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Versions: (draft-rosen-ecrit-data-only-ea) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

ECRIT                                                           B. Rosen
Internet-Draft                                             NeuStar, Inc.
Intended status: Standards Track                          H. Schulzrinne
Expires: January 19, 2017                                    Columbia U.
                                                           H. Tschofenig
                                                             ARM Limited
                                                              R. Gellens
                                                           July 18, 2016


                       Data-Only Emergency Calls
                  draft-ietf-ecrit-data-only-ea-12.txt

Abstract

   RFC 6443 'Framework for Emergency Calling Using Internet Multimedia'
   describes how devices use the Internet to place emergency calls and
   how Public Safety Answering Points (PSAPs) handle Internet multimedia
   emergency calls natively.  The exchange of multimedia traffic for
   emergency services involves a SIP session establishment starting with
   a SIP INVITE that negotiates various parameters for that session.

   In some cases, however, the transmission of application data is all
   that is needed.  Examples of such environments include alerts issued
   by a temperature sensor, burglar alarm, or chemical spill sensor.
   Often these alerts are conveyed as one-shot data transmissions.
   These type of interactions are called 'data-only emergency calls'.
   This document describes a container for the data based on the Common
   Alerting Protocol (CAP) and its transmission using the SIP MESSAGE
   transaction.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on January 19, 2017.




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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   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 Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Architectural Overview  . . . . . . . . . . . . . . . . . . .   4
   4.  Protocol Specification  . . . . . . . . . . . . . . . . . . .   6
     4.1.  CAP Transport . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Profiling of the CAP Document Content . . . . . . . . . .   7
     4.3.  Sending a Data-Only Emergency Call  . . . . . . . . . . .   8
   5.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  425 (Bad Alert Message) Response Code . . . . . . . . . .   9
     5.2.  The AlertMsg-Error Header Field . . . . . . . . . . . . .   9
   6.  Call Backs  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  Handling Large Amounts of Data  . . . . . . . . . . . . . . .  11
   8.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Registration of the
            'application/EmergencyCallData.cap+xml' MIME type  . . .  17
     10.2.  IANA Registration of 'cap' Additional Data Block . . . .  18
     10.3.  IANA Registration for 425 Response Code  . . . . . . . .  18
     10.4.  IANA Registration of New AlertMsg-Error Header Field . .  19
     10.5.  IANA Registration for the SIP AlertMsg-Error Codes . . .  19
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     12.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22








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1.  Introduction

   RFC 6443 [RFC6443] describes how devices use the Internet to place
   emergency calls and how Public Safety Answering Points (PSAPs) handle
   Internet multimedia emergency calls natively.  The exchange of
   multimedia traffic for emergency services involves a SIP session
   establishment starting with a SIP INVITE that negotiates various
   parameters for that session.

   In some cases, however, there is only application data to be conveyed
   from the end devices to a PSAP or an intermediary.  Examples of such
   environments includes sensors issuing alerts, or vehicles sending
   crash data.  These messages may be one-shot alerts to emergency
   authorities and do not require establishment of a session.  These
   type of interactions are called 'data-only emergency calls'.  In this
   document, we use the term "call" so that similarities between data-
   only (non-interactive) alerts and sessions with interactive media are
   more obvious.

   Data-only emergency calls are similar to regular emergency calls in
   the sense that they require the emergency indications, emergency call
   routing functionality and may even have the same location
   requirements.  However, the communication interaction will not lead
   to the exchange of interactive media, that is, Real-Time Protocol
   packets, such as voice, video data or real-time text.

   The Common Alerting Protocol (CAP) [cap] is a 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 is concerned with
   citizen to authority "alerts", where the alert is a call without any
   interactive media.

   This document describes a method of including a CAP message in a SIP
   transaction, either by value (the CAP message is in the body of the
   message, using a CID) or by reference (a URI is included in the
   message, which when dereferenced returns the CAP message) by defining
   it as a block of "additional data" as defined in
   [I-D.ietf-ecrit-additional-data].  The additional data mechanism is
   also used to send alert specific data beyond that available in the
   CAP message.  This document also describes how a SIP MESSAGE
   [RFC3428] transaction can be used to send a data-only call.

