SIMPLE WG T. Moran
Internet-Draft
Expires: July 26, 2004 H. Khartabil
E. Leppanen
Nokia
January 26, 2004
Requirements for Presence Specific Event Notification Filtering
draft-ietf-simple-pres-filter-reqs-03
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Copyright Notice
Copyright (C) The Internet Society (2004). 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. Event Filtering Model . . . . . . . . . . . . . . . . . . . 3
3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Requirements for Specification of Filters . . . . . . . . . 4
4.1 Package Identification . . . . . . . . . . . . . . . . . . . 4
4.2 Target URI . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.3 Notification Triggering . . . . . . . . . . . . . . . . . . 5
4.4 Notification Content . . . . . . . . . . . . . . . . . . . . 5
5. Requirements for Uploading Filters (Operational Rules) . . . 6
5.1 Subscription . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1.1 Maintaining a Filter . . . . . . . . . . . . . . . . . . . . 6
5.1.2 Changing a Filter . . . . . . . . . . . . . . . . . . . . . 6
5.2 Server Support For Filters . . . . . . . . . . . . . . . . . 6
6. Interaction with Other Features . . . . . . . . . . . . . . 7
6.1 Resource Lists . . . . . . . . . . . . . . . . . . . . . . . 7
6.2 Partial Notifications . . . . . . . . . . . . . . . . . . . 7
6.3 Authorization . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . 7
8. Example Applications for Notification Filtering . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. Changes from previous versions . . . . . . . . . . . . . . . 9
10.1 Main changes from version 02 . . . . . . . . . . . . . . . . 9
10.2 Main changes from version 01 . . . . . . . . . . . . . . . . 9
10.3 Main changes from version 00 . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . 12
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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 and
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 4 and Section 5 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 8 provides a few example applications of notification
filtering.
2. Event Filtering Model
There are two parts to the event filtering model. From a Presence
service view point, presence information is collected by a Presence
Agent and is published by one or more Presence User Agents. The first
part of the model enables the watcher to limit the presence
information delivered to it. Allowing the watcher to select the
information of interest to it results in the ability to limit the
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contents of a presence information document, therefore reducing the
size of a notification message.
+--+
--| |PUA
PA --- +--+
Watcher +---------+ ----
+-----+ | | ---
| | | |-- +--+
| |--------------| |--------------| |PUA
| | | |-- +--+
+-----+ | | ---
+---------+ ----
--- +--+
--| |PUA
+--+
The second part of the model defines the triggering. In a filter-less
subscription, it might be a Presence Agent's default policy to
deliver a notification message every time there is a change to the
presence information of a presentity or whenever a PUA publishes new
and updated presence information from its own point of view. This
model enables the watcher to select the events or changes in presents
information that trigger notifications to be sent. Other changes that
are not defined as triggers in a filter do not result in a
notification message being delivered to the watcher.
3. 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.
4. Requirements for Specification of Filters
The following requirements relate to the creation of filters.
4.1 Package Identification
REQ A1: It MUST be possible for the creator of the filter to specify
the package the filter applies to.
4.2 Target URI
REQ A2: It MUST be possible for the watcher to indicate, in the
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filter, the target presentity whose presence information a certain
filter is applied to.
REQ A3: It MUST be possible for the watcher to indicate, in the
filter, the target domain that a certain filter is applied to. For
example an event list might have many resources from different
domains, a watcher needs to be able to set a filter for one of those
domains.
4.3 Notification Triggering
This chapter presents requirements for specifying the triggering
conditions that result in notifications to be sent to the watcher.
REQ B1: The triggering conditions MUST be based on the presence
information. For example, the change of value of the <status>
element.
REQ B2:It MUST be possible to define a set of conditions for the
values of certain elements in a presence document that determine when
to send notifications.
REQ B3: It MUST be possible to construct one filter that combines
multiple triggering conditions.
4.4 Notification Content
This chapter presents requirements for specifying the filter for
choosing content to be sent in the notifications.
REQ C1: 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 C2: 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 C3: 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 C4: It MUST be possible for the watcher to specify presence
information in any extension to be delivered in the notifications,
based on namespaces.
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REQ C5: It MUST be possible to construct one filter that combine
multiple elements and attributes to be included the notifications.
REQ C6: It MUST be possible for the watcher to specify presence
information in PIDF or any any extension to it to be excluded from
the notifications, based on elements and/or attributes.
5. Requirements for Uploading Filters (Operational Rules)
REQ D1: It MUST be possible for the watcher to upload filters to the
server (notifier) and know the status - accepted or rejected, if the
server policy allows.
5.1 Subscription
REQ D2: It MUST be possible to place a filter in the body of the
SUBSCRIBE request.
REQ D3: 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.
