INTERNET-DRAFT
<draft-ietf-ipp-notify-poll-00.txt>                      Carl-Uno Manros
                                                            Tom Hastings                                            Robert Herriot
<draft-ietf-ipp-notify-poll-01.txt>                          Xerox Corp.
                                                            Tom Hastings
                                                             Xerox Corp.
                                                         Carl-Uno Manros
                                                             Xerox Corp.
                                                             Harry Lewis
                                                              IBM, Corp.
                                                           March 8,
                                                            July 7, 2000
                   Internet Printing Protocol (IPP):
                      The 'ipp' Notification Polling 'ipp-get' Delivery 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 IPP notification specification [ipp-ntfy] is an OPTIONAL extension document [ipp-ntfy] defines operations that a
client can perform in order to IPP/1.0 create Subscription Objects in a Printer
and IPP/1.1 carry out other operations on them. A Subscription Object represents
a Subscription abstraction. The Subscription Object specifies that requires the definition of when
one or more
delivery methods for dispatching of the specified Events occurs, the Printer sends an asynchronous
Event Notification reports to the specified Notification Recipients. 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 describes the semantics is one
such document, and
syntax of it specifies the 'ipp' event Notification 'ipp-get' delivery method.  For this
delivery method,

The 'ipp-get' Delivery Method is a 'pull' Delivery Method. That is, the client uses an explicit IPP Get-Notifications
Printer operation in order to request (pull) saves Event Notifications from Notification for a period of time and expects the IPP Printer.
Notification Recipient to fetch the Event Notifications.

When a Printer supports the 'ipp' delivery method, this Delivery Method, it holds each Event
Notification for a certain length of time. The an amount of time is time, called the "event-lease time".. A Printer may assign the same event-lease time
to each Event Notification or different times. If Lease
Time.

When a Notification Recipient does not want wants to miss receive Event Notifications, it
performs an IPP operation called 'Get-Notifications', which this
document defines. This operation causes the time between
consecutive pollings of Subscription objects must be less than the
event-lease time of Printer to return all Event
Notifications held for the events Notification Recipient along with information
that occur between pollings.  The Get-
Notifications request indicates whether tells the client wants when to receive all
pending event Notifications perform this operation again.

The full set of IPP documents includes:

  Design Goals for (1) any Subscription an Internet Printing Protocol [RFC2567]
  Rationale for which the
client is the owner, (2) any Subscription associated with a Job, (3) any
Subscription with a particular delivery-method URL, or (4) an identified

                      Expires: September 8, 2000

set of Subscription objects. With the Get-Notifications operation, the
Printer returns all existing Event Notifications along with two time
intervals. One specifies the minimum time at which event-leases of
future events of the type returned will begin to expire and the other
specifies the recommended interval for the client to wait before sending
the next Get-Notifications operation. The second time interval is less
than the first.

The Printer may keep the channel open if the recommended 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-lease time, consecutive responses will normally
contain some Event Notifications 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.

                      Expires: September 8, 2000

The full set of IPP documents includes:

  Design Goals for an Internet Printing Protocol [RFC2567]
  Rationale for the Structure and Model and Protocol for 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' '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.

                      Expires: September 8, 2000

The "Event Notification Specification" document defines OPTIONAL
operations that allow 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 include "Per-Job subscriptions" and "Per-Printer
subscriptions". Events. Subscriptions are
modeled as Subscription objects.
Four other operations are defined for subscription objects:  get
attributes, get subscriptions, renew a subscription, and cancel a
subscription.

                      Expires: September 8, 2000
                           Table of Contents

1  Introduction......................................................6

2  Terminology.......................................................7

3  Model and Operation...............................................7

4  Get-Notifications operation.......................................8
 4.1GET-NOTIFICATIONS REQUEST........................................9
 4.2GET-NOTIFICATIONS RESPONSE......................................11

5  Extension to Print-Job, Print-URI, Create-Job, Create-Printer- Objects.  The Subscription and Create-Printer-Subscription.........................12
 5.1RESPONSE........................................................12

6  Encoding.........................................................13

7  IANA Considerations..............................................13

8  Internationalization Considerations..............................14

9  Security Considerations..........................................14

10 References.......................................................14

11 Authors' Addresses...............................................15

12 Full Copyright Statement.........................................15

                      Expires: September 8, 2000

1  Introduction

IPP printers Object specifies that support
when one of the OPTIONAL IPP notification extension [ipp-
ntfy] either a) accept, store, and use notification subscriptions to
generate specified Event occurs, the Printer sends an
asynchronous Event Notification reports and implement one or more delivery
methods for notifying interested parties, 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 b) support by submitting a subset 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.

