wdiff rfc9027xml2.original.xml rfc9027.xml

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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft-ietf-stir-rph-emergency-services-07" category="std"> number="9027" obsoletes="" updates=""
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  <!-- xml2rfc v2v3 conversion 3.5.0 -->
  <front>
    <title abbrev="RPH Values for Emergency Services">Assertion Values for a Resource Priority Header Claim and a SIP Priority Header Claim Claims in Support of Emergency Services Networks</title>
    <seriesInfo name="RFC" value="9027"/>
    <author initials="M." surname="Dolly" fullname="Martin Dolly">
      <organization>AT&amp;T</organization>
      <address>
        <email>md3135@att.com</email>
      </address>
    </author>
    <author initials="C." surname="Wendt" fullname="Chris Wendt">
      <organization>Comcast</organization>
      <address>
        <postal>
          <street>Comcast Technology Center</street>
          <city>Philadelphia, PA  19103</city>
          <country>USA</country>
	  <city>Philadelphia</city>
	  <region>PA</region>
	  <code>19103</code>
          <country>United States of America</country>
        </postal>
        <email>chris-ietf@chriswendt.net</email>
      </address>
    </author>
    <date year="2021" month="March" day="11"/> month="June"/>
    <area>ART</area>
    <workgroup>STIR</workgroup>
    <keyword>Internet-Draft</keyword>
    <keyword>rph</keyword>
    <keyword>PASSporT</keyword>
    <keyword>esnet</keyword>

<abstract>
      <t>This document adds new assertion values for a Resource Priority Header (“rph”) ("rph") claim and a new SIP Priority Header ("sph") claim (“sph”) for protection of the “psap-callback” "psap-callback" value as part of the “rph” PASSporT extension, "rph" Personal Assertion Token (PASSporT) extension in support of the security of Emergency Services Networks emergency services networks for emergency call origination and callback.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction" title="Introduction">

<t>Personal numbered="true" toc="default">
      <name>Introduction</name>
      <t>"Personal Assertion Token (PASSporT) Extension for Resource Priority Authorization Authorization" <xref target="RFC8443"/> target="RFC8443" format="default"/> extended the Personal Assertion Token (PASSporT) specification defined in <xref target="RFC8225"/> target="RFC8225" format="default"/> to allow the inclusion of cryptographically signed assertions of authorization for the values populated in the Session Initiation Protocol (SIP) “Resource-Priority” 'Resource-Priority' header field <xref target="RFC4412"/>. target="RFC4412" format="default"/>. <xref target="I-D.rosen-stir-emergency-calls"/> target="I-D.rosen-stir-emergency-calls" format="default"/> introduces the need and justification for the protection of both the SIP “Resource-Priority” 'Resource-Priority' and “Priority” 'Priority' header fields, used for categorizing the priority use of the call in the telephone network, specifically for emergency calls.</t>
      <t>Compromise of the SIP “Resource-Priority” 'Resource-Priority' or “Priority” 'Priority' header fields could lead to misuse of network resources (i.e., during congestion scenarios), impacting the application services supported using the SIP “Resource-Priority” 'Resource-Priority' header field and the handling of Public Saftey Safety Answering Point (PSAP) callbacks.</t>

      <t><xref target="RFC8225"/> target="RFC8225" format="default"/> allows extensions by which an authority on the originating side verifying the authorization of a particular communication for the SIP “Resource-Priority” 'Resource-Priority' header field or the SIP “Priority” 'Priority' header field can use PASSPorT PASSporT claims to cryptographically sign the information associated with either the SIP “Resource-Priority” 'Resource-Priority' or “Priority” the 'Priority' header field and convey assertion of those values by the signing party authorization.  A signed SIP “Resource-Priority” 'Resource-Priority' or “Priority” 'Priority' header field will allow a receiving entity (including entities located in different network domains/boundaries) to verify the validity of assertions to act on the information with confidence that the information it has not been spoofed or compromised.</t>

