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INTERNET-DRAFT                                            Robert Herriot
<draft-ietf-ipp-notify-poll-02.txt>                          Xerox Corp.
                                                            Tom Hastings
                                                             Xerox Corp.
                                                         Carl-Uno Manros
                                                             Xerox Corp.
                                                             Harry Lewis
                                                              IBM, Corp.
                                                         August 15, 2000
                   Internet Printing Protocol (IPP):
                The 'ipp-get' Notification Polling Method

    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 'ipp-get' delivery method.

The 'ipp-get' Delivery Method is a 'pull' Delivery Method. That is, the
Printer saves Event Notification for a period of time and expects the
Notification Recipient to fetch the 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



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Notifications held for the Notification Recipient along with information
that tells the client when to perform this operation again.






















































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The full 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 [ipp-mod]
  Internet Printing Protocol/1.1: Encoding and Transport [ipp-pro]
  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 'ipp-get' 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 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



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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......................................................6

2  Terminology.......................................................6

3  Model and Operation...............................................6

4  General Information...............................................8

5  Get-Notifications operation.......................................8
 5.1  GET-NOTIFICATIONS REQUEST......................................9
 5.2  GET-NOTIFICATIONS RESPONSE....................................10

6  Extensions to Subscription Creation Operations...................14
 6.1  RESPONSE......................................................14

7  Encoding.........................................................14

8  IANA Considerations..............................................15

9  Internationalization Considerations..............................15

10 Security Considerations..........................................15

11 References.......................................................15

12 Authors' Addresses...............................................16

13 Full Copyright Statement.........................................16

























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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 'ipp-get' delivery method.

The 'ipp-get' Delivery Method is a 'pull' Delivery Method. That is, the
Printer saves Event Notification for a period of time and expects the
Notification Recipient to fetch the 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 along with information
that tells the client when to perform this operation again.

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 [ipp-mod
section 13.1 on conformance terminology, most of which is taken from RFC
2119 [RFC2119].

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 "ipp-get", the client is
requesting that the Printer use the 'ipp-get' Delivery Method for the
Event Notifications associated with the new Subscription Object. The
client MUST choose a value for the address part of the "notify-



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recipient-uri" attribute that uniquely identifies the Notification
Recipient.

When an Event occurs, the Printer MUST generate an Event Notification
and MUST assign it an Event Notification Lease Time. The Printer MUST
hold an Event Notification for its assigned Event Notification Lease
Time and MUST discard it when its Event Notification Lease Time expires.
The Printer MAY assign the same Event Notification Lease Time to each
Event Notification or it MAY assign a different time.

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 along with two time-intervals.

The first returned time-interval is the suggested time a Notification
Recipient should wait before performing the Get-Notifications operation
again. The second time-interval is the time that Event Notification
Leases begin to expire for Event Notifications created after the Get-
Notifications operation. A Notification Recipient SHOULD perform this
operation at the suggested time and somewhat before the Event
Notification Leases begin to expire.

The Notification Recipient identifies its own Event Notifications with a
"notify-recipient-uri" Operation attribute in the request. It matches
any Event Notifications associated with a Subscription Object whose
"notify-recipient-uri" attribute has the same value as the "notify-
recipient-uri" Operation attribute of the request. To avoid getting
Event Notification that belong to another Notification Recipient, a
client SHOULD pick values for the "notify-recipient-uri" attribute that
are unique, e.g. the client's host address.

If a Notification Recipient performs the Get-Notifications operation
twice in quick succession, it will receive nearly the same Event
Notification both times. There are two possible differences. Some old
Event Notifications may not be present in the second response because
their Event Notification Leases have expired.  Some new Event
Notifications may be present in the second response but not the first
response.

The Printer may keep the channel open if the suggested time-interval is
sufficiently short, but in any case the client performs a new Get-
Notifications operation each time it wants more Event Notifications.
Since the time interval between consecutive client requests is normally
less than the Event Notification Lease Time, consecutive responses will
normally contain some events that are identical.   The youngest ones in
the previous response will become the oldest in the next response.  The
client is expected to filter out these duplicates, which is easy to do
because of the sequence number in each Event Notification.  The reason
for not removing the Event Notifications from the Printer with every
Get-Notifications request, is so that multiple Notification Recipients
can be polling the same Subscription Object and so the Get-Notification
operation satisfies the rule of idempotency.  The former is useful if
someone is logged in to several desktops at the same time and wants to
see the same events at both places. The latter is useful if the network
loses the response.