                           Table of
these tasks Contents

1  Introduction ......................................................6

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

3  Model and farm out the remaining tasks Operation ...............................................7

4  Get-Notifications operation .......................................8
 4.1 GET-NOTIFICATIONS REQUEST.......................................11
 4.2 GET-NOTIFICATIONS RESPONSE......................................11

5  Extensions to a Notification Delivery
Service. Print-Job, Print-URI, Create-Job, Create-Printer-
Subscription and Create-Printer-Subscription.........................16
 5.1 RESPONSE........................................................16

6  Encoding .........................................................17

7  IANA Considerations ..............................................17

8  Internationalization Considerations ..............................17

9  Security Considerations ..........................................17

10 References .......................................................18

11 Authors' Addresses ...............................................18

12 Full Copyright Statement .........................................19

1  Introduction

The 'ipp' Event Notification delivery method specified in this notification extension document [ipp-ntfy] defines a Get-Notifications operation operations that may be used a
client can perform in order to create Subscription Objects in a
variety of notification scenarios.  Its primary intended use is for
clients Printer
and carry out other operations on them. A Subscription Object represents
a Subscription abstraction. The Subscription Object specifies that want to be when
one of the specified Events occurs, the Printer sends an asynchronous
Event Notification Recipients. However, to the Get-
Notifications operation may also be used by 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
Services Method. That is, the
Printer saves Event Notification for subsequent distribution to a period of time and expects the Ultimate
Notification
Recipients. Recipient to fetch the Event Notifications.

When a Printer supports the 'ipp' delivery method, this Delivery Method, it holds each Event
Notification for a certain length of time. The an amount of time is time, called the "event-lease time". A Printer may assign the same event-lease time
to each event or different times.  If Event Notification Lease
Time.

When a Notification Recipient does not
want wants to miss receive Event Notifications, it
performs an IPP operation called 'Get-Notifications', which this
document defines. This operation causes the time between consecutive pollings
of Subscription objects must be less than the event-lease time of the
Event Notifications that occur between pollings.  The Get-Notifications
request indicates whether the client wants Printer to receive return all pending Event
Notifications held for (1) any Subscription for which the Notification Recipient along with information
that tells the client is when to perform this operation again.

2  Terminology

This section defines the
owner, (2) any Subscription 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 a particular Job, (3) any
Subscription with a particular notification recipient URL, or (4) an
identified set of Subscription objects. With Event
Notification. When the Get-Notifications
operation, lease expires, the Printer returns all existing Event Notifications along
with two time intervals. One specifies discards the minimum
associated Event Notification.

Event Notification Lease Time: The expiration time at which event-
leases of future events of the type returned will begin assigned to expire 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 other specifies value of the recommended interval for "notify-
recipient-uri" attributes has the client to wait
before sending scheme "ipp-get", the next Get-Notifications operation. The second time
interval client is less than
requesting that the first.

The Printer may keep use the channel open if the recommended interval is
sufficiently short, but in any case 'ipp-get' Delivery Method for the client performs a new Get-
Event Notifications operation each time it wants more Notifications. Since the
time interval between consecutive client requests is normally less than
the event-lease time, consecutive responses will normally contain some
events that are identical.   The youngest ones in the previous response
will become the oldest in associated with the next response. new Subscription Object. The
client is expected to
filter out these duplicates, which is easy to do because of the sequence
number in each Notification.  The reason MUST choose a value for not removing the
Notifications from the Subscription object 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 address part 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.