      <t>This document adds new “auth” "auth" array key values for a Resource Priority Header (“rph”) ("rph") claim defined in <xref target="RFC8443"/>, target="RFC8443" format="default"/>, in support of Emergency Services Networks emergency services networks for emergency call origination and callback. This document additionally defines a new PASSporT claim, “sph”, "sph", including protection of the SIP Priority 'Priority' header field for the indication of an emergency service call-back callback assigned the value “psap-callback” "psap-callback", as defined in <xref target="RFC7090"/>. target="RFC7090" format="default"/>.
The use of the newly defined claim and key values corresponding to the SIP ‘Resource-Priority’ 'Resource-Priority' and ‘Priority’ 'Priority' header fields for emergency services is introduced in <xref target="I-D.rosen-stir-emergency-calls"/> target="I-D.rosen-stir-emergency-calls" format="default"/> but otherwise out-of-scope is out of scope of this document.  In addition, the PASSPorT PASSporT claims and values defined in this document are intended for use in environments where there are means to verify that the signer of the SIP ‘Resource-Priority’ 'Resource-Priority' and ‘Priority’ 'Priority' header fields is authoritative.</t>
    </section>
    <section anchor="terminology" title="Terminology">

<t>The numbered="true" toc="default">
      <name>Terminology</name>
        <t>
    The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
    NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and “OPTIONAL” "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
    described in BCP 14 BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
    when, and only when, they appear in all capitals, as shown here.</t> here.
        </t>
    </section>
    <section anchor="new-assertion-values-for-rph-claim" title="New numbered="true" toc="default">
      <name>New Assertion Values for “rph” claim"> "rph" Claim</name>
      <t>This specification defines the ability to sign the SIP Resource-Priority Header 'Resource-Priority' header field namespace for local emergency communications defined in <xref target="RFC7135"/> target="RFC7135" format="default"/> and represented by the string “esnet.x” "esnet.x", where x is the priority-level priority level allowed in the esnet namespace. As of the writing of this specification specification, the priority-level priority level is between 0 and 4, inclusive, but may be extended by future specifications.</t>
      <t>Similar to the values defined by <xref target="RFC8443"/> target="RFC8443" format="default"/> for the “auth” "auth" JSON object key inside the “rph” "rph" claim, the string “esnet.x” "esnet.x" with the appropriate value should be used when resource priority is required for local emergency communications corresponding and exactly matching the SIP Resource-Priority 'Resource-Priority' header field representing the namespace invoked in the call.</t>
      <t>When using “esnet.x” "esnet.x" as the “auth” "auth" assertion value in emergency service destined emergency-service-destined calls, the “orig” "orig" claim of the PASSporT MUST <bcp14>MUST</bcp14> represent the calling party number that initiates the call to emergency services.  The “dest” "dest" claim MUST either <bcp14>MUST</bcp14> be either a country country- or region specific region-specific dial string (e.g., “911” "911" for North America or “112” GSM defined a "112" GSM-defined string used in Europe and other countries) or “urn:service:sos” "urn:service:sos", as defined in <xref target="RFC5031"/>, target="RFC5031" format="default"/>, representing the emergency services destination of the call.</t>
      <t>The following is an example of an “rph” "rph" claim for the SIP ‘Resource-Priority’ 'Resource-Priority' header field with an “esnet.1” "esnet.1" assertion:</t>

<figure><artwork><![CDATA[

<sourcecode type="json"><![CDATA[
  {
    "dest":{"uri":["urn:service:sos"]},
    "iat":1615471428,
    "orig":{"tn":“12155551212"},
    "orig":{"tn":"12155551212"},
    "rph":{"auth":["esnet.1"]}
  }
]]></artwork></figure>
]]></sourcecode>
      <t>For emergency services callbacks, the “orig” "orig" claim of the “rph” "rph" PASSporT MUST <bcp14>MUST</bcp14> represent the Public Saftey Safety Answering Point (PSAP) telephone number. The “dest” "dest" claim MUST <bcp14>MUST</bcp14> be the telephone number representing the original calling party of the emergency service call that is being called back.</t>
      <t>The following is an example of an “rph” "rph" claim for the SIP ‘Resource-Priority’ 'Resource-Priority' header field with a “esnet.0” an "esnet.0" assertion:</t>

