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Versions: 00 01 02 03 04 05 06                                          
IPTEL WG                                                    R. Mahy, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Expires: December 21, 2003                                 June 22, 2003

             The Calling Party's Category tel URI Parameter

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 21, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.


   This document specifies a new parameter for the tel URI that
   represents the Calling Party's Category, a parameter used in SS7 ISUP

1. Introduction

   SS7 ISUP [3] defines a Calling Party's Category (CPC) parameter that
   characterizes the station used to originate a call and carries other
   important state that can describe the originating party. When
   telephone numbers are contained in URIs, such as the tel URI [1], it
   may be desirable to communicate any CPC associated with that
   telephone number or, in the context of a call, the party calling from

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   Note that in some networks (including North America), the Originating
   Line Information (OLI) parameter is used to carry this information in
   ISUP rather than the CPC parameter. Legacy multifrequency (MF)
   signaling networks carry this information in the ANI II Digits [7].
   The tel URI parameter specified in this document is designed to carry
   data from these sources as well.

2. Parameter Definition

   The Calling Party's Category is represented as a tel URI parameter.
   The ABNF [2] syntax is as follows:

      cpc                   = cpc-tag "=" cpc-value
      cpc-tag               = "cpc"
      cpc-value             = string

   CPC values ("cpc-value" strings) must be registered with IANA. The
   following values are pre-registered by this document:

      ordinary: The caller has been identified, and has no special

      priority: This call has priority/emergency status.

      data: This call will contain voice-band data.

      test: This is a test call that has been originated as part of a
      maintenance procedure.

      operator: The call was generated by an operator position.

      payphone: The calling station is a payphone.

      prison: The calling station is in a prison.

      hotel: The calling station is in a hotel or motel.  (This value is
      currently used in ANI II.)

      unknown: The CPC could not be ascertained.

   In addition to the list above, the authors may consider inclusion of
   the following additional values if a stable reference which describes
   their use can be provided.

      hospital: The calling station is in a medical facility.

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      police: The calling station is associated with a branch of law

      cellular: The calling station is a radio-telephone operating in
      its home network.

      cellular-roaming: The calling station is a radio-telephone roaming
      in another network

   An example of the syntax of the CPC parameter (in a small fragment of
   a SIP [5] message) is given below:

           INVITE sip:bob@biloxi.example.com SIP/2.0
           To: "Bob" <sip:bob@biloxi.example.com>
           From: <tel:+17005554141;cpc=payphone>;tag=1928301774

3. Usage

   The CPC is generally useful only when describing the originator of a
   telephone call. Therefore, when this parameter is used in an
   application such as SIP, it is recommended that the parameter be
   applied to URIs that characterize the originator of a call (such as a
   SIP URI or tel URI in the From header field of a SIP message). Note
   that many Calling Party Category values from the PSTN were
   intentionally excluded from the cpc parameter as they are either
   meaningless outside of the PSTN or can be represented using another
   existing concept. For example, the language of an operator can be
   expressed more richly using the Accept-Language header in SIP than in
   the cpc parameter.

   It is anticipated that this URI will be used primarily by gateways
   that interwork ISUP networks with SIP networks. Various SIP network
   intermediaries might consult the CPC as they make routing decisions,
   although no specific behavior is prescribed in this document. While
   no specific mapping of the various ISUP parameters that contain CPC
   data is offered in this document, creating such a mapping would be

   If the CPC parameter is not present, consumers of the CPC should
   treat the URI as if it specified a CPC of "unknown".

   Generally, only one instance of the CPC will be associated with a
   particular URI.

4. Security Considerations

   The information contained in the CPC parameter may be of a private

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   nature, and it may not be appropriate for this value to be revealed
   to the destination user (typically it would not be so revealed in the
   PSTN).  For more information about Privacy issues in SIP see RFC3323

   Otherwise, this mechanism adds no new security considerations to
   those discussed in [1].

5. IANA Considerations

   This document requests the creation of an IANA registry for Calling
   Party's Category values. The values of the CPC parameter in use in
   ISUP are unfortunately quite specific to national networks, and thus
   it is very difficult to uncover all the usages that may be in place
   in various networks. Note that in North American networks, the
   Originating Line Information parameter contains information common
   found in the Calling Party's Category elsewhere; it is therefore
   legitimate to register values associated with the Originating Line
   Information in this registry.

   In order to file a registration, interested parties must contact IANA
   and supply them with both a new "cpc-value" and a short reason phrase
   describing the usage of the new CPC. Some values are given in Section
   2; we ask that these values be pre-registered upon publication of
   this document as an RFC. It is not expected that this registry will
   require any expert supervision.

6. Contributors

   The original version of this document was written by Jon Peterson.

Normative References

   [1]  Schulzrinne, H. and A. Vaha-Sipila, "The tel URI for Telephone
        Calls", draft-antti-2806bis-08.txt (work in progress), Feb 2003.

   [2]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [3]  International Telecommunications Union, "Recommendation Q.763:
        Signalling System No. 7: ISDN user part formats and codes",
        September 1997, <http://www.itu.int>.

Informational References

   [4]  Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April

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   [5]  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.

   [6]  Peterson, J., "A Privacy Mechanism for the Session Initiation
        Protocol (SIP)", RFC 3323, November 2002.


   [7]  <http://www.nanpa.com/number_resource_info/

Author's Address

   Rohan Mahy (editor)
   Cisco Systems, Inc.
   101 Cooper St
   Santa Cruz, CA  95060

   EMail: rohan@cisco.com

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   Funding for the RFC Editor function is currently provided by the
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