One document matched: draft-patel-ecrit-sos-parameter-11.xml

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<!-- <!DOCTYPE rfc SYSTEM "rfc2629.dtd">-->
<?rfc toc="yes" ?>
<?rfc compact="yes" ?>
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<rfc category="std" docName="draft-patel-ecrit-sos-parameter-11.txt"
     ipr="trust200811">
  <front>
    <title abbrev="SOS URI Parameter for SIP Emergency">SOS Uniform Resource
    Identifier (URI) Parameter for Marking of Session Initiation Protocol
    (SIP) Requests related to Emergency Services</title>

    <author fullname="Milan Patel" initials="M." surname="Patel">
      <organization>InterDigital Communications </organization>

      <address>
        <postal>
          <street />

          <city />

          <region />
        </postal>

        <email>Milan.Patel@interdigital.com</email>
      </address>
    </author>

    <date month="November" year="2010" />

    <area>RAI</area>

    <workgroup>ECRIT Working Group</workgroup>

    <keyword>Emergency</keyword>

    <keyword>Session Initiation Protocol</keyword>

    <abstract>
      <t>This document defines a new Session Initiation Protocol (SIP) Uniform
      Resource Identifier (URI) parameter intended for marking SIP
      registration requests related to emergency calls and allow admission
      control to ensure successful initiation of emergency calls. The usage of
      this new URI parameter complements the usage of the Service Uniform
      Resource Name (URN) and is not intended to replace it.</t>
    </abstract>
  </front>

  <middle>
    <!-- Introduction -->

    <section anchor="sec-intro" title="Introduction">
      <t>One way to differentiate a SIP-based emergency call from an ordinary
      call is by the presence of the Service URN as defined in RFC 5031 <xref
      target="RFC5031" /> (and used in the IETF emergency services
      architecture described in PhoneBCP<xref
      target="I-D.ietf-ecrit-phonebcp" />). The 3GPP IP Multimedia Subsystem
      (IMS) emergency services architecture, illustrated in 3GPP TS 23.167
      <xref target="3GPP.23.167" />, specifies that the User Equipment (UE)
      needs to perform emergency registration prior to or during the
      initiation of an emergency call. <t /><t /></t>

      <t>In some countries, it is a regulatory requirement that devices be
      able to place emergency calls in circumstances where other calls may not
      be permitted. When a UAC issues an emergency marked REGISTER request it
      indicates to the registrar that roaming and barring restrictions should
      not be applied for the registered address-of-record in order to
      successfully initiate an emergency session. Furthermore, distinguishing
      emergency registration from non-emergency registration allows the
      registrar to ensure that the contact address associated with previous
      registration of the address-of-record included in the emergency REGISTER
      request is not replaced.</t>

      <t>Emergency registration is possible only when the UE has sufficient
      credentials to register with its home network and can detect that an
      emergency session is initiated. Unfortunately, marking of the emergency
      registration cannot be fulfilled by the use of the Service URN. The
      circumstances where such an emergency registration is beneficial are
      listed below:</t>

      <t> - the UE is not registered with its home network;</t>

      <t> - the UE is currently registered but roaming (to ensure that the
      emergency call is handled in the visited network, as required by some
      jurisdictions).</t>

      <t>This document concentrates on a use case defined by 3GPP as described
      above. However, the solution proposed does not preclude other systems
      that require emergency registration to occur prior to placing an
      emergency call, to ensure that any subscription related restrictions are
      removed to allow successful initiation of emergency calls. </t>

      <t>This document proposes a way to mark a REGISTER request as an
      emergency registration.</t>
    </section>

    <!-- Terminology-->

    <section anchor="sec-conv" title="Terminology">
      <t>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 <xref
      target="RFC2119" /></t>
    </section>

    <!--Requirements-->

    <section anchor="sec-req" title="Requirements">
      <t>Req: Where emergency registration is required prior to placing an
      emergency call, it shall be possible to distinguish emergency
      registration from non-emergency registration.</t>
    </section>

    <!-- solution-->

    <section anchor="sec-solution" title="The "sos" URI Parameter">
      <t>This section provides an overview of the proposed new URI parameter
      to be used for marking REGISTER requests related to emergency services.
      </t>

      <t>A new URI parameter "sos" is defined in this document. The "sos"
      parameter is appended to a URI consistent with RFC 3261 <xref
      target="RFC3261" />. It is proposed that use of this URI parameter is
      restricted to the Contact header included in the REGISTER request (and
      the 2xx response to the REGISTER request) related to an emergency call
      only. </t>

      <t>Inclusion of the "sos" URI parameter in a REGISTER request SHALL
      indicate that the REGISTER request pertains to emergency registration.
      The "sos" URI parameter MUST NOT be considered as a replacement for the
      Service URN for emergency calls originated by a UA.</t>

      <section anchor="sec-register" title="REGISTER Request">
        <t>In networks where the UA sends a REGISTER request for emergency
        registration prior to placing an emergency call, the "sos" URI
        parameter MUST be appended to the URI in the Contact header. This
        serves as an indication to the registrar that the request is for
        emergency registration thus requesting the registrar to not apply any
        restrictions to the user's service which might prevent emergency calls
        from successfully being initiated.</t>

        <t>Example:<t>Contact: "Alice" <sip:alice@example.com;sos>
        ;q=0.7; expires=3600</t></t>

        <t>In the event that more than one Contact header field is included in
        the REGISTER request, only the contact addresses that include the
        "sos" URI parameter shall be considered as emergency registered
        contact addresses. </t>

        <t>The "sos" URI parameter MUST NOT be included in non-REGISTER
        requests, and MUST NOT be included in REGISTER requests that do not
        pertain to emergency calls. </t>
      </section>

