





Internet Engineering Task Force (IETF)                       C. Holmberg
Request for Comments: 8055                                      Ericsson
Category: Standards Track                                       Y. Jiang
ISSN: 2070-1721                                             China Mobile
                                                            January 2017


      Session Initiation Protocol (SIP) Via Header Field Parameter
                       to Indicate Received Realm

Abstract

   This specification defines a new Session Initiation Protocol (SIP)
   Via header field parameter, 'received-realm', which allows a SIP
   entity acting as an entry point to a transit network to indicate from
   which adjacent upstream network a SIP request is received by using a
   network realm value associated with the adjacent network.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8055.

Copyright Notice

   Copyright (c) 2017 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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Use Case: Transit Network Application Services  . . . . .   3
     1.3.  Use Case: Transit Network Routing . . . . . . . . . . . .   4
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Via 'received-realm' Header Field Parameter . . . . . . . . .   5
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Operator Identifier . . . . . . . . . . . . . . . . . . .   5
     5.3.  JWS Header  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.4.  JWS Payload . . . . . . . . . . . . . . . . . . . . . . .   6
     5.5.  JWS Serialization . . . . . . . . . . . . . . . . . . . .   7
     5.6.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . .   8
       5.6.1.  General . . . . . . . . . . . . . . . . . . . . . . .   8
       5.6.2.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.7.  Example: SIP Via Header Field . . . . . . . . . . . . . .   8
   6.  User Agent and Proxy Behavior . . . . . . . . . . . . . . . .   8
     6.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.2.  Behavior of a SIP Entity Acting as a Network Entry Point    8
     6.3.  Behavior of a SIP Entity Consuming the 'received-realm'
           Value . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Example: SIP INVITE Request and Response  . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  'received-realm' Via Header Field Parameter . . . . . . .  10
     8.2.  JSON Web Token Claims Registration  . . . . . . . . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

















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1.  Introduction

1.1.  General

   When Session Initiation Protocol (SIP) [RFC3261] sessions are
   established between networks belonging to different operators or
   between interconnected networks belonging to the same operator (or
   enterprise), the SIP requests associated with the session might
   traverse transit networks.

   Such transit networks might provide different kinds of services.  In
   order to provide such services, a transit network often needs to know
   to which operator (or enterprise) the adjacent upstream network from
   which the SIP session initiation request is received belongs.

   This specification defines a new SIP Via header field parameter,
   'received-realm', which allows a SIP entity acting as an entry point
   to a transit network to indicate from which adjacent upstream network
   a SIP request is received by using a network realm value associated
   with the adjacent network.

   NOTE: As the adjacent network can be an enterprise network, an Inter
   Operator Identifier (IOI) cannot be used to identify the network
   because IOIs are not defined for enterprise networks.

   The following sections describe use cases where the information is
   needed.

1.2.  Use Case: Transit Network Application Services

   The Third Generation Partnership Project (3GPP) TS 23.228
   [TS.3GPP.23.228] specifies how an IP Multimedia Subsystem (IMS)
   network can be used to provide transit functionality.  An operator
   can use its IMS network to provide transit functionality, e.g., to
   non-IMS customers, to enterprise networks, and to other network
   operators.

   The transit network operator can provide application services to the
   networks for which it is providing transit functionality.  Transit
   application services are typically not provided on a per user basis,
   as the transit network does not have access to the user profiles of
   the networks for which the application services are provided.
   Instead, the application services are provided per served network.

   When a SIP entity that provides application services (e.g., an
   Application Server) within a transit network receives a SIP request,
   in order to apply the correct services, it needs to know the adjacent
   upstream network from which the SIP request is received.



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1.3.  Use Case: Transit Network Routing

   A transit network operator normally interconnects to many different
   operators, including other transit network operators, and provides
   transit routing of SIP requests received from one operator network
   towards the destination.  The destination can be within an operator
   network to which the transit network operator has a direct
   interconnect or within an operator network that only can be reached
   via one or more interconnected transit operators.

   For each customer (i.e., interconnected network operator) for which
   the transit network operator routes SIP requests towards the
   requested destination, a set of transit routing policies are defined.
   These policies are used to determine how a SIP request shall be
   routed towards the requested destination to meet the agreement the
   transit network operator has with its customer.

