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Mark Foster
Internet Draft Tom McGarry
Document: <draft-ietf-enum-e164-gstn-np-01.txt> James Yu
NeuStar, Inc.
Category: Informational February 9, 2001
Number Portability in the GSTN: An Overview
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC].
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.
To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
1. Abstract
This document provides an overview of E.164 telephone number
portability (NP) in the Global Switched Telephone Network (GSTN).
There are three types of number portability: service provider number
portability (SPNP), location portability, and service portability.
Service provider portability, the focus of the present draft, is a
regulatory imperative in many countries seeking to liberalize local
telephony service competition, by enabling end-users to retain pre-
existing telephone numbers while changing service providers.
Implementation of NP within national GSTN entails potentially
significant changes to numbering administration, network element
signaling, call routing and processing, billing, service management,
and other functions. NP changes the fundamental nature of a dialed
E.164 number from a hierarchical physical routing address to a
virtual address, thereby requiring the transparent translation of
the later to the former. In addition, there are various regulatory
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 [1]
Number Portability in the GSTN: An Overview February 9, 2000
constraints that establish relevant parameters for NP
implementation, most of which are not network technology specific.
Consequently, the implementation of NP behavior consistent with
applicable regulatory constraints, as well as the need for
interoperation with the existing GSTN NP implementations, are
relevant topics for numerous areas of IP telephony work-in-progress
at IETF.
2. Introduction
This document provides an overview of E.164 telephone number
portability in the Global Switched Telephone Network (GSTN). There
are considered to be three types of number portability (NP): service
provider portability (SPNP), location portability (not to be
confused with terminal mobility), and service portability.
Service provider portability (SPNP), the focus of the present draft,
is a regulatory imperative in many countries seeking to liberalize
telephony service competition, especially local service.
Historically, local telephony service (as compared to long distance
or international service) has been regulated as a utility-like form
of service. While a number of countries had begun liberalization
(e.g. privatization, de-regulation, or re-regulation) some years
ago, the advent of NP is relatively recent (since ~1995).
E.164 numbers can be non-geographic and geographic numbers. Non-
geographic numbers do not reveal the locations information of those
numbers. Geographic E.164 numbers were intentionally designed as
hierarchical routing addresses which could systematically be digit-
analyzed to ascertain the country, serving network provider, serving
end-office switch, and specific line of the called party. As such,
without NP a subscriber wishing to change service providers would
incur a number change as a consequence of being served off of a
different end-office switch operated by the new service provider.
The cost and convenience impact to the subscriber of changing
numbers is seen as barrier to competition. Hence NP has become
associated with GSTN infrastructure enhancements associated with a
competitive environment driven by regulatory directives.
Forms of SPNP have been deployed or are being deployed widely in the
GSTN in various parts of the world, including the U.S., Canada,
Western Europe, Australia, and the Pacific Rim (e.g. Hong Kong).
Other regions, such as South America (e.g. Brazil) are actively
considering it.
Implementation of NP within a national telephony infrastructure
entails potentially significant changes to numbering administration,
network element signaling, call routing and processing, billing,
service management, and other functions.
NP changes the fundamental nature of a dialed E.164 number from a
hierarchical physical routing address to a virtual address. NP
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 2
Number Portability in the GSTN: An Overview February 9, 2000
implementations attempt to encapsulate the impacts to the GSTN and
make NP transparent to subscribers by incorporating a translation
function to map a dialed, potentially ported E.164 address, into a
network routing address (either a number prefix or another E.164
address) which can be hierarchically routed.
This is roughly analogous to the use of network address translation
on IP addresses to enable IP address portability by containing the
impact of the address change to the edge of the network and retain
the use of CIDR blocks in the core which can be route aggregated by
the network service provider to the rest of the internet.
NP bifurcates the historical role of a subscriber<65>s E.164 address
into two or more data elements (a dialed or virtual address, and a
network routing address) that must be made available to network
elements through an NP translations database, carried by forward
call signaling, and recorded on call detail records. Not only is
call processing and routing affected, but also so is SS7/C7
messaging. A number of TCAP-based SS7 messaging sets utilize an
E.164 address as an application-level network element address in the
global title address (GTA) field of the SCCP message header.
Consequently, SS7/C7 signaling transfer points (STPs) and gateways
need to be able to perform n-digit global title translation (GTT) to
translate a dialed E.164 address into its network address
counterpart via the NP database.
In addition, there are various national regulatory constraints that
establish relevant parameters for NP implementation, most of which
are not network technology specific. Consequently, implementations
of NP behavior in IP telephony consistent with applicable regulatory
constraints, as well as the need for interoperation with the
existing GSTN NP implementations, are relevant topics for numerous
areas of IP telephony work-in-progress at IETF.
