Network Working Group A. Niemi Internet-Draft Nokia Expires: August 28, 2003 February 27, 2003 Requirements for Limiting the Rate of Event Notifications draft-niemi-sipping-event-throttle-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 August 28, 2003. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract All event packages are required to specify a maximum rate at which event notifications are generated by a single notifier. Such a limit is provided in order to reduce network congestion. In addition to the fixed limits introduced by specific event packages, further mechanisms for limiting the rate of event notification are also allowed to be defined by event package specifications but none have been specified so far. This memo discusses the requirements for a throttle mechanism that allows a subscriber to further limit the rate of event notification. Niemi Expires August 28, 2003 [Page 1] Internet-Draft Event Throttle Requirements February 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Event Throttle Model . . . . . . . . . . . . . . . . . . . . . . 3 4. Example Use Case . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Normative References . . . . . . . . . . . . . . . . . . . . . . 6 Informative References . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 A. Changes to draft-niemi-sipping-event-throttle-reqs-00 . . . . . 7 B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . 8 Niemi Expires August 28, 2003 [Page 2] Internet-Draft Event Throttle Requirements February 2003 1. Introduction The SIP events framework described in RFC 3265 [2] mandates that each event package specification defines an absolute maximum on the rate at which notifications are allowed to be generated by a single notifier. Such a limit is provided in order to reduce network congestion. All of the existing event package specifications include a maximum notification rate recommendation, ranging from once in every five seconds [3], [4], [5] to once per second [6]. Per the SIP events framework, each event package specification is also allowed to define additional throttling mechanisms which allow the subscriber to further limit the rate of event notification. So far none of the event package specifications have defined such throttling mechanisms. This memo discusses the requirements for a generic throttling mechanism, which allows the subscriber to limit the rate of event notifications. It is intended that the throttle mechanism is not event package specific, but commonly available to be used with all event subscriptions. 2. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [1]. 3. Event Throttle Model The model assumed for the event throttle mechanism is similar to the one described in [6]. In it, the notifier employs a quarantine for outgoing notifications, in which outgoing notifications are kept for a certain amount of time before they are actually sent out to the subscriber. In general, the policy by which queueing notifications inside the quarantine are treated is not specified. For example, an incoming notification might simply replace an existing notification [6], or the quarantine could merge the states of all of the quarantined notifications. The throttle mechanism is intended to enable the quarantine period to be configured by the subscriber. Further, the quarantine can be strict, or can also employ a leaky-bucket style algorithm, in which on average the quarantine period might hold, but occasional bursts might also be allowed. Niemi Expires August 28, 2003 [Page 3] Internet-Draft Event Throttle Requirements February 2003 OPEN ISSUE: Do we want to consider both models for event throttles, or is only the strict limit really usable? The main implication of this model for event throttles is that they are lossy. Either some state changes are lost, or some level of accuracy in notifications is lost. The former will affect state changes that occur more frequent than what the throttled rate defines; and the latter will affect notifications of "stateless" nature, e.g., location updates within a quarantine period will be lost. 4. Example Use Case There are many applications that potentially would make use of a throttle mechanism. This chapter only illustrates one possible use case, in which a mobile device uses the event throttling mechanism to limit the amount of traffic it may receive. A mobile application is watching the state of 100 presentities each generating notifications at a maximum rate of once per five seconds. Assuming that the arrival times of notifications are evenly distributed, this will result in a maximum notification frequency of: f = 100 * (1 / 5s) = 100 / 5 Hz = 20 Hz experienced by the mobile. The same watcher subscribing using a throttle mechanism to limit the maximum rate at which notifications are to be generated to once per 20 seconds can expect a maximum notification frequency of: f = 100 * (1 / 20s) = 100 / 20 Hz = 5 Hz thus resulting in 75% reduction in the maximum rate of incoming presence notifications. Note that the actual rate of notification is the sum of many factors, and this example only makes a very broad assumption on the absolute maximum rate at which the notifications might be generated. 