5.1.1 Maintaining a Filter
REQ D4: The watcher MUST NOT be required to re-set a filter at any
time during the subscription, once the filter has been set. This
includes subscription refreshes
REQ D5: modifying a filter across subscription refreshes SHOULD be
bandwidth efficient.
REQ D6: It MUST NOT be required for a watcher to explicitly remove a
filter if the subscription was terminated or has expired. I.e. The
filter is automatically removed with the subscription.
5.1.2 Changing a Filter
REQ E1: It MUST be possible to change the filter during a
subscription.
REQ E2: It MUST be possible for the watcher to remove a set filter,
reverting back to a server defined default.
5.2 Server Support For Filters
REQ F1: It MUST be possible for a server not supporting filtering to
inform the watcher of the failure.
REQ F2: It MUST be possible for a server not understanding a
filtering to inform the watcher of the failure.
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REQ F3: It MUST be possible for a server not accepting a filter to
inform the watcher of the reasons for not accepting the filter.
REQ F4: It MUST be possible for the server to terminate a
subscription if a filter is no longer acceptable, e.g., due to policy
change or server load.
6. Interaction with Other Features
6.1 Resource Lists
REQ G1: It MUST be possible to support filtering for subscriptions to
event lists [8].
REQ G2: It MUST be possible for the watcher to indicate, in the
filter, the target event list that a certain filter is applied to by
the Resource List Server.
REQ G3: It MUST be possible for a watcher to specify individual
filters for any resource in an event list if the subscription is for
an event list.
REQ G4: It MUST be possible to specify a filter for an event list and
a filters for resources within that list in the same subscription
request.
REQ G5: Some event lists may contain an other event list as a
resource. I.e. nested lists. It MUST be possible for the watcher to
indicate, in the filter, a nested event list that a certain filter is
applied to.
REQ G6: It MUST be possible for a watcher to specify different filter
for resources within any nested list of an event list, if the
subscription is for an event list.
REQ G7: It MUST be possible for each watcher to define his/her own
filters within an event list subscription if there are several
simultaneous watchers using the same list.
6.2 Partial Notifications
REQ H1: It MUST be possible to use filtering along with the partial
notification [9] within the same subscription.
6.3 Authorization
7. Security Considerations
Security requirements specified for [5] also applies to presence
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filtering. Additional security considerations are described as
follows.
REQ I1: It SHOULD be possible for the server to hide the fact that a
filter was not acceptable.
REQ I2: The presence of filters 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 MUST be possible to authenticate messages
carrying filters and authorise the watcher to upload filters.
REQ I3: Modification to filters 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 filters SHOULD be integrity protected between
those nodes that are authorised to modify it (e.g., the resource list
servers).
REQ I4: Processing of requests and looking up filters 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
filters allowed in a request should be limited.
REQ I5: Requests containing filters 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).
REQ I6: The resource list servers SHOULD NOT forward filters targeted
to a different domain than a fanned out subscription request.
REQ I7: Authorization SHOULD occur irrespective of the filtering.
8. Example Applications for Notification Filtering
o A watcher wishes to get to know presentity's availability and
willingness for messaging (e.g. IM and MMS).
o A watcher is interested in getting information about the
communication means and contact addresses the presentity is
currently available for communication.
o A watcher requires a notification if the state of a buddy has
changed to 'open'.
o A watcher only wants to be notified when the presentity's location
is Dallas or Fort Worth. The notification should include the
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vehicle license, driver name, and city.
o A Basic location tracking service requires notification when the
presentity's cell id changes. The notification should include the
cell id.
o A watcher is interested in being notified when a presentity gains
a new communication capability such as a new networked
multi-player game.
9. Acknowledgements
The authors would like to thank Andrew Allen, Sreenivas Addagatla,
Mikko Lonnfors, Juha Kalliokulju, Aki Niemi, Jose Costa-Requena,
Markus Isomaki, Paul Kyzivat, Aki Niemi and Chris Boulton for their
valuable input.
10. Changes from previous versions
10.1 Main changes from version 02
o Added filtering model section.
o Rephrased some requirements for clarity.
o Rearranged requirements into more appropriate sections.
10.2 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.
o Updated the Authors of this ID
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10.3 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., "RPID -- Rich Presence Information Data
Format", draft-ietf-simple-rpid-00.txt, July 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] Roach, A., "A Session Initiation Protocol (SIP) Event
Notification Extension for Resource Lists",
draft-ietf-simple-event-list-03.txt, June 2003.
[9] Lonnfors, M., "Partial Notification of Presence Information",
draft-lonnfors-simple-partial-notify-01.txt, May 2003.
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Authors' Addresses
Tim Moran
2800 Britt Drive
Argyle, Texas 76226
USA
Phone: +1 972 849 8821
EMail: tl_moran@att.net
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
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