DISPATCH Working Group M. Patel
Internet-Draft Nortel
Intended status: Standards Track R. Jesske
Expires: April 29, 2010 Deutsche Telekom
M. Dolly
AT&T
October 26, 2009
Uniform Resource Identifier (URI) Parameters for indicating the Calling
Party's Catagory and Originating Line Identity
draft-patel-dispatch-cpc-oli-parameter-01.txt
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Abstract
This document defines two new URI parameters to describe the calling
party's category and toll class of service originating line
information which are parameters also used in SS7 ISUP and other
telephony signalling protocols. The intended use of these URI
parameters is for the tel URI and SIP URI address schemes.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Parameter Definitions . . . . . . . . . . . . . . . . . . . . . 3
4. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
SS7 ISUP[ITU-ISUP] 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. One
example of such information is the call may originate from a
payphone; such information can be used by the network to handle the
call in a specific way. When telephone numbers are contained in
URIs, such as the tel URI [RFC3966] or equivalent SIP URI, 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. This
document proposes a method of carrying CPC data in SIP messages.
In some networks (including North America), the Originating Line
Information (OLI) parameter defined in ANSI ISUP [ANSI-ISUP] is used
to carry information related to the calling party and the class of
service for a call. Legacy multifrequency (MF) signalling networks
carry this information in the ANI II Digits
<http://www.nanpa.com/number_resource_info/ani_ii_assignments.html>.
The call can originate from a multitude of devices or stations. For
example, a coin operated phone or a phone located inside a prison can
be used to originate a call. In such cases, it can be desirable to
handle calls originating from such stations in a specific manner, or
to restrict certain services to the calling party. This document
proposes a method of carrying OLI data in SIP messages.
Other use cases may exist where is it useful to transfer information
about the endpoint even when interworking with the PSTN does not
occur. In such cases, the calling party's catagory or originating
line identity can be added when the calling party is identified by
either a tel URI or a SIP URI.
2. Terminology
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 RFC 2119 [RFC2119].
3. Parameter Definitions
The Calling Party's Category (CPC) and the Originating Line
Information (OLI) are represented as URI parameters for the tel URI
scheme and the SIP URI representation of telephone numbers. The ABNF
[RFC5234] syntax is as follows. The 'par' production is defined in
RFC 3966 [RFC3966]. The "/=" syntax indicates an extension of the
production on the left-hand side:
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par /= cpc / oli
cpc = cpc-tag "=" cpc-value
oli = oli-tag "=" oli-value
cpc-tag = "cpc"
oli-tag = "isup-oli"
cpc-value = 8*8BIT / "ordinary" / "test" / "operator" / "payphone"
/ "unknown" / genvalue
oli-value = 8*8BIT / "hotel" / "prison" / "cellular" / "cellular-
roaming" / genvalue
genvalue = 1*(alphanum / "-" / "." )
The semantics of these CPC and OLI 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.
unknown: The CPC could not be ascertained.
hotel: The calling station is in a hotel or motel.
prison: The calling station is in a prison.
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.
The 8 bit values are assigned by ITU-T/ANSI [ITU-ISUP][ANSI-ISUP] and
for the OLI, are binary equivalaents of the decimal codes used in the
II digits of the ANI sequence for in-band signalling system
<http://www.nanpa.com/number_resource_info/ani_ii_assignments.html>.
The "cpc" and "isup-oli" URI parameters are optional parameters. At
the most, one "cpc" and/or one "isup-oli" parameter may be included
in a URI of the calling party. In SIP the calling party is generally
identified by the identity given in the From header field, or
alternatively, in the P-Asserted-Identity header field if this is
used. Usage is discussed in the following sections of this document.
An example of the syntax of the "cpc" parameter is given below:
From: <tel:+17005554141;cpc=payphone>;tag=1928301774
Alternatively, the tel URI may be included in the P-Asserted-Identity
header field [RFC3325]:
P-Asserted-Identity: <tel: +17005554141;cpc=payphone>
The "isup-oli" URI parameter usage is given in the following example,
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which uses the SIP URI representation of telephone numbers:
From: <sip: +1700554141@example.com;isup-oli=00011101>;tag=1928301774
The "isup-oli" parameter with value 00011101 indicates that the
device that the call is initiated from is located within a prison.