This document describes three types of number portability and the
four schemes that have been standardized to support SPNP for
geographic E.164 numbersspecifically. Following that, specific
information regarding the call routing and database query
implementations are described for several regions (North American
and Europe) and industries (wireless vs. wireline). The Number
Portability Database (NPDB) interfaces and the call routing schemes
that are used in the North America and Europe are described to show
the variety of standards that may be implemented worldwide. A
glance of the NP implementations worldwide is provided. Number
pooling is briefly discussed to show how NP is being enhanced in the
U.S. to conserve North American area codes. The conclusion briefly
touches the potential impacts of NP on IP & Telecommunications
Interoperability. Appendix A provides some specific technical and
regulatory information on NP in North America. Appendix B describes
the number portability administration process that manages the
number portability database in North America.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 3
Number Portability in the GSTN: An Overview February 9, 2000
3. Abbreviations and Acronyms
ACQ All Call Query
AIN Advanced Intelligent Network
AMPS Advanced Mobile Phone System
ANSI American National Standards Institute
CDMA Code Division Multiple Access
CdPA Called Party Address
CdPN Called Party Number
CH Code Holder
CMIP Common Management Information Protocol
CS1 Capability Set 1
CS2 Capability Set 2
DN Directory Number
DNS Domain Name System
ETSI European Technical Standards Institute
FCI Forward Call Indicator
GAP Generic Address Parameter
GMSC Gateway Mobile Services Switching Center or Gateway Mobile
Switching Center
GSM Global System for Mobile Communications
GSTN Global Switched Telephone Network
GW Gateways
HLR Home Location Register
IAM Initial Address Message
IETF Internet Engineering Task Force
ILNP Interim LNP
IN Intelligent Network
INAP Intelligent Network Application Part
INP Interim NP
IP Internet Protocol
IS-41 Interim Standards Number 41
ISDN Integrated Services Digital Network
ISUP ISDN User Part
ITN Individual Telephony Number
ITU International Telecommunication Union
ITU-TS ITU-Telecommunication Sector
LDAP Lightweight Directory Access Protocol
LEC Local Exchange Carrier
LNP Local Number Portability
LRN Location Routing Number
MAP Mobile Application Part
MNP Mobile Number Portability
MSRN Mobile Station Roaming Number
MTP Message Transfer Part
NANP North American Numbering Plan
NP Number Portability
NPDB Number Portability Database
NRN Network Routing Number
OR Onward Routing
OSS Operation Support System
PCS Personal Communication Services
PNTI Ported Number Translation Indicator
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 4
Number Portability in the GSTN: An Overview February 9, 2000
PODP Public Office Dialing Plan
PUC Public Utility Commission
QoR Query on Release
RN Routing Number
RTP Return to Pivot
SCCP Signaling Connection Control Part
SCP Service Control Point
SIP Session Initiation Protocol
SMR Special Mobile Radio
SMS Service Management System
SPNP Service Provider Number Portability
SRF Signaling Relaying Function
SRI Send Routing Information
SS7 Signaling System Number 7
STP Signaling Transfer Point
TCAP Transaction Capabilities Application Part
TDMA Time Division Multiple Access
TN Telephone Number
TRIP Telephony Routing Information Protocol
URL Universal Resource Locator
U.S. United States
4. Types of Number Portability
As there are several types of E.164 numbers (telephone numbers, or
just TN) in the GSTN, there are correspondingly several types of
E.164 NP in the GSTN. First there are so-call non-geographic E.164
numbers, commonly used for service-specific applications such as
freephone (800 or 0800). Portability of these numbers is called
non-geographic number portability (NGNP). NGNP, for example, was
deployed in the U.S. in 1986-92.
Geographic number portability, which includes traditional fixed or
wireline numbers as well as mobile numbers which are allocated out
of geographic number range prefixes, is called NP or GNP or in the
U.S. local number portability (LNP).
Number portability allows the telephony subscribers in the Global
Switched Telephone Network (GSTN) to keep their phone numbers when
they change their service providers or subscribed services, or when
they move to a new location.
The ability to change the service provider while keeping the same
phone number is called service provider portability (SPNP) also
known as "operator portability."
The ability to change the subscriber<65>s fixed service location while
keeping the same phone number is called location portability.
The ability to change the subscribed services (e.g., from the plain
old telephone service to Integrated Services Digital Network (ISDN)
services) while keeping the same phone number is called service
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 5
Number Portability in the GSTN: An Overview February 9, 2000
portability. Another aspect of service portability is to allow the
subscribers to enjoy the subscribed services in the same way when
they roam outside their home networks as is supported by the
cellular/wireless networks.
In addition, mobile number portability (MNP) refers to specific NP
implementation in mobile networks either as part of a broader NP
implementation in the GSTN or on a stand-alone basis. Where
interoperation of LNP and MNP is supported, service portability
between fixed and mobile service types is possible.
At present, SPNP has been the primary form of NP deployed due to its
relevance in enabling local service competition.
Also in use in the GSTN are the terms interim NP (INP) or Interim
LNP (ILNP) and true NP. Interim NP usually refers to the use of
remote call forwarding-like measures to forward calls to ported
numbers through the donor network to the new service network. These
are considered interim relative to true NP, which seeks to remove
the donor network or old service provider from the call or signaling
path altogether. Often the distinction between interim and true NP
is a national regulatory matter relative to the
technical/operational requirements imposed on NP in that country.
Implementations of true NP in certain countries (e.g. U.S., Canada,
Spain, Belgium, Denmark) may pose specific requirements for IP
telephony implementations as a result of regulatory and industry
requirements for providing call routing and signaling independent of
the donor network or last previous serving network.
5. Service Provider Number Portability Schemes
Four schemes can be used to support service provider portability and
are briefly described below. But first, some further terms are
introduced.
The donor network is the network that first assigned a telephone
number (e.g., TN +1-202-533-1234) to a subscriber, out of a number
range administratively (e.g., +1 202-533) assigned to it. The
current service provider (new SP) or new serving network is the
network that currently serves the ported number. The old serving
network (or old SP) is the network that previously served the ported
number before the number was ported to the new serving network.
Since a TN can port a number of times, the old SP is not necessarily
the same as the donor network, except for the first time the TN
ports away, or if the TN ports back into the donor network and away
again. While the new SP and old SP roles are transitory as a TN
ports around, the donor network is always the same for any
particular TN based on the service provider to whom the subtending
number range was administratively assigned. See the discussion
below on number pooling, as this enhancement to NP further
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 6
Number Portability in the GSTN: An Overview February 9, 2000
bifurcates the role of donor network into two (the number range or
code holder network, and the block holder network).
To simplify the illustration, all the transit networks are ignored,
the originating or donor network is the one that performs the
database queries or call redirection, and the dialed directory
number (TN) has been ported out of the donor network before.
