SIMPLE WG H. Khartabil
Internet-Draft E. Leppanen
Expires: February 12, 2004 Nokia
T. Moran
August 14, 2003
Requirements for Presence Specific Event Notification Filtering
draft-ietf-simple-pres-filter-reqs-02
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This document is an Internet-Draft and is in full conformance with
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines a set of structured requirements whereby a
presence information subscriber may select specific information to be
received in the presence information notification sent by the
notifier. The purpose is to limit the content and frequency of
notifications so that only essential information on a need basis is
delivered by the server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements for Specification of Filters . . . . . . . . . 4
3.1 Package Identification . . . . . . . . . . . . . . . . . . . 4
3.2 Target URI . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3 Notification Triggering . . . . . . . . . . . . . . . . . . 4
3.4 Notification Content . . . . . . . . . . . . . . . . . . . . 5
4. Requirements for Uploading Filter Criteria (Operational
Rules) . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1 Subscription . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1.1 Maintaining a Filter . . . . . . . . . . . . . . . . . . . . 5
4.1.2 Changing a Filter . . . . . . . . . . . . . . . . . . . . . 6
4.2 Server Support For Filters . . . . . . . . . . . . . . . . . 6
5. Interaction with Other Features . . . . . . . . . . . . . . 6
5.1 Resource Lists . . . . . . . . . . . . . . . . . . . . . . . 6
5.2 Partial Notifications . . . . . . . . . . . . . . . . . . . 7
5.3 Authorization . . . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . 7
7. Example Applications for Notification Filtering . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. Main changes from version 01 . . . . . . . . . . . . . . . . 8
10. Main changes from version 00 . . . . . . . . . . . . . . . . 9
References . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . 11
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1. Introduction
SIP event notification is described in [6]. It defines a general
framework for subscriptions and notifications for SIP event packages.
Concrete applications of the general event framework to a specific
group of events are described in [5] (user presence) and [7] (watcher
information).
The presence information refers to a set of presence attributes
describing the availability and willingness of the user (presentity)
for communication. The user makes his presence information available
for other users (watchers).
As the inherent usage of event packages grows, the client needs some
mechanisms for controlling the event notifications at the source.
Evidence of this need is found in [4].
The document describing the Presence event package [5] mentions the
possibility for filtering. Accordingly, the SUBSCRIBE request may
contain a body for filtering the presence information subscription.
However, the definition of filtering was considered out of scope was
left as future work.
These mechanisms are expected to be particularly valuable to users of
wireless devices. The characteristics of these devices typically
include low bandwidth, low data processing capabilities, small
display and limited battery power. Such devices can benefit from the
ability to filter the amount of information generated at the source
of the event notifications.
However, it is expected that the control mechanisms for event
notifications add value for all users irrespectively of their device
or network access characteristics.
Section 3 and Section 4 of this draft propose a set of requirements
whereby a client may specify which notifications it is interested in.
That is, a means to specify filtering rules to be executed by the
server. Section 7 provides a few example applications of notification
filtering.
2. Conventions
In this document, the key words 'MUST', 'MUST NOT', 'REQUIRED',
'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY',
and 'OPTIONAL' are to be interpreted as described in RFC 2119 [1]
and indicate requirement levels for compliant implementations.
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3. Requirements for Specification of Filters
The following requirements relate to the creation of filter criteria.
3.1 Package Identification
REQ xx: It MUST be possible for the creator of the filter to specify
the package the filter applies to.
3.2 Target URI
REQ xx: It MUST be possible for the watcher to indicate, in the
filter, the target presentity whose presence information a certain
filter is applied to.
REQ xx: It MUST be possible for the watcher to indicate, in the
filter criteria, the target presentity list whose presence
information a certain filter is applied to.
REQ xx: It MUST be possible for the watcher to indicate, in the
filter criteria, the target presentity sub-list whose presence
information a certain filter is applied to.
REQ xx: It MUST be possible for the watcher to indicate, in the
filter criteria, the target domain that contains presentities whose
presence information a certain filter is applied to.
3.3 Notification Triggering
This chapter presents requirements for specifying the triggering
conditions that result in notifications to be sent to the client.