<figure><artwork><![CDATA[
<sourcecode type="json"><![CDATA[
  {
    "dest":{"tn":["12155551212"]},
    "iat":1615471428,
    "orig":{"tn":"12155551213"},
    "rph":{"auth":["esnet.0"]}
  }
]]></artwork></figure>
]]></sourcecode>
      <t>After the header and claims PASSporT objects have been constructed, their signature is generated normally per the guidance in <xref target="RFC8225"/> target="RFC8225" format="default"/>, using the full form of PASSPorT. PASSporT.  The credentials (i.e., Certificate) used to create the signature must have authority over the namespace of the “rph” "rph" claim, and there is only one authority per claim. The authority MUST <bcp14>MUST</bcp14> use its credentials associated with the specific service supported by the resource priority namespace in the claim. If r-values are added or dropped by the intermediaries along the path, the intermediaries must generate a new “rph” "rph" identity header and sign the claim with their own authority.</t>
    </section>
    <section anchor="the-sip-priority-header-sph-claim" title="The numbered="true" toc="default">
      <name>The SIP Priority header “sph” claim"> Header ("sph") Claim</name>
      <t>As defined in <xref target="RFC7090"/> target="RFC7090" format="default"/>, the SIP Priority 'Priority' header field may be set to the value “psap-callback” "psap-callback" for emergency services callback calls.  Because some SIP networks may act on this value and provide priority or other special routing based on this value, it is important to protect and validate the authoritative use associated with it.</t>
      <t>Therefore, we define a new claim key as part of the “rph” "rph" PASSporT, “sph”. "sph".  This is an optional claim that MUST <bcp14>MUST</bcp14> only be used only with an “auth” "auth" claim with an “esnet.x” "esnet.x" value indicating an authorized emergency callback call and corresponding to a SIP Priority 'Priority' header field with the value “psap-callback”.</t> "psap-callback".</t>
      <t>The value of the “sph” "sph" claim key should only be “psap-callback” "psap-callback", which MUST <bcp14>MUST</bcp14> match the SIP Priority 'Priority' header field value for authorized emergency services callbacks. If the value is anything other than “psap-callback”, "psap-callback", the PASSporT validation MUST <bcp14>MUST</bcp14> be considered a failure case.</t>

<t>Note: Because
      <t>Note that because the intended use of this specification is only for emergency services, there is also an explicit assumption that the signer of the “rph” "rph" PASSporT can authoritatively represent both the content of the Resource Priority Header 'Resource-Priority' header field and Priority Header 'Priority' header field information associated specifically with a an emergency services callback case where both could exist. This document is not intended to be a general mechanism for protecting the SIP Priority Header fields, 'Priority' header fields; this could be accomplished as part of future work with a new PASSporT extension or new claim added to either an existing PASSporT or PASSporT extension usage.</t>
      <t>The following is an example of an “sph” "sph" claim for the SIP ‘Priority’ 'Priority' header field with the value “psap-callback”:</t>

<figure><artwork><![CDATA[ "psap-callback":</t>
<sourcecode type="json"><![CDATA[
  {
    "dest":{"tn":["12155551212"]},
    "iat":1615471428,
    "orig":{"tn":"12155551213"},
    "rph":{"auth":["esnet.0"]},
    "sph":"psap-callback"
  }
]]></artwork></figure>
]]></sourcecode>
    </section>
    <section anchor="order-of-claim-keys" title="Order numbered="true" toc="default">
      <name>Order of Claim Keys"> Keys</name>
      <t>The order of the claim keys MUST <bcp14>MUST</bcp14> follow the rules of <xref target="RFC8225"/> Section 9 target="RFC8225" sectionFormat="of" section="9"/>, which defines the deterministic JSON serialization used for signature generation (and validation); the claim keys MUST <bcp14>MUST</bcp14> appear in lexicographic order. Therefore, the claim keys discussed in this document appear in the PASSporT Payload in the following order,</t>