   When a SIP entity that performs the transit routing functionality
   receives a SIP request, in order to apply the correct set of transit
   routing policies, it needs to know from which of its customers (i.e.,
   adjacent upstream network) the SIP request is received.

2.  Applicability

   The mechanism defined in this specification MUST only be used by SIP
   entities that are able to verify from which adjacent upstream network
   a SIP request is received.

   The mechanism for verifying from which adjacent upstream network a
   SIP request is received is outside the scope of this specification.
   Such a mechanism might be based on, for instance, receiving the SIP
   request on an authenticated Virtual Private Network (VPN), on a
   specific IP address, or on a specific network access.

3.  Conventions

   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 BCP 14, RFC 2119
   [RFC2119].











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4.  Definitions

   SIP entity: A SIP User Agent (UA), or SIP proxy, as defined in RFC
   3261.

   Adjacent upstream SIP network: The adjacent SIP network in the
   direction from which a SIP request is received.

   Network entry point: A SIP entity on the border of the network, which
   receives SIP requests from adjacent upstream networks.

   Inter Operator Identifier (IOI): A globally unique identifier to
   correlate billing information generated within the IP Multimedia
   Subsystem (IMS).

   JWS: A JSON Web Signature, as defined in [RFC7515].

5.  Via 'received-realm' Header Field Parameter

5.1.  General

   The Via 'received-realm' header field parameter value is represented
   as a combination of an operator identifier whose value represents the
   adjacent network and a serialized JSON Web Signature (JWS) [RFC7515].
   The JWS Payload consists of the operator identifier and other SIP
   information element values.

   The procedures for encoding the JWS and calculating the signature are
   defined in [RFC7515].  As the JWS Payload information is found in
   other SIP information elements, the JWS Payload is detached from the
   serialized JWS conveyed in the header field parameter, as described
   in Appendix F of [RFC7515].  The operator identifier and the
   serialized JWS are separated using a colon character.

5.2.  Operator Identifier

   The operator identifier is a token value that represents the adjacent
   operator.  The scope of the value is only within the network that
   inserts the value.

   The operator identifier value is case insensitive.










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5.3.  JWS Header

   The following header parameters MUST be included in the JWS.

   o  The "typ" parameter MUST have a "JWT" value.

   o  The "alg" parameter MUST have the value of the algorithm used to
      calculate the JWS.

   NOTE: Operators need to agree on the set of supported algorithms for
   calculating the JWT signature.

   NOTE: The "alg" parameter values for specific algorithms are listed
   in the IANA JSON Web Signature and Encryption Algorithms sub-registry
   of the JSON Object Signing and Encryption (JOSE) registry.  Operators
   need to use algorithms for which an associated "alg" parameter value
   has been registered.  The procedures for defining new values are
   defined in [RFC7518].

   Example:

   {
           "typ":"JWT",
           "alg":"HS256"
   }

5.4.  JWS Payload

   The following claims MUST be included in the JWS Payload:

   o  The "sip_from_tag" claim has the value of the From 'tag' header
      field parameter of the SIP message.

   o  The "sip_date" claim has the value of the Date header field in the
      SIP message, encoded in JSON NumericDate format [RFC7519].

   o  The "sip_callid" claim has the value of the Call-ID header field
      in the SIP message.

   o  The "sip_cseq_num" claim has the numeric value of the CSeq header
      field in the SIP message.

   o  The "sip_via_branch" claim has the value of the Via branch header
      field parameter of the Via header field, in the SIP message, to
      which the 'received-realm' header field parameter is attached.






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   o  The "sip_via_opid" claim has the value of the operator identifier
      part of the Via 'received-realm' header field parameter of the Via
      header field, in the SIP message, to which the 'received-realm'
      header field parameter is attached.

   Example:

   {
           "sip_from_tag":"1928301774",
           "sip_date":1472815523,
           "sip_callid":"a84b4c76e66710@pc33.atlanta.com",
           "sip_cseq_num":"314159",
           "sip_via_branch":"z9hG4bK776asdhds",
           "sip_via_opid":"myoperator"
   }

5.5.  JWS Serialization

   As the JWS Payload is not carried in the 'received-realm' parameter,
   in order to make sure that the sender and the receiver construct the
   JWS Payload object in the same way, the JSON representation of the
   JWS Payload object MUST be computed as follows:

   o  All claims MUST be encoded using lowercase characters.

   o  The claims MUST be in the same order as listed in Section 5.4.

   o  All claims except "sip_date" MUST be encoded as StringOrURI JSON
      string value [RFC7519].

   o  The "sip_date" claim MUST be encoded as a JSON NumericDate value
      [RFC7519].

   o  The JWS Payload MUST follow the rules for the construction of the
      thumbprint of a JSON Web Key (JWK) as defined in Section 3, Step 1
      only, of [RFC7638].