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.

   1.  Emergency alerts containing only data are targeted to an
       intermediary recipient responsible for evaluating the next steps.
       These steps could include:

       1.  Sending a non-interactive call containing only data toward a
           Public Safety Answering Point (PSAP);

       2.  Establishing a third-party initiated emergency call towards a
           PSAP that could include audio, video, and data.

   2.  Emergency alerts may be targeted to a Service URN used for IP-
       based emergency calls where the recipient is not known to the
       originator.  In this scenario, the alert may contain only data
       (e.g., a CAP, Geolocation header field and one or more Call-Info
       header fields containing Additional Data
       [I-D.ietf-ecrit-additional-data] in a SIP MESSAGE).

   Figure 1 shows a deployment variant where a sensor 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 to the alert.
   For example, a security firm may use different sensor inputs to
   dispatch their security staff to a building they protect or to
   initiate a third-party emergency call.






















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    +------------+              +------------+
    | Sensor     |              | 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 a Service URN.  An emergency services
   routing proxy (ESRP) may use LoST to determine the next hop proxy to
   route the alert message to.  A possible receiver is a PSAP and the
   recipient of the alert may be a call taker.  In the generic case,
   there is very likely no prior relationship between the originator and
   the receiver, e.g., a PSAP.  A PSAP, for example, is likely to
   receive and accept alerts from entities it cannot authorize.  This
   scenario corresponds to the classic emergency services use case and
   the description in [RFC6881] is applicable.  In this use case, the
   only difference between an emergency call and an emergency data-only
   call is that the former uses INVITE, creates a session, and
   negotiates one or more media streams, while the latter uses MESSAGE,
   does not create a session, and does not have media.














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                           +-----------+                  +----------+
      +--------+           | ESRP      |                  | PSAP     |
      | Sensor |           |           |                  |          |
      +---+----+           +---+-------+                  +---+------+
          |                    |                              |
       Sensors                 |                              |
       trigger                 |                              |
       emergency               |                              |
       alert                   |                              |
          |                    |                              |
          |                    |                              |
          | MESSAGE with CAP   |                              |
          | (including Service URN,                           |
          | such as urn:service:sos)                          |
          |------------------->|                              |
          |                    |                              |
          |              ESRP 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

4.  Protocol Specification

4.1.  CAP Transport

   A CAP message may be sent in the initial message of any SIP
   transaction.  However, this document only addresses sending a CAP
   message in a SIP INVITE that initiates an emergency call, or in a SIP
   MESSAGE transaction for a one-shot, data-only emergency call.
   Behavior with other transactions is not defined.





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   The CAP message is included in a SIP message as an additional-data
   block [I-D.ietf-ecrit-additional-data].  Accordingly, it is
   introduced to the SIP message with a Call-Info header field with a
   purpose of "EmergencyCallData.cap".  The header field may contain a
   URI that is used by the recipient (or in some cases, an intermediary)
   to obtain the CAP message.  Alternative, the Call-Info header field
   may contain a Content Indirect url [RFC2392] and the CAP message
   included in the body of the message.  In the latter case, the CAP
   message is located in a MIME block of the type 'application/
   emergencyCallData.cap+xml'.

   If the SIP server does not support the functionality required to
   fulfill the request then a 501 Not Implemented MUST be returned as
   specified in RFC 3261 [RFC3261].  This is the appropriate response
   when a UAS does not recognize the request method and is not capable
   of supporting it for any user.

   The 415 Unsupported Media Type error MUST be returned as specified in
   RFC 3261 [RFC3261] if the SIP server is refusing to service the
   request because the message body of the request is in a format not
   supported by the server for the requested method.  The server MUST
   return a list of acceptable formats using the Accept, Accept-
   Encoding, or Accept-Language header fields, depending on the specific
   problem with the content.

