IPTEL Working Group J. Yu
Internet Draft NeuStar
Document: draft-ietf-iptel-tel-np-01.txt April 2004
Category: Standards Track
New Parameters for the "tel" URI to Support Number Portability
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All rights reserved.
Abstract
This document defines several new parameters in the "tel" Uniform
Resource Identifier (URI) 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. The "rn-context" and "cic-context"
parameters describe the "rn" and "cic" parameters respectively when
the "rn" and "cic" parameters contain information in the "local"
format.
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1. Conventions used in this document
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 [2].
2. Introduction
Number portability (NP) [3] 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 [4] for protocols such as
the Session Initiation Protocol (SIP) [5] and H.323 [6] 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 also 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 for the "tel" Uniform
Resource Identifier (URI) [4] to support NP. Section 3 lists the
abbreviations used in this document. Section 4 provides the formal
syntax definition. Section 5 describes the rules for a network node
that deals with some or all of the defined parameters in a "tel"
URI. Section 6 provides a few examples to show how those defined
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parameters are added to a "tel" URI after retrieving NP-related
information from the NP database. Sections 7 and 8 are the security
considerations and IANA considerations.
3. Abbreviations
ANSI American National Standards Institute
BNF Backus-Naur Form
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
URI Uniform Resource Identifier
VoIP Voice over IP
4. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC-2234 [7].
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
phonedigit = DIGIT / [ visual-separator ]
phonedigit-hex = HEXDIG / "*" / "#" / [ visual-separator ]
visual-separator = "-" / "." / "(" / ")"
domainname = *( domainlabel "." ) toplabel ["."]
domainlabel = alphanum
/ alphanum *( alphanum / "-" ) alphanum
toplabel = ALPHA / ALPHA *( alphanum / "-" ) alphanum
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alphanum = ALPHA / DIGIT
npdb-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 [8] country code.
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.
5. 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 add 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.
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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 to the two database accesses as "the first freephone
database access" and "the second freephone database access".
5.1 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.
If the network node does not know how to route based on the CIC or
routing information, the local policies SHALL decide whether to stop
the call processing or continue the call processing by ignoring the
invalid/unknown information.
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
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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 remove the "rn" parameter if the routing
number in the "rn" parameter points to this network node (e.g.,
the call has reached the intended network node). It SHALL look
for the freephone number or geographical telephone number for
making the routing decision.
- The network node SHALL remove the "rn" parameter if the routing
number in the "rn" parameter points to 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). It SHALL look for the
freephone number or geographical telephone number for making the
routing decision. The network node MAY access the NP database for
routing information if it is set to do so.
-
- Otherwise, the network node SHALL make the routing decision based
on the routing number in the "rn" parameter. How the call is
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 5.2 for rules in
adding the defined parameter or parameters to the "tel" URI if the
network node is set to access the NP database.
5.2 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 5.2.1 and 5.2.2 for a "tel"
URI that is used for routing.
Section 5.2.3 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 5.3.4
discusses the addition of the defined parameter or parameters to the
"tel" URI due to protocol conversion.
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5.2.1 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. It SHALL
also 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 5.1 for
using the information in the "tel" URI to make the routing decision.
5.2.2 Retrieving NP-related information for a freephone number
When a network node performs the first or second freephone database
access for a freephone number:
- 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
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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 5.1 for
using the information in the "tel" URI to make the routing decision.
5.2.3 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.
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. For example, if the network node
is a PSTN gateway that receives an ISUP message that contains the
JIP, the "rn" parameter in the "tel" URI would normally contain the
correct location information.
Please note that the information in the "rn" parameter may not be
authenticated; therefore, the use of the information by the
recipient of the "tel" URI for anything related to charging is done
at its own risk.
5.2.4 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
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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 [4] 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" SHALL appear in the "tel" URI. It is outside
the scope of this document how to include the "rn" parameter if the
local policies require the network node to do so.
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 MAY 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.
6. 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 providerÆs 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
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"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
7. Security Considerations
In addition to those security implications discussed in the revised
"tel" URI [4], 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
query may be performed to retrieve the routing number information
and have the "npdi" included again.
It is RECOMMENDED that protocols carrying the "tel" URI ensure
message integrity during the message transfer between the two
communicating network nodes so as to detect any unauthorized changes
to the content of the "tel" URI and other information.
8. IANA Considerations
The five parameters defined in this document are to be registered
with IANA as the new parameters to the "tel" URI [4].
1. Parameter name û rn
Applicability û used to carry a routing number
Mandatory or optional û optional
Restrictions on syntax û see Section 5
Reference to a specification û defined in this document
2. Parameter name û npdi
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Applicability û its presence indicates that NPDB dip for a
geographical telephone number has been performed
Mandatory or optional û optional
Restrictions on syntax û see Section 5
Reference to a specification û defined in this document
3. Parameter name û cic
Applicability û used to carry a Carrier ID Code
Mandatory or optional û optional
Restrictions on syntax û see Section 5
Reference to a specification û defined in this document
4. Parameter name û rn-context
Applicability û used to define a routing number in the "local-rn"
format
Mandatory or optional û optional
Restrictions on syntax û see Section 5
Reference to a specification û defined in this document
5. Parameter name û cic-context
Applicability û used to define a Carrier ID Code in the "local-
cic" format
Mandatory or optional û optional
Restrictions on syntax û see Section 5
Reference to a specification û defined in this document
Based on [4], a network node shall not process a "tel" URI with
unknown mandatory parameters. If the five parameters shown above
are mandatory parameters, any network node that does not understand
them in the "tel" URI will drop the call. To prevent that from
happening, they are defined as optional parameters so that a network
node that does not understand them can still route based on the
phone number in the "tel" URI. A network node in the downstream
call setup path that understands those parameters can route
correctly based on the information in those parameters.
9. Normative References
[1] S. Bradner, RFC2026, "The Internet Standards Process -- Revision
3", October 1996.
[2] S. Bradner, RFC2119, "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[4] H. Schulzrinne, draft-ietf-iptel-rfc2806bis-05.txt, "The tel URI
for Telephone Calls", March 20, 2004.
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[7] D. Crocker and P. Overell, RFC2234, "Augmented BNF for Syntax
Specifications: ABNF", November 1997.
[8] ITU-T Recommendation E.164, "The international public
telecommunication numbering plan", May 1997.
10. Informative References
[3] M. Foster, T. McGarry and J. Yu, RFC3482, "Number Portability in
the GSTN: An Overview", February 2003.
[5] J. Rosenberg, et al., RFC3261, "SIP: Session Initiation
Protocol", June 2002.
[6] ITU-T Recommendation H.323, "Packet-Based Multimedia
Communications Systems", November 2000.
11. Acknowledgments
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.
12. 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
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