IPTEL Working Group James Yu
Internet Draft NeuStar, Inc.
Expires: September 18, 2004 March 18, 2004
New Parameters for the "tel" URI to Support Number Portability
<draft-ietf-iptel-tel-np-00.txt>
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
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2004). All rights reserved.
ABSTRACT
This document defines several new parameters in the "tel" Uniform
Resource Locator (URL) to support number portability (NP) for
geographical telephone numbers and freephone numbers. The rn
parameter carries the routing number for a ported geographical
telephone number. The presence of the npdi parameter indicates
that NP database dip has been performed on a geographical telephone
number. The cic parameter identifies the freephone service
provider for a freephone number.
James Yu Expired September 18, 2004 [Page 1]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
1. Introduction
Number portability (NP)[1] allows the telephony subscribers to keep
their telephone numbers when they change service provider (service
provider portability), move to a new location (location
portability), or change the subscribed services (service
portability). The NP implementations in many countries presently
support service provider portability for geographic telephone
numbers and freephone numbers (e.g., 800 numbers in the North
America). It has been identified that NP has impacts on several
works-in-progress at the IETF. One impact is the need to carry the
NP-related information in the tel URI[2] for protocols such as
the Session Initiation Protocol (SIP)[3] and H.323[4] after the NP
database dip has been performed. Another impact is for a Voice
over IP (VoIP) server to use the NP-related information in a
received tel URI to determine routing.
A routing number is associated with a geographical telephone number
that has been ported out from a donor carrier to another carrier.
A donor carrier is the initial carrier where a geographical
telephone number was located before ever being ported. A non-
ported geographical telephone number does not have any routing
number associated with it because the first N digits of the
geographical telephone number can be used for routing. A routing
number can also be used to indicate the switch or network node that
originates a call or service similar to the Jurisdiction
Information Parameter in Signaling System Number 7 (SS7) Integrated
Services Digital Network User Part (ISUP).
The NP database dip indicator is used to inform the downstream
servers or switches during call set up that there is no need to
perform the NP database dip for a geographical telephone number
again.
A Carrier Identification Code (CIC) identifies the current
freephone service provider for a freephone number. This parameter
can be used to carry the pre-subscribed or dialed long distance
carrier information; however, that is outside the scope of this
document.
This document defines several new parameters in the "tel" Uniform
Resource Locator (URL)[2] to support NP. Section 2 lists the
abbreviations used in this document. Section 3 provides the syntax
definition. Section 4 describes the rules for a network node that
deals with some or all of the defined parameters in a tel URI.
Section 5 provides a few examples to show how those defined
parameters are added to a tel URI after retrieving NP-related
information from the NP database.
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 RFC2119[5].
James Yu Expired on September 18, 2004 [Page 2]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
2. Abbreviations
ANSI American National Standards Institute
CIC Carrier Identification Code (also cic)
CIP Carrier Identification Parameter
FCI Forward Call Indicator
GAP Generic Address Parameter
IC Identification Code
IP Internet Protocol
IETF Internet Engineering Task Force
IP Internet Protocol
ISUP Integrated Services Digital Network User Part
JIP Jurisdiction Information Parameter
NP Number Portability
NPDB Number Portability Database
npdi NP database dip indicator
rn Routing Number
PSTN Public Switched Telephone Network
PNTI Ported Number Translation Indicator
SIP Session Initiation Protocol
SS7 Signaling System Number 7
URL Uniform Resource Locator
VoIP Voice over IP
3. Syntax Definition
The parameters defined for the tel URI to support NP has the
following syntax:
rn = *1(routing-number)
npdi = *1(npdb-dip-indicator)
cic = *1(carrier-id-code)
routing-number = "rn=" global-rn / local-rn
global-rn = "+" 1*phonedigit-hex
local-rn = 1*phonedigit-hex rn-context
rn-context = ;rn-context= rn-descriptor
rn-descriptor = domainname / global-hex-digits
global-hex-digits = "+" 1*3(phonedigit) *phonedigit-hex
npdi-dip-indicator = "npdi"
carrier-id-code = "cic=" global-cic / local-cic
global-cic = "+" 1*phonedigit-hex
local-cic = 1*phonedigit-hex cic-context
cic-context = ;cic-context= rn-descriptor
The routing-number, npdb-dip-indicator or carrier-id-code
each can appear in the tel URI at most once.