4.2.  Profiling of the CAP Document Content

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

   sender:  The following restrictions and conditions apply to setting
      the value of the <sender> element:

      Originator is a SIP entity, Author indication irrelevant:  When
         the alert was created by a SIP-based originator and it is not
         useful to be explicit about the author of the alert, then the
         <sender> element MUST be populated with the SIP URI of the user
         agent.

      Originator is a non-SIP entity, Author indication irrelevant:
      When the alert was created by a non-SIP based entity and the
      identity of this original sender is to be preserved, then this
      identity MUST be placed into the <sender> element.  In this
      situation it is not useful to be explicit about the author of the
      alert.  The specific type of identity being used will depend on
      the technology used by the original originator.




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   Author indication relevant:  When the author is different from the
      actual originator of the message and this distinction should be
      preserved, then the <sender> element MUST NOT contain the SIP URI
      of the user agent.


   incidents:  The <incidents> element MUST be present.  This incident
      identifier MUST be chosen in such a way that it is unique for a
      given <sender, expires, incidents> combination.  Note that the
      <expires> element is optional and may not be present.


   scope:  The value of the <scope> element MAY be set to "Private" if
      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 in other SIP header fields.
      Populating information twice into different parts of the message
      may lead to inconsistency.



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


   area:  It is RECOMMENDED to omit this element when constructing a
      message.  If the CAP message already contains an <area> element,
      then the specified location information SHOULD be copied into the
      PIDF-LO structure of the 'geolocation' header field.

4.3.  Sending a Data-Only Emergency Call

   A data-only emergency call is sent using a SIP MESSAGE transaction
   with a CAP URI or body as described above in a manner similar to how
   an emergency call with interactive media is sent, as described in
   [RFC6881].  The MESSAGE transaction does not create a session nor
   send media, but otherwise, the header content of the transaction,
   routing, and processing of data-only calls are the same as those of
   other emergency calls.

5.  Error Handling

   This section defines a new error response code and a header field for
   additional information.






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5.1.  425 (Bad Alert Message) Response Code

   This SIP extension creates a new location-specific response code,
   defined as follows:

      425 (Bad Alert Message)

   The 425 response code is a rejection of the request due to its
   included alert content, indicating that it was malformed or not
   satisfactory for the recipient's purpose.

   A SIP intermediary can also reject an alert it receives from a UA
   when it understands that the provided alert is malformed.

   Section 5.2 describes an AlertMsg-Error header field with more
   details about what was wrong with the alert message in the request.
   This header field MUST be included in the 425 response.

   It is only appropriate to generate a 425 response when the responding
   entity has no other information in the request that is usable by the
   responder.

   A 425 response code MUST NOT be sent in response to a request that
   lacks an alert message, as the user agent in that case may not
   support this extension.

   A 425 response is a final response within a transaction, and MUST NOT
   terminate an existing dialog.

5.2.  The AlertMsg-Error Header Field

   The AlertMsg-Error header field provides additional information about
   what was wrong with the original request.  In some cases the provided
   information will be used for debugging purposes.

   The AlertMsg-Error header field has the following ABNF [RFC5234]:


      message-header   /= AlertMsg-Error
                              ; (message-header from 3261)
      AlertMsg-Error   = "AlertMsg-Error" HCOLON
                              ErrorValue
      ErrorValue       =  error-code
                               *(SEMI error-params)
      error-code       = 1*3DIGIT
      error-params     = error-code-text
                               / generic-param ; from RFC3261
      error-code-text  = "code" EQUAL quoted-string ; from RFC3261



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   HCOLON, SEMI, and EQUAL are defined in RFC3261 [RFC3261].  DIGIT is
   defined in RFC5234 [RFC5234].

   The AlertMsg-Error header field MUST contain only one ErrorValue to
   indicate what was wrong with the alert payload the recipient
   determined was bad.

   The ErrorValue contains a 3-digit error code indicating what was
   wrong with the alert in the request.  This error code has a
   corresponding quoted error text string that is human understandable.
   The text string are OPTIONAL, but RECOMMENDED for human readability,
   similar to the string phrase used for SIP response codes.  That said,
   the strings are complete enough for rendering to the user, if so
   desired.  The strings in this document are recommendations, and are
   not standardized -- meaning an operator can change the strings -- but
   MUST NOT change the meaning of the error code.  Similar to how RFC
   3261 specifies, there MUST NOT be more than one string per error
   code.