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4  General Information

According to the notification extension document [ipp-ntfy], this
document MUST contain the following information:

1.The URL scheme name for the Delivery Method is: 'ipp-get'

2.Printer support for this delivery method is OPTIONAL.

3.For Event Notification content, a Printer MUST use the following
  transport and delivery protocol, i.e., entire network stack:  IPP
  with one new operation.

4.Several Event Notifications can be combined into a compound Event
  Notification. See section 5.

5.The Notification Recipient MUST initiate the Delivery Method

6.The Delivery Method is Machine Consumable.

7.The representation and encoding for each value is the same as for IPP
  (see section 5).

8.In the Event Notification content, a Printer MUST send all attributes
  specified in section 5.

9.Frequently occurring Events NEED NOT be moderated because the
  Delivery Method is a 'pull' Delivery Method. An implementation of the
  Get-Notifications operation SHOULD consider how often it recommends a
  Notification Recipient to poll again.

10.  This Delivery Method has the same latency and reliability as the
  underlying HTTP transport.

11.  This Delivery Method has the same security aspects as the
  underlying HTTP transport.

12.  This Delivery Method has no content length restrictions.

13.  There are no additional values that a Printer MUST send in a
  Notification content.

14.  There are no additional Subscription Template and/or Subscription
  Description attributes.

15.  There are no additional Printer Description attributes.

5  Get-Notifications operation

This operation causes the Printer to return all Event Notifications held
for the Notification Recipient along with information about when to
perform this operation again.

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



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     b)Whose associated Subscription Object's "notify-recipient-uri"
       attribute has a scheme value of 'ipp-get'  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.

When a Printer performs this operation, it MUST also return two time-
intervals:

     a)the suggested time for a Notification Recipient to perform the
       Get-Notifications operation again.

     b)the time at which the Printer will begin to discard Event
       Notifications that occur after this operation. This may be the
       Event Notification Lease Time (see section 5.2 for details).

Note: the Subscription Creation Operations also return these two time-
intervals (see section 6).

The Printer MUST respond to this operation immediately with whatever
Event Notifications it currently holds. It MUST NOT wait for additional
Events to occur before sending a response.

The Printer MUST accept the request in any state (see [ipp-mod]
"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
operation from any user. Otherwise, the authenticated user (see [ipp-
mod] 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 [ipp-mod]
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 [ipp-mod] section 3.1.4.1.

  Target:
     The "printer-uri" (uri) operation attribute which is the target for
     this operation as described in [ipp-mod] section 3.1.5.

  Requesting User Name:
     The "requesting-user-name" (name(MAX)) attribute SHOULD be supplied
     by the client as described in [ipp-mod] section 8.3.




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  "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.

     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.

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 [ipp-mod] sections 13 and 3.1.6.

     The Printer can return any status codes defined in [ipp-mod]. 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.

  Natural Language and Character Set:
     The "attributes-charset" and "attributes-natural-language"
     attributes as described in [ipp-mod] 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



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     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.

  "suggested-ask-again-time-interval" (integer(0:MAX)):
     The value of this attribute is the suggested number of seconds that
     SHOULD elapse before the client performs the Get-Notifications
     operation again for these Subscription Objects. A client MAY
     perform the Get-Notifications operation at any time, and a Printer
     MUST respond with all unexpired Event Notifications. A Notification
     Recipient waits until this time interval has elapsed in order to be
     a "good network citizen". It is RECOMMENDED that the value of this
     attribute be 80% of the "begin-to-expire-time-interval" (see the
     next attribute) in order to give a Notification Recipient plenty of
     time to perform the Get-Notifications operation again before new
     Event Notifications expire.