                      Expires: September 8, 2000

2  Terminology

This section defines the following additional terms "notify-
recipient-uri" attribute that are used
throughout this document:

  REQUIRED: if an implementation supports uniquely identifies the extensions described in
     this document, it MUST support a REQUIRED feature.
  OPTIONAL: if Notification
Recipient.

When an implementation supports Event occurs, the extensions described in
     this document, it MAY support Printer MUST generate an OPTIONAL feature.
  Notification Recipient - See [ipp-ntfy]
  Subscription object - See [ipp-ntfy]
  Ultimate Event Notification Recipient - See [ipp-ntfy]

3  Model
and Operation

In the IPP MUST assign it an Event Notification Model [ipp-ntfy], one or more Per-Job
Subscriptions can be supplied in the Job Creation operation or
OPTIONALLY as subsequent Create-Job-Subscription operations; one Per-
Printer Subscription can be supplied in the Create-Printer operation. Lease Time. The client that creates these Subscription objects becomes the owner of
the Subscription object.

When creating each Subscription object, the client supplies the "notify-
recipient" (uri) attribute.  The "notify-recipient" attribute specifies
both a single Printer MUST
hold an Event Notification Recipient that is to receive the
Notifications when subsequent events occur and the method for its assigned Event Notification delivery that the IPP Lease
Time and MUST discard it when its Event Notification Lease Time expires.
The Printer is to use.  For MAY assign the same Event Notification delivery method defined in this document, the scheme of the
URL is 'ipp' and the host SHOULD be the client host's URL. In addition,
the URL MAY contains a path Lease Time to allow for applications to have a unique
URL.

ISSUE 1: The 'ipp' is a convenient reuse of 'ipp', but does each
Event Notification or it imply the
existence of MAY assign a print service at each client that is not different time.

When a reality?

For most Notification delivery methods, a Printer sends Event
Notifications Recipient wants to the delivery URL and the Printer does not perform any
authentication or authorization with the receivers of the Event
Notifications. For the Notification delivery method defined in this
document, the client requests receive Event Notifications from Notifications, it
performs the Printer via a Get-Notifications operation, and the Printer performs the same
authentication and authorization as it does for which causes the Get-Job-Attributes
operation. That is, a Printer MAY allow a client to perform a Get-
return all unexpired Event Notifications operation on any Subscription object or it MAY restrict
access as follows. Any client that is authenticated (1) as an operator
or administrator or (2) as held for the owner of Notification
Recipient along with two time-intervals.

The first returned time-interval is the Subscription object can
initiate suggested time a Notification
Recipient should wait before performing the Get-Notifications operation for
again. The second time-interval is the time that Subscription object.

Because a Printer has Event Notification
Leases begin to wait expire for a client to request Event Notifications for the 'ipp' delivery method, any Printer that supports created after the 'ipp' notification delivery method MUST hold each Event Get-
Notifications operation. A Notification Recipient SHOULD perform this
operation at least for the event-lease suggested time that it advertises and somewhat before the Event
Notification Leases begin to clients.  With
this rule, expire.

The Notification Recipient identifies its own Event Notifications with a single user can login at different places, say his/her
office, the lab, and/or several desktops
"notify-recipient-uri" Operation attribute in the same room, and receive

                      Expires: September 8, 2000

the same request. It matches
any Event Notifications from associated with a single Subscription object. In
addition, 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 gets no response, perhaps because of
are unique, e.g. the client's host address.

If a network
failure, can perform Notification Recipient performs the Get-Notifications operations two or more times operation
twice in quick succession and get succession, it will receive nearly the same results except for a few newly
arrived Event Notifications and a few
Notification both times. There are two possible differences. Some old
Event Notifications whose
event-leases may not be present in the second response because
their Event Notification Leases have expired.