   The AlertMsg-Error header field MAY be included in any response if an
   alert message was in the request part of the same transaction.  For
   example, a UA includes an alert in an MESSAGE to a PSAP.  The PSAP
   can accept this MESSAGE, thus creating a dialog, even though its UA
   determined that the alert message contained in the MESSAGE was bad.
   The PSAP merely includes an AlertMsg-Error header field value in the
   200 OK to the MESSAGE, thus informing the UA that the MESSAGE was
   accepted but the alert provided was bad.

   If, on the other hand, the PSAP cannot accept the transaction without
   a suitable alert message, a 425 response is sent.

   A SIP intermediary that requires the UA's alert message in order to
   properly process the transaction may also sends a 425 with an
   AlertMsg-Error code.

   This document defines an initial list of AlertMsg-Error values for
   any SIP response, including provisional responses (other than 100
   Trying) and the new 425 response.  There MUST be no more than one
   AlertMsg-Error code in a SIP response.

   AlertMsg-Error: 100 ; code="Cannot Process the Alert Payload"

   AlertMsg-Error: 101 ; code="Alert Payload was not present or could
   not be found"

   AlertMsg-Error: 102 ; code="Not enough information to determine the
   purpose of the alert"




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   AlertMsg-Error: 103 ; code="Alert Payload was corrupted"

   Additionally, if an entity cannot or chooses not to process the alert
   message from a SIP request, a 500 (Server Internal Error) SHOULD be
   used with or without a configurable Retry-After header field.

6.  Call Backs

   This document does not describe any method for the recipient to call
   back the sender of a data-only call.  Usually, these alerts are sent
   by automata, which do not have a mechanism to receive calls of any
   kind.  The identifier in the 'From' header field may be useful to
   obtain more information, but any such mechanism is not defined in
   this document.  The CAP message may contain related contact
   information for the sender.

7.  Handling Large Amounts of Data

   It is not atypical for sensors to have large quantities of data that
   they may wish to send.  Including large amounts of data in a MESSAGE
   is not advisable, because SIP entities are usually not equipped to
   handle very large messages.  In such cases, the sender SHOULD make
   use of the by-reference mechanisms defined in
   [I-D.ietf-ecrit-additional-data], which involves making the data
   available via HTTPS (either at the originator or at another entity),
   placing a URI to the data in the 'Call-Info' header field, and the
   recipient using HTTPS to retrieve the data.  The CAP message itself
   can be sent by-reference using this mechanism, as well as any or all
   of the Additional Data blocks that may contain sensor-specific data.

8.  Example

   This example shows a CAP document indicating a BURGLARY alert issued
   by a sensor called 'sensor1@domain.com'.  The location of the sensor
   can be obtained from the attached location information provided via
   the 'geolocation' header field contained in the SIP MESSAGE
   structure.  Additionally, the sensor provided some data along with
   the alert message, using proprietary information elements intended
   only to be processed by the receiver, a SIP entity acting as an
   aggregator.


      MESSAGE sip:aggregator@domain.com SIP/2.0
      Via: SIP/2.0/TCP sensor1.domain.com;branch=z9hG4bK776sgdkse
      Max-Forwards: 70
      From: sip:sensor1@domain.com;tag=49583
      To: sip:aggregator@domain.com
      Call-ID: asd88asd77a@1.2.3.4



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      Geolocation: <cid:abcdef@domain.com>
        ;routing-allowed=yes
      Supported: geolocation
      Accept: application/pidf+xml,application/EmergencyCallData.cap+xml
      CSeq: 1 MESSAGE
      Call-Info: cid:abcdef2@domain.com;purpose=EmergencyCallData.cap
      Content-Type: multipart/mixed; boundary=boundary1
      Content-Length: ...