It is assumed that the old serving network, the new serving network
and the donor network are different networks so as to show which
networks are involved in call handling and routing and database
queries in each of four schemes. Please note that the port of the
number (process of moving it from one network to another) happened
prior to the call setup and is not included in the call steps.
Information carried in the signaling messages to support each of the
four schemes is not discussed to simplify the explanation.
5.1 All Call Query (ACQ)
Figure 1 shows the call steps for the ACQ scheme. Those call steps
are as follows:
+-------------+ +-----------+ Number +-----------+
| Centralized | | New Serv. | ported | Old Serv. |
| NPDB | +-------->| Network |<------------| Network |
+-------------+ | +-----------+ +-----------+
^ | |
| | |
1| | 3.|
| | 2. |
| | |
| v |
+----------+ | +----------+ +----------+
| Orig. |------+ | Donor | | Internal |
| Network | | Network | | NPDB |
+----------+ +----------+ +----------+
Figure 1 - All Call Query (ACQ) Scheme.
(1) The Originating Network receives a call from the caller and
sends a query to a centrally administered Number Portability
Database (NPDB), a copy of which is usually resident on a
network element within its network or through a third party
provider.
(2) The NPDB returns the routing number associated with the dialed
directory number. The routing number is discussed later in
Section 7.
(3) The Originating Network uses the routing number to route the
call to the new serving network.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 7
Number Portability in the GSTN: An Overview February 9, 2000
5.2 Query on Release (QoR)
Figure 2 shows the call steps for the QoR scheme. Those call steps
are as follows:
(1) The Originating Network receives a call from the caller and
routes the call to the donor network.
(2) The donor network releases the call and indicates that the
dialed directory number has been ported out of that switch.
(3) The Originating Network sends a query to its copy of the
centrally administered NPDB.
(4) The NPDB returns the routing number associated with the dialed
directory number.
(5) The Originating Network uses the routing number to route the
call to the new serving network.
+-------------+ +-----------+ Number +-----------+
| Centralized | | New Serv. | ported | Old Serv. |
| NPDB | | Network |<------------| Network |
+-------------+ +-----------+ +-----------+
^ | ^
| | 4. |
3.| | 5. |
| | +----------------------+
| | |
| v |
+----------+ 2. +----------+ +----------+
| Orig. |<---------------| Donor | | Internal |
| Network |--------------->| Network | | NPDB |
+----------+ 1. +----------+ +----------+
Figure 2 - Query on Release (QoR) Scheme.
5.3 Call Dropback
Figure 3 shows the call steps for the Dropback scheme. This scheme
is also known as "Return to Pivot (RTP)." Those call steps are as
follows:
(1) The Originating Network receives a call from the caller and
routes the call to the donor network.
(2) The donor network detects that the dialed directory number has
been ported out of the donor switch and checks with an internal
network-specific NPDB.
(3) The internal NPDB returns the routing number associated with the
dialed directory number.
(4) The donor network releases the call by providing the routing
number.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 8
Number Portability in the GSTN: An Overview February 9, 2000
(5) The Originating Network uses the routing number to route the
call to the new serving network.
+-------------+ +-----------+ Number +-----------+
| Centralized | | New Serv. | porting | Old Serv. |
| NPDB | | Network |<------------| Network |
+-------------+ +-----------+ +-----------+
/\
|
5. |
+------------------------+
|
|
+----------+ 4. +----------+ 3. +----------+
| Orig. |<---------------| Donor |<----------| Internal |
| Network |--------------->| Network |---------->| NPDB |
+----------+ 1. +----------+ 2. +----------+
Figure 3 - Dropback Scheme.
5.4 Onward Routing (OR)
Figure 4 shows the call steps for the OR scheme. This scheme is also
called Remote Call Forwarding. Those call steps are as follows:
(1) The Originating Network receives a call from the caller and
routes the call to the donor network.
(2) The donor network detects that the dialed directory number has
been ported out of the donor switch and checks with an internal
network-specific NPDB.
(3) The internal NPDB returns the routing number associated with the
dialed directory number.
(4) The donor network uses the routing number to route the call to
the new serving network.
+-------------+ +-----------+ Number +-----------+
| Centralized | | New Serv. | porting | Old Serv. |
| NPDB | | Network |<------------| Network |
+-------------+ +-----------+ +-----------+
/\
|
4.|
|
+----------+ +----------+ 3. +----------+
| Orig. | | Donor |<----------| Internal |
| Network |--------------->| Network |---------->| NPDB |
+----------+ 1. +----------+ 2. +----------+
Figure 4 - Onward Routing (OR) Scheme.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 9
Number Portability in the GSTN: An Overview February 9, 2000
5.5 Comparisons of the Four Schemes
Only the ACQ scheme does not involve the donor network when routing
the call to the new serving network of the dialed ported number.
The other three schemes involve call setup to or signaling with the
donor network.
Only the OR scheme requires the setup of two physical call segments,
one from the Originating Network to the donor network and the other
from the donor network to the new serving network. The OR scheme is
the least efficient in terms of using the network resources. The
QoR and Dropback schemes set up calls to the donor network first but
release the call back to the Originating Network that then initiates
a new call to the Current Serving Network. For the QoR and Dropback
schemes, circuits are still reserved one by one between the
Originating Network and the donor network when the Originating
Network sets up the call towards the donor network. Those circuits
are released one by one when the call is released from the donor
network back to the Originating Network. The ACQ scheme is the most
efficient in terms of using the switching and transmission
facilities for the call.
Both the ACQ and QoR schemes involve Centralized NPDBs for the
Originating Network to retrieve the routing information.
