Assertion Values for a Resource Priority Header Claim in Support of Emergency Services Networks
draft-ietf-stir-rph-emergency-services-01

Abstract

This document adds new assertion values for a Resource Priority Header (“rph”) claim defined in RFC 8443, in support of Emergency Services Networks for emergency call origination and callback.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. New Assertion Values
• 3.1. ESorig
• 3.2. EScallback
• 4. IANA Considerations
• 4.1. PASSporT Resource Priority Header (rph) Types
• 5. Security Considerations
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Authors' Addresses

1. Introduction

Personal Assertion Token (PASSporT) Extension for Resource Priority Authorization [RFC8443] extended the Personal Assertion Token (PASSporT) specification defined in [RFC8225] 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.

Compromise of the SIP ‘Resource-Priority’ header field [RFC4412] could lead to misuse of network resources (i.e., during congestion scenarios), impacting the application services supported using the SIP ‘Resource-Priority’ header field.

[RFC8225] allows extensions by which an authority on the originating side verifying the authorization of a particular communication for the SIP ‘Resource-Priority’ header field can use a PASSPorT claim to cryptographically sign the SIP ‘Resource-Priority’ header field and convey assertion of the authorization for the SIP ‘Resource-Priority’ header field. A signed SIP ‘Resource-Priority’ header field will allow a receiving entity (including entities located in different network domains/boundaries) to verify the validity of assertions authorizing the SIP ‘Resource-Priority’ header field and to act on the information with confidence that the information has not been spoofed or compromised.

This document adds new assertion values for a Resource Priority Header (“rph”) claim defined in [RFC8443], in support of Emergency Services Networks for emergency call origination and callback. How these new assertion values for real-time communications supported using the SIP ‘Resource-Priority’ header field is outside the scope of this document. In addition, the PASSPorT extension defined in this document is intended for use in environments where there are means to verify that the signer of the SIP ‘Resource-Priority’ header field is authoritative.

2. Terminology

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. New Assertion Values

This specification defines new assertions values for:

*  “ESorig”: Emergency Services call origination
*  “EScallback”: Emergency Services callback.

3.1. ESorig

When using “ESorig” as the “rph” assertion value, the “orig” claim of the PASSporT MUST represent the calling party number that initiates the call to emergency services. The “dest” claim MUST either be a country or region specific dial string (e.g., “911” for North America or “112” GSM defined string used in Europe and other countries) or “urn:service:sos” as defined in TBD, representing the emergency services destination of the call.

The following is an example of an “rph” claim for SIP ‘Resource-Priority’ header field with a “ESorig” assertion:

  {
    "orig":{"tn":“12155551212"},
    "dest":{["tn":“urn:service:sos"]},
    "iat":1443208345,
    "rph":{“ESorig":[“esnet,x"]}
  }

3.2. EScallback

When using “EScallback” as the “rph” assertion value, the “orig” claim of the PASSporT MUST represent the emergency network telephone number. The “dest” claim MUST be the telephone number representing the original calling party of the emergency service call that is being called back.

The following is an example of an “rph” claim for SIP ‘Resource-Priority’ header field with a “EScallback” assertion:

  {
    "orig":{"tn":“12155551213"},
    "dest":{["tn":“12155551212"]},
    "iat":1443208345,
    "rph":{“EScallback":[“esnet,x"]}
  }

After the header and claims PASSporT objects have been constructed, their signature is generated normally per the guidance in [RFC8225] using the full form of PASSPorT. The credentials (i.e., Certificate) used to create the signature must have authority over the namespace of the “rph” claim, and there is only one authority per claim. The authority MUST 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” header and sign the claim with their own authority.

The use of the compact form of PASSporT is not specified in this document.

4. IANA Considerations

4.1. PASSporT Resource Priority Header (rph) Types

This specification requests that the IANA add two new assertion values to the “PASSporT Resource Priority Header (rph) Types” Registry as defined in [RFC8443].

The following assertion values will be added to the registry:

* “ESorig”: Emergency Services call origination
* “EScallback”: Emergency Services callback

    +--------------+------------+
    | rph Type     | Reference  |
    +--------------+------------+
    | ESorig       | [this RFC] |
    +--------------+------------+
    | EScallback   | [this RFC] |
    +--------------+------------+

5. Security Considerations

The security considerations discussed in [RFC8224], Section 12, are applicable here.

6. References

6.1. Normative References

6.2. Informative References

Authors' Addresses