      --boundary1

      Content-Type: application/EmergencyCallData.cap+xml
      Content-ID: <abcdef2@domain.com>
      Content-Disposition: by-reference;handling=optional
     <?xml version="1.0" encoding="UTF-8"?>

     <alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
       <identifier>S-1</identifier>
       <sender>sip:sensor1@domain.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>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE1</valueName>
             <value>123</value>
           </parameter>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE2</valueName>
             <value>TRUE</value>
           </parameter>
       </info>
      </alert>

      --boundary1

      Content-Type: application/pidf+xml
      Content-ID: <abcdef2@domain.com>
      Content-Disposition: by-reference;handling=optional
      <?xml version="1.0" encoding="UTF-8"?>



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          <presence
             xmlns="urn:ietf:params:xml:ns:pidf"
             xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
             xmlns:gbp=
                    "urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
             xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
             xmlns:gml="http://www.opengis.net/gml"
             xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
             entity="pres:alice@atlanta.example.com">
           <dm:device id="sensor">
             <gp:geopriv>
               <gp:location-info>
                 <gml:location>
                   <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                     <gml:pos>32.86726 -97.16054</gml:pos>
                   </gml:Point>
                </gml:location>
               </gp:location-info>
               <gp:usage-rules>
                 <gbp:retransmission-allowed>false
                 </gbp:retransmission-allowed>
                 <gbp:retention-expiry>2010-11-14T20:00:00Z
                 </gbp:retention-expiry>
               </gp:usage-rules>
               <gp:method>802.11</gp:method>
             </gp:geopriv>
             <dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
           </dm:device>
         </presence>
      --boundary1--

       Figure 3: Example Message conveying an Alert to an aggregator

   This shows the same CAP document sent as a data-only emergency call
   towards a PSAP.


      MESSAGE urn:service:sos SIP/2.0
      Via: SIP/2.0/TCP sip:aggreg.1.example.com;branch=z9hG4bK776abssa
      Max-Forwards: 70
      From: sip:aggregator@example.com;tag=32336
      To: 112
      Call-ID: asdf33443a@example.com
      Route: sip:psap1.example.gov
      Geolocation: <cid:abcdef@example.com>
        ;routing-allowed=yes
      Supported: geolocation
      Accept: application/pidf+xml,application/EmergencyCallData.cap+xml



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      Call-info: cid:abcdef2@domain.com;purpose=EmergencyCallData.cap
      CSeq: 1 MESSAGE
      Content-Type: multipart/mixed; boundary=boundary1
      Content-Length: ...

      --boundary1

      Content-Type: application/EmergencyCallData.cap+xml
      Content-ID: <abcdef2@example.com>
     <?xml version="1.0" encoding="UTF-8"?>

     <alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
       <identifier>S-1</identifier>
       <sender>sip:sensor1@domain.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>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE1</valueName>
             <value>123</value>
           </parameter>
           <parameter>
             <valueName>SENSOR-DATA-NAMESPACE2</valueName>
             <value>TRUE</value>
           </parameter>
       </info>
      </alert>

      --boundary1

      Content-Type: application/pidf+xml
      Content-ID: <abcdef2@domain.com>
      <?xml version="1.0" encoding="UTF-8"?>
          <presence
             xmlns="urn:ietf:params:xml:ns:pidf"
             xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
             xmlns:gbp=
                    "urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
             xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"



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             xmlns:gml="http://www.opengis.net/gml"
             xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
             entity="pres:alice@atlanta.example.com">
           <dm:device id="sensor">
             <gp:geopriv>
               <gp:location-info>
                 <gml:location>
                   <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                     <gml:pos>32.86726 -97.16054</gml:pos>
                   </gml:Point>
                </gml:location>
               </gp:location-info>
               <gp:usage-rules>
                 <gbp:retransmission-allowed>false
                 </gbp:retransmission-allowed>
                 <gbp:retention-expiry>2010-11-14T20:00:00Z
                 </gbp:retention-expiry>
               </gp:usage-rules>
               <gp:method>802.11</gp:method>
             </gp:geopriv>
             <dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
           </dm:device>
         </presence>
      --boundary1--

          Figure 4: Example Message conveying an Alert to a PSAP

9.  Security Considerations

   This section discusses security considerations when SIP user agents
   issue emergency alerts utilizing MESSAGE and CAP.  Location specific
   threats are not unique to this document and are discussed in
   [RFC7378] and [RFC6442].