   "begin-to-expire-time-interval" (integer(0:MAX)):
     The value of this attribute is the minimum number of seconds that
     MUST elapse before Event Notification Leases begin to expire on
     Event Notifications produced by matching Subscriptions Objects
     after the Printer sends the Get-Notifications response. The Printer
     MUST discard an Event Notification when its Event Notification
     Lease has expired. That is, if the Printer performs the Get-
     Notifications operation before the time specified by the "begin-to-
     expire-time-interval" attribute returned in the previous operation,
     the Printer MUST still have all of the Event Notifications that
     have occurred since the previous operation. If the Printer assigns
     the same Event Notification Lease Time to all Event Notifications,
     the value of this attribute MUST equal the Event Notification Lease
     Time. If a Notification Recipient waits until after this time or
     even slightly less than this time, the Notification Recipient MUST
     expect to lose some Event Notifications.

  "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.

Group 2: Unsupported Attributes

     See [ipp-mod] 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




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     The Printer responds with one Event Notification Attributes Group
     per matched Event Notification. The matched Event Notifications are
     all un-expired Event Notification associated with the matched
     Subscription Objects. 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 [ipp-pro] and may be encoded in any order. Note: the
     Get-Jobs response in [ipp-mod] 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
     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 1 . 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 ***


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                    Source Value                 Sends   Source Object

     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.

     ** 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 2 . 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 3.


      Table 3 . 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'



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     For Event Notification for Printer Events, the Printer includes the
     following additional attributes.

      Table 4 . 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  Extensions to Subscription Creation Operations

6.1 Response

When a Subscription Creation Operation contains a "notify-recipient-uri"
attribute and the scheme in its value is 'ipp-get', the response MUST
contain two additional Operation Attributes that pertain to this
Delivery Method. Note: Subscription Creation Operations include: Print-
Job, Print-URI, Create-Job, Create-Job-Subscriptions and Create-Printer-
Subscriptions.

Group 1: Operation Attributes

  "suggested-ask-again-time-interval" (integer(0:MAX)):
     This attribute has the same meaning as the "suggested-ask-again-
     time-interval" attribute in the Get-Notifications operation except
     that it suggests when to perform the Get-Notifications operation
     for the first time on all Subscription Objects in the response
     whose "notify-recipient-uri" scheme is 'ipp-get'.

  "begin-to-expire-time-interval" (integer(0:MAX)):
     This attribute has the same meaning as the "begin-to-expire-time-
     interval" attribute in the Get-Notifications operation except that
     it indicates when the Event Notification Lease begins to expire for
     all Subscription Objects in the response whose "notify-recipient-
     uri" scheme is 'ipp-get'.

7  Encoding

The operation-id assigned for the Get-Notifications operation is:

     0x001C

and should be added to the next version of [ipp-mod] section 4.4.15
"operations-supported".

This notification delivery method uses the IPP transport and encoding
[ipp-pro] for the Get-Notifications operation with one extension:

          notification-attributes-tag = %x07; tag of 7




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8  IANA Considerations

There is nothing to register.

9  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.

10 Security Considerations

The IPP Model and Semantics document [ipp-mod] 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.

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.

11 References

[ipp-mod]
     R. deBry, T. Hastings, R. Herriot, S. Isaacson, P. Powell,
     "Internet Printing Protocol/1.1: Model and Semantics", <draft-ietf-
     ipp-model-v11-07.txt>, May 22, 2000.

[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>, July 13, 2000.

[ipp-pro]
     Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
     Protocol/1.1: Encoding and Transport", draft-ietf-ipp-protocol-v11-
     06.txt, May 30, 2000.

[rfc2026]
     S. Bradner, "The Internet Standards Process -- Revision 3", RFC
     2026, October 1996.






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[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.

12 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

   Tom Hastings
   Xerox Corporation
   737 Hawaii St.  ESAE 231
   El Segundo, CA  90245

   Phone: 310-333-6413
   Fax: 310-333-5514
   e-mail: hastings@cp10.es.xerox.com

   Carl-Uno Manros
   Xerox Corporation
   701 Aviation Blvd.
   El Segundo, CA 90245

   Phone: 310-333-8273
   Fax:  310-333-5514
   e-mail: manros@cp10.es.xerox.com

   Harry Lewis
   IBM
   P.O. Box 1900
   Boulder, CO 80301-9191

   Phone: (303) 924-5337
   FAX:
   e-mail:  harryl@us.ibm.com


13 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



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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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