For a global-rn, the routing number information after + MUST
begin with a valid E.164[6] country code.
James Yu Expired on September 18, 2004 [Page 3]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
For a local-rn, the routing number in the rn parameter MUST be
meaningful in terms of rn-context. For example, if a national
routing number is in the rn parameter, the rn-context MUST
contain a valid E.164 country code after + if it is in the
global-hex-digits format.
For a global-cic, the CIC information after + MUST begin with a
valid E.164 country code.
For a local-cic, the CIC value in the cic parameter MUST be
meaningful in terms of cic-context. For example, if the national
CIC value is in the cic parameter, the cic-context SHALL
contain a valid E.164 country code after +if it is in the
global-hex-digits format.
4. Normative Rules
This section discusses how a network node handles a received tel
URI that contains one or more of the defined parameters or has
accessed an NP database for a freephone number or geographical
telephone number and needs to adds some of the defined parameters
to a tel URI.
In countries where there is no freephone number portability or
geographical telephone number portability, the call routing can be
based on the leading digits of the freephone number or geographical
telephone number. This document does not describe those scenarios.
Please note that two accesses to the freephone databases are
normally done for routing a call to a freephone number. The first
one is done by the originating network that queries a freephone
database for the CIC information so that the call can be routed to
the serving freephone service provider of the called freephone
number. When the call reaches the serving freephone provider, the
second database access is performed to map the freephone number to
a geographical telephone number and/or internal routing
information. This document does not address the case where
internal routing information is returned.
The first freephone database contains the CIC information for all
the active freephone numbers while the second one usually contains
mapping information only for those freephone numbers served by a
freephone service provider. Because the originating carrier may
provide freephone service, its freephone database would contain the
CIC information for all the active freephone numbers plus the
mapping information for those freephone numbers it serves. This
document refers the two database accesses as the first freephone
database access and the second freephone database access.
James Yu Expired on September 18, 2004 [Page 4]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
4.1 Handling tel URI with Defined Parameter or Parameters
If the tel URI contains the npdi parameter, the network node
SHALL NOT retrieve the NP-related information for geographical
telephone numbers even if it is set to do so.
If the tel URI contains the cic parameter whose CIC value is
different from the one this network node is associated with, this
network node SHALL NOT retrieve the NP-related information for the
geographical telephone number or perform the first freephone
database access for the freephone number in the tel URI.
For the cic and rn parameters and either a freephone number or
geographical telephone number, the order of processing is to look
for the cic parameter first for call routing. If the CIC
information is not useful or the cic parameter does not exist,
then the next step is to look for the rn parameter. If the
information in the rn parameter is not useful or the rn
parameter does not exist, then the freephone number or geographical
telephone number is used.
When looking for the cic parameter and that parameter exists in
the tel URI:
- The network node SHALL ignore the cic parameter if it
identifies a carrier or service provider associated with that
node, or if that parameter contains a code for indicating that a
geographic number is supplied (e.g., +1-0110 means local,
translated geographical telephone number provided). The network
node SHALL remove the cic parameter and look for the rn
parameter for making the routing decision.
- Otherwise, the network node SHALL make the routing decision based
on the CIC. The network node SHALL NOT remove the cic
parameter unless it is handing over the call to the carrier or
service provider identified by the CIC and the local policies
require it to remove the cic parameter. How the call is
actually routed based on the CIC value in the cic parameter is
outside the scope of this document.
