IPTEL WG R. Mahy, Ed.
Internet-Draft Plantronics
Expires: February 2, 2007 Aug 2006
The Calling Party's Category tel URI Parameter
draft-mahy-iptel-cpc-04.txt
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Copyright (C) The Internet Society (2006).
Abstract
This document specifies a new parameter for the tel URI that
represents the Calling Party's Category, a parameter used in SS7 ISUP
signaling.
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
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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
it.
Note that in some networks (including North America), the Originating
Line Information (OLI) parameter is used to carry this information in
ANSI ISUP [6] 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 = "ordinary" / "prison" / "police" / "test"
"operator" / "payphone" / "unknown" /
"hospital" / "cellular" / "cellular-roaming" /
genvalue
genvalue = 1*(alphanum / "-" / "." )
The semantics of these Calling Party's Category values are described
below:
ordinary: The caller has been identified, and has no special
features.
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.
hospital: The calling station is in a medical facility.
police: The calling station is associated with a branch of law
enforcement.
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
unknown: The CPC could not be ascertained.
An example of the syntax of the CPC parameter (in a small fragment of
a SIP [4] message) is given below:
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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's 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. Similarly the priority of a call is a
characteristic of the call and not the calling party.
It is anticipated that this URI parameter 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 trivial.
If the CPC parameter is not present, consumers of the CPC should
treat the URI as if it specified a CPC of "ordinary".
At most, one instance of the CPC can be associated with a particular
URI.
4. Security Considerations
The information contained in the CPC parameter may be of a private
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
[5].
Otherwise, this mechanism adds no new security considerations to
those discussed in [1].
5. IANA Considerations
This document requires no action by IANA.
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6. Contributors and Acknowledgments
The original version of this document was written by Jon Peterson.
Thanks to Takuya Sawada for a detailed review.
7. References
7.1 Normative References
[1] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
[2] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
[3] International Telecommunications Union, "Recommendation Q.763:
Signalling System No. 7: ISDN user part formats and codes",
December 1999, <http://www.itu.int>.
7.2 Informational References
[4] 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.
[5] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November 2002.
[6] American National Standards Institute, "ANSI T1.113-2000,
Signaling System No. 7, ISDN User Part", 2000,
<http://www.ansi.org>.
URIs
[7] <http://www.nanpa.com/number_resource_info/
ani_ii_assignments.html>
Author's Address
Rohan Mahy (editor)
Plantronics
Email: rohan@ekabal.com
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