SIMPLE WG T. Moran
Internet-Draft
Expires: December 17, 2003 S. Addagatla
E. Leppanen
Nokia
A. Allen
June 18, 2003
Requirements for Presence Specific Event Notification Filtering
draft-ietf-simple-pres-filter-reqs-01
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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 infomation 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. Overview of functionality . . . . . . . . . . . . . . . . . 4
4. Requirements for Specification of Filters . . . . . . . . . 4
4.1 Common Syntax . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 Package Identification . . . . . . . . . . . . . . . . . . . 4
4.3 Target URI . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.4 Notification Triggering . . . . . . . . . . . . . . . . . . 4
4.5 Notification Content Limiting . . . . . . . . . . . . . . . 5
4.6 Discovery of Items . . . . . . . . . . . . . . . . . . . . . 5
5. Requirements for Uploading Filter Criteria (Operational
Rules) . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1 SUBSCRIBE Method . . . . . . . . . . . . . . . . . . . . . . 6
5.1.1 Retention of Filter Criteria . . . . . . . . . . . . . . . . 6
5.1.2 Changing Filter Criteria . . . . . . . . . . . . . . . . . . 6
5.2 Server does not Support Filters . . . . . . . . . . . . . . 6
5.3 Server does not Support Filter Criteria . . . . . . . . . . 6
5.4 Server can no Longer Support Filter Criteria . . . . . . . . 7
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. Main changes from version 00 . . . . . . . . . . . . . . . . 9
References . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
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 Internet Draft describing the Presence event package [5] mentions
the possibility for a filtering. Accordingly, the SUBSCRIBE request
may contain a body for filtering the presence information
subscription. However, the definition of the filtering has been left
out of the scope of the Internet Draft. As an example, the body of
the SUBSCRIBE request may include a restriction on the set of data
returned in NOTIFY requests.
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 notification.
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. 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. Overview of functionality
Filter Criteria set by a watcher may be set based on some
predetermined knowledge of the structure of the presence information,
or the filtering mechanism may itself be used to first discover the
structure of the presence information thus enabling the setting new
filter criteria to deliver the values of interest.
The filtering may be performed either by the presence server of the
presentity (the notifier) or by some intermediate server between the
notifier and the watcher. The filtering should be considered as a
post processing operation on the presence document after it has been
modified due the rules of the authorization. As a result the
authorization policy always overides any of the data or notifications
requested by any of the filter criteria.
Subscriptions containing filter criteria may either be accepted or
rejected by the notifier based on the presence of filter criteria.
4. Requirements for Specification of Filters
The following requirements relate to the creation of filter criteria.
4.1 Common Syntax
A common set of constructs MUST be defined for the creation of rules.
There MUST be a common set of operations that follow a common syntax.
The user MUST be possible to define different rules for different
purposes using a common filtering mechanism.
4.2 Package Identification
A means is REQUIRED whereby the user may specify the package the
rules apply to.
4.3 Target URI
It MUST be possible for the watcher in the filter criteria to
indicate the target presentity, resource list or sub list of the
resource list to which a certain filter criteria is applied if this
is different from the Request-URI in the subscription.
4.4 Notification Triggering
This chapter presents requirements for specifying the desired
conditions for when notifications are to be sent to the client.
The scope of the 'when' part is to allow a possibility for the user
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to specify such rules for the notification triggering where the
criteria is based on the presence information, e.g., the value of the
status element.
The notification triggering criteria would override the default
trigger conditions of the server/service as defined in the package
when they are within the server's local policy constraints.
It MUST be possible to specify logical expressions based on the value
of elements defined in the package for the purpose of when to send
notifications. This covers expressions (tests) related to the change
of an element's value, and reaching a certain value of an element.
It MUST be possible to construct expressions that combine multiple
tests.
4.5 Notification Content Limiting
This chapter presents requirements for specifying the content to be
sent in the notifications.