<t><list style="symbols">
  <t>dest</t>
  <t>iat</t>
  <t>orig</t>
  <t>rph</t>
  <t>sph</t>
</list></t> order:</t>
      <ul spacing="normal">
        <li>dest</li>
        <li>iat</li>
        <li>orig</li>
        <li>rph</li>
        <li>sph</li>
      </ul>
    </section>
    <section anchor="compact-form-of-passport" title="Compact numbered="true" toc="default">
      <name>Compact Form of PASSporT"> PASSporT</name>
      <t>The use of the compact form of PASSporT is not specified in this document or recommended for ‘rph’ "rph" PASSporTs.</t>
    </section>
    <section anchor="acknowledgements" title="Acknowledgements">

<t>The authors would like to thank Brian Rosen, Terry Reese, and Jon Peterson for helpful suggestions, comments, and corrections.</t>

</section>
<section anchor="iana-considerations" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <section anchor="json-web-token-claims" title="JSON numbered="true" toc="default">
        <name>JSON Web Token claims"> Claims</name>
        <t>This specification requests that the IANA add one new claim to the JSON "JSON Web Token Claims registry Claims" registry, as defined in <xref target="RFC7519"/>.</t>

<t>Claim Name: “sph”</t>

<t>Claim Description: SIP Priority header field</t>

<t>Change Controller: IESG</t>

<t>Specification Document(s): [RFCThis]</t> target="RFC7519" format="default"/>.</t>
<dl newline="false" spacing="compact">
        <dt>Claim Name:</dt>
	<dd>sph</dd>
        <dt>Claim Description:</dt>
	<dd>SIP Priority header field</dd>
        <dt>Change Controller:</dt>
	<dd>IESG</dd>
        <dt>Specification Document(s):</dt>
	<dd>RFC 9027</dd>
</dl>
      </section>
    </section>
    <section anchor="security-considerations" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>The security considerations discussed in <xref target="RFC8224"/>, target="RFC8224" format="default"/>, <xref target="RFC8225"/>, target="RFC8225" format="default"/>, and <xref target="RFC8443"/> target="RFC8443" format="default"/> are applicable here.</t>
    </section>
  </middle>
  <back>

    <references title='Normative References'>

<reference  anchor="RFC4412" target='https://www.rfc-editor.org/info/rfc4412'>
<front>
<title>Communications Resource Priority for the Session Initiation Protocol (SIP)</title>
<author initials='H.' surname='Schulzrinne' fullname='H. Schulzrinne'><organization /></author>
<author initials='J.' surname='Polk' fullname='J. Polk'><organization /></author>
<date year='2006' month='February' />
<abstract><t>This document defines two new Session Initiation Protocol (SIP) header fields for communicating resource priority, namely, &quot;Resource-Priority&quot; and &quot;Accept-Resource-Priority&quot;.  The &quot;Resource-Priority&quot; header field can influence the behavior of SIP user agents (such as telephone gateways and IP telephones) and SIP proxies.  It does not directly influence the forwarding behavior of IP routers.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4412'/>
<seriesInfo name='DOI' value='10.17487/RFC4412'/>
</reference>

<reference  anchor="RFC5031" target='https://www.rfc-editor.org/info/rfc5031'>
<front>
<title>A Uniform Resource Name (URN) for Emergency and Other Well-Known Services</title>
<author initials='H.' surname='Schulzrinne' fullname='H. Schulzrinne'><organization /></author>
<date year='2008' month='January' />
<abstract><t>The content of many communication services depends on the context, such as the user's location.  We describe a 'service' URN that allows well-known context-dependent services that can be resolved in a distributed manner

<displayreference target="I-D.rosen-stir-emergency-calls" to="EMERGENCY-CALLS"/>

    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4412.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5031.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7090.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7135.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8224.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8225.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7519.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8443.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
      </references>
      <references>
        <name>Informative References</name>
        <xi:include href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.rosen-stir-emergency-calls.xml"/>
      </references>
    </references>
    <section anchor="acknowledgements" numbered="false" toc="default">
      <name>Acknowledgements</name>
      <t>The authors would like to be identified.  Examples include emergency services, directory assistance, and call-before-you-dig hot lines.  [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5031'/>
<seriesInfo name='DOI' value='10.17487/RFC5031'/>
</reference>