An "isup-oli" with value "prison" is equally valid.
For the case where a call is originared by a SIP UA where the caller
is identified by a SIP URI that does not contain a telephone number,
"isup-oli" URI parameter usage is given in the following example,
which uses the SIP URI representation of telephone numbers:
P-Asserted-Identity: <sip: alice@example.com;isup-oli=cellular>
The "isup-oli" parameter with value "cellular" indicates that the
device that the call is initiated from is a mobile device operating
in its home cellular network.
4. Usage
The CPC and OLI are generally useful only when describing the
originator of a telephone call or the station from where a telephone
call is originated. 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 P-Asserted-Identity header field or the
From header field of a SIP message). Note that many Calling Party's
Category values from the PSTN are 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 "cpc" and "isup-oli" URI parameters will be
used primarily by gateways that interwork ISUP or ANI II networks
with SIP networks. However, scenarios where interworking with the
PSTN does not occur are not precluded. Various SIP network
intermediaries might consult the CPC or OLI information 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 or OLI data is offered in this document,
creating such a mapping would be trivial.
While the CPC and OLI could be conveyed using the ISUP tunneling
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mechanism described in RFC 3372 [RFC3372], this technique is widely
regarded by the implementation community as overkill for the problem
of conveying CPC and OLI information. For example, the "cpc" and
"isup-oli" parameters provides a convenient way for SIP
intermediaries to make routing decisions based on the CPC and OLI
information without having to implement an ISUP parser. The "cpc"
and "isup-oli" URI parameters provide a simple, convenient form of
CPC and OLI interoperability of SIP with ISUP and ANI II, which is
otherwise poorly addressed in RFC 3372[RFC3372]. Indeed when a SIP
intermediary makes routing decisions for a call where both the
originating and the terminating gateways natively use ANI II, the
ISUP tunneling approach is especially unattractive, requiring each of
the three devices to perform a translation into an otherwise unneeded
PSTN protocol.
If the "cpc" URI parameter is not present, consumers of the CPC
information should treat the URI as if it specified a CPC of
"ordinary". If the "isup-oli" URI parameter is not present,
consumers of the OLI information should treat the URI as if no OLI
information is provided. If a SIP intermediary does not support the
"cpc" or "isup-oli" URI parameters and receives a SIP message where
the calling party URI in the From or P-Asserted-header fields
includes a "cpc" or "isup-oli" URI parameter, then the SIP
intermediary silently ignores the URI parameter in accordance with
RFC 3261[RFC3261].
At most, one instance of the "cpc" parameter and/or one instance of
the "isup-oli" parameter can be associated with a particular URI
within a SIP request. It is recommended that the "cpc" and "oli" URI
parameters are associated with URIs included in the P-Asserted-
Identity header field. Where the P-Asserted-Identity header field is
not supported or included, another header field used to carry a URI
to characterize the originator of a call may be used. One example of
such a header field is the From header field. The following section
discusses further the motivation behind this recommendation.
5. Security Considerations
There are three potential risks specific to the information provided
by the Calling Party's Category or Originating Line Identity:
- leakage of potentially private information;
- the threat of tampering with the CPC or OLI to add false CPC or OLI
values; and
- the threat of tampering with the CPC or OLI to remove actual CPC or
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OLI values.
The information contained in the "cpc" or "isup-oli" 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). However, the calling party's category is
often discoverable or easily guessable from the calling party's phone
number. For that reason it is unlikely that this information is
significantly more privacy sensitive than the telephone number
itself. The same techniques used to provide complete or partial
telephone number privacy in SIP are appropriate to apply to the "cpc"
and "isup-oli" parameters as well. For more information about
privacy issues in SIP see RFC 3323[RFC3323]. The mechanism described
in RFC 3325 [RFC3325] may also be relevant for maintaining partial
privacy or the CPC or OLI within a trusted administrative domain or
federation of domains as described in RFC 3324[RFC3324].
