Internationalization Considerations..............................21
        
        13 Security Considerations..........................................21
        
        14 References.......................................................22
        
        15 Authors' Addresses...............................................22
        
        16 Full Copyright Statement.........................................23
        
        
        
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                                    Table of Tables
        
        Table 1 - Information about the Delivery Method.......................9
        
        Table 2 - Attributes in Event Notification Content...................16
        
        Table 3 - Additional Attributes in Event Notification Content for Job
           Events...........................................................17
        
        Table 4 - Combinations of Events and Subscribed Events for "job-
           impressions-completed"...........................................17
        
        Table 5 - Additional Attributes in Event Notification Content for
           Printer Events...................................................18
        
        Table 6 - Operation-id assignments...................................19
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
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        1  Introduction
        
        The notification extension document [ipp-ntfy] defines operations that
        a client can perform in order to create Subscription Objects in a
        Printer and carry out other operations on them. A Subscription Object
        represents a Subscription abstraction. The Subscription Object
        specifies that when one of the specified Events occurs, the Printer
        sends an asynchronous Event Notification to the specified Notification
        Recipient via the specified Delivery Method (i.e., protocol).
        
        The notification extension document [ipp-ntfy] specifies that each
        Delivery Method is defined in another document. This document is one
        such document, and it specifies the 'ippget' delivery method.
        
        The 'ippget' Delivery Method is a 'pull and push' Delivery Method. That
        is, the Printer saves Event Notification for a period of time and
        expects the Notification Recipient to fetch the Event Notifications
        (the pull part). The Printer continues to send Event Notifications to
        the Notification Recipient as Events occur (the push part) if the
        client has selected the option to wait for additional Event
        Notifications.
        
        When a Printer supports this Delivery Method, it holds each Event
        Notification for an amount of time, called the Event Notification Lease
        Time.
        
        When a Notification Recipient wants to receive Event Notifications, it
        performs an IPP operation called 'Get-Notifications', which this
        document defines. This operation causes the Printer to return all Event
        Notifications held for the Notification Recipient. If the Notification
        Recipient has selected the option to wait for additional Event
        Notifications, the Printer the Printer continues to send Event
        Notifications to the Notification Recipient as Events occur.
        
        
        2  Terminology
        
        This section defines the following terms that are used throughout this
        document:
        
        Capitalized terms, such as MUST, MUST NOT, REQUIRED, SHOULD, SHOULD
        NOT, MAY, NEED NOT, and OPTIONAL, have special meaning relating to
        conformance to this specification.  These terms are defined in [RFC2911
        section 13.1 on conformance terminology, most of which is taken from
        RFC 2119 [RFC2119].
        
        
        
        
        
        
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        Event Notification Lease: The lease that is associated with an Event
        Notification. When the lease expires, the Printer discards the
        associated Event Notification.
        
        Event Notification Lease Time: The expiration time assigned to a lease
        that is associated with an Event Notification.
        
        Event Notification Attributes Group: The attributes group in a response
        that contains attributes that are part of an Event Notification.
        
        For other capitalized terms that appear in this document, see [ipp-
        ntfy].
        
        
        3  Model and Operation
        
        In a Subscription Creation Operation, when the value of the "notify-
        recipient-uri" attributes has the scheme 'ippget', the client is
        requesting that the Printer use the 'ippget' Delivery Method for the
        Event Notifications associated with the new Subscription Object. The
        client SHOULD choose a value for the address part of the "notify-
        recipient-uri" attribute that uniquely identifies the Notification
        Recipient.
        
        When an Event occurs, the Printer MUST generate an Event Notification
        and MUST assign it the Event Notification Lease Time. The Printer MUST
        hold an Event Notification for its assigned Event Notification Lease
        Time. The Printer MUST assign the same Event Notification Lease Time to
        each Event Notification.
        
        When a Notification Recipient wants to receive Event Notifications, it
        performs the Get-Notifications operation, which causes the Printer to
        return all unexpired Event Notifications held for the Notification
        Recipient. If the Notification Recipient has selected the option to
        wait for additional Event Notifications, the response to the Get-
        Notifications request continues indefinitely as the Printer continues
        to send Event Notifications in the response as Events occur. For the
        Get-Notification operation, the Printer sends only those Event
        Notifications that are generated from Subscription Objects whose
        "notify-recipient-uri" equals the "notify-recipient-uri" Operation
        Attribute in the Get-Notifications operation.
        