   Example:

   {"sip_from_tag":"1928301774","sip_date":1472815523,
   "sip_callid":"a84b4c76e66710@pc33.atlanta.com",
   "sip_cseq_num":"314159","sip_via_branch":"z9hG4bK776asdhds",
   "sip_via_opid":"myoperator"}

   NOTE: Line breaks are for display purposes only.






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5.6.  Syntax

5.6.1.  General

   This section describes the syntax extensions to the ABNF syntax
   defined in [RFC3261] by defining a new Via header field parameter,
   'received-realm'.  The ABNF defined in this specification is
   conformant to RFC 5234 [RFC5234].  "EQUAL", "LDQUOT", "RDQUOT", and
   "ALPHA" are defined in [RFC3261].  "DIGIT" is defined in [RFC5234].

5.6.2.  ABNF

   via-params     =/ received-realm
   received-realm = "received-realm" EQUAL LDQUOT op-id COLON jws RDQUOT
   op-id          = token
   jws            = header ".." signature
   header         = 1*base64-char
   signature      = 1*base64-char
   base64-char    = ALPHA / DIGIT / "/" / "+"

   EQUAL, COLON, token, LDQUOT, RDQUOT, ALPHA, and DIGIT are as defined
   in [RFC3261].

   NOTE: The two adjacent dots in the 'jws' part are due to the detached
   payload being replaced by an empty string [RFC7515].

5.7.  Example: SIP Via Header Field

   Via: SIP/2.0/UDP pc33.example.com;branch=z9hG4bK776;
   received-realm="myoperator:eyJ0eXAiOiJKV1QiLA0KICJhbGciOiJIUzI1N..
   dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"

   NOTE: Line breaks are for display purposes only.

6.  User Agent and Proxy Behavior

6.1.  General

   This section describes how a SIP entity, acting as an entry point to
   a network, uses the 'received-realm' Via header field parameter.

6.2.  Behavior of a SIP Entity Acting as a Network Entry Point

   When a SIP entity acting as a network entry point forwards a SIP
   request or initiates a SIP request on its own (e.g., a Public
   Switched Telephone Network (PSTN) gateway), the SIP entity adds a Via
   header field to the SIP request, according to the procedures in RFC
   3261 [RFC3261].  In addition, if the SIP entity is able to assert the



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   adjacent upstream network and if the SIP entity is aware of a network
   realm value defined for that network, the SIP entity can add a
   'received-realm' Via header field parameter conveying the network
   realm value as the operator identifier (Section 5.2) part of the
   header field parameter, to the Via header field added to the SIP
   request.

   In addition, the SIP entity MUST also calculate a JWS (Section 5.4)
   and add the calculated JWS Header and JWS Signature as the 'jws' part
   of the Via header field parameter.

6.3.  Behavior of a SIP Entity Consuming the 'received-realm' Value

   When a SIP entity receives a Via 'received-realm' header field
   parameter and intends to perform actions based on the header field
   parameter value, it MUST first recalculate the JWS and check whether
   the result matches the JWS received.  If there is not a match, the
   SIP entity MUST discard the received 'received-realm' header field
   parameter.  The SIP entity MAY also take additional actions (e.g.,
   rejecting the SIP request) based on local policy.

7.  Example: SIP INVITE Request and Response

   This section shows an example of a SIP INVITE request and the
   associated response, which contains a Via header field (inserted into
   the request and removed from the response by the T_EP SIP proxy) with
   a 'received-realm' header field parameter.