When looking for the rn parameter and that parameter exists in
the tel URI:
- The network node SHALL ignore the rn parameter if the routing
number points to this network node or a network this network node
is in (e.g., in some countries the routing number gets the call
to the serving carrier network where another NP database access
is required to locate the serving switch), this network node
SHALL remove the rn parameter and look for the freephone number
or geographical telephone number for making the routing decision.
- Otherwise, the network node SHALL make the routing decision based
on the routing number in the rn parameter. How the call is
James Yu Expired on September 18, 2004 [Page 5]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
actually routed based on the routing number in the rn parameter
is outside the scope of this document.
When the cic or rn parameter is not used for routing, the
network node uses the freephone number or geographical telephone
number for making routing decision. It may access the NP database
if it is set to do so or may route the call to a designated network
node that will access the NP database or may route the call based
on the local routing table. How the call is handled at this stage
is outside the scope of this document. See Section 4.2 for rules
in adding the defined parameter or parameters to the tel URI if
the network node is set to access the NP database.
4.2 Adding Defined Parameter or Parameters to the tel URI
There are two cases in terms of NP database access. One is for a
geographical telephone number and the other is for a freephone
number. They are discussed in Sections 4.2.1 and 4.2.2 for a tel
URI that is used for routing.
Section 4.2.3 discusses a special case where the rn parameter is
added to a tel URI that is associated with the first network node
that handles the call request from the caller. Section 4.3.4
discusses the addition of the defined parameter or parameters to
the tel URI due to protocol conversion.
4.2.1 Retrieving NP-related information for a geographical telephone
number
When a network node accesses an NP database for a geographical
telephone number:
- If the network node retrieves a routing number, it SHALL add the
rn parameter to the tel URI to carry the routing number
information in the global-rn or local-rn format and SHALL add
the npdi parameter.
- If the network node does not retrieve a routing number (e.g., for
a non-ported geographical telephone number), it SHALL add the
npdi parameter to the tel URI.
The network node SHALL follow the rules described in Section 4.1
for using the information in the tel URI to make the routing
decision.
4.2.2 Retrieving NP-related information for a freephone number
When a network node performs the first or second freephone database
access for a freephone number:
James Yu Expired on September 18, 2004 [Page 6]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
- If the network node retrieves a CIC that identifies a carrier or
service provider associated with that network node, or indicates
that a geographic number is supplied (e.g., +1-0110 means
local, translated geographical telephone number provided), it
would have retrieved a geographical telephone number. The
network node SHALL NOT add the cic parameter and SHALL replace
the freephone number in the tel URI with the retrieved
geographical telephone number in either the global-number or
local-number format.
Some freephone databases may not return the geographical
telephone number but internal routing information in a
proprietary format (e.g., switch ID and trunk group ID). That
case is outside the scope of this document.
- If the network node retrieves a CIC that belongs to another
freephone service provider, the network node SHALL add the cic
parameter to the tel URI that contains the CIC in the global-
cic or local-cic format.
The originating carrier may have business agreements with a
freephone service provider to return the geographical telephone
number in addition to the CIC. When a geographical telephone
number is returned, the network node SHALL replace the freephone
number in the tel URI with the returned geographical telephone
number in either the global-number or local-number format.
- If the network node retrieves a geographical telephone number
that is the typical case for the second freephone database
access, the network node SHALL replace the freephone number in
the tel URI with the retrieved geographical telephone number in
either the global-number or local-number format.
When a geographical telephone number is returned in the response,
it is possible that the NP-related information for that
geographical telephone number could also be returned. In that
case, the network node SHALL add the npdi parameter and SHALL add
the rn parameter to contain the routing number in either the
global-rn or local-rn format only when the routing number is
available.
The network node SHALL follow the rules described in Section 4.1
for using the information in the tel URI to make the routing
decision.
4.2.3 Adding location information about the caller
In SS7 ISUP, the JIP identifies the switch that originates the call
and the information in it may be used by the serving carrier to
determine the call charge to the caller or by the involved carriers
to determine the settlement amount between them.