The event-lease time assigned to  Some new Event
Notifications MAY may be different
for each implementation. Furthermore, a particular implementation MAY
assign different event-lease times to each Event Notification. If 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
Printer assigns different event-lease times to new Get-
Notifications operation each time it wants more Event Notification, Notifications.
Since the event-lease time returned with Get-Notifications MUST be a value
that ensures a interval between consecutive client will not miss future requests is normally
less than the Event Notifications. Notification Lease Time, consecutive responses will
normally contain some events that are identical.   The client issues a Get-Notifications Printer operation youngest ones in order to
initiate
the delivery 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 pending sequence number in each Event Notification.  The reason
for not removing the Event Notifications held by from the Printer
for with every
Get-Notifications request, is so that multiple Notification Recipients
can be polling the same Subscription objects requested. Object and so the Get-Notification
operation satisfies the rule of idempotency.  The client can indicate former is useful if
someone is logged in to several desktops at the
Get-Notifications request whether it same time and wants to receive all pending
Notifications for:

  1) any existing Subscription objects for which
see the client same events at both places. The latter is useful if the
     owner,

  2) any existing Subscription objects whose notification-recipient network
loses the response.

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
     specified URL

  3) any existing Subscription objects associated Printer MUST IPP with one new
  operation.

4.Several Event Notifications MAY be combined into a job-id or

  4) particular Subscription object(s) (for which it compound Event
  Notification. See section 5.

5.The Notification Recipient MUST initiate the Delivery Method

6.The Delivery Method sends Machine Consumable Event Notifications.

7.The representation and encoding for each value MUST be the owner
     or have read-access rights).

In any case, same as
  for IPP (see section 5).

8.In the Notifications are returned in Event Notification content, a response to the Get-
Notifications request.

If Printer MUST send all attributes
  specified in section 5.

9.Frequently occurring Events NEED NOT be moderated because the client requests
  Delivery Method is a persistent channel, then 'pull' Delivery Method. An implementation of the Printer MAY keep
  Get-Notifications operation SHOULD consider how often it recommends a
  Notification Recipient to poll again.

10.  This Delivery Method has the channel open. Either same latency and reliability as the client or
  underlying HTTP transport.

11.  This Delivery Method has the IPP Printer can disconnect same security aspects as the
  underlying HTTP connection.

4 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 REQUIRED operation allows causes the client Printer to request that pending return all Event Notifications be delivered as a response held
for the Notification Recipient along with information about when to
perform this request.  The client operation again.

A Printer MUST be the owner or have read-access rights of the Subscription objects
that are involved support this operation.

When a Printer performs this operation, it MUST return all and the delivery method specified when the only
those Event Notifications:

     a)Whose associated Subscription objects were created MUST be ipp'.  When Object's "notify-recipient-uri"
       attribute equals the Printer
creates a "notify-recipient-uri" Operation attribute
       AND

     b)Whose associated Subscription Object, either with a Job Creation operation or
with a Create-Printer-Subscription or Create-Job-Subscription operation
and Object's "notify-recipient-uri"
       attribute has a subscription object contains the 'ipp' scheme value for the "notify-
recipient" operation attribute, the Printer returns of 'ipp-get'  AND

     c)Whose Event Notification Lease Time has not yet expired AND

     d)Where the event-lease time
for Events and Notification Recipient is the recommended time interval before owner of or has read-
       access rights to the client 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
performs the next Get-Notifications operation.  The client SHOULD perform a the
       Get-Notifications operation again.

     b)the time at about the recommended interval

                      Expires: September 8, 2000

and if which the Printer receives the Get-Notifications before the event-lease
time has elapsed, it MUST have all of the will begin to discard Event
       Notifications since that occur after this operation. This may be the
previous Get-Notification operation or
       Event Notification Lease Time (see section 5.2 for details).

Note: the Subscription object creation,
whichever was most recent.

Issue 2: Now that the Get-Notification Creation Operations also return these two time-
intervals (see section 6).

The Printer MUST respond to this operation does not affect the immediately with whatever
Event Notifications in the Printer, it should not require write access currently holds. It MUST NOT wait for additional
Events to access them. occur before sending a response.

The IPP 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: The 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] [ipp-
mod] section 8.3) performing this operation must MUST either be the Subscription object owner
(as determined when the of
each Subscription object was created Object identified by the Job
Creation operation, Create-Job-Subscription, or Create-Printer- "notify-recipient-uri"
Operation attribute (as determined during a Subscription operations) Creation
Operation) or an operator or administrator of the Printer
object (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.