   Operator 1    T_EP                                 T_AS

   - INVITE ------>
     Via: SIP/2.0/UDP IP_UA
                 -- INVITE ---------------------------->
                    Via: SIP/2.0/UDP IP_TEP;branch=z9hG4bK776;
                     received-realm="myoperator:eyJ0eXAiOiJKV1QiLA0KICJh
                     bGciOiJIUzI1N..dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW
                     1gFWFOEjXk"
                    Via: SIP/2.0/UDP IP_UA; received=IP_UA

                 <- 200 OK ----------------------------
                    Via: SIP/2.0/UDP IP_TEP;branch=z9hG4bK776;
                     received-realm="myoperator:eyJ0eXAiOiJKV1QiLA0KICJh
                     bGciOiJIUzI1N..dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW
                     1gFWFOEjXk"
                    Via: SIP/2.0/UDP IP_UA; received=IP_UA

   <- 200 OK------
      Via: SIP/2.0/UDP IP_UA; received=IP_UA



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8.  IANA Considerations

8.1.  'received-realm' Via Header Field Parameter

   This specification defines a new Via header field parameter called
   'received-realm' in the "Header Field Parameters and Parameter
   Values" sub-registry created by [RFC3968].  The syntax is defined in
   Section 5.6.  The required information is:

                                                  Predefined
   Header Field            Parameter Name         Values      Reference
   ----------------------  ---------------------  ----------  ---------
   Via                     received-realm         No          RFC 8055

8.2.  JSON Web Token Claims Registration

   This specification defines new JSON Web Token claims in the "JSON Web
   Token Claims" sub-registry created by [RFC7519].

      Claim Name: sip_from_tag
      Claim Description: SIP From tag header field parameter value
      Change Controller: IESG
      Reference: RFC 8055, RFC 3261

      Claim Name: sip_date
      Claim Description: SIP Date header field value
      Change Controller: IESG
      Reference: RFC 8055, RFC 3261

      Claim Name: sip_callid
      Claim Description: SIP Call-Id header field value
      Change Controller: IESG
      Reference: RFC 8055, RFC 3261

      Claim Name: sip_cseq_num
      Claim Description: SIP CSeq numeric header field parameter value
      Change Controller: IESG
      Reference: RFC 8055, RFC 3261

      Claim Name: sip_via_branch
      Claim Description: SIP Via branch header field parameter value
      Change Controller: IESG
      Reference: RFC 8055, RFC 3261








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9.  Security Considerations

   As the 'received-realm' Via header field parameter can be used to
   trigger applications, it is important to ensure that the parameter
   has not been added to the SIP message by an unauthorized SIP entity.

   The 'received-realm' Via header field parameter is inserted, signed,
   verified, and consumed within an operator network.  The operator MUST
   discard parameters received from another network, and the parameter
   MUST only be inserted by SIP entities that are able to verify from
   which adjacent upstream network a SIP request is received.

   The operator also needs to take great care in ensuring that the key
   used to calculate the JWS Signature value is only known by the
   network entities signing and adding the JWS Signature to the
   'received-realm' Via header field parameter of a SIP message and to
   network entities verifying and consuming the parameter value.

   The operator MUST use a key management policy that protects against
   unauthorized access to the stored keys within nodes where the keys
   associated with the JWS Signature are stored and that protects
   against cryptoanalysis attacks using captured data sent on the wire.

   A SIP entity MUST NOT use the adjacent network information if there
   is a mismatch between the JWS Signature received in the SIP header
   field and the JWS Signature calculated by the receiving entity.

   Generic security considerations for JWS are defined in [RFC7515].

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.



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   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <http://www.rfc-editor.org/info/rfc7519>.

   [RFC7638]  Jones, M. and N. Sakimura, "JSON Web Key (JWK)
              Thumbprint", RFC 7638, DOI 10.17487/RFC7638, September
              2015, <http://www.rfc-editor.org/info/rfc7638>.

10.2.  Informative References

   [RFC3968]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Header Field Parameter Registry for the Session
              Initiation Protocol (SIP)", BCP 98, RFC 3968,
              DOI 10.17487/RFC3968, December 2004,
              <http://www.rfc-editor.org/info/rfc3968>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <http://www.rfc-editor.org/info/rfc7518>.

   [TS.3GPP.23.228]
              3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP
              TS 23.228 14.1.0, September 2016,
              <http://www.3gpp.org/ftp/Specs/html-info/23228.htm>.

Acknowledgements

   Thanks to Adam Roach and Richard Barnes for providing comments and
   feedback on the document.  Francis Dupoint performed the Gen-ART
   review.

















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Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Yi Jiang
   China Mobile
   No.32 Xuanwumen West Street
   Beijing  Xicheng District 100053
   China

   Email: jiangyi@chinamobile.com

































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