      <section anchor="sec-response" title="2xx Response to REGISTER Request">
        <t>If the registrar receives a REGISTER request that includes the
        "sos" URI parameter in the Contact header field, the registrar MUST
        include the "sos" URI parameter in the Contact header field in the 200
        (OK) response sent by the registrar upon successful registration. The
        "sos" URI parameter is appended to the URI included in the Contact
        header.</t>
      </section>

      <section anchor="backwards-compatible"
               title="Backwards compatibility issues">
        <t>The backwards compatibility scenario considered in this document is
        where a legacy registrar does not support the "sos" URI parameter. In
        this case, if the registrar receives a REGISTER request that includes
        the "sos" URI parameter in the Contact header field, the registrar
        proceeds with registration procedures and silently ignores the
        URI-parameter in accordance with RFC 3261<xref target="RFC3261" />.
        This ensures the user is registered and thus can successfully initiate
        an emergency call.</t>

        <t>The drawback of proceeding with registration is if the
        address-of-record is for example barred or has roaming restrictions
        applied, then these restrictions will not be lifted and thus
        registration will be unsuccessful. This can limit the UAC's ability to
        successfully place an emergency call.</t>

        <t>If registration is successful, the 200 (OK) response from a legacy
        registrar includes the "sos" URI parameter in the Contact header
        field. Thus the UA is unaware that the registrar does not support the
        “sos” URI parameter. Providing the registration was successful, the
        UA’s ability to place an emergency call is not compromised. The UA
        need not know that the registrar does not support the URI
        parameter.</t>

        <t>The consequence of the registrar not supporting the “sos” URI
        parameter, in addition to the drawback pertaining to restrictions
        applied to the address-of-record, are as follows:</t>

        <t>- the risk of the registrar overwriting previous registrations of
        the registered address-of-record, and thus disrupting any on-going
        non-emergency sessions associated with the UA, its address-of-record
        and previously registered contact address.</t>

        <t>- incoming calls, such as a PSAP call back (to a previously made
        emergency call) to the registered address-of-record might not be
        routed correctly to the UA that placed the emergency call, due to not
        suppressing any network based services such as call forwarding, or UA
        based services which can divert the call elsewhere, or if the
        address-of-record is associated to more than one contact address.</t>
      </section>
    </section>

    <section anchor="sec-syntax" title="Formal Syntax">
      <t>The following syntax specification uses the augmented Backus-Naur
      Form (BNF) as described in RFC 5234 <xref target="RFC5234" />.<t>The
      "sos" URI parameter is a "uri-parameter", as defined by RFC
      3261</t><xref target="RFC3261" />.<t>uri-parameter =/
      sos-param</t><t>sos-param = "sos" </t></t>
    </section>

    <!-- IANA Considerations -->

    <section anchor="sec:IANA" title="IANA Considerations">
      <t>This specification defines one new SIP URI parameter, as per the
      registry created by RFC 3969 <xref target="RFC3969" /><t>Parameter Name:
      sos</t><t>Predefined Values: none</t><t>Reference: [RFCXXXX]</t><t>[NOTE
      TO IANA: Please replace XXXX with the RFC number of this
      specification.]</t></t>
    </section>

    <!-- Security Considerations -->

    <section anchor="sec-security" title="Security Considerations">
      <t>As an identifier, the "sos" parameter itself does not raise any
      particular security issues. The semantics described by the "sos"
      parameter are meant to be well-known so privacy considerations do not
      apply to the URI parameter. The main possibility of attack involves use
      of the "sos" parameter to bypass the normal procedures in order to
      achieve fraudulent use of services or to bypass security procedures. The
      usage of this parameter as described in this document is purely for the
      purpose of the REGISTER request and hence in presence of user
      authentication it is ensured that the respective user can be held
      accountable. </t>

      <t>It is RECOMMENDED to log events of misuse of the "sos" URI parameter,
      for example by including it in a request or response not related to an
      emergency call.</t>

      <t>Emergency registration can result in removing restrictions for
      roaming and/or barring of services. Misuse of the emergency registered
      AoR and contact address can be identified within the network and thus
      requests for unauthorized service will be rejected. Thus, no security
      considerations related to hijacking of services are foreseen as a result
      of applying a marking of emergency registrations through the use of a
      SIP URI parameter.</t>
    </section>

    <!-- Acknowledgements -->

    <section anchor="sec-acks" title="Acknowledgements">
      <t>The author would like to thank Keith Drage, Milo Orsic, Deb Barclay,
      John-Luc Bakker, Andrew Allen, Hiroshi Ishikawa, Sean Schneyer, Peter
      Leis, Georg Mayer, Marvin Bienn, Ricky Kaura, Steve Norreys, Laura
      Liess, AC Mahendran, Roozbeh Atarius, Ramachandran Subramanian and
      Sandeep Sharma, Brian Rosen, Hannes Tschofenig, Christer Holmberg and
      Henning Schulzrinne for the discussions and contributions that led to
      this work.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <!--Key words for use in RFCs to Indicate Requirement Levels-->

      <?rfc include="reference.RFC.2119"?>

      <!--SIP-->

      <?rfc include="reference.RFC.3261"?>

      <!--ABNF-->

      <?rfc include="reference.RFC.5234"?>

      <!--IANA-->

      <?rfc include="reference.RFC.3969"?>
    </references>

    <references title="Informative References">
      <!-- Best Current Practice for Communications Services in support of Emergency Calling-->

      <?rfc include="reference.I-D.ietf-ecrit-phonebcp"?>

      <!-- A Uniform Resource Name (URN) for Emergency and Other Well-Known Services-->

      <?rfc include="reference.RFC.5031"?>

      <!--IP Multimedia Subsystem (IMS) emergency sessions-->

      <?rfc include="reference.3GPP.23.167"?>
    </references>
  </back>
</rfc>