REQ xx: It MUST NOT be possible to break any server side policy
constraints when applying the triggering conditions. For example, it
must not be possible for a watcher to request a notification when the
<status> element value of a certain presentity has changed from OPEN
to CLOSED when there is a local server policy constraining the
delivery of any tuple with a <status> element value of CLOSED.
REQ xx: The triggering conditions MUST be based on the presence
information. For example, the change of value of the <status>
element.
REQ xx: It MUST be possible to specify logical expressions based on
the value of elements defined in the package for the purpose of
triggering. This covers expressions (tests) related to the change of
an element's value, and reaching a certain value of an element.
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REQ xx: It MUST be possible to construct one filter that combine
multiple triggering conditions.
3.4 Notification Content
This chapter presents requirements for specifying the filter for
choosing content to be sent in the notifications.
REQ xx: It MUST NOT be possible to break any server side policy
constraints when applying the content filter. For example, it must
not be possible for a watcher to request a notification to contain
the <contact> element of a certain presentity when there is a local
server policy constraining the delivery of the <contact> element.
REQ xx: It MUST be possible for the watcher to specify the presence
information elements (XML elements and/or attributes) in [2] to be
delivered in the notification.
REQ xx: It MUST be possible for the watcher to specify presence
information in any extension to PIDF to be delivered in the
notifications, based on XML elements and/or attributes. See for
example [3].
REQ xx: It MUST be possible for the watcher to specify presence
information in any extension to be delivered in the notifications,
based on namespaces.
REQ xx: It MUST be possible to construct one filter that combine
multiple elements and attributes to be included the notifications.
4. Requirements for Uploading Filter Criteria (Operational Rules)
REQ xx: It MUST be possible for the watcher to upload filter criteria
to the server (notifier) and know the status - accepted or rejected.
4.1 Subscription
REQ xx: It MUST be possible to place a filter in the body of the
SUBSCRIBE request.
REQ xx: It MAY be possible to deliver a filter to a server using
other means. For example, it may be possible for the filter to be
(permanently) stored in the server.
4.1.1 Maintaining a Filter
REQ xx: The watcher MUST NOT be required to re-set a filter at any
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time during the subscription, once the filter has been set.
REQ xx: The watcher SHOULD NOT be required to re-set a filter when
refreshing a subscription, once the filter has been set.
REQ xx: Maintaining a filter across subscription refreshes SHOULD be
bandwidth efficient.
4.1.2 Changing a Filter
REQ xx: It MUST be possible to change the filter during a
subscription.
REQ xx: It MUST be possible for the watcher to remove a set filter,
reverting back to a server defined default.
4.2 Server Support For Filters
REQ xx: It MUST be possible for a server not supporting filtering to
inform the watcher of the failure.
REQ xx: It MUST be possible for a server not understanding a
filtering to inform the watcher of the failure.
REQ xx: It MUST be possible for a server not accepting a filter to
inform the watcher of the reasons for not accepting the filter.
REQ xx: It MUST be possible for a server to terminate a subscription
based on a filter becoming invalid due to sever local policy change.
(How do I word this in a requirement text?)
5. Interaction with Other Features
5.1 Resource Lists
REQ xx: It MUST be possible to support filtering for subscriptions to
resource lists [8].
REQ xx: It MUST be possible for a watcher to specify filter criteria
for a resource list and/or any nested sub list of the resource list.
REQ xx: It MUST be possible for a watcher to specify different filter
for any individual member of a resource list in a resource list
subscription.
REQ xx: It MUST be possible for a watcher to specify different filter
criteria for individual members of any of nested sub lists of a
resource list in a resource list subscription. Any of the nested sub
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lists may be located in a different domain from the parent list.
REQ xx: It MUST be possible for each watcher to define own filter
criteria within resource list subscription if there are several
simultaneous watchers using the same list.
5.2 Partial Notifications
REQ xx: It MUST be possible to use filtering along with the partial
notification [9] within the same subscription.
5.3 Authorization
REQ xx: Authorization SHOULD occur irrespective of the filtering.
6. Security Considerations
Security requirements specified for [5] also applies to the presence
filtering. Additional security considerations related to the presence
filtering are described as follows.
REQ xx: It SHOULD be possible for the server to hide the fact that a
filter was not acceptable.