<reference  anchor="RFC7090" target='https://www.rfc-editor.org/info/rfc7090'>
<front>
<title>Public Safety Answering Point (PSAP) Callback</title>
<author initials='H.' surname='Schulzrinne' fullname='H. Schulzrinne'><organization /></author>
<author initials='H.' surname='Tschofenig' fullname='H. Tschofenig'><organization /></author>
<author initials='C.' surname='Holmberg' fullname='C. Holmberg'><organization /></author>
<author initials='M.' surname='Patel' fullname='M. Patel'><organization /></author>
<date year='2014' month='April' />
<abstract><t>After an emergency call is completed (terminated either prematurely by the emergency caller or normally by the call taker), the call taker may feel the need thank <contact fullname="Brian Rosen"/>, <contact fullname="Terry Reese"/>, and <contact fullname="Jon Peterson"/> for further communication.  For example, the call may have been dropped by accident without the call taker having sufficient information about the current state of an accident victim. A call taker may trigger a callback to the emergency caller using the contact information provided with the initial emergency call.  This callback could, under certain circumstances, be treated like any other call and, as a consequence, it may get blocked by authorization policies or may get forwarded to an answering machine.</t><t>The IETF emergency services architecture specification already offers a solution approach for allowing Public Safety Answering Point (PSAP) callbacks to bypass authorization policies in order to reach the caller without unnecessary delays.  Unfortunately, the specified mechanism only supports limited scenarios.  This document discusses shortcomings of the current mechanisms and illustrates additional scenarios where better-than-normal call treatment behavior would be desirable.  We describe a solution based on a new header field value for the SIP Priority header field, called &quot;psap-callback&quot;, to mark PSAP callbacks.</t></abstract>
</front>
<seriesInfo name='RFC' value='7090'/>
<seriesInfo name='DOI' value='10.17487/RFC7090'/>
</reference>

<reference  anchor="RFC7135" target='https://www.rfc-editor.org/info/rfc7135'>
<front>
<title>Registering a SIP Resource Priority Header Field Namespace for Local Emergency Communications</title>
<author initials='J.' surname='Polk' fullname='J. Polk'><organization /></author>
<date year='2014' month='May' />
<abstract><t>This document creates the new Session Initiation Protocol (SIP) Resource Priority header field namespace 'esnet' and registers this namespace with IANA.  The new header field namespace allows for local emergency session establishment to a public safety answering point (PSAP), between PSAPs, and between a PSAP and first responders and their organizations.</t></abstract>
</front>
<seriesInfo name='RFC' value='7135'/>
<seriesInfo name='DOI' value='10.17487/RFC7135'/>
</reference>

<reference  anchor="RFC8224" target='https://www.rfc-editor.org/info/rfc8224'>
<front>
<title>Authenticated Identity Management in the Session Initiation Protocol (SIP)</title>
<author initials='J.' surname='Peterson' fullname='J. Peterson'><organization /></author>
<author initials='C.' surname='Jennings' fullname='C. Jennings'><organization /></author>
<author initials='E.' surname='Rescorla' fullname='E. Rescorla'><organization /></author>
<author initials='C.' surname='Wendt' fullname='C. Wendt'><organization /></author>
<date year='2018' month='February' />
<abstract><t>The baseline security mechanisms in the Session Initiation Protocol (SIP) are inadequate for cryptographically assuring the identity of the end users that originate SIP requests, especially in an interdomain context.  This document defines a mechanism for securely identifying originators of SIP requests.  It does so by defining a SIP header field for conveying a signature used for validating the identity and for conveying a reference to the credentials of the signer.</t><t>This document obsoletes RFC 4474.</t></abstract>
</front>
<seriesInfo name='RFC' value='8224'/>
<seriesInfo name='DOI' value='10.17487/RFC8224'/>
</reference>