        If a Notification Recipient performs the Get-Notifications operation
        twice in quick succession, it will receive nearly the same Event
        Notification both times because most of the Event Notifications are
        those that the Printer saves for a few seconds after the Event occurs.
        There are two possible differences. Some old Event Notifications may
        not be present in the second response because their Event Notification
        
        
        
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        Leases have expired.  Some new Event Notifications may be present in
        the second response but not the first response.
        
        When the Notification Recipient requests Event Notifications for per-
        Job Subscription Objects, the Notification Recipient typically performs
        the Get-Notifications operation within a second of performing the
        Subscription Creation operation.  Because the Printer is likely to save
        Event Notifications for several seconds, the Notification Recipient is
        unlikely to miss any Event Notifications that occur between the
        Subscription Creation and the Get-Notifications operation.
        
        
        4  General Information
        
        If a Printer supports this Delivery Method, the following are its
        characteristics.
        
        
                    Table 1 - Information about the Delivery Method
        
             Document Method Conformance        Delivery Method Realization
                     Requirement
        
          1.What is the URL scheme name     ippget
            for the Delivery Method?
        
          2.Is the Delivery Method          RECOMMENDED
            REQUIRED, RECOMMENDED or
            OPTIONAL for an IPP Printer to
            support?
        
          3.What transport and delivery     IPP with one new operation.
            protocols does the Printer use
            to deliver the Event
            Notification Content, i.e.,
            what is the entire network
            stack?
        
          4.Can several Event               Yes.
            Notifications be combined into
            a Compound Event Notification?
        
          5.Is the Delivery Method          This Delivery Method is a pull and
            initiated by the Notification   a push.
            Recipient (pull), or by the
            Printer (push)?
        
          6.Is the Event Notification       Machine Consumable
            content Machine Consumable or
        
        
        
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            Human Consumable?
        
          7.What section in this document   Section 5
            answers the following
            question? For a Machine
            Consumable Event Notification,
            what is the representation and
            encoding of values defined in
            section 9.1 of [ipp-ntfy] and
            the conformance requirements
            thereof? For a Human
            Consumable Event Notification,
            what is the representation and
            encoding of pieces of
            information defined in section
            9.2 of [ipp-ntfy] and the
            conformance requirements
            thereof?
        
          8.What are the latency and        Same as IPP and the underlying HTTP
            reliability of the transport    transport
            and delivery protocol?
        
          9.What are the security aspects   Same as IPP and the underlying HTTP
            of the transport and delivery   transport
            protocol, e.g., how it is
            handled in firewalls?
        
          10.  What are the content length  None
            restrictions?
        
          11.  What are the additional      None
            values or pieces of
            information that a Printer
            sends in an Event Notification
            content and the conformance
            requirements thereof?
        
          12.  What are the additional      None
            Subscription Template and/or
            Subscription Description
            attributes and the conformance
            requirements thereof?
        
          13.  What are the additional      None
            Printer Description attributes
            and the conformance
        
        
        
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            requirements thereof?
        
        
        
        
        5  Get-Notifications operation
        
        This operation causes the Printer to return all Event Notifications
        held for the Notification Recipient.
        
        A Printer MUST support this operation.
        
        When a Printer performs this operation, it MUST return all and only
        those Event Notifications:
        
             a)Whose associated Subscription Object's "notify-recipient-uri"
               attribute equals the "notify-recipient-uri" Operation attribute
               AND
        
             b)Whose associated Subscription Object's "notify-recipient-uri"
               attribute has a scheme value of 'ippget'  AND
        
             c)Whose Event Notification Lease Time has not yet expired AND
        
             d)Where the Notification Recipient is the owner of or has read-
               access rights to the associated Subscription Object.
        
        The Printer MUST respond to this operation immediately with whatever
        Event Notifications it currently holds. If the Notification Recipient
        has selected the option to wait for additional Event Notifications, the
        Printer MUST continue to send Event Notifications as they occur until
        all of the associated Subscription Objects are cancelled.  A
        Subscription Object is cancelled either via the Cancel-Subscription
        operation or by the Printer (e.g. the Subscription Object is cancelled
        when the associated Job completes).
        