   The ECRIT emergency services architecture [RFC6443] considers classic
   individual-to-authority emergency calling where the identity of the
   emergency caller does not play a role at the time of the call
   establishment itself, i.e., a response to the emergency call does not
   depend on the identity of the caller.  In the case of emergency
   alerts generated by devices such as sensors, the processing may be
   different in order to reduce the number of falsely generated
   emergency alerts.  Alerts may get triggered based on certain sensor
   input that may have been caused by factors other than the actual
   occurrence of an alert relevant event.  For example, a sensor may
   simply be malfunctioning.  For this reason, not all alert messages
   are directly sent to a PSAP, but rather may be pre-processed by a
   separate entity, potentially under supervision by a human, to filter




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   alerts and potentially correlate received alerts with others to
   obtain a larger picture of the ongoing situation.

   In any case, for alerts initiated by sensors, the identity may play
   an important role in deciding whether to accept or ignore an incoming
   alert message.  With the scenario shown in Figure 1 it is very likely
   that only authorized sensor input will be processed.  For this
   reason, it needs to be possible to refuse to accept alert messages
   from an unknown origin.  Two types of information elements can be
   used for this purpose:

   1.  SIP itself provides security mechanisms that allow the
       verification of the originator's identity.  These mechanisms can
       be re-used, such as P-Asserted-Identity [RFC3325] or SIP Identity
       [RFC4474].  The latter provides a cryptographic assurance while
       the former relies on a chain of trust model.

   2.  CAP provides additional security mechanisms and the ability to
       carry further information about the sender's identity.
       Section 3.3.2.1 of [cap] specifies the signing algorithms of CAP
       documents.

   In addition to the desire to perform identity-based access control,
   the classic communication security threats need to be considered,
   including integrity protection to prevent forgery or replay of alert
   messages in transit.  To deal with replay of alerts, a CAP document
   contains the mandatory <identifier>, <sender>, <sent> elements and an
   optional <expire> element.  Together, these elements make the CAP
   document unique for a specific sender and provide time restrictions.
   An entity that has already received a CAP message 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 [RFC4474], to
   tie the CAP message to the SIP message.  To provide protection of the
   entire SIP message exchange between neighboring SIP entities, the
   usage of TLS is MANDATORY.

   Note that none of the security mechanism in this document protect
   against a compromised sensor sending crafted alerts.

10.  IANA Considerations









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10.1.  Registration of the 'application/EmergencyCallData.cap+xml' MIME
       type

   To:  ietf-types@iana.org



   Subject:  Registration of MIME media type application/
      EmergencyCallData.cap+xml


   MIME media type name:  application


   MIME subtype name:  cap+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).  RFC XXX [Replace
      by the RFC number of this specification] discusses security
      considerations for this.


   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 and email address to contact for further information:  Hannes
      Tschofenig, hannes.tschofenig@gmx.net


   Intended usage:  Limited use


   Author/Change controller:  IETF ECRIT 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/cap+xml.


10.2.  IANA Registration of 'cap' Additional Data Block

   This document registers a new block type in the sub-registry called
   'Emergency Call Data Types' of the Emergency Call Additional Data
   Registry defined in [I-D.ietf-ecrit-additional-data].  The token is
   "cap", the Data About is "The Call" and the reference is this
   document.

10.3.  IANA Registration for 425 Response Code

   In the SIP Response Codes registry, the following is added

   Reference: RFC-XXXX (i.e., this document)

   Response code: 425 (recommended number to assign)

   Default reason phrase: Bad Alert Message


      Registry:
        Response Code                               Reference
        ------------------------------------------  ---------
        Request Failure 4xx
          425 Bad Alert Message                   [this doc]

   This SIP Response code is defined in Section 5.





