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 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 at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 17, 2003. 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 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. Moran, et al. Expires December 17, 2003 [Page 1] Internet-Draft Presence Filtering Requirements June 2003 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 Moran, et al. Expires December 17, 2003 [Page 2] Internet-Draft Presence Filtering Requirements June 2003 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. Moran, et al. Expires December 17, 2003 [Page 3] Internet-Draft Presence Filtering Requirements June 2003 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 Moran, et al. Expires December 17, 2003 [Page 4] Internet-Draft Presence Filtering Requirements June 2003 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 Moran, et al. Expires December 17, 2003 [Page 5] Internet-Draft Presence Filtering Requirements June 2003 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. Moran, et al. Expires December 17, 2003 [Page 6] Internet-Draft Presence Filtering Requirements June 2003 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. Moran, et al. Expires December 17, 2003 [Page 7] 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 Moran, et al. Expires December 17, 2003 [Page 8] Internet-Draft Presence Filtering Requirements June 2003 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. Moran, et al. Expires December 17, 2003 [Page 9] Internet-Draft Presence Filtering Requirements June 2003 [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 Moran, et al. Expires December 17, 2003 [Page 10] Internet-Draft Presence Filtering Requirements June 2003 Andrew Allen 1937 McRae Lane Mundelein, Illinois 60060 USA EMail: AndrewAllen007@aol.com Moran, et al. Expires December 17, 2003 [Page 11] Internet-Draft Presence Filtering Requirements June 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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