        Note, the Printer terminates the operation in the same way that it
        normally terminates IPP operations. For example, if the Printer is
        sending chunked data, it can send a 0 length chunk to denote the end of
        the operation or it can close the connection.  If the Notification
        Recipient wishes to terminate the Get-Notifications operation, it can
        close the connection.
        
        The Printer MUST accept the request in any state (see [RFC2911]
        "printer-state" and "printer-state-reasons" attributes) and MUST remain
        in the same state with the same "printer-state-reasons".
        
        Access Rights: If the policy of the Printer is to allow all users to
        access all Event Notifications, then the Printer MUST accept this
        
        
        
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        operation from any user. Otherwise, the authenticated user (see
        [RFC2911] section 8.3) performing this operation MUST either be the
        owner of each Subscription Object identified by the "notify-recipient-
        uri" Operation attribute (as determined during a Subscription Creation
        Operation) or an operator or administrator of the Printer (see
        [RFC2911] Sections 1 and 8.5).  Otherwise, the IPP object MUST reject
        the operation and return: 'client-error-forbidden', 'client-error-not-
        authenticated', or 'client-error-not-authorized' as appropriate.
        
        
        5.1 Get-Notifications Request
        
        The following groups of attributes are part of the Get-Notifications
        Request:
        
        Group 1: Operation Attributes
        
          Natural Language and Character Set:
             The "attributes-charset" and "attributes-natural-language"
             attributes as described in [RFC2911] section 3.1.4.1.
        
          Target:
             The "printer-uri" (uri) operation attribute which is the target
             for this operation as described in [RFC2911] section 3.1.5.
        
          Requesting User Name:
             The "requesting-user-name" (name(MAX)) attribute SHOULD be
             supplied by the client as described in [RFC2911] section 8.3.
        
          "notify-recipient-uri" (url):
             The client MUST supply this attribute.  The Printer object MUST
             support this attribute. The Printer matches the value of this
             attribute (byte for byte with no case conversion) against the
             value of the "notify-recipient-uri" in each Subscription Object in
             the Printer. If there are no matches, the IPP Printer MUST return
             the 'client-error-not-found' status code.  For each matched
             Subscription Object, the IPP Printer MUST return all unexpired
             Event Notifications associated with it. The Printer MUST send
             additional Event Notifications as Events occur if and only if the
             value of the "notify-no-wait" attribute is 'false' or not supplied
             by the client (see the next attribute below).
        
             Note: this attribute allows a subscribing client to pick URLs that
             are unique, e.g. the client's own URL or a friend's URL, which in
             both cases is likely the URL of the person's host. An application
             could make a URL unique for each application.
        
        
        
        
        
        
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          "notify-no-wait" (boolean):
             The client MAY supply this attribute.  The Printer object MUST
             support this attribute. If the value of this attribute is 'false',
             the Printer MUST send all un-expired Event Notifications (as
             defined in the previous attribute) and it MUST continue to send
             responses for as long as the Subscription Objects associated with
             the specified "notify-recipient-uri" continue to exist. If the
             value of this attribute is 'true', the Printer MUST send all un-
             expired Event Notifications (as defined in the previous attribute)
             and the Printer MUST conclude the operation without waiting for
             any additional Events to occur. If the client doesn't supply this
             attribute, the Printer MUST behave as if the client had supplied
             this attribute with the value of 'false'.
        
        5.2 Get-Notifications Response
        
        The following groups of attributes are part of the Get-Notifications
        Response:
        
        Group 1: Operation Attributes
        
          Status Message:
             In addition to the REQUIRED status code returned in every
             response, the response OPTIONALLY includes a "status-message"
             (text(255)) and/or a "detailed-status-message" (text(MAX))
             operation attribute as described in [RFC2911] sections 13 and
             3.1.6.
        
