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Versions: 00 01 02 03 04                                                
SIPPING                                                         B. Rosen
Internet-Draft                                             NeuStar, Inc.
Intended status: Standards Track                          H. Schulzrinne
Expires: January 3, 2008                                     Columbia U.
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                            July 2, 2007


Session Initiation Protocol (SIP) Event Package for the Common Alerting
                             Protocol (CAP)
                     draft-rosen-sipping-cap-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on January 3, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   The Common Alerting Protocol (CAP) is an XML document format for
   exchanging emergency alerts and public warnings.  This document
   allows CAP documents to be distributed via the event notification
   mechanism available with the Session Initiation Protocol (SIP).



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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  The 'common-alerting-protocol' Event Package . . . . . . . . .  3
     3.1.  Package Name . . . . . . . . . . . . . . . . . . . . . . .  3
     3.2.  Event Package Parameters . . . . . . . . . . . . . . . . .  4
     3.3.  SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . .  4
     3.4.  Subscription Duration  . . . . . . . . . . . . . . . . . .  4
     3.5.  NOTIFY Bodies  . . . . . . . . . . . . . . . . . . . . . .  4
     3.6.  Notifier Processing of SUBSCRIBE Requests  . . . . . . . .  5
     3.7.  Notifier Generation of NOTIFY Requests . . . . . . . . . .  5
     3.8.  Subscriber Processing of NOTIFY Requests . . . . . . . . .  5
     3.9.  Handling of Forked Requests  . . . . . . . . . . . . . . .  6
     3.10. Rate of Notifications  . . . . . . . . . . . . . . . . . .  6
     3.11. State Agents . . . . . . . . . . . . . . . . . . . . . . .  6
     3.12. Examples . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.13. Use of URIs to Retrieve State  . . . . . . . . . . . . . .  6
     3.14. PUBLISH Bodies . . . . . . . . . . . . . . . . . . . . . .  6
     3.15. PUBLISH Response Bodies  . . . . . . . . . . . . . . . . .  7
     3.16. Multiple Sources for Event State . . . . . . . . . . . . .  7
     3.17. Event State Segmentation . . . . . . . . . . . . . . . . .  7
     3.18. Rate of Publication  . . . . . . . . . . . . . . . . . . .  7
   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  Known Open Issues  . . . . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Registration of the 'common-alerting-protocol' Event
           Package  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.2.  Registration of the
           'application/common-alerting-protocol+xml' MIME type . . .  9
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12














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1.  Introduction

   The Common Alerting Protocol (CAP) [cap] is an XML document format
   for exchanging emergency alerts and public warnings.  This document
   allows CAP documents to be distributed via the event notification
   mechanism available with the Session Initiation Protocol (SIP).


2.  Terminology

   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 RFC 2119 [RFC2119].


3.  The 'common-alerting-protocol' Event Package

   RFC 3265 [RFC3265] defines a SIP extension for subscribing to remote
   nodes and receiving notifications of changes (events) in their
   states.  It leaves the definition of many aspects of these events to
   concrete extensions, known as event packages.  This document defines
   such an event package.  This section fills in the information
   required for all event packages by RFC 3265.

   Additionally, RFC 3903 [RFC3903] defines an extension that allows SIP
   User Agents to publish event state.  According to RFC 3903, any event
   package intended to be used in conjunction with the SIP PUBLISH
   method has to include a considerations section.  This section also
   fills the information for all event packages to be used with PUBLISH
   requests.

   We define a new "common-alerting-protocol" event package.  Event
   Publication Agents (EPA) use PUBLISH requests to inform an Event
   State Compositor (ESC) of changes in the common-alerting-protocol
   event package.  Acting as a notifier, the ESC notifies subscribers
   about emergency alerts and public warnings.

3.1.  Package Name

   The name of this package is "common-alerting-protocol".  As specified
   in RFC 3265 [RFC3265], this value appears in the Event header field
   present in SUBSCRIBE and NOTIFY requests.  As specified in RFC 3903
   [RFC3903], this value also appears in the Event header field present
   in PUBLISH requests.