James Yu Expired on September 18, 2004 [Page 7]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
A network node that is the first to handle the call request from
the caller MAY include the rn parameter to the tel URI
associated with the caller, if one exists.
4.2.4 Adding the defined parameter or parameters due to protocol
conversion
A Public Switched Telephone Network (PSTN) gateway needs to convert
between SS7 ISUP and the VoIP protocol such as SIP or H.323. This
type of network node SHALL add the corresponding information from
the ISUP to the defined parameters to the tel URI for routing and
the tel URI associated with the caller and vice versa. Since
ISUP support for NP depends on the supporting country, the
following discussion applies to a situation when a network node is
to map the NP information in the American National Standards
Institute (ANSI) ISUP to the NP-related parameters in the tel
URI.
For a ported geographical telephone number, the network node SHALL
convert the routing number in the ISUP Called Party Number
parameter to a routing number in either the global-rn or local-
rn format and carry it in the "rn" parameter for a tel URI that
is used for routing. The network node SHALL convert the phone
number that is marked as the "ported number" in the ISUP Generic
Address Parameter (GAP) to a phone number in either the global-
number or local-number format[2] and put it after "tel:" in the
tel URI that is used for routing.
For a non-ported geographical telephone number, the network node
SHALL convert the phone number in the ISUP Called Party Number
parameter to a phone number in either the global-number or
local-number format and put it after "tel:" in the tel URI that
is used for routing. No rn will appear in the tel URI.
The network node SHALL include the npdi parameter in the tel
URI that is used for routing when the Ported Number Translation
Indicator (PNTI) bit in the Forward Call Indicator (FCI) parameter
is set to "1."
The network node SHALL include the "cic" parameter in either the
global-cic or local-cic format in the tel URI that is used
for routing when the ISUP Carrier Identification Parameter (CIP) is
present.
The network node SHALL include the rn parameter in the tel URI
associated with the caller information when the ISUP JIP is
present.
Mapping NP-related parameters in a tel URI to the NP-related
information in the ISUP message depends on the national ISUP
implementation and is outside the scope of this document.
James Yu Expired on September 18, 2004 [Page 8]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
5. Examples
A. A tel URI, tel:+1-800-123-4567, contains a freephone number
+1-800-123-4567. Assume that this freephone number is served
by a freephone service provide with a CIC +1-6789. After
retrieving the NP-related information, the tel URI would be
set to
tel:+1-800-123-4567;cic=+1-6789
B. A tel URI, tel:+1-800-123-4567;cic=+1-6789, is handled by a
network node in the serving freephone service providers
network. Assume that the freephone number is mapped to a
geographical telephone number +1-202-533-1234. After
retrieving the NP-related information, the tel URI would be
set to
tel:+1-202-533-1234
C. A tel URI, tel:+1-202-533-1234, contains a geographical
telephone number +1-202-533-1234. Assume that this
geographical telephone number is ported and is associated with a
routing number 1-202-544-0000. After retrieving the NP-
related information, the tel URI would be set to
tel:+1-202-533-1234;rn=+1-202-544-0000;npdi
D. A tel URI, tel:+1-202-533-6789, contains a geographical
telephone number +1-202-533-6789. Assume that this
geographical telephone number is not ported. After accessing
the NP database, the tel URI would be set to
tel:+1-202-533-6789;npdi
6. Security Considerations
In addition to those security implications discussed in the revised
tel URI[2], there are new security implications associated with
the defined parameters.
If the value of the rn or cic in the tel URI is changed
illegally when the signaling message carrying the tel URI is en
route to the destination entity, the signaling message or call may
be routed to the wrong network or network node causing the call
setup to be rejected.
If the npdi is illegally inserted into the tel URI when the
signaling message carrying the tel URI is en route to the
destination entity, the call may be routed to the wrong network or
network node causing the call setup to be rejected. It is less a
problem if the npdi is illegally removed. An additional NPDB
James Yu Expired on September 18, 2004 [Page 9]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
query may be performed to retrieve the routing number information
and have the npdi included again.