<reference  anchor="RFC8225" target='https://www.rfc-editor.org/info/rfc8225'>
<front>
<title>PASSporT: Personal Assertion Token</title>
<author initials='C.' surname='Wendt' fullname='C. Wendt'><organization /></author>
<author initials='J.' surname='Peterson' fullname='J. Peterson'><organization /></author>
<date year='2018' month='February' />
<abstract><t>This document defines a method for creating and validating a token that cryptographically verifies an originating identity or, more generally, a URI or telephone number representing the originator of personal communications.  The Personal Assertion Token, PASSporT, is cryptographically signed to protect the integrity of the identity of the originator and to verify the assertion of the identity information at the destination.  The cryptographic signature is defined with the intention that it can confidently verify the originating persona even when the signature is sent to the destination party over an insecure channel.  PASSporT is particularly useful for many personal-communications applications over IP networks and other multi-hop interconnection scenarios where the originating and destination parties may not have a direct trusted relationship.</t></abstract>
</front>
<seriesInfo name='RFC' value='8225'/>
<seriesInfo name='DOI' value='10.17487/RFC8225'/>
</reference>

<reference  anchor="RFC7519" target='https://www.rfc-editor.org/info/rfc7519'>
<front>
<title>JSON Web Token (JWT)</title>
<author initials='M.' surname='Jones' fullname='M. Jones'><organization /></author>
<author initials='J.' surname='Bradley' fullname='J. Bradley'><organization /></author>
<author initials='N.' surname='Sakimura' fullname='N. Sakimura'><organization /></author>
<date year='2015' month='May' />
<abstract><t>JSON Web Token (JWT) is a compact, URL-safe means of representing claims to be transferred between two parties.  The claims in a JWT are encoded as a JSON object that is used as the payload of a JSON Web Signature (JWS) structure or as the plaintext of a JSON Web Encryption (JWE) structure, enabling the claims to be digitally signed or integrity protected with a Message Authentication Code (MAC) and/or encrypted.</t></abstract>
</front>
<seriesInfo name='RFC' value='7519'/>
<seriesInfo name='DOI' value='10.17487/RFC7519'/>
</reference>

<reference  anchor="RFC8443" target='https://www.rfc-editor.org/info/rfc8443'>
<front>
<title>Personal Assertion Token (PASSporT) Extension for Resource Priority Authorization</title>
<author initials='R.' surname='Singh' fullname='R. Singh'><organization /></author>
<author initials='M.' surname='Dolly' fullname='M. Dolly'><organization /></author>
<author initials='S.' surname='Das' fullname='S. Das'><organization /></author>
<author initials='A.' surname='Nguyen' fullname='A. Nguyen'><organization /></author>
<date year='2018' month='August' />
<abstract><t>This document extends the Personal Assertion Token (PASSporT) specification defined in RFC 8225 to allow the inclusion of cryptographically signed assertions of authorization for the values populated in the Session Initiation Protocol (SIP) 'Resource-Priority' header field, which is used for communications resource prioritization.</t></abstract>
</front>
<seriesInfo name='RFC' value='8443'/>
<seriesInfo name='DOI' value='10.17487/RFC8443'/>
</reference>

    </references>

    <references title='Informative References'>

<reference anchor="I-D.rosen-stir-emergency-calls">
<front>
<title>Non-Interactive Emergency Calls</title>

<author initials='B' surname='Rosen' fullname='Brian Rosen'>
    <organization />
</author>

<date month='March' day='9' year='2020' />

<abstract><t>Emergency calls from citizens to authorities, and call back of such emergency calls by authorities to citizens need assurances that headers intended to get appropriate priority from the networks they traverse, and in some cases, appropriate routing.  Protection of the SIP Resource Priority Header and the SIP Priority header is needed for such calls.  This document describes the environment for placing emergency calls and call backs which motivate the need and use of the mechanisms described in other documents</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-rosen-stir-emergency-calls-00' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-rosen-stir-emergency-calls-00.txt' />
</reference>

<reference  anchor="RFC2119" target='https://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized. This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion helpful suggestions, comments, and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>

<reference  anchor="RFC8174" target='https://www.rfc-editor.org/info/rfc8174'>
<front>
<title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
<author initials='B.' surname='Leiba' fullname='B. Leiba'><organization /></author>
<date year='2017' month='May' />
<abstract><t>RFC 2119 specifies common key words that may be used in protocol  specifications.  This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the  defined special meanings.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='8174'/>
<seriesInfo name='DOI' value='10.17487/RFC8174'/>
</reference>

    </references> corrections.</t>
    </section>
  </back>

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