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Versions: 00 01 draft-ietf-ecrit-data-only-ea

ECRIT                                                           B. Rosen
Internet-Draft                                             NeuStar, Inc.
Intended status: Experimental                             H. Schulzrinne
Expires: September 7, 2010                                   Columbia U.
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                           March 6, 2010


 Common Alerting Protocol (CAP) based Data-Only Emergency Alerts using
                 the Session Initiation Protocol (SIP)
                 draft-rosen-ecrit-data-only-ea-01.txt

Abstract

   The Common Alerting Protocol (CAP) is an XML document format for
   exchanging emergency alerts and public warnings.  CAP is mainly used
   for conveying alerts and warnings between authorities and from
   authorities to citizen/individuals.  This document describes how
   data-only emergency alerts allow to utilize the same CAP document
   format.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   This Internet-Draft will expire on September 7, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Architectural Overview . . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Specification . . . . . . . . . . . . . . . . . . . .  7
     4.1.  CAP Transport  . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  Profiling of the CAP Document Content  . . . . . . . . . .  7
   5.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
     6.1.  Forgery  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Replay Attack  . . . . . . . . . . . . . . . . . . . . . .  9
     6.3.  Injecting False Alerts . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Registration of the
           'application/common-alerting-protocol+xml' MIME type . . . 11
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

















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1.  Introduction

   The Common Alerting Protocol (CAP) [cap] is an XML document format
   for exchanging emergency alerts and public warnings.  CAP is mainly
   used for conveying alerts and warnings between authorities and from
   authorities to citizen/individuals.  This document describes how
   data-only emergency calls are able to utilize the same CAP document
   format.  Data-only emergency alerts may be similar to regular
   emergency calls in the sense that they have the same emergency call
   routing and location requirements; they do, however, not lead to the
   establishment of a voice channel.  There are, however, data-only
   emergency alerts that are targeted directly to a dedicated entity
   responsible for evaluating the alerts and for taking the necessary
   steps, including triggering an emergency call towards a Public Safety
   Answering Point (PSAP).




































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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].














































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3.  Architectural Overview

   This section illustrates two envisioned usage modes; targeted and
   location-based emergency alert routing.  Figure 1 shows a deployment
   variant where a device is pre-configured (using techniques outside
   the scope of this document) to issue an alert to an aggregator that
   processes these messages and performs whatever steps are necessary to
   appropriately react on the alert.  In many cases the device has the
   address of the aggregator pre-configured and corresponding security
   mechanisms are in place to ensure that only alert from authorized
   devices are processed.



    +--------+                  +------------+
    | Device |                  | Aggregator |
    +---+----+                  +------+-----+
        |                              |
     Sensors                           |
     trigger                           |
     emergency                         |
     alert                             |
        |        MESSAGE with CAP      |
        |----------------------------->|
        |                              |
        |                           Aggregator
        |                           processes
        |                           emergency
        |                           alert
        |        200 (OK)              |
        |<-----------------------------|
        |                              |
        |                              |

                Figure 1: Targeted Emergency Alert Routing

   In Figure 2 a scenario is shown whereby the alert is routed using
   location information and the Service URN.  In this case the device
   issuing the alert may not know the message recipient (in case the
   LoST resolution is done at an emergency services routing proxy rather
   than at the end host).  In any case, a trust relationship between the
   alert-issuing device and the PSAP cannot be assumed, i.e., the PSAP
   is likely to receive alerts from entities it cannot authorize.  This
   scenario corresponds more to the classical emergency services
   classical and the description in [I-D.ietf-ecrit-phonebcp] is
   applicable.





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                           +-------+
      +--------+           | SIP   |                      +------+
      | Device |           | Proxy |                      | PSAP |
      +---+----+           +---+---+                      +---+--+
          |                    |                              |
       Sensors                 |                              |
       trigger                 |                              |
       emergency               |                              |
       alert                   |                              |
          |                    |                              |
          |                    |                              |
          | MESSAGE with CAP   |                              |
          | (including Service URN,                           |
          | such as urn:service:sos)                          |
          |------------------->|                              |
          |                    |                              |
          |              SIP Proxy performs                   |
          |              emergency alert                      |
          |              routing                              |
          |                    |  MESSAGE with CAP            |
          |                    |  (including identity info)   |
          |                    |----------------------------->|
          |                    |                              |
          |                    |                           PSAP
          |                    |                           processes
          |                    |                           emergency
          |                    |                           alert
          |                    |        200 (OK)              |
          |                    |<-----------------------------|
          |                    |                              |
          |  200 (OK)          |                              |
          |<-------------------|                              |
          |                    |                              |
          |                    |                              |

             Figure 2: Location-Based Emergency Alert Routing















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4.  Protocol Specification

4.1.  CAP Transport

   Since alerts structured via CAP require a "push" medium, they SHOULD
   be sent via the SIP MESSAGE.  The MIME type is set to 'application/
   common-alerting-protocol+xml'.

      Alternatively, the SIP PUBLISH mechanism or other SIP messages
      could be used.  However, the usage of SIP MESSAGE is a simple
      enough approach from an implementation point of view.