Issue 3: Is it possible for this operation to have an option that causes
it to delay completing its response?  It would initially returns all
existing Event Notifications. Then it would return additional
notifications as they occur for some period of time. The client would
receive these Event Notifications as they occur.  The question is
whether http servers or proxies would behave in this manner so that the
client would get the Event Notifications without delay after they are
sent by the http server?  It has been suggested that the Printer send
each burst of Event Notifications be in a separate message body where
each message body is part administrator of a multipart MIME content-type.

4.1 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.

                      Expires: September 8, 2000
  "notification-recipient" (url):
     The client OPTIONALLY supplies this attribute.  The Printer object
     MUST support this attribute. It is a URL that identifies one or
     more Subscription objects for which Event Notifications are being
     requested.  If the client supplies this attribute, but no
     notification-recipients are found, the IPP Printer MUST return the
     'client-error-not-found' status code.  If some are found and others
     are not, the ones that are not found are return in the Unsupported
     Attributes.   By definition, if a notification-recipient URL
     exists, there must be at least one Subscription object.

     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 if it wants.  If a
     client uses such a URL as the value of this attribute, the client
     gets event Notifications for all Subscription objects whose
     "notification-recipient" is the specified URL.  This mechanism is
     more general than getting all subscriptions owned by a client. It
     allows clients who didn't subscribe to get Event Notifications
     without knowing job-ids or subscription-ids.

ISSUE 4: The "notification-recipient" option allows a client to group
multiple Subscription-ids with a single URL. A client might decide to
use the same URL for all subscriptions for a user, or it might have a
separate URL for each client program.  In addition a client might use an
URL belonging to some other known user and let that user access Event
Notifications using that URL.  Is

  Requesting User Name:
     The "requesting-user-name" (name(MAX)) attribute SHOULD be supplied
     by the above option useful?

  "subscription-ids" (1setOf integer(1:MAX)): client as described in [ipp-mod] section 8.3.

  "notify-recipient-uri" (url):
     The client OPTIONALLY supplies MUST supply this attribute.  The Printer object MUST
     support this attribute. It is an integer The Printer matches the value that identifies
     one or more Subscription objects of this
     attribute (byte for which Event Notifications are
     being requested.  If byte with no case conversion) against the client supplies this attribute, but none value
     of the "notify-recipient-uri" in each Subscription objects are found, the IPP Printer MUST return
     the 'client-error-not-found' status code.  If some are found and
     others are not, the ones that are not found are return Object in the
     Unsupported Attributes.

  "job-ids" (1setOf integer(1:MAX)):
     The client OPTIONALLY supplies this attribute.  The Printer object
     MUST support this attribute. It is an integer value that identifies
     one or more job-ids.  These job-ids identify the Subscription
     objects for which Event Notifications are being requested.
     Printer. If the
     client supplies this attribute, but no Jobs there are found, no matches, the IPP Printer MUST return the
     'client-error-not-found' status code.  If
     some are found and others are not, the ones that are not found are
     returned in the Unsupported Attributes.   It is not an error if
     there are no  For each matched
     Subscription objects for a Job.

                      Expires: September 8, 2000
     If the client supplies none of the last three attributes described
     for this operation, then Object, the IPP Printer returns Event
     Notifications for all Subscription objects for which the client is
     the owner and the "notify-recipients" attribute is 'ipp'.  It is
     not an error if there are currently no Subscription objects for
     this client; the response then contains no Notifications.

ISSUE 5: Does the mechanism described in the above paragraph describe a
useful option that "notification-recipient" alone cannot do? Should this
case be an error instead?

     If a client supplies more than one of the last three attributes
     described for this operation, the Printer returns Event
     Notifications for all Subscription objects specified by all
     attributes.  If these attributes describe duplicate Event
     Notifications, the Printer MAY remove them.

ISSUE 6: Is it better if "notification-recipient" is the only way to
request MUST return all unexpired
     Event Notification?  If so, this behaves more like other
notification delivery methods where a recipient receives those and only
those events Notifications associated with its delivery URL.  Furthermore, if there is a single
mechanism of "notification-recipient" for it.