REQ xx: The presence of filter criteria in the body in a SIP message
has a significant effect on the way in which the request is handled
at a server. As a result, it is especially important that messages
containing filter criteria are authenticated and authorized.
REQ xx: Modification to the Filter Criteria by an intermediary could
also result in the watcher either not receiving notifications of
presence information they are interested in or receiving a very large
presence document. Therefore the filter criteria SHOULD be integrity
protected between those nodes that are authorised to modify it (e.g.,
the resource list servers).
REQ xx: Processing of requests and looking up filter criteria
requires some amount of computation. This enables a DoS attack
whereby a user can send requests with substantial numbers messages
with large contents, in the hopes of overloading the server. To
prevent this the number of filter criteria allowed in a request
should be limited.
REQ xx: Requests containing filter criteria can reveal sensitive
information about a UA's capabilities. If this information is
sensitive, it SHOULD be encrypted using methods that allow it to be
read by those nodes that need to do so (e.g., the resource list
servers).
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REQ xx: The resource list servers SHOULD convey only those parts of
filter information targeted to the same destination as the fanned out
individual subscriptions, if the filter information is conveyed
further within the subscription.
7. Example Applications for Notification Filtering
1. A watcher wishes to get to know presentity's availability and
willingness for messaging (e.g. IM and MMS).
2. A watcher is interested in getting information about the
communication means and contact addresses the presentity is
currently available for communication.
3. A watcher requires a notification if the state of a buddy has
changed to 'open'.
4. A watcher only wants to be notified when the presentity's
location is Dallas or Fort Worth. The notification should include
the vehicle license, driver name, and city.
5. A Basic location tracking service requires notification when the
presentity's cell id changes. The notification should include the
cell id.
6. A watcher is interested in being notified when a presentity gains
a new communication capability such as a new networked
multi-player game.
8. Acknowledgements
The authors would like to thank Andrew Allen, Sreenivas Addagatla,
Mikko Lonnfors, Juha Kalliokulju, Aki Niemi, Jose Costa-Requena and
Markus Isomaki for their valuable input.
9. Main changes from version 01
o "Overview of Operation" section removed .
o "Common Syntax" section removed.
o "Discovery of Items" section removed as agreed in IETF 57
o Added requirement about filtering using namespaces.
o Added requirement about filtering using domain name.
o Clarified and split larger requirements into smaller more concrete
requirements.
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o Updated the Authors of this ID
10. Main changes from version 00
o Overview of functionality chapter added.
o More specific requirements for supporting filtering with the
resource lists, and nested lists.
o Interaction with other features chapter added.
o More specific requirements to support getting information about
the structure of presence document, and changes in it.
o Several filter specific additions to security considerations.
o Several editorial changes, e.g., reference and terminology
updates.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Sugano, H., "CPIM Presence Information Data Format",
draft-ietf-impp-cpim-pidf-08.txt, May 2003.
[3] Schulzrinne, H., "RPIDS -- Rich Presence Information Data Format
for Presence Based on the Session Initiation Protocol (SIP)",
draft-schulzrinne-simple-rpids-01.txt, February 2003.
[4] Kiss, K., "Requirements for Presence Service based on 3GPP
specifications and wireless environment characteristics",
draft-kiss-simple-presence-wireless-reqs-02, February 2003.
[5] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions for
Presence", draft-ietf-simple-presence-10.txt, January 2003.
[6] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[7] Rosenberg, J., "A Watcher Information Event Template-Package for
the Session Initiation Protocol (SIP)",
draft-ietf-simple-winfo-package-05.txt, January 2003.
[8] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Notification Extension for Resource Lists",
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draft-ietf-simple-event-list-03.txt, May 2003.
[9] Lonnfors, M., "Partial Notification of Presence Information",
draft-lonnfors-simple-partial-notify-01.txt, May 2003.
Authors' Addresses
Hisham Khartabil
Nokia
P.O BOX 321
Helsinki
Finland
Phone: +358 7180 76161
EMail: hisham.khartabil@nokia.com
Eva Leppanen
Nokia
P.O BOX 785
Tampere
Finland
Phone: +358 7180 77066
EMail: eva-maria.leppanen@nokia.com
Tim Moran
2800 Britt Drive
Argyle, Texas 76226
USA
Phone: +1 972 849 8821
EMail: tl_moran@att.net
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