             The Printer can return any status codes defined in [RFC2911]. If
             the status code is not 'successful-', the Printer MUST NOT return
             any Event Notification Attribute groups. The following is a
             description of the important status codes:
        
               successful-ok: the response contains all Event Notification
                  associated with the specified "notify-recipient-uri". If the
                  specified Subscription Objects have no associated Event
                  Notification, the response MUST contain zero Event
                  Notifications.
               client-error-not-found: The Printer has no Subscription
                  Object's whose "notify-recipient-uri" attribute equals the
                  "notify-recipient-uri" Operation attribute.
               server-error-busy: The Printer is too busy to accept this
                  operation. If the "suggested-ask-again-time-interval"
                  operation attribute is present in the Operation Attributes of
                  the response, then the Notification Recipient SHOULD wait for
                  the number of seconds specified by the "suggested-ask-again-
                  time-interval" attribute before performing this operation
                  again. If the "suggested-ask-again-time-interval" Operation
                  Attribute is not present, the Notification Recipient should
        
        
        
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                  use the normal network back-off algorithms for determining
                  when to perform this operation again.
               redirection-other-site: The Printer does not handle this
                  operation and requests the Notification Recipient to perform
                  the operation with the uri specified by the "notify-ippget-
                  redirect" Operation Attribute in the response.
        
          Natural Language and Character Set:
             The "attributes-charset" and "attributes-natural-language"
             attributes as described in [RFC2911] section 3.1.4.2.
        
             The Printer MUST use the values of "notify-charset" and "notify-
             natural-language", respectively, from one Subscription Object
             associated with the Event Notifications in this response.
        
             Normally, there is only one matched Subscription Object, or the
             value of the "notify-charset" and "notify-natural-language"
             attributes is the same in all Subscription Objects. If not, the
             Printer MUST pick one Subscription Object from which to obtain the
             value of these attributes. The algorithm for picking the
             Subscription Object is implementation dependent. The choice of
             natural language is not critical because 'text' and 'name' values
             can override the "attributes-natural-language" Operation
             attribute. The Printer's choice of charset is critical because a
             bad choice may leave it unable to send some 'text' and 'name'
             values accurately.
        
          "printer-up-time" (integer(0:MAX)):
             The value of this attribute is the Printer's "printer-up-time"
             attribute at the time the Printer sends this response. Because
             each Event Notification also contains the value of this attribute
             when the event occurred, the value of this attribute lets a
             Notification Recipient know when each Event Notification occurred
             relative to the time of this response.
        
           "suggested-ask-again-time-interval" (integer(0:MAX)):
             The value of this attribute is the number of seconds that the
             Notification Recipient SHOULD wait before trying this operation
             again when
                  a)the Printer returns the 'server-error-busy' status code OR
                  b)the Printer returns the 'successful-ok' status code and
                    the client supplied the "notify-no-wait" attribute with a
                    value of 'true'.
             This value is intended to help the client be a good network
             citizen.
        
        
        
        
        
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          "notify-ippget-redirect" (uri):
             The value of this attribute is uri that the Notification Recipient
             MUST use for the Get-Notifications operation. This attribute is
             present in the Operation Attributes if and only if the status code
             has the value 'redirection-other-site'.
        
        Group 2: Unsupported Attributes
        
             See [RFC2911] section 3.1.7 for details on returning Unsupported
             Attributes.
        
             If the "subscription-ids" attribute contained subscription-ids
             that do not exist, the Printer returns them in this group as value
             of the "subscription-ids" attribute.
        
        Group 3 through N: Event Notification Attributes
        
             The Printer responds with one Event Notification Attributes Group
             per matched Event Notification. The initial matched Event
             Notifications are all un-expired Event Notification associated
             with the matched Subscription Objects. If the Notification
             Recipient has selected the option to wait for additional Event
             Notifications, the Printer the subsequent Event Notifications in
             the response are Event Notifications associated with the matched
             Subscription Objects as the corresponding Event occurs.
        
             From the Notification Recipient's view, the response appears as an
             initial burst of data, which includes the Operation Attributes
             Group and one Event Notification Attributes Groups per Event
             Notification that the Printer is holding.  After the initial burst
             of data, if the Notification Recipient has selected the option to
             wait for additional Event Notifications, the Notification
             Recipient receives occasional Event Notification Attribute Groups.
             Proxy servers may delay some Event Notifications or cause time-
             outs to occur. The client MUST be prepared to perform the Get-
             Notifications operation again when time-outs occur.
        