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3.2.  Event Package Parameters

   RFC 3265 [RFC3265] allows event packages to define additional
   parameters carried in the Event header field.  This event package,
   "common-alerting-protocol", does not define additional parameters.

3.3.  SUBSCRIBE Bodies

   According to RFC 3265 [RFC3265], a SUBSCRIBE request can contain a
   body.  The purpose of the body depends on its type.

   [Editor's Note: It is an open issue whether subscriptions to the
   "common-alerting-protocol" event package carry information in their
   body, such as a polygon defining an area for which notifications
   should be received.  See Section 6.]

3.4.  Subscription Duration

   The default expiration time for subscriptions within this package is
   3600 seconds.  As per RFC 3265 [RFC3265], the subscriber MAY specify
   an alternate expiration in the Expires header field.

3.5.  NOTIFY Bodies

   As described in RFC 3265 [RFC3265], the NOTIFY message will contain
   bodies describing the state of the subscribed resource.  This body is
   in a format listed in the Accept header field of the SUBSCRIBE
   request, or a package-specific default format if the Accept header
   field was omitted from the SUBSCRIBE request.

   In this event package, the body of the notification contains a Common
   Alerting Protocol (CAP) document, i.e., an XML document.  The format
   of the XML documents used by CAP are described in [cap].

   For an initial notify, unlike for other event packages, there is no
   current initial state, unless there's a pending alert.  Hence,
   returning a NOTIFY with a non-empty body only makes sense if there
   are indeed active alerts.

   All subscribers and notifiers of the "common-alerting-protocol" event
   package MUST support the "application/common-alerting-protocol+xml"
   data format.  The SUBSCRIBE request MAY contain an Accept header
   field.  If no such header field is present, it has a default value of
   "application/common-alerting-protocol+xml" (assuming that the Event
   header field contains a value of "common-alerting-protocol").  If the
   Accept header field is present, it MUST include "application/
   common-alerting-protocol+xml".




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3.6.  Notifier Processing of SUBSCRIBE Requests

   The contents of a CAP document contains public information.  Hence,
   providing CAP documents may not require authorization by subscribers.

3.7.  Notifier Generation of NOTIFY Requests

   RFC 3265 [RFC3265] details the formatting and structure of NOTIFY
   messages.  However, packages are mandated to provide detailed
   information on when to send a NOTIFY, how to compute the state of the
   resource, how to generate neutral or fake state information, and
   whether state information is complete or partial.  This section
   describes those details for the common-alerting-protocol event
   package.

   A notifier MAY send a NOTIFY at any time.  Typically, it will send
   one when an alert or early warning message is available.  The NOTIFY
   request contains a body containing one or multiple CAP document(s).
   The times at which the NOTIFY is sent for a particular subscriber,
   and the contents of the body within that notification, are subject to
   any rules specified by the authorization policy that governs the
   subscription.

   In the case of a pending subscription, when final authorization is
   determined, a NOTIFY can be sent.  If the result of the authorization
   decision was success, a NOTIFY SHOULD be sent and SHOULD contain a
   complete CAP document.  If the subscription is rejected, a NOTIFY MAY
   be sent.  As described in RFC 3265 [RFC3265], the Subscription-State
   header field indicates the state of the subscription.

   The body of the NOTIFY MUST be sent using one of the types listed in
   the Accept header field in the most recent SUBSCRIBE request, or
   using the type "application/common-alerting-protocol+xml" if no
   Accept header field was present.

   Notifiers will typically act as Event State Compositors (ESC) and
   thus will learn the 'common-alerting-protocol' event state via
   PUBLISH requests sent from authorized Event Publication Agents
   (EPAs).

3.8.  Subscriber Processing of NOTIFY Requests

   RFC 3265 [RFC3265] leaves it to event packages to describe the
   process followed by the subscriber upon receipt of a NOTIFY request,
   including any logic required to form a coherent resource state.






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3.9.  Handling of Forked Requests

   RFC 3265 [RFC3265] requires each package to describe handling of
   forked SUBSCRIBE requests.

   This specification only allows a single dialog to be constructed as a
   result of emitting an initial SUBSCRIBE request.