Centralized NPDB means that the NPDB contains ported number
information from multiple networks. This is in contrast to the
internal network-specific NPDB that is used for the Dropback and OR
schemes. The internal NPDB only contains information about the
numbers that were ported out of the donor network. The internal
NPDB can be a stand-alone database that contains information about
all or some ported-out numbers from the donor network. It can also
reside on the donor switch and only contains information about those
numbers ported out of the donor switch. In that case, no query to a
stand-alone internal NPDB is required. The donor switch for a
particular phone number is the switch to which the number range is
assigned from which that phone number was originally assigned.
For example, number ranges in the North American Numbering Plan
(NANP) are usually assigned in the form of central office codes (CO
codes) comprising a six-digit prefix formatted as a NPA+NXX. Thus a
switch serving +1-202-533 would typically serve +1-202-533-0000
through +1-202-533-9999. In major cities, switches usually host
several CO codes. NPA stands for Numbering Plan Area that is also
known as the area code. It is three-digit long and has the format
of NXX where N is any digit from 2 to 9 and X is any digit from 0 to
9. NXX in the NPA+NXX format is known as the office code that has
the same format as the NPA. When the first number out of an NPA+NXX
code is ported out to another switch, that NPA+NXX is called
"portable NPA+NXX."
Similarly, in other national E.164 numbering plans, number ranges
cover a contiguous range of numbers within that range. Once a
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 10
Number Portability in the GSTN: An Overview February 9, 2000
number within that range has ported away from the donor network, all
numbers in that range are considered potentially ported and should
be queried in the NPDB.
The ACQ scheme has two versions. One version is for the Originating
Network to always query the NPDB when a call is received from the
caller regardless whether the dialed directory number is ported or
not. The other version is to check whether the dialed directory
number belongs to any portable number range. If yes, an NPDB query
is sent. If not, no NPDB query is sent. The former performs better
when there are many portable number ranges. The latter performs
better when there are not too many portable number ranges at the
expense of checking every call to see whether NPDB query is needed.
The latter ACQ scheme is similar to the QoR scheme except that the
QoR scheme uses call setup and relies on the donor network to
indicate "number ported out" before launching the NPDB query.
6. Database Queries in the NP Environment
As indicated earlier, the ACQ and QoR schemes require that a switch
query the NPDB for routing information. Various standards have been
defined for the switch-to-NPDB interface. Those interfaces with
their protocol stacks are briefly described below. The term "NPDB"
is used for a stand-alone database that may support just one or some
or all of the interfaces mentioned below. The NPDB query contains
the dialed directory number and the NPDB response contains the
routing number. There are certainly other information that is sent
in the query and response. The primary interest is to get the
routing number from the NPDB to the switch for call routing.
6.1 U.S. and Canada
One of the following five NPDB interfaces can be used to query an
NPDB:
(a) Advanced Intelligent Network (AIN) using the American National
Standards Institute (ANSI) version of the Intelligent Network
Application Part (INAP) [ANSI SS] [ANSI DB]. The INAP is
carried on top of the protocol stack that includes the (ANSI)
Message Transfer Part (MTP) Levels 1 through 3, ANSI Signaling
Connection Control Part (SCCP), and ANSI Transaction
Capabilities Application Part (TCAP). This interface can be
used by the wireline or wireless switches, is specific to the NP
implementation in North America, and is modeled on the Public
Office Dialing Plan (PODP) trigger defined in the Advanced
Intelligent Network (AIN) 0.1 call model.
(b) Intelligent Network (IN), which is similar to the one used for
querying the 800 databases. The IN protocol is carried on top
of the protocol stack that includes the ANSI MTP Levels 1
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 11
Number Portability in the GSTN: An Overview February 9, 2000
through 3, ANSI SCCP, and ANSI TCAP. This interface can be used
by the wireline or wireless switches.
(c) ANSI IS-41 [IS41] [ISNP], which is carried on top of the
protocol stack that includes the ANSI MTP Levels 1 through 3,
ANSI SCCP, and ANSI TCAP. This interface can be used by the IS-
41 based cellular/Personal Communication Services (PCS) wireless
switches (e.g., AMPS, TDMA and CDMA). Cellular systems use
spectrum at 800 MHz range and PCS systems use spectrum at 1900
MHz range.
(d) Global System for Mobile Communication Mobile Application Part
(GSM MAP) [GSM], which is carried on top of the protocol stack
that includes the ANSI MTP Levels 1 through 3, ANSI SCCP, and
International Telecommunication Union - Telecommunication Sector
(ITU-TS) TCAP. It can be used by the PCS1900 wireless switches
that are based on the GSM technologies. GSM is a series of
wireless standards defined by the European Telecommunications
Standards Institute (ETSI).
(e) ISUP triggerless translation. NP translations are performed
transparently to the switching network by the signaling network
(e.g. Signaling Transfer Points (STPs) or signaling gateways).
ISUP IAM messages are examined to determine if the CdPN field
has already been translated, and if not, an NPDB query is
performed, and the appropriate parameters in the IAM message
modified to reflect the results of the translation. The
modified IAM message is forwarded by the signaling node on to
the designated DPC in a transparent manner to continue call
setup. The NPDB can be integrated with the signaling node or be
accessed via an API locally or by a query to a remote NPDB using
a proprietary protocol or the schemes described above.
Wireline switches have the choice of using either (a), (b), or (e).
IS-41 based wireless switches have the choice of using (a), (b),
(c), or (e). PCS1900 wireless switches have the choice of using
(a), (b), (d), or (e). In the United States, service provider
portability will be supported by both the wireline and wireless
systems, not only within the wireline or wireless domain but also
across the wireline/wireless boundary. However, this is not true in
Europe where service provider portability is usually supported only
within the wireline or wireless domain, not across the
wireline/wireless boundary due to explicit use of service-specific
number range prefixes. The reason is to avoid caller confusion
about the call charge. GSM systems in Europe are assigned
distinctive destination network codes, and the caller pays a higher
charge when calling a GSM directory number.