     Note: this attribute allows a subscribing client to specify Event
Notifications, pick URLs that
     are unique, e.g. the client's own URL or a Printer can better optimize event-leases because it
knows friend's URL, which events will be accessed together. If client can specify
subscription-ids, each request can contain a different mix in
     both cases is likely the URL of
subscription-ids.

4.2 the person's host. An application
     could make a URL unique for each application.

5.2 Get-Notifications Response

The Printer object returns either an immediate error response or a
successful response with status code: 'successful-ok' when the first
event occurs, i.e., when the Printer delivers following groups of attributes are part of the first Event
Notification. 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.

  "recommended-time-interval" "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
     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 recommended suggested number of seconds that
     SHOULD elapse before the client performs this the Get-Notifications
     operation again for these Subscription objects. Objects. A client MAY
     perform this the Get-Notifications operation

                      Expires: September 8, 2000 at any time, and a Printer
     MUST respond with all existing unexpired Event Notifications. A client observes Notification
     Recipient waits until this value time interval has elapsed in order to be
     a "good network citizen". The value It is RECOMMENDED that a Printer returns for the value of this
     attribute MUST NOT exceed be 80% of the "event-lease-time-interval" "begin-to-expire-time-interval" (see the
     next attribute) in order to give a client Notification Recipient plenty of
     time to perform another Get-
     Notifications the Get-Notifications operation again before the event-lease of the oldest new
     Event Notifications expire.

  "event-lease-time-interval"

   "begin-to-expire-time-interval" (integer(0:MAX)):
     The value of this attribute is the minimum number of seconds until
     the event-lease expiration time for all future that
     MUST elapse before Event Notification Leases begin to expire on
     Event Notifications
     associated with produced by matching Subscriptions Objects
     after the Subscription objects generating Printer sends the requested Get-Notifications response. The Printer
     MUST discard an Event Notifications. Thus this number is Notification when its Event Notification
     Lease has expired. That is, if the maximum number of
     seconds that elapses before this client SHOULD issue this Printer performs the Get-
     Notifications operation
     again for these Subscription objects. A before the time specified by the "begin-to-
     expire-time-interval" attribute returned in the previous operation,
     the Printer MUST preserve still have all of the Event Notifications that occur for
     have occurred since the number previous operation. If the Printer assigns
     the same Event Notification Lease Time to all Event Notifications,
     the value of seconds specified by this attribute starting at MUST equal the time it is sent in Event Notification Lease
     Time. If a response. A
     client MAY perform Notification Recipient waits until after this time or
     even slightly less than this operation at any time, and a Printer the Notification Recipient MUST
     respond with all existing
     expect to lose some Event Notifications. If a

  "printer-up-time" (integer(0:MAX)):
     The value of this attribute is the Printer's "printer-up-time"
     attribute at the time the Printer
     receives sends this operation after response. Because each
     Event Notification also contains the value of this time interval, it MAY have
     discarded some Notifications since attribute when
     the event occurred, the value of this attribute lets a Notification
     Recipient know when each Event Notification occurred relative to
     the last 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

     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 ***

     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 object responds with one MUST send the "job-impressions-completed" attribute
     in an Event Notification per Group only for each 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'
     For Event Notification that meets for Printer Events, the criteria specified by Printer includes the
     request.(see [ipp-ntfy]).

5  Extension
     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 Print-Job, Print-URI, Create-Job, Create-Printer- Subscription and Create-Printer-Subscription

5.1 Creation Operations

6.1 Response

When Print-Job, Print-URI or Create-Job a Subscription Creation Operation contains a "job-notify" "notify-recipient-uri"
attribute and the "notify-recipient" is 'ipp', the response contains two
additional Operation Attributes that pertain to subscriptions.

