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Versions: 00 01 02                                                      
Network Working Group                                           A. Niemi
Internet-Draft                                                     Nokia
Expires: July 23, 2003                                  January 22, 2003


       Requirements for Limiting the Rate of Event Notifications
               draft-niemi-sipping-event-throttle-reqs-00

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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   This Internet-Draft will expire on July 23, 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.






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Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2. Conventions  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3. Example Use Case . . . . . . . . . . . . . . . . . . . . . . . . 3
   4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5. Security Considerations  . . . . . . . . . . . . . . . . . . . . 4
      Normative References . . . . . . . . . . . . . . . . . . . . . . 5
      Informative References . . . . . . . . . . . . . . . . . . . . . 5
      Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
      Intellectual Property and Copyright Statements . . . . . . . . . 7








































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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. 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:



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        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.


4. 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.

   REQ2: The subscriber MUST be able to indicate that it requires the
         use of a throttle mechanism in the subscription.

   REQ3: The subscriber SHOULD be allowed to indicate support for the
         throttle mechanism without requiring it.

   REQ4: The notifier MUST be able to indicate that it does not support
         the use of a throttle mechanism in the subscription.

   REQ5: If the throttle mechanism isn't required by the subscriber, the
         notifier SHOULD be able to ignore it.

   REQ6: It MUST be possible to use the throttle mechanism in
         subscriptions to all events.

   REQ7: It MUST be possible to use the throttle mechanism together with
         any event filtering mechanism.

   REQ8: The notifier MUST be allowed to use a maximum rate lower than
         the one given by the subscriber.

   REQ9: Authentication and integrity protection SHOULD be applied to
         subscriptions that apply the throttle mechanism.

      Note that Section 5 contains further discussion on the security
      implications of the throttle mechanism.


5. Security Considerations

   Naturally all of the security considerations for event subscriptions



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   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
      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.

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-09 (work
        in progress), December 2002.

   [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-04 (work in progress), December



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        2002.

   [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


































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Intellectual Property Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

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   Internet Society.











































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