5. Requirements REQ1: The subscriber MUST be able to limit using a throttle mechanism the maximum rate at which the notifier is allowed to generate notifications in a subscription. Niemi Expires August 28, 2003 [Page 4] Internet-Draft Event Throttle Requirements February 2003 REQ2: The subscriber MUST be able to indicate that it requires the use of a throttle mechanism in the subscription. REQ3: The notifier MUST be able to indicate that it does not support the use of a throttle mechanism in the subscription. REQ4: It MUST be possible to use the throttle mechanism in subscriptions to all events. REQ5: It MUST be possible to use the throttle mechanism together with any event filtering mechanism. REQ6: The notifier MUST be allowed to use a maximum rate lower than the one given by the subscriber. For example, local policy could dictate an even lower rate of notification than what the subscriber requires. REQ7: Authentication and integrity protection SHOULD be applied to subscriptions that apply the throttle mechanism. Note that Section 6 contains further discussion on the security implications of the throttle mechanism. 6. Security Considerations Naturally all of the security considerations for event subscriptions and notifications also apply to subscriptions and notifications that use the throttle mechanism. In addition, using the event throttle mechanism introduces some new security issues to consider: The throttle mechanism might allow a subscriber to set a very low maximum notification rate - one that possibly exceeds the subscription expiration. Such a limit inserted by a malicious third party would result in very few if any notifications to be generated, which could be perceived as theft of service to the subscriber. Similarly, the throttle mechanism might allow the subscriber to set a very high maximum rate of notification that possibly is higher than the default recommended rate of notification. Such a high rate inserted by a malicious third party could result in denial of service of the notifier due to performance issues. Using the throttle mechanism potentially allows a subscriber to increase the number of active subscriptions due to the decrease in the maximum rate of notifications generated by a single notifier. If a malicious third party is able to remove the throttle from the Niemi Expires August 28, 2003 [Page 5] Internet-Draft Event Throttle Requirements February 2003 subscriptions, the subscriber might be flooded with notifications. All of the above problems can be avoided by ensuring that the integrity and authenticity of subscriptions is protected by applying relevant security measures. 7. Open Issues This chapter lists the main open issues within this document. ISSUE1: Is the offered model accurate and appropriate? ISSUE2: Within the model, do we have a need to enable both the leaky-bucket and the strict rate limiting models at the same time, or is only one of them enough? ISSUE3: Is it enough to leave the handling of notifications in the qarantine out-of-scope, or are there requirements for that as well that should be captured by this document ISSUE4: Are the threats listed in the security section really valid ISSUE5: Is the added value of event throttles enough to merit their standardization? Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Informative References [2] Roach, A., "Session Initiation Protocol (SIP)-Specific Event Notification", RFC 3265, June 2002. [3] Rosenberg, J., "A Presence Event Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-presence-10 (work in progress), January 2003. [4] Rosenberg, J., "A Session Initiation Protocol (SIP) Event Package for Registrations", draft-ietf-sipping-reg-event-00 (work in progress), October 2002. [5] Rosenberg, J., "A Watcher Information Event Template-Package for the Session Initiation Protocol (SIP)", draft-ietf-simple-winfo-package-05 (work in progress), January 2003. Niemi Expires August 28, 2003 [Page 6] Internet-Draft Event Throttle Requirements February 2003 [6] Mahy, R., "A Message Summary and Message Waiting Indication Event Package for the Session Initiation Protocol (SIP)", draft-ietf-sipping-mwi-01 (work in progress), November 2002. Author's Address Aki Niemi Nokia P.O. Box 321 NOKIA GROUP, FIN 00045 Finland Phone: +358 50 389 1644 EMail: aki.niemi@nokia.com Appendix A. Changes to draft-niemi-sipping-event-throttle-reqs-00 Changes to this version include: o Added the chapter describing the model for event throttles. o Reworded the requirements to reflect the model discussion o Added acknowledgements, changelog, and open issues sections Appendix B. Acknowledgements The author would like to thank Tim Moran, Jonathan Rosenberg, Hisham Khartabil, Juha Kalliokulju, Paul Kyzivat and Henning Schulzrinne for their valuable comments. Niemi Expires August 28, 2003 [Page 7] Internet-Draft Event Throttle Requirements February 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. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright (C) The Internet Society (2003). 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, 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 assignees. 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 Niemi Expires August 28, 2003 [Page 8] Internet-Draft Event Throttle Requirements February 2003 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Niemi Expires August 28, 2003 [Page 9]