Protocols carrying the tel URI MAY need to ensure message
integrity during the message transfer between two communicating
network nodes so as to detect any unauthorized changes to the
content of the tel URI and other information.
7. IANA Considerations
The fourteen parameters defined in this document are to be
registered with IANA as the new parameters to the tel URI[2].
1. Parameter name rn
Applicability used to carry a routing number
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
2. Parameter name npdi
Applicability its presence indicates that NPDB dip for a
geographical telephone number has been performed
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
3. Parameter name cic
Applicability used to carry a Carrier ID Code
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
4. Parameter name routing-number
Applicability used to carry a routing number
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
5. Parameter name global-rn
Applicability used to carry an international routing number
with a leading +
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
James Yu Expired on September 18, 2004 [Page 10]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
6. Parameter name local-rn
Applicability used to carry a routing number in the format
defined by rn-context
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
7. Parameter name rn-context
Applicability used to define a routing number in the local-
rn format
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
8. Parameter name rn-descriptor
Applicability used to define a number in the local-rn format
or other applicable formats such as the local-cic format
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
9. Parameter name global-hex-digits
Applicability used to define an international number with a
leading + where hex-decimal digit is allowed after a valid
E.164 country code
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
10.
Parameter name npdi-dip-indicator
Applicability its presence indicates that NPDB dip for a
geographical telephone number has been performed
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
11.
Parameter name carrier-id-code
Applicability used to carry a Carrier ID Code
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
12.
Parameter name global-cic
Applicability used to carry a Carrier ID Code with a leading
+
Mandatory or optional optional
Restrictions on syntax see Section 3
James Yu Expired on September 18, 2004 [Page 11]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
Reference to a specification defined in this document
13.
Parameter name local-cic
Applicability used to carry a Carrier ID Code in the format
described by cic-context
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
14.
Parameter name cic-context
Applicability used to define a Carrier ID Code in the local-
cic format
Mandatory or optional optional
Restrictions on syntax see Section 3
Reference to a specification defined in this document
8. Normative References
[1] M. Foster, T. McGarry and J. Yu, RFC3482, "Number Portability
in the GSTN: An Overview," February 2003.
[2] H. Schulzrinne and A. Vaha-Sipila, "The tel URI for Telephone
Calls," draft-ietf-iptel-rfc2806bis-04.txt, February 15, 2004.
[3] J. Rosenberg, et al., RFC3261, "SIP: Session Initiation
Protocol," June 2002.
[4] ITU-T Recommendation H.323, "Packet-Based Multimedia
Communications Systems," November 2000.
[5] Scott Bradner, RFC2119," Key words for use in RFCs to Indicate
Requirement Levels," March 1997.
[6] ITU-T Recommendation E.164, "The international public
telecommunication numbering plan," May 1997.
9. Acknowledgements
The author would like to thank Penn Pfautz, Jon Peterson, Jonathan
Rosenberg, Henning Schulzrinne, Antti Vaha-Sipila, Flemming
Andreasen and Mike Hammer for their discussions and comments.
James Yu Expired on September 18, 2004 [Page 12]
New Parameters for the tel URI to Support March 18, 2004
Number Portability
10. Author's Address
James Yu
NeuStar, Inc.
46000 Center Oak Plaza
Sterling, VA 20166
U.S.A.
Phone: +1-571-434-5572
Email: james.yu@neustar.biz
Full Copyright Statement
"Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain
it or assist in its implementation may be prepared, copied,
published and distributed, in whole or in part, without restriction
of any kind, provided that the above copyright notice and this
paragraph are included on all such copies and derivative works.
However, this document itself may not be modified in any way, such
as by removing the copyright notice or references to the Internet
Society or other Internet organizations, except as needed for the
purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards process
must be followed, or as required to translate it into languages
other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
James Yu Expired on September 18, 2004 [Page 13]