3.10.  Rate of Notifications

   RFC 3265 [RFC3265] requires each package to specify the maximum rate
   at which notifications can be sent.

   Notifiers SHOULD NOT generate notifications for a single user at a
   rate of more than once every five seconds.

3.11.  State Agents

   RFC 3265 [RFC3265] requires each package to consider the role of
   state agents in the package and, if they are used, to specify how
   authentication and authorization are done.  This specification allows
   state agents to be located in the network.

3.12.  Examples

   An example is provided in Section 4.

3.13.  Use of URIs to Retrieve State

   RFC 3265 [RFC3265] allows packages to use URIs to retrieve large
   state documents.

   CAP documents are fairly small.  This event package does not provide
   a mechanism to use URIs to retrieve large state documents.

3.14.  PUBLISH Bodies

   RFC 3903 [RFC3903] requires event packages to define the content
   types expected in PUBLISH requests.

   In this event package, the body of a PUBLISH request may contain a
   CAP document.  A CAP document describes an emergency alert or an
   early warning event.

   All EPAs and ESCs MUST support the "application/
   common-alerting-protocol+xml" data format and MAY support other
   formats.




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   Note that this document does not mandate how CAP documents are made
   available to the Public Warning System, for example by authorities or
   similar organizations.  The PUBLISH mechanism is one way.

3.15.  PUBLISH Response Bodies

   This specification assumes that a PUBLISH also conveys a CAP document
   that is later sent further on to watchers.

3.16.  Multiple Sources for Event State

   RFC 3903 [RFC3903] requires event packages to specify whether
   multiple sources can contribute to the event state view at the ESC.

   This event package allows different EPAs to publish CAP documents for
   a particular user.  The concept of composition is not applicable for
   this application usage.

3.17.  Event State Segmentation

   RFC 3903 [RFC3903] defines segments within a state document.  Each
   segment is defined as one of potentially many identifiable sections
   in the published event state.

   This event package defines does not differentiate between different
   segments.

3.18.  Rate of Publication

   RFC 3903 [RFC3903] allows event packages to define their own rate of
   publication.

   There are no rate-limiting recommendations for common-alerting-
   protocol publication.  Since emergency alerts and early warning
   events are typically rare there is no periodicity, nor a minimum or
   maximum rate of publication.


4.  Examples

   Here is an example of a CAP document.










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   <?xml version="1.0" encoding="UTF-8"?>

   <alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
       <identifier>KSTO1055887203</identifier>
       <sender>KSTO@NWS.NOAA.GOV</sender>
       <sent>2003-06-17T14:57:00-07:00</sent>
       <status>Actual</status>
       <msgType>Alert</msgType>
       <scope>Public</scope>
       <info>
           <category>Met</category>
           <event>SEVERE THUNDERSTORM</event>
           <urgency>Severe</urgency>
           <certainty>Likely</certainty>
           <eventCode>same=SVR</eventCode>
           <senderName>NATIONAL WEATHER SERVICE SACRAMENTO</senderName>
           <headline>SEVERE THUNDERSTORM WARNING</headline>
           <description> AT 254 PM PDT...
               NATIONAL WEATHER SERVICE
               DOPPLER RADAR INDICATED A SEVERE
               THUNDERSTORM OVER SOUTH CENTRAL ALPINE COUNTY...
               OR ABOUT 18 MILES SOUTHEAST OF
               KIRKWOOD... MOVING SOUTHWEST AT 5 MPH. HAIL...
               INTENSE RAIN AND STRONG DAMAGING WINDS
               ARE LIKELY WITH THIS STORM </description>
           <instruction> TAKE COVER IN A SUBSTANTIAL SHELTER
               UNTIL THE STORM PASSES </instruction>
           <contact>BARUFFALDI/JUSKIE</contact>
           <area>
               <areaDesc> EXTREME NORTH CENTRAL TUOLUMNE COUNTY
                   IN CALIFORNIA, EXTREME NORTHEASTERN
                   CALAVERAS COUNTY IN CALIFORNIA, SOUTHWESTERN
                   ALPINE COUNTY IN CALIFORNIA </areaDesc>
               <polygon> 38.47,-120.14 38.34,-119.95 38.52,-119.74
                   38.62,-119.89 38.47,-120.14 </polygon>
               <geocode>fips6=006109</geocode>
               <geocode>fips6=006109</geocode>
               <geocode>fips6=006103</geocode>
           </area>
       </info>
   </alert>

                 Example for a Severe Thunderstorm Warning








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5.  Security Considerations

   [Editor's Note: A future version of this document will describe
   security considerations.]