4.2.  Profiling of the CAP Document Content

   The usage of CAP MUST conform to the specification provided with
   [cap].  For the usage with SIP the following additional requirements
   are imposed:

   sender:  When the CAP was created by a SIP-based entity then the
      element MUST be populated with the SIP URI of that entity.


   incidents:  The <incidents> element MUST be present whenever there is
      a possibility that alert information needs to be updated.  The
      initial message will then contain an incident identifier carried
      in the <incidents> element.  This incident identifier MUST be
      chosen in such a way that it is unique for a given sender /
      expires combination.


   scope:  The value of the <scope> element MUST be set to "private" as
      the alert is not meant for public consumption.  The <addresses>
      element is, however, not used by this specification since the
      message routing is performed by SIP and the respective address
      information is already available there.  Populating address
      information twice into different parts of the message can quickly
      lead to inconsistency.


   parameter:  The <parameter> element MAY contain additional
      information specific to the sensor.


   area:  For geodetic information the polygon and circle location
      shapes are available.  The ability to conveying a structured
      format of civic location information is missing and hence civic
      information is encoded as a text string in the <areaDesc> element.




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5.  Example

   Figure 3 shows a CAP document indicating a BURLARY alert issued by
   sensor1@example.com indicating that the alert was issued from the
   civic address NATURAL HISTORY MUSEUM, BURGRING 7, 1010 VIENNA,
   AUSTRIA.  Additionally, the sensor provided some additional data long
   with the alert message using non-standardized information elements.



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

   <alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
       <identifier>S-1</identifier>
       <sender>sensor1@example.com</sender>
       <sent>2008-11-19T14:57:00-07:00</sent>
       <status>Actual</status>
       <msgType>Alert</msgType>
       <scope>Private</scope>
       <incidents>abc1234</incidents>
       <info>
           <category>Security</category>
           <event>BURGLARY</event>
           <urgency>Expected</urgency>
           <certainty>Likely</certainty>
           <severity>Moderate</severity>
           <senderName>SENSOR 1</senderName>
           <area>
               <areaDesc>NATURAL HISTORY MUSEUM,
                BURGRING 7, 1010 VIENNA, AUSTRIA
               </areaDesc>
           </area>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE1</valueName>
             <value>123</value>
           </parameter>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE2</valueName>
             <value>TRUE</value>
           </parameter>
       </info>
   </alert>

           Figure 3: Example for an alert triggered by a sensor







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6.  Security Considerations

   This section discusses security considerations when using SIP to make
   data-only emergency alerts utilizing CAP.

6.1.  Forgery

   Threat:

      An adversary could forge or alter a CAP document to report false
      emergency alarms.


   Countermeasures:

      To avoid this kind of attack, the entities must assure that proper
      mechanisms for protecting the CAP documents are employed, e.g.,
      signing the CAP document itself.  Section 3.3.2.1 of [cap]
      specifies the signing of CAP documents.  This does not protect
      against a legitimate sensor sending phrank alerts after being
      compromised.

6.2.  Replay Attack

   Threat:

      Theft of CAP documents described in this document and replay of it
      at a later time.


   Countermeasures:

      A CAP document contains the mandatory <identifier>, <sender>,
      <sent> elements and an optional <expire> element.  These
      attributes make the CAP document unique for a specific sender and
      provide time restrictions.  An entity that has received a CAP
      message already within the indicated timeframe is able to detect a
      replayed message and, if the content of that message is unchanged,
      then no additional security vulnerability is created.
      Additionally, it is RECOMMENDED to make use of SIP security
      mechanisms, such as SIP Identity, to tie the CAP message to the
      SIP message.

6.3.  Injecting False Alerts







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   Threat:

      When an entity receives a CAP message it has to determine whether
      the entity distributing the CAP messages is genuine to avoid
      accepting messages that are injected by adversaries.


   Countermeasures:

      For some types of data-only emergency calls the entity issuing the
      alert and the entity consuming the alert have a relationship with
      each other and hence it is possible (using cryptographic
      authentication ) to verify whether a message was indeed issued by
      an authorized entity.  There are, however, other types of data-
      only emergency calls where there is no such relationship between
      the sender and the consumer.  In that case incoming alerts need to
      be treated more carefully, as the possibilities to place phrank
      calls are higher than with regular emergency calls that at least
      setup an audio channel.
































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7.  IANA Considerations

7.1.  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].


   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 warnings according to the CAP standard.







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   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.
































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8.  Acknowledgments

   The authors would like to thank the participants of the Early Warning
   adhoc meeting at IETF#69 for their feedback.  Additionally, we would
   like to thank the members of the NENA Long Term Direction Working
   Group for their feedback.













































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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.

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

9.2.  Informative References

   [I-D.ietf-ecrit-phonebcp]
              Rosen, B. and J. Polk, "Best Current Practice for
              Communications Services in support of Emergency Calling",
              draft-ietf-ecrit-phonebcp-14 (work in progress),
              January 2010.






















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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
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone: +358 (50) 4871445
   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


















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