6.2 Europe
One of the following three interfaces can be used to query an NPDB:
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 12
Number Portability in the GSTN: An Overview February 9, 2000
(a) Capability Set 1 (CS1) of the ITU-TS INAP [CS1], which is
carried on top of the protocol stack that includes the ITU-TS
MTP Levels 1 through 3, ITU-TS SCCP, and ITU-TS TCAP.
(b) Capability Set 2 (CS2) of the ITU-TS INAP [CS2], which is
carried on top of the protocol stack that includes the ITU-TS
MTP Levels 1 through ITU-TS MTP Levels 1 through 3, ITU-TS SCCP,
and ITU-TS TCAP.
(c) ISUP triggerless translation. NP translations are performed
transparently to the switching network by the signaling network
(e.g. STPs or signaling gateways). ISUP IAM messages are
examined to determine if the CdPN field has already been
translated, and if not, an NPDB query is performed, and the
appropriate parameters in the IAM message modified to reflect
the results of the translation. The modified IAM message is
forwarded by the signaling node on to the designated DPC in a
transparent manner to continue call setup.
Wireline switches have the choice of using either (a), (b), or (c);
however, all the implementations in Europe so far are based on CS1.
As indicated earlier that number portability in Europe does not go
across the wireline/wireless boundary. The wireless switches can
also use (a) or (b) to query the NPDBs if those NPDBs contains
ported wireless directory numbers. The term "Mobile Number
Portability (MNP)" is used for the support of service provider
portability by the GSM networks in Europe.
In most, if not all, cases in Europe, the calls to the wireless
directory numbers are routed to the wireless donor network first.
Over there, an internal NPDB is queried to determine whether the
dialed wireless directory number has been ported out or not. In
this case, the interface to the internal NPDB is not subject to
standardization.
MNP in Europe can also be supported via MNP Signaling Relay Function
(MNP-SRF). Again, an internal NPDB or a database integrated at the
MNP-SRF is used to modify the SCCP Called Party Address parameter in
the GSM MAP messages so that they can be re-directed to the wireless
serving network. Call routing involving MNP will be explained in
Section 7.2.
7. Call Routing in the NP Environment
This section discusses the call routing after the routing
information has been retrieved either through an NPDB query or an
internal database lookup at the donor switch, or from the Integrated
Services Digital Network User Part (ISUP) signaling message (e.g.,
for the Dropback scheme). For the ACQ, QoR and Dropback schemes, it
is the Originating Network that has the routing information and is
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Number Portability in the GSTN: An Overview February 9, 2000
ready to route the call. For the OR scheme, it is the donor network
that has the routing information and is ready to route the call.
A number of triggering schemes may be employed that determine where
in the call path the NPDB query is performed. In the U.S. an <20>N-1<>
policy is used, which essentially says that for domestic calls, the
originating local carriers performs the query, otherwise, the long
distance carrier is expected to. To ensure independence of the
actual trigger policy employed in any one carrier, forward call
signaling is used to flag that an NPDB query has already been
performed and to therefore suppress any subsequent NP triggers that
may be encountered in downstream switches, in downstream networks.
This allows the earliest able network in the call path to perform
the query without introducing additional costs and call setup delays
were redundant queries performed downstream.
7.1 U.S. and Canada
In the U.S. and Canada, a ten-digit North American Numbering Plan
(NANP) number called Location Routing Number (LRN) is assigned to
every switch involved in NP. In the NANP, a switch is not reachable
unless it has a unique number range (CO code) assigned to it.
Consequently, the LRN for a switch is always assigned out of a CO
code that is assigned to that switch.
The LRN assigned to a switch currently serving a particular ported
telephone number is returned as the network routing address in the
NPDB response. The service portability scheme that was adopted in
the North America is very often referred to as the LRN scheme or
method.
LRN serves as a network address for terminating calls served off
that switch using ported numbers. The LRN is assigned by the switch
operator using any of the unique CO codes (NPA+NXX) assigned to that
switch. The LRN is considered a non-dialable address, as the same
10-digit number value may be assigned to a line on that switch. A
switch may have more than one LRN.
During call routing/processing, a switch performs an NPDB query to
obtain the LRN associated with the dialed directory number. NPDB
queries are performed for all the dialed directory numbers whose
NPA+NXX codes are marked as portable NPA+NXX at that switch. When
formulating the ISUP Initial Address Message (IAM) to be sent to the
next switch, the switch puts the ten-digit LRN in the ISUP Called
Party Number (CdPN) parameter and the originally dialed directory
number in the ISUP Generic Address parameter (GAP). A new code in
the GAP was defined to indicate that the address information in the
GAP is the dialed directory number. A new bit in the ISUP Forward
Call Indicator (FCI) parameter, the Ported Number Translation
Indicator (PNTI) bit, is set to imply that NPDB query has already
been performed. All the switches in the downstream will not perform
the NPDB query if the PNTI bit is set.
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Number Portability in the GSTN: An Overview February 9, 2000
When the terminating switch receives the IAM and sees the PNTI bit
in the FCI parameter set and its own LRN in the CdPN parameter, it
retrieves the originally dialed directory number from the GAP and
uses the dialed directory number to terminate the call.
A dialed directory number with a portable NPA+NXX does not imply
that directory number has been ported. The NPDBs currently do not
store records for non-ported directory numbers. In that case, the
NPDB will return the same dialed directory number instead of the
LRN. The switch will then set the PNTI bit but keep the dialed
directory number in the CdPN parameter.
In the real world environment, the Originating Network is not always
the one that performs the NPDB query. For example, it is usually
the long distance carriers that query the NPDBs for long distance
calls. In that case, the Originating Network operated by the local
exchange carrier (LEC) simply routes the call to the long distance
carrier that is to handle that call. A wireless network acting as
the Originating Network can also route the call to the
interconnected local exchange carrier network if it does not want to
support the NPDB interface at its mobile switches.