             Each Event Notification Group MUST start with an 'event-
             notification-attributes-tag' (see the section "Encodings of
             Additional Attribute Tags" in [ipp-ntfy]).
        
             Each attribute is encoded using the IPP rules for encoding
             attributes [RFC2910] and may be encoded in any order. Note: the
             Get-Jobs response in [RFC2911] acts as a model for encoding
             multiple groups of attributes.
        
             Each Event Notification Group MUST contain all of attributes
             specified in section 9.1 ("Content of Machine Consumable Event
        
        
        
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             Notifications") of [ipp-ntfy] with exceptions denoted by asterisks
             in the tables below.
        
             The tables below are copies of the tables in section 9.1 ("Content
             of Machine Consumable Event Notifications") of [ipp-ntfy] except
             that each cell in the "Sends" column is a  "MUST".
        
             For an Event Notification for all Events, the Printer includes the
             following attributes.
        
                     Table 2 - Attributes in Event Notification Content
        
                            Source Value                 Sends   Source Object
        
             notify-subscription-id (integer(1:MAX))     MUST   Subscription
        
             notify-printer-uri (uri)                    MUST   Subscription
        
             notify-subscribed-event (type2 keyword)     MUST   Event
                                                                  Notification
        
             printer-up-time (integer(MIN:MAX))          MUST   Printer
        
             printer-current-time (dateTime)*            MUST   Printer
        
             notify-sequence-number (integer (0:MAX))    MUST   Subscription
        
             notify-charset (charset)                    MUST   Subscription
        
             notify-natural-language (naturalLanguage)   MUST   Subscription
        
             notify-user-data (octetString(63)) **       MUST   Subscription
        
             notify-text (text)                          MUST   Event
                                                                  Notification
        
             attributes from the "notify-attributes"     MUST   Printer
             attribute ***
        
             attributes from the "notify-attributes"     MUST   Job
             attribute ***
        
             attributes from the "notify-attributes"     MUST   Subscription
             attribute ***
        
        
             * The Printer MUST send "printer-current-time" if and only if it
             supports the "printer-current-time" attribute on the Printer
             object.
        
        
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             ** If the associated Subscription Object does not contain a
             "notify-user-data" attribute, the Printer MUST send an octet-
             string of length 0.
        
             *** If the "notify-attributes" attribute is present on the
             Subscription Object, the Printer MUST send all attributes
             specified by the "notify-attributes" attribute. Note: if the
             Printer doesn't support the "notify-attributes" attribute, it is
             not present on the associated Subscription Object.
        
             For Event Notifications for Job Events, the Printer includes the
             following additional attributes.
        
             Table 3 - Additional Attributes in Event Notification Content for
                                         Job Events
        
                            Source Value                 Sends   Source Object
        
             job-id (integer(1:MAX))                     MUST   Job
        
             job-state (type1 enum)                      MUST   Job
        
             job-state-reasons (1setOf type2 keyword)    MUST   Job
        
             job-impressions-completed                   MUST   Job
             (integer(0:MAX)) *
        
        
             *  The Printer MUST send the "job-impressions-completed" attribute
             in an Event Notification only for the combinations of Events and
             Subscribed Events shown in Table 4.
        
        
              Table 4 - Combinations of Events and Subscribed Events for "job-
                                   impressions-completed"
        
             Job Event                 Subscribed Job Event
        
             'job-progress'            'job-progress'
        
             'job-completed'           'job-completed'
        
             'job-completed'           'job-state-changed'
        
        
             For Event Notification for Printer Events, the Printer includes
             the following additional attributes.
        
        
        
        
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             Table 5 - Additional Attributes in Event Notification Content for
                                       Printer Events
        
                            Source Value                 Sends   Source Object
        
             printer-state (type1 enum)                  MUST   Printer
        
             printer-state-reasons (1setOf type2         MUST   Printer
             keyword)
        
             printer-is-accepting-jobs (boolean)         MUST   Printer
        
        
        6  Subscription Template Attributes
        
        This section defines the Subscription object conformance requirements
        for Printers.
        
        
        6.1 Subscription Template Attribute Conformance
        
        The 'ippget' Delivery Method has the same conformance requirements for
        Subscription Template attributes as defined in [ipp-ntfy].  The
        'ippget' Delivery Method does not define any addition Subscription
        Template attributes.
        