It MUST be possible for the watcher to specify the presence
information elements [2] (XML elements and/or attributes) to be
delivered in the notification. The specified elements MUST be
possible to cover also extensions to PIDF formated presence
information, see for example [3].
E.g. the following two cases must be possible:
o It MUST be possible for the watcher to define a criteria which
allows the complete tuple and all information within a tuple to be
transmitted.
o It MUST be possible for the watcher to define a criteria which
result notifies to contain values only for defined attributes.
It MUST be possible to specify logical expressions based on the value
of elements defined in the package for the purpose of determining
what to send in the notification. The existence of an element SHOULD
be considered as a criterion.
It MUST be possible to construct expressions that combine multiple
tests.
4.6 Discovery of Items
It MUST be possible for the watcher to request to learn new items of
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the presence information that the notifier may make available to the
watcher. E.g., to discover additions of new tuples and/or other new
presence information items.
It MUST be possible for the watcher using the filter criteria to
determine what presence information is available before subscribing
to presence information with the actual values.
5. Requirements for Uploading Filter Criteria (Operational Rules)
It MUST be possible for the watcher to upload filter criteria to the
server (notifier) and know the status - accepted or rejected.
5.1 SUBSCRIBE Method
Placing filter criteria in the body of the subscription MUST be
supported. Other means of delivering the filter criteria to the
server MAY be supported. E.g. it should be possible for the rules to
be (permanently) stored in the server, as in a resource list case.
5.1.1 Retention of Filter Criteria
The server MUST retain the filter criteria through the lifetime of
the subscription dialog until there is a modification to the filter
settings.
5.1.2 Changing Filter Criteria
It MUST be possible to change the filter settings during a
subscription.
It MUST be possible for the watcher to reset the filter settings to
the service (server) defined default.
Changing filter criteria SHOULD be bandwidth efficient.
5.2 Server does not Support Filters
If the server does not support filters (the content type) then it
MUST be possible to indicate so in a response.
5.3 Server does not Support Filter Criteria
It MUST be possible for the server to explicitly indicate that it
does not support or understand the filter criteria. This indication
MAY include a reason about the refusal of the subscription.
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5.4 Server can no Longer Support Filter Criteria
The server MUST be able to terminate the subscription if the any of
the active filters are no longer applicable due to a policy in the
server.
6. Interaction with Other Features
6.1 Resource Lists
It MUST be possible to support filtering for subscriptions to
resource lists [8].
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.
It MUST be possible for a watcher to specify different filter for any
individual member of a resource list in a resource list subscription.
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
lists may be located in a different domain from the parent list.
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.
6.2 Partial Notifications
It MUST be possible to use filtering along with the partial
notification [9] within the same subscription.
6.3 Authorization
Authorization SHOULD occur irrespective of the filtering.
7. 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.
The filter criteria should not be rejected based on the authorization
policy since this would enable the watcher by experimentation with
the use of filter criteria to determine the authorization policy the
presentity has set for him and thus discover what the presentity
wants to hide from him.
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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.
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).
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.
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).
The resource list servers should convey only those parts of filter
information targetted to the same destination as the fanned out
individual subscriptions, if the filter information is conveyed
further within the subscription.
8. 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 Subscriber 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 intrested in being notified when a presentity gains
a new communication capability such as a new networked
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multi-player game.
9. Acknowledgements
The authors would like to thank Hisham Khartabil, Mikko Lonnfors,
Juha Kalliokulju, Aki Niemi, Jose Costa-Requena and Markus Isomaki
for their valuable input.
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.
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[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",
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
Tim Moran
2800 Britt Drive
Argyle, Texas 76226
USA
Phone: +1 972 849 8821
EMail: tl_moran@att.net
Sreenivas Addagatla
Nokia
6000 Connection Drive
Irving, Texas 75039
USA
Phone: +1 972 374 1917
EMail: sreenivas.addagatla@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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Andrew Allen
1937 McRae Lane
Mundelein, Illinois 60060
USA
EMail: AndrewAllen007@aol.com
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