7.2 Europe
In Europe, a routing number is prefixed to the dialed directory
number. The ISUP CdPN parameter in the IAM will contain the routing
prefix and the dialed directory number. For example, United Kingdom
uses routing prefixes with the format of 5XXXXX and Italy uses
C600XXXXX as the routing prefix. The networks use the information
in the ISUP CdPN parameter to route the call to the New/Current
Serving Network.
The routing prefix can identify the Current Serving Network or the
Current Serving Switch of a ported number. For the former case,
another query to the "internal" NPDB at the Current Serving Network
is required to identify the Current Serving Switch before routing
the call to that switch. This shields the Current Serving Switch
information for a ported number from the other networks at the
expense of an additional NPDB query. Another routing number, may be
meaningful within the Current Serving Network, will replace the
previously prefixed routing number in the ISUP CdPN parameter. For
the latter case, the call is routed to the Current Serving Switch
without an additional NPDB query.
When the terminating switch receives the IAM and sees its own
routing prefix in the CdPN parameter, it retrieves the originally
dialed directory number after the routing prefix, and uses the
dialed directory number to terminate the call.
In addition to the addition of the routing prefix to the CdPN
parameter, some other information may be added/modified as is listed
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 15
Number Portability in the GSTN: An Overview February 9, 2000
in the draft ITU-T Recommendation Q.769.1 [ISUP]. Those
enhancements in the ISUP to support number portability are briefly
described below.
Three methods can be used to transport the Directory Number (DN) and
the Routing Number (RN):
(a) Two separate parameters with the CdPN parameter containing the
RN and a new Called Directory Number (CdDN) parameter containing
the DN. A new value for the Nature of Address (NOA) indicator in
the CdPN parameter is defined to indicate that the RN is in the
CdPN parameter. The switches use the CdPN parameter to route the
call as is done today.
(b) Two separate parameters with the CdPN parameter containing the
DN and a new Network Routing Number (NRN) parameter containing
the RN. This method requires that the switches use the NRN
parameter to route the call.
(c) Concatenated parameter with the CdPN parameter containing the RN
plus the DN. A new Nature of Address (NOA) indicator in the CdPN
parameter is defined to indicate that the RN is concatenated with
the DN in the CdPN parameter. Some countries may not use new NOA
value because the routing prefix does not overlap with the dialed
directory numbers. But if the routing prefix overlaps with the
dialed directory numbers, a new NOA value must be assigned.
Spain uses "XXXXXX" as the routing prefix to identify the new
serving network and uses a new NOA value of 126.
There is also a network option to add a new ISUP parameter called
Number Portability Forwarding Information parameter. This parameter
has a four-bit Number Portability Status Indicator field that can
provide an indication whether number portability query is done for
the called directory number and whether the called directory number
is ported or not if the number portability query is done.
Please note that all those enhancements are for national use. This
is because number portability is supported within a nation. Within
each nation, the telecommunications industry or the regulatory
bodies can decide which method or methods to use. Number
portability related parameters and coding are never passed across
the national boundaries.
As indicated earlier, an originating wireless network can query the
NPDB and concatenate the RN with DN in the CdPN parameter and route
the call directly to the Current Serving Network.
If NPDBs do not contain information about the wireless directory
numbers, the call, originated from either a wireline or a wireless
network, will be routed to the Wireless donor network. Over there,
an internal NPDB is queried to retrieve the RN that then is
concatenated with the DN in the CdPN parameter.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 16
Number Portability in the GSTN: An Overview February 9, 2000
If MNP-SRF is supported, the Gateway Mobile Services Switching
Center (GMSC) at the wireless donor network, when receiving a call
from the wireline network, can send the GSM MAP Send Routing
Information (SRI) message to the MNP-SRF. The MNP-SRF interrogates
an internal or integrated NPDB for the RN of the MNP-SRF of the
wireless Current Serving Network and prefixes the RN to the dialed
wireless directory number in the global title address information in
the SCCP Called Party Address (CdPA) parameter. This SRI message
will be routed to the MNP-SRF of the wireless Current Serving
Network, which then responds with an acknowledgement by providing
the RN plus the dialed wireless directory number as the Mobile
Station Roaming Number (MSRN). The GMSC of the wireless donor
network formulates the ISUP IAM with the RN plus the dialed wireless
directory number in the CdPN parameter and routes the call to the
wireless Current Serving Network. A GMSC of the wireless Current
Serving Network receives the call and sends an SRI message to the
associated MNP-SRF where the global title address information of the
SCCP CdPA parameter contains only the dialed wireless directory
number. The MNP-SRF then replaces the global title address
information in the SCCP CdPA parameter with the address information
associated with a Home Location Register (HLR) that hosts the dialed
wireless directory number and forwards the message to that HLR after
verifying that the dialed wireless directory number is a ported-in
number. The HLR then returns an acknowledgement by providing an
MSRN for the GMSC to route the call to the MSC that currently serves
the mobile station that is associated with the dialed wireless
directory number. Please see [MNP] for details and additional
scenarios.
8. NP Implementations for Geographic E.164 Numbers
This section shows the known SPNP implementations worldwide.