        
        6.2 Additional Information about Subscription Template Attributes
        
        This section defines additional information about Subscription Template
        attributes defined in [ipp-ntfy].
        
        
        6.2.1notify-recipient-uri (uri)
        
        This section describes the syntax of the value of this attribute for
        the 'ippget' Delivery Method. The syntax for values of this attribute
        for other Delivery Method is defined in other Delivery Method
        Documents.
        
        
        In order to support the 'ippget' Delivery Method and Protocol, the
        Printer MUST support the following syntax:
        
            The 'ippget://' URI scheme.  The remainder of the URI indicates
            something unique about the Notification Recipient, such as its host
            and address that the Printer uses to match the "notify-recipient-
            uri" Operation attribute supplied in the Get-Notifications request.
        
        
        
        
        
        
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        6.3 Subscription Description Attribute Conformance
        
        The 'ippget' Delivery Method has the same conformance requirements for
        Subscription Description attributes as defined in [ipp-ntfy].  The
        'ippget' Delivery Method does not define any addition Subscription
        Description attributes.
        
        
        7  Additional Printer Description Attributes
        
        This section defines the Printer Description Attributes conformance
        requirements for Printers.
        
        
        7.1 Printer Description Attribute Conformance
        
        The 'ippget' Delivery Method has the same conformance requirements for
        Printer Description attributes as defined in [ipp-ntfy].  The 'ippget'
        Delivery Method does not define any addition Printer Description
        attributes.
        
        
        7.2 New Values for Existing Printer Description Attributes
        
        This section defines additional values for existing Printer Description
        attributes.
        
        
        7.2.1notify-schemes-supported (1setOf uriScheme)
        
        The following "notify-schemes-supported" value is added in order to
        support the new Delivery Method defined in this document:
        
          'ippget'  - The IPP Notification Delivery Method defined in this
             document.
        
        7.2.2operations-supported (1setOf type2 enum)
        
        Table 6 lists the "operation-id" value added in order to support the
        new operation defined in this document.
        
        
                          Table 6 - Operation-id assignments
        
             Value       Operation Name
        
             0x001C      Get-Notifications
        
        
        
        
        
        
        
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        7.3 begin-to-expire-time-interval (integer(0:MAX))
        
        This attribute specifies the number of seconds that a Printer keeps an
        Event Notification that is associated with this Delivery Method.
        
        The Printer MUST support this attribute if it supports this Delivery
        Method.
        
        The value of this attribute is the minimum number of seconds that MUST
        elapse between the time the Printer creates an Event Notification
        object for this Delivery Method and the time the Printer discards the
        same Event Notification.
        
        For example, assume the following:
        
          1. a client performs a Job Creation operation that creates a
             Subscription Object associated with this Delivery Method, AND
        
          2. an Event associated with the new Job occurs immediately after the
             Subscription Object is created, AND
        
          3. the same client or some other client performs a Get-Notifications
             operation N seconds after the Job Creation operation.
        
        Then, if N is less than the value of this attribute, the client
        performing the Get-Notifications operations can expect not miss any
        Event-Notifications, barring some unforeseen lack of memory space in
        the Printer.
        
        
        
        8  New Status Codes
        
        The following status codes are defined as extensions for this Delivery
        Method and are returned as the status code of the Get-Notifications
        operation.
        
        
        8.1 redirection-other-site (0x300)
        
        This status code means that the Printer doesn't perform that Get-
        Notifications operation and that the "notify-ippget-redirect" Operation
        Attribute in the response contains the uri that the Notification
        Recipient MUST use for performing the Get-Notifications operation.
        
        9  Encoding
        
        This notification delivery method uses the IPP transport and encoding
        [RFC2910] for the Get-Notifications operation with one extension:
        
        
        
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                  notification-attributes-tag = %x07                   ; tag of
                  7
        
        
        10 Conformance Requirements
        
        If the Printer supports the 'ippget' Delivery Method, the Printer MUST:
        
        1.meet the conformance requirements defined in [ipp-ntfy].
        
        2.support the Get-Notifications operation defined in section 5.
        
        3.support the Subscription object attributes as defined in section 6.
        
