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
draft-mahy-iptel-cpc-00
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
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
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.
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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
features.
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
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
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
trivial.
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
[6].
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
2000.
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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.
URIs
[7] <http://www.nanpa.com/number_resource_info/
ani_ii_assignments.html>
Author's Address
Rohan Mahy (editor)
Cisco Systems, Inc.
101 Cooper St
Santa Cruz, CA 95060
USA
EMail: rohan@cisco.com
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