6.  Known Open Issues

   Frequently, alerting events are only of regional interest since they
   only have regional impact.  For example: The public in NYC does not
   really need to be alerted about a wild fire at Lake Tahoe.  One
   possible solution is the ability to allow SUBSCRIBE bodies to have a
   region description that describes the geographic region of interest,
   as a polygon.

   LoST may also play a role here, namely to get back a list of URLs
   where I can send the SUBSCRIBE requests to.  There may be a need for
   urn:service:alerts service URN registry.


7.  IANA Considerations

7.1.  Registration of the 'common-alerting-protocol' Event Package

   This specification registers an event package, based on the
   registration procedures defined in RFC 3265 [RFC3265].  The following
   is the information required for such a registration:
   Package Name:  common-alerting-protocol
   Package or Template-Package:  This is a package.
   Published Document:  RFC XXX [Replace by the RFC number of this
      specification].
   Person to Contact:  Hannes Tschofenig, Hannes.Tschofenig@nsn.com

7.2.  Registration of the 'application/common-alerting-protocol+xml'
      MIME type

   To:  ietf-types@iana.org
   Subject:  Registration of MIME media type application/ common-
      alerting-protocol+xml
   MIME media type name:  application
   MIME subtype name:  common-alerting-protocol+xml
   Required parameters:  (none)
   Optional parameters:  charset; Indicates the character encoding of
      enclosed XML.  Default is UTF-8 [RFC3629].







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   Encoding considerations:  Uses XML, which can employ 8-bit
      characters, depending on the character encoding used.  See RFC
      3023 [RFC3023], Section 3.2.
   Security considerations:  This content type is designed to carry
      payloads of the Common Alerting Protocol (CAP).
   Interoperability considerations:  This content type provides a way to
      convey CAP payloads.
   Published specification:  RFC XXX [Replace by the RFC number of this
      specification].
   Applications which use this media type:  Applications that convey
      alerts and early warnings according to the CAP standard.
   Additional information:  OASIS has published the Common Alerting
      Protocol at http://www.oasis-open.org/committees/
      documents.php&wg_abbrev=emergency
   Person & email address to contact for further information:  Hannes
      Tschofenig, Hannes.Tschofenig@nsn.com
   Intended usage:  Limited use
   Author/Change controller:  IETF SIPPING working group
   Other information:  This media type is a specialization of
      application/xml RFC 3023 [RFC3023], and many of the considerations
      described there also apply to application/
      common-alerting-protocol+xml.


8.  Acknowledgments

   The authors would like to thank Cullen Jennings for supporting this
   work.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [cap]      Jones, E. and A. Botterell, "Common Alerting Protocol v.
              1.1", October 2005.

   [RFC3265]  Roach, A., "Session Initiation Protocol (SIP)-Specific
              Event Notification", RFC 3265, June 2002.

   [RFC3903]  Niemi, A., "Session Initiation Protocol (SIP) Extension
              for Event State Publication", RFC 3903, October 2004.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.



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   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

9.2.  Informative References


Authors' Addresses

   Brian Rosen
   NeuStar, Inc.
   470 Conrad Dr
   Mars, PA  16046
   US

   Phone:
   Email: br@brianrosen.net


   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   US

   Phone: +1 212 939 7004
   Email: hgs+ecrit@cs.columbia.edu
   URI:   http://www.cs.columbia.edu


   Hannes Tschofenig
   Nokia Siemens Networks
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739
   Germany

   Email: Hannes.Tschofenig@nsn.com
   URI:   http://www.tschofenig.com













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Full Copyright Statement

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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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