        4.support the additional values for IPP/1.1 Printer Description
          attributes defined in section 7.2.
        
        5.support the "begin-to-expire-time-interval" Printer Description
          attribute defined in section 7.3.
        
        6.support the "redirection-other-site" status code defined 8.1
        
        
        11 IANA Considerations
        
        The 'ippget' URL scheme for the 'ippget' Delivery Method will be
        registered with IANA according to the procedures of [RFC2717].
        
        
        12 Internationalization Considerations
        
        The IPP Printer MUST localize the "notify-text" attribute as specified
        in section 14 of [ipp-ntfy].
        
        In addition, when the client receives the Get-Notifications response,
        it is expected to localize the attributes that have the 'keyword'
        attribute syntax according to the charset and natural language
        requested in the Get-Notifications request.
        
        
        13 Security Considerations
        
        The IPP Model and Semantics document [RFC2911] discusses high-level
        security requirements (Client Authentication, Server Authentication and
        Operation Privacy).  Client Authentication is the mechanism by which
        the client proves its identity to the server in a secure manner.
        Server Authentication is the mechanism by which the server proves its
        identity to the client in a secure manner.  Operation Privacy is
        defined as a mechanism for protecting operations from eavesdropping.
        
        
        
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        Unlike other Event Notification delivery methods in which the IPP
        Printer initiates the Event Notification, with the method defined in
        this document, the Notification Recipient is the client who   s the
        Get-Notifications operation.  Therefore, there is no chance of "spam"
        notifications with this method.  Furthermore, such a client can close
        down the HTTP channel at any time, and so can avoid future unwanted
        Event Notifications at any time.
        
        
        14 References
        
         [ipp-ntfy]
             R. Herriot, Hastings, T., Isaacson, S., Martin, J., deBry, R.,
             Shepherd, M., Bergman, R., "Internet Printing Protocol/1.1: IPP
             Event Notification Specification", <draft-ietf-ipp-not-spec-
             04.txt>, June 30, 2000.
        
         [rfc2026]
             S. Bradner, "The Internet Standards Process -- Revision 3", RFC
             2026, October 1996.
        
        [RFC2616]
             R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P.
             Leach, T. Berners-Lee, "Hypertext Transfer Protocol - HTTP/1.1",
             RFC 2616, June 1999.
        
        [RFC2910]
             Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
             Protocol/1.1: Encoding and Transport", RFC 2910, September 2000.
        
        [RFC2911]
             R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
             "Internet Printing Protocol/1.1: Model and Semantics", RFC 2911,
             September 2000.
        
        
        15 Authors' Addresses
        
        
           Robert Herriot
           Xerox Corp.
           3400 Hill View Ave, Building 1
           Palo Alto, CA 94304
        
           Phone: 650-813-7696
           Fax:  650-813-6860
           e-mail: robert.herriot@pahv.xerox.com
        
           Carl Kugler
        
        
        
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           IBM
           P.O. Box 1900
           Boulder, CO 80301-9191
        
           Phone:
           Fax:
           e-mail: kugler@us.ibm.com
        
           Harry Lewis
           IBM
           P.O. Box 1900
           Boulder, CO 80301-9191
        
           Phone: 303-924-5337
           FAX:
           e-mail:  harryl@us.ibm.com
        
        
        16 Full Copyright Statement
        
        Copyright (C) The Internet Society (2000). All Rights Reserved.
        
        This document and translations of it may be copied and furnished to
        others, and derivative works that comment on or otherwise explain it or
        assist in its implementation may be prepared, copied, published and
        distributed, in whole or in part, without restriction of any kind,
        provided that the above copyright notice and this paragraph are
        included on all such copies and derivative works.  However, this
        document itself may not be modified in any way, such as by removing the
        copyright notice or references to the Internet Society or other
        Internet organizations, except as needed for the  purpose of developing
        Internet standards in which case the procedures for copyrights defined
        in the Internet Standards process must be followed, or as required to
        translate it into languages other than English.
        
        The limited permissions granted above are perpetual and will not be
        revoked by the Internet Society or its successors or assigns.
        
        This document and the information contained herein is provided on an
        "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
        TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
        NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL
        NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
        FITNESS FOR A PARTICULAR PURPOSE.
        
        
        
        
        
        
        
        
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