When Create-Job-Subscription or Create-Printer-Subscription operation
contains a "notify-recipient" that scheme in its value is 'ipp', 'ipp-get', the response contains MUST
contain two additional Operation Attributes that pertain to subscriptions. 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

                      Expires: September 8, 2000
  "recommended-time-interval" (integer(0:MAX)):
     The value of this attribute is the recommended number of seconds
     that SHOULD elapse before the client SHOULD perform the Get-
     Notification operation for the first time with any Subscription
     objects returned with this job. A client MAY perform the Get-
     Notification operation at any time, and a Printer MUST respond with
     all existing Notifications. A client observes this value in order
     to be a "good network citizen". The value that a Printer returns
     for this attribute MUST NOT exceed 80% of the "event-lease-time-
     interval" in order to give a client plenty of time to perform
     another Get-Notifications operation before the event-lease of the
     oldest events expire.

  "event-lease-time-interval"

  "suggested-ask-again-time-interval" (integer(0:MAX)):
     The value of this
     This attribute is the minimum number of seconds until
     the event-lease expiration time for all future Event Notifications
     associated with the Subscription objects generating has the requested
     Event Notifications. Thus this number is same meaning as the maximum number of
     seconds "suggested-ask-again-
     time-interval" attribute in the Get-Notifications operation except
     that elapses before a client SHOULD it suggests when to perform the Get-
     Notification Get-Notifications operation
     for the first time with any Subscription
     objects returned with this job. A Printer MUST preserve on all
     Notifications that occur for Subscription Objects in the number of seconds specified by
     this response
     whose "notify-recipient-uri" scheme is 'ipp-get'.

  "begin-to-expire-time-interval" (integer(0:MAX)):
     This attribute starting at has the time it is sent same meaning as the "begin-to-expire-time-
     interval" attribute in a response. A
     client MAY perform the Get-Notification operation at any time, and
     a Printer MUST respond with all existing Event Notifications. If a
     Printer receives a Get-Notification Get-Notifications operation after this time
     interval, except that
     it may have discarded some Notifications since indicates when the last
     response.

6 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-Notification Get-Notifications operation is:

     0x00??

     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

7

8  IANA Considerations

There is nothing to register.

                      Expires: September 8, 2000

8

9  Internationalization Considerations

With the 'ipp' method defined in this document, the client cannot
request the Human Consumable form by supplying the "notify-format"
operation attribute (see [ipp-ntfy]).

The only supported value for this
delivery method is "application/ipp". Therefore, the IPP Printer does
not have to perform any localization with this notification delivery
method.  However, MUST localize the client "notify-text" attribute as specified
in section 14 of [ipp-ntfy].

In addition, when it the client receives the Get-Notifications
response 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.

9

10 Security Considerations

The IPP Model and Semantics document [ipp-mod] discusses high level 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 issues   s the
Get-Notifications 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.

10

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-v11-06.txt>, March 1, 2000.

[ipp-ntfy]
     R. Herriot, Hastings, T., Isaacson, S., Martin, J., deBry, R., Hastings, T.,
     Shepherd, M., Bergman, R., "Internet Printing Protocol/1.1: IPP
     Event Notification Specification", <draft-ietf-ipp-not-spec-02.txt>,
     March 8, <draft-ietf-ipp-not-spec-
     04.txt>, June 30, 2000.

[ipp-pro]
     Herriot, R., Butler, S., Moore, P., Tuner, R., "Internet Printing
     Protocol/1.1: Encoding and Transport", draft-ietf-ipp-protocol-v11-
     05.txt, March 1, 2000.

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

                      Expires: September 8, 2000

[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.

11

12 Authors' Addresses

   Carl-Uno Manros

   Robert Herriot
   Xerox Corporation
   701 Aviation Blvd.
   El Segundo, Corp.
   3400 Hill View Ave, Building 1
   Palo Alto, CA 90245 94304

   Phone: 310-333- 650-813-7696
   Fax:  310-333-5514  650-813-6860
   e-mail: manros@cp10.es.xerox.com 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

   Robert Herriot

   Carl-Uno Manros
   Xerox Corp.
   3400 Hill View Ave, Building 1
   Palo Alto, Corporation
   701 Aviation Blvd.
   El Segundo, CA 94304 90245

   Phone: 650-813-7696 310-333-
   Fax:  650-813-6860  310-333-5514
   e-mail: robert.herriot@pahv.xerox.com 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

12

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,

                      Expires: September 8, 2000
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.

                      Expires: September 8, 2000