+-------------+----------------------------------------------------+
+ Country + SPNP Implementation +
+-------------+----------------------------------------------------+
+ Argentina + Analyzing operative viability now. Will determine +
+ + whether portability should be made obligatory +
+ + after a technical solution has been determined. +
+-------------+----------------------------------------------------+
+ Australia + NP supported by wireline operators since 11/30/99. +
+ + NP among wireless operators in March/April 2000, +
+ + but may be delayed to 1Q01. The access provider +
+ + or long distance provider has the obligation to +
+ + route the call to the correct destination. The +
+ + donor network is obligated to maintain and make +
+ + available a register of numbers ported away from +
+ + its network. Telstra uses onward routing via an +
+ + on-switch solution. +
+-------------+----------------------------------------------------+
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Number Portability in the GSTN: An Overview February 9, 2000
+ Austria + Uses onward routing at the donor network. Routing +
+ + prefix is "86xx" where "xx" identifies the +
+ + recipient switch. +
+-------------+----------------------------------------------------+
+ Belgium + ACQ selected by the industry. Routing prefix is +
+ + "Cxxxx" where "xxxx" identifies the recipient +
+ + switch. Another routing prefix is "C00xx" with "xx"+
+ + identifying the recipient network. Plan to use NOA+
+ + to identify concatenated numbers and abandon the +
+ + hexadecimal routing prefix. +
+-------------+----------------------------------------------------+
+ Brazil + Considering NP for wireless users. +
+-------------+----------------------------------------------------+
+ Chile + There has been discussions lately on NP. +
+-------------+----------------------------------------------------+
+ Colombia + There was an Article 3.1 on NP to support NP prior +
+ + to December 31, 1999 when NP becomes technically +
+ + possible. Regulator has not yet issued regulations +
+ + concerning this matter. +
+-------------+----------------------------------------------------+
+ Denmark + Uses ACQ. Routing number not passed between +
+ + operators; however, NOA is set to "112" to +
+ + indicate "ported number." QoR can be used based +
+ + on bilateral agreements. +
+-------------+----------------------------------------------------+
+ Finland + Uses ACQ. Routing prefix is "1Dxxy" where "xxy" +
+ + identifies the recipient network and service type. +
+-------------+----------------------------------------------------+
+ France + Uses onward routing. Routing prefix is "Z0xxx" +
+ + where "xxx" identifies the recipient switch. +
+-------------+----------------------------------------------------+
+ Germany + The originating network needs to do necessary +
+ + rerouting. Operators decide their own solution(s).+
+ + Deutsche Telekom uses ACQ. Routing prefix is +
+ + "Dxxx" where "xxx" identifies the recipient +
+ + network. +
+-------------+----------------------------------------------------+
+ Hong Kong + Recipient network informs other networks about +
+ + ported-in numbers. Routing prefix is "14x" where +
+ + "14x" identifies the recipient network, or a +
+ + routing number of "4x" plus 7 or 8 digits is used +
+ + where "4x" identifies the recipient network and +
+ + the rest of digits identify the called party. +
+-------------+----------------------------------------------------+
+ Ireland + Operators choose their own solution but use onward +
+ + routing now. Routing prefix is "1750" as the intra-+
+ + network routing code (network-specific) and +
+ + "1752xxx" to "1759xxx" for GNP where "xxx" +
+ + identifies the recipient switch. +
+-------------+----------------------------------------------------+
+ Italy + Uses onward routing. Routing prefix is "C600xxxxx" +
+ + where "xxxxx" identifies the recipient switch. +
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 18
Number Portability in the GSTN: An Overview February 9, 2000
+ + Telecom Italia uses IN solution and other operators+
+ + use on-switch solution. +
+-------------+----------------------------------------------------+
+ Japan + Uses onward routing. Donor switch uses IN to get +
+ + routing number. +
+-------------+----------------------------------------------------+
+ Mexico + NP is considered in the Telecom law; however, the +
+ + regulator (Cofetel) or the new local entrants have +
+ + started no initiatives on this process. +
+-------------+----------------------------------------------------+
+ Netherlands + Operators decide NP scheme to use. Operators have +
+ + chosen ACQ or QoR. KPN implemented IN solution +
+ + similar to U.S. solution. Routing prefix is not +
+ + passed between operators. +
+-------------+----------------------------------------------------+
+ Norway + OR for short-term and ACQ for long-term. QoR is +
+ + optional. Routing prefix can be "xxx" with NOA=8, +
+ + or "142xx" with NOA=3 where "xxx" or "xx" +
+ + identifies the recipient network. +
+------------ +----------------------------------------------------+
+ Peru + Wireline NP may be supported in 2001. +
+-------------+----------------------------------------------------+
+ Portugal + No NP today. +
+-------------+----------------------------------------------------+
+ Spain + Uses ACQ. Telefonica uses QoR within its network. +
+ + Routing prefix is "xxyyzz" where "xxyyzz" +
+ + identifies the recipient network. NOA is set to +
+ + 126. +
+-------------+----------------------------------------------------+
+ Sweden + Standardized the ACQ but OR for operators without +
+ + IN. Routing prefix is "xxx" with NOA=8 or "394xxx" +
+ + with NOA=3 where "xxx" identifies the recipient +
+ + network. But operators decide NP scheme to use. +
+ + Telia uses onward routing between operators. +
+-------------+----------------------------------------------------+
+ Switzerland + Uses OR now and QoR in 2001. Routing prefix is +
+ + "980xxx" where "xxx" identifies the recipient +
+ + network. +
+-------------+----------------------------------------------------+
+ UK + Uses onward routing. Routing prefix is "5xxxxx" +
+ + where "xxxxx" identifies the recipient switch. NOA +
+ + is 126. BT uses the dropback scheme in some parts +
+ + of its network. +
+-------------+----------------------------------------------------+
+ US + Uses ACQ. "Location Routing Number (LRN)" is used +
+ + in the Called Party Number parameter. Called party+
+ + number is carried in the Generic Address Parameter +
+ + Use a PNTI indicator in the Forward Call Indicator +
+ + parameter to indicate that NPDB dip has been +
+ + performed. +
+-------------+----------------------------------------------------+
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Number Portability in the GSTN: An Overview February 9, 2000
9. Number Conservation Methods Enabled by NP
In addition to porting numbers NP provides the ability for number
administrators to assign numbering resources to operators in smaller
increments. Today it is common for numbering resources to be
assigned to telephone operators in a large block of consecutive
telephone numbers (TNs). For example, in North America each of
these blocks contains 10,000 TNs and is of the format NXX+0000 to
NXX+9999. Operators are assigned a specific NXX, or block. That
operator is referred to as the block holder. In that block there
are 10,000 TNs with line numbers ranging from 0000 to 9999.