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10.4.  IANA Registration of New AlertMsg-Error Header Field

   The SIP AlertMsg-error header field is created by this document, with
   its definition and rules in Section 5, to be added to the IANA
   Session Initiation Protocol (SIP) Parameters registry with two
   actions:

   1.  Update the Header Fields registry with




      Registry:
        Header Name        compact    Reference
        -----------------  -------    ---------
        AlertMsg-Error             [this doc]

   2.  In the portion titled "Header Field Parameters and Parameter
       Values", add




                                               Predefined
      Header Field        Parameter Name       Values      Reference
      -----------------   -------------------  ----------  ---------
      AlertMsg-Error      code                 yes         [this doc]

10.5.  IANA Registration for the SIP AlertMsg-Error Codes

   This document creates a new registry for SIP, called "AlertMsg-Error
   Codes".  AlertMsg-Error codes provide reasons for an error discovered
   by a recipient, categorized by the action to be taken by the error
   recipient.  The initial values for this registry are shown below.

   Registry Name: AlertMsg-Error Codes

   Reference: [this doc]

   Registration Procedures: Specification Required











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   Code Default Reason Phrase                                 Reference
   ---- ---------------------------------------------------   ---------
   100  "Cannot Process the Alert Payload"                    [this doc]

   101  "Alert Payload was not present or could not be found" [this doc]

   102  "Not enough information to determine
         the purpose of the alert"                            [this doc]

   103  "Alert Payload was corrupted"                         [this doc]

   Details of these error codes are in Section 5.

11.  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.

   Additionally, we would like to thank Martin Thomson, James
   Winterbottom, Shida Schubert, Bernard Aboba, and Marc Linsner for
   their review comments.

12.  References

12.1.  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.

   [RFC2392]  Levinson, E., "Content-ID and Message-ID Uniform Resource
              Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
              <http://www.rfc-editor.org/info/rfc2392>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.








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   [RFC3428]  Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
              Huitema, C., and D. Gurle, "Session Initiation Protocol
              (SIP) Extension for Instant Messaging", RFC 3428,
              DOI 10.17487/RFC3428, December 2002,
              <http://www.rfc-editor.org/info/rfc3428>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [RFC3023]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media
              Types", RFC 3023, DOI 10.17487/RFC3023, January 2001,
              <http://www.rfc-editor.org/info/rfc3023>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <http://www.rfc-editor.org/info/rfc3629>.

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              DOI 10.17487/RFC6442, December 2011,
              <http://www.rfc-editor.org/info/rfc6442>.

   [RFC6881]  Rosen, B. and J. Polk, "Best Current Practice for
              Communications Services in Support of Emergency Calling",
              BCP 181, RFC 6881, DOI 10.17487/RFC6881, March 2013,
              <http://www.rfc-editor.org/info/rfc6881>.

   [I-D.ietf-ecrit-additional-data]
              Gellens, R., Rosen, B., Tschofenig, H., Marshall, R., and
              J. Winterbottom, "Additional Data Related to an Emergency
              Call", draft-ietf-ecrit-additional-data-38 (work in
              progress), April 2016.

12.2.  Informative References

   [RFC7378]  Tschofenig, H., Schulzrinne, H., and B. Aboba, Ed.,
              "Trustworthy Location", RFC 7378, DOI 10.17487/RFC7378,
              December 2014, <http://www.rfc-editor.org/info/rfc7378>.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474,
              DOI 10.17487/RFC4474, August 2006,
              <http://www.rfc-editor.org/info/rfc4474>.





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   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              DOI 10.17487/RFC3325, November 2002,
              <http://www.rfc-editor.org/info/rfc3325>.

   [RFC6443]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
              "Framework for Emergency Calling Using Internet
              Multimedia", RFC 6443, DOI 10.17487/RFC6443, December
              2011, <http://www.rfc-editor.org/info/rfc6443>.

Authors' Addresses

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

   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
   ARM Limited
   Austria

   Email: Hannes.Tschofenig@gmx.net
   URI:   http://www.tschofenig.priv.at


   Randall Gellens

   Email: rg+ietf@randy.pensive.org






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