ECRIT                                                           B. Rosen
Internet-Draft                                             NeuStar, Inc.
Intended status: Experimental                             H. Schulzrinne
Expires: September May 13, 2012 2013                                        Columbia U.
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                          March 12,
                                                        November 9, 2012

                       Data-Only Emergency Calls


   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) can handle Internet
   multimedia emergency calls natively.  The exchange of multimedia
   traffic typically 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
   everything that is needed.  Examples of such environments include a
   temperature sensors issuing alerts, or vehicles sending crash data.
   Often these alerts are conveyed as one-shot data transmissions and in
   some rare cases they may require a session to be established.  These
   type of interactions are called 'data-only emergency calls'.

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

   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 September May 13, 2012. 2013.

Copyright Notice

   Copyright (c) 2012 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
   ( 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  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Architectural Overview . . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Specification . . . . . . . . . . . . . . . . . . . .  8
     4.1.  CAP Transport  . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Profiling of the CAP Document Content  . . . . . . . . . .  8
   5.  Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  425 (Bad Alert Message) Response Code  . . . . . . . . . . 10
     5.2.  The AlertMsg-Error Header Field  . . . . . . . . . . . . . 10
   6.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  Registration of the 'application/cap+xml' MIME type  . . . 17
     8.2.  IANA Registration for 425 Response Code  . . . . . . . . . 18
     8.3.  IANA Registration of New AlertMsg-Error Header Field . . . 18
     8.4.  IANA Registration for the SIP AlertMsg-Error Codes . . . . 19
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 20
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 21
     10.2. Informative References . . . . . . . . . . . . . . . . . . 22 21
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23

1.  Introduction

   RFC 6443 [RFC6443] describes how devices use the Internet to place
   emergency calls and how Public Safety Answering Points (PSAPs) can
   handle Internet multimedia emergency calls natively.  The exchange of
   multimedia traffic typically 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 some other intermediary.  Examples
   of such environments includes sensors issuing alerts, or vehicles
   sending crash data.  These messages may be one-shot data
   transmissions (i.e., SIP message handling that requires no
   establishment of a session) and interactions where a sequence of
   messages are transmitted in which case a session setup is useful to
   ensure that all messages are indeed routed to the same PSAP.  These
   type of interactions are called 'data-only emergency calls'.

   Data-only emergency calls are nevertheless 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 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 uses the CAP payload to convey the semantic of a data-
   only emergency call.  Note that further data may be added using the
   already available 'additional data' structure
   [I-D.ietf-ecrit-additional-data].  Whenever data can be encoded in
   the additional data structure it shall be used.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 a recipient
       responsible for evaluating the next steps, which could include:

       1.  Sending an alert containing only data toward a Public Safety
           Answering Point (PSAP);

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

   2.  Emergency alerts 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 and a PIDF-LO payload 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 on 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.

    +------------+              +------------+
    | 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 the 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 call taker.  In the generic case, there
   is very likely no prior relationship between the originator and the
   receiver, e.g.  PSAP.  A PSAP, for example, is likely to receive and
   accept alerts from entities it cannot authorize.  This scenario
   corresponds more to the classical emergency services use case and the
   description in [I-D.ietf-ecrit-phonebcp] is applicable.

                           +-----------+                  +----------+
      +--------+           | 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

   To convey CAP payloads the SIP MESSAGE [RFC3428] is used for
   exchanges where no session establishment is needed, i.e.., one-shot
   message exchange, and the SIP INVITE [RFC3261] where the
   establishment of session is useful (e.g., when multiple independent
   messages have to be logically tied together).

   The MIME type is set to 'application/cap+xml'.

   If the server does not support the functionality required to fulfill
   the request then a 501 Not Implemented MUST be returned by 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 by RFC 3261
   [RFC3261] if the 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 field, depending on the specific problem with the

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:  A few sub-categories for putting a value in the <sender>
      element have to be considered:

      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

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

      Author indication relevant:  In case the author is different from
         the actual originator of the message and this distinction wants
         to be preserved then the <sender> element MUST NOT contain the
         SIP URI.

   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, incidents> combination.  Note that the <expires> element
      is optional and may not be present.

   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 in other SIP headers.  Populating
      information twice into different parts of the message may lead to

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

   area:  It is RECOMMENDED to omit this element when constructing a
      message.  In case that the CAP message already contained an <area>
      element then the specified location information MUST be copied
      into the PIDF-LO structure of the 'geolocation' header.

5.  Error Handling

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

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 are usable by the

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

   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 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       =  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

   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

   The AlertMsg-Error header field MAY be included in any response as 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 his UA
   determined the alert message contained in the MESSAGE was bad.  The
   PSAP merely includes an AlertMsg-Error header value in the 200 OK to
   the MESSAGE informing the UA that the MESSAGE was accepted but the
   alert provided was bad.

   If, on the other hand, the PSAP cannot accept the MESSAGE 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 MESSAGE may also sends a 425 with a AlertMsg-
   Error code.