Making a call with a falsified CPC or OLI (i.e. "operator") could
allow the caller to gain access to resources or information not
otherwise available. Likewise removing an "undesirable" CPC or OLI
value (ex: prison or hotel) could allow the caller to bypass various
restrictions in the telephone network. For that reason, agents which
expect CPC or OLI values SHOULD take care to insure the integrity and
authenticity of the "cpc" or "isup-oli" URI parameter. The
RECOMMENDED mechanism to protect the entire calling party address
along with the "cpc" or "isup-oli" URI parameter is the SIP Identity
mechanism [RFC4474] . Alternatively, agents within an administrative
domain or federation of domains MAY use the mechanism described in
RFC 3325[RFC3325] to place the "cpc" or "isup-oli" URI parameter in a
P-Asserted-Identity header field. When such mechanism is used, the
"cpc" or "isup-oli" URI parameter is added by a network entity or SIP
intermediary if knowledge of the calling party's category or
originating line identity (class of service) is known.
When the end-device, acting as a UAC originating a call, is not
trusted, the value of a "cpc" or "isup-oli" URI parameter included by
the UAC may be removed or modified by a trusted network entity. If a
request containing CPC or OLI is sent towards a non-trusted entity,
this information should be removed.
The SIP Identity mechanism provides a signature over the URI in the
From header field of a SIP request. It can sign a SIP URI or a tel
URI alone or a tel URI embedded in a SIP or SIPS URI, but it provides
stronger protection against tampering when the tel URI is embedded in
a SIP or SIPS URI. Because there is no direct correlation between a
tel URI and an Internet domain, the receiver can use a list of
domains from which it will trust CPC or OLI information, or a list of
root certificates which are associated with trusting CPC or OLI
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information.
Otherwise, this mechanism adds no new security considerations to
those discussed in RFC 3261[RFC3261].
6. IANA Considerations
This document extends the registry of URI parameters for the Tel URI
and SIP URI as defined RFC 3969[RFC3969] and RFC 5341[RFC5341]. Two
new URI parameters for the Tel URI and SIP URI schemes are defined in
this document as follows:
Parameter Name: cpc, isup-oli
Predefined Values: Yes
Reference: This document
7. Acknowledgements
The original version of this document was written by Jon Peterson as
a result of spliiting the appendix from draft-ietf-sip-privacy-04 and
subsequently authored by Rohan Mahy.
This document is based on draft-mahy-iptel-cpc-06.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[RFC5341] Jennings, C. and V. Gurbani, "The Internet Assigned Number
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Authority (IANA) tel Uniform Resource Identifier (URI)
Parameter Registry", RFC 5341, September 2008.
[RFC3261] 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.
[ITU-ISUP]
International Telecommunications Union, "Recommendation
Q.763: Signalling System No. 7: ISDN user part formats and
codes", December 1999, <http://www.itu.int>.
8.2. Informative References
[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[ANSI-ISUP]
American National Standards Institute, "ANSI T1.113-2000,
Signaling System No. 7, ISDN User Part", 2000,
<http://www.ansi.org>.
[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
Extensions to the Session Initiation Protocol (SIP) for
Asserted Identity within Trusted Networks", RFC 3325,
November 2002.
[RFC3372] Vemuri, A. and J. Peterson, "Session Initiation Protocol
for Telephones (SIP-T): Context and Architectures",
BCP 63, RFC 3372, September 2002.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
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Authors' Addresses
Milan Patel
Nortel
Maidenhead Office Park, Westacott Way
Maidenhead, Berkshire, UK
Email: milanpa@nortel.com
Roland Jesske
Deutsche Telekom
Heinrich-Hertz-Strasse 3-7
Darmstadt, 64307, Germany
Email: r.jesske@telekom.de
Martin Dolly
AT&T
200 Laurel Ave
Middletown, NJ,, US
Email: mdolly@att.com
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