   This document defines an initial list of error code ranges 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"

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

   Additionally, if an LR 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.  Example

   Figure 3 shows a CAP document indicating a BURGLARY alert issued by a
   sensor called ''.  The location of the sensor can
   be obtained from the attached location information provided via the
   'geolocation' header contained in the SIP MESSAGE structure.
   Additionally, the sensor provided some data long with the alert
   message using proprietary information elements only to be processed
   by the receiver, a SIP entity acting as an aggregator.  This example
   reflects the description in Figure 1.

    Via: SIP/2.0/TCP;branch=z9hG4bK776sgdkse
    Max-Forwards: 70
    Call-ID: asd88asd77a@
    Geolocation: <>
    Supported: geolocation
    Accept: application/pidf+xml, application/cap+xml
    CSeq: 1 MESSAGE
    Content-Type: multipart/mixed; boundary=boundary1
    Content-Length: ...


    Content-Type: cap+xml
    Content-ID: <>
   <?xml version="1.0" encoding="UTF-8"?>

   <alert xmlns="urn:oasis:names:tc:emergency:cap:1.1">
         <senderName>SENSOR 1</senderName>


    Content-Type: application/pidf+xml
    Content-ID: <>
    <?xml version="1.0" encoding="UTF-8"?>
         <dm:device id="sensor">
                 <gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
                   <gml:pos>32.86726 -97.16054</gml:pos>

               Figure 3: Example Message conveying an Alert

7.  Security Considerations

   This section discusses security considerations when SIP user agents
   issue emergency alerts utilizing CAP.  Location specific threats are
   not unique to this document and are discussed in
   [I-D.ietf-ecrit-trustworthy-location] and [RFC6442].

   The ECRIT emergency services architecture [I-D.ietf-ecrit-phonebcp]
   considers classical individual-to-authority emergency calling and 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
   will not depend on the identity of the caller.  In case of emergency
   alerts generated by devices, like 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 other factors than the actual
   occurrence of an alert relevant event.  For example, a sensor may
   simply be malfunctioning.  For this purpose not all alert messages
   are directly sent to a PSAP but are rather pre-processed by a
   separate entity, potentially under supervision by a human, to filter
   alerts and potentially correlate received alerts with others to
   obtain a larger picture of the ongoing situation.  These two message
   routing examples are shown in Figure 1 and in Figure 2.

   In any case, for alerts that are 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 purpose it needs to be ensured that no alert messages from an
   unknown origin are accepted.  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 additional information about the sender's identity.
       Section of [cap] specifies the signing algorithms of CAP

   In addition to the desire to perform identity-based access control
   the classical communication security threats need to be considered,
   including integrity protection to prevent forgery and 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.  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 [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

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

8.  IANA Considerations

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


   Subject:  Registration of MIME media type application/ 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).

   Interoperability considerations:  This content type provides a way to
      convey CAP payloads.

   Published specification:  RFC XXX [Replace by the RFC number of this

   Applications which use this media type:  Applications that convey
      alerts and warnings according to the CAP standard.

   Additional information:  OASIS has published the Common Alerting
      Protocol at

   Person and email address to contact for further information:  Hannes

   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.

8.2.  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

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

   This SIP Response code is defined in Section 5.

8.3.  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 sip-
   parameters registry with two actions:

   1.  Update the Header Fields registry with

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

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

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

8.4.  IANA Registration for the SIP AlertMsg-Error Codes

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

   Registry Name: AlertMsg-Error Codes

   Reference: [this doc]

   Registration Procedures: Specification Required

   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.

9.  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.

10.  References

10.1.  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.

   [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.

              Rosen, B. and J. Polk, "Best Current Practice for
              Communications Services in support of Emergency Calling",
              draft-ietf-ecrit-phonebcp-20 (work in progress),
              September 2011.

   [RFC6442]  Polk, J., Rosen, B., and J. Peterson, "Location Conveyance
              for the Session Initiation Protocol", RFC 6442,
              December 2011.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3311]  Rosenberg, J., "The Session Initiation Protocol (SIP)
              UPDATE Method", RFC 3311, October 2002.

   [RFC3428]  Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C.,
              and D. Gurle, "Session Initiation Protocol (SIP) Extension
              for Instant Messaging", RFC 3428, December 2002.

   [RFC6086]  Holmberg, C., Burger, E., and H. Kaplan, "Session
              Initiation Protocol (SIP) INFO Method and Package
              Framework", RFC 6086, January 2011.

   [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.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

              Rosen, B., Tschofenig, H., and R. Marshall, "Additional
              Data related to an Emergency Call",
              draft-ietf-ecrit-additional-data-05 (work in progress),
              October 2011. 2012.

10.2.  Informative References

              Rosen, B., Schulzrinne, H., Tschofenig, H., and S.
              Norreys, "Requirements, Terminology and Framework for
              Exigent Communications", draft-ietf-atoca-requirements-02
              (work in progress), October 2011.

              Tschofenig, H., Schulzrinne, H., and B. Aboba,
              "Trustworthy Location Information",
              draft-ietf-ecrit-trustworthy-location-02 Location",
              draft-ietf-ecrit-trustworthy-location-04 (work in
              progress), May 2011. October 2012.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC6443]  Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
              "Framework for Emergency Calling Using Internet
              Multimedia", RFC 6443, December 2011.

Authors' Addresses

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


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

   Phone: +1 212 939 7004

   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600

   Phone: +358 (50) 4871445