Instead of assigning an entire block to the operator NP allows the
administrator to assign a sub-block or even an individual telephone
number. This is referred to as block pooling and individual
telephone number (ITN) pooling, respectively.
9.1 Block Pooling
Block Pooling refers to the process whereby the number administrator
assigns a range of numbers defined by a logical sub-block of the
existing block. Using North America as an example, block pooling
would allow the administrator to assign sub-blocks of 1,000 TNs to
multiple operators. That is, NXX+0000 to NXX+0999 can be assigned
to operator A, NXX+1000 to NXX+1999 can be assigned to operator B,
NXX-2000 to 2999 can be assigned to operator C, etc. In this
example block pooling divides one block of 10,000 TNs into ten
blocks of 1,000 TNs.
Porting the sub-blocks from the block holder enables block pooling.
Using the example above operator A is the block holder, as well as,
the holder of the first sub-block, NXX+0000 to NXX+0999. The second
sub-block, NXX+1000 to NXX+1999, is ported from operator A to
operator B. The third sub-block, NXX+2000 to NXX+2999, is ported
from operator A to operator C, and so on. NP administrative
processes and call processing will enable proper and efficient
routing.
From a number administration and NP administration perspective block
pooling introduces a new concept, that of the sub-block holder.
Block pooling requires coordination between the number
administrator, the NP administrator, the block holder, and the sub-
block holder. Block pooling must be implemented in a manner that
allows for NP within the sub-blocks. Each TN can have a different
serving operator, sub-block holder, and block holder.
9.2 ITN Pooling
ITN pooling refers to the process whereby the number administrator
assigns individual telephone numbers to operators. Using the North
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Number Portability in the GSTN: An Overview February 9, 2000
American example, one block of 10,000 TNs can be divided into 10,000
ITNs. ITN is more commonly deployed in freephone services.
In ITN the block is not assigned to an operator but to a central
administrator. The administrator then assigns ITNs to operators.
NP administrative processes and call processing will enable proper
and efficient routing.
10. Conclusion
There are three general areas of impact to IP telephony work-in-
progress at IETF:
1. Interoperation between NP in GSTN and IP telephony
2. NP implementation or emulation in IP telephony
3. Interconnection to NP administrative environment
A good understanding of how number portability is supported in the
GSTN is important when addressing the interworking issues between IP
based networks and the GSTN. This is especially important when the
IP based network needs to route the calls to the GSTN. As shown in
Section 6, there are a variety of standards with various protocol
stacks for the switch-to-NPDB interface. Not only that, the
national variations of the protocol standards make it very
complicate to deal with in a global environment. If an entity in
the IP-based network needs to query those existing NPDBs for routing
number information to terminate the calls to the destination GSTN,
it would be impractical, if not an impossible, job for that entity
to support all those interface standards to access the NPDBs in many
countries.
Several alternatives may address this particular problem. One
alternative is to use certain entities in the IP-based networks for
dealing with NP query, similar to the International Switches that
are used in the GSTN to interwork different national ISUP
variations. This will force signaling information associated with
the calls to certain NP-capable networks in the terminating GSTN to
be routed to those IP entities that support the NP functions. Those
IP entities then query the NPDBs in the terminating country. This
will limit the number of NPDB interfaces that certain IP entities
need to support. Another alternative can be to define a "common"
interface to be supported by all the NPDBs so that all the IP
entities use that standardized protocol to query them. The
existing NPDBs can support this additional interface, or new NPDBs
can be deployed that contain the same information but support the
common IP interface. The candidates for such a common interface
include Lightweight Directory Access Protocol (LDAP) and SIP
[SIP](e.g., using the SIP redirection capability). Certainly
another possibility is to use interworking function to convert from
one protocol to another.
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 21
Number Portability in the GSTN: An Overview February 9, 2000
IP-based networks can handle the domestic calls between two GSTNs.
If the originating GSTN has performed NPDB query, SIP will need to
transport and make use of some of the ISUP signaling information
even if ISUP signaling may be encapsulated in SIP. Also, IP-based
networks may perform the NPDB queries, as the N-1 carrier. In that
case, SIP also needs to transport the NP related information while
the call is being routed to the destination GSTN. There are three
pieces of NP related information that SIP needs to transport. They
are 1) the called directory number, 2) a routing number, and 3) a
NPDB dip indicator. The NPDB dip indicator is needed so that the
terminating GSTN will not perform another NPDB dip. The routing
number is needed so that it is used to route the call to the
destination network or switch in the destination GSTN. The called
directory number is needed so that the terminating GSTN switch can
terminate the call. When the routing number is present, the NPDB
dip indicator may not be present because there are cases where
routing number is added for routing the call even if NP is not
involved. One issue is how to transport the NP related information
via SIP. The SIP Universal Resource Locator (URL) is one mechanism.
Another better choice may be to add an extension to the "tel" URL
[TEL] that is also supported by SIP. If the called directory is +1-
202-533-1234, and its associated routing number is +1-202-544-0000,
the "tel" URL may look like tel:+1-202-533-1234;rn=+1-202-544-
0000;npdi=yes where "rn" stands for "routing number" and "npdi"
stands for "NPDB dip indicator." "rn" and "npdi" will be two new
parameters to be added as extensions to the "tel" URL to support NP.
Since the "fax" URL is similar to the "tel" URL where NP can impact
the fax calls as well as the telephone calls, the same extensions to
the "tel" URL need to be applied to the "fax" URL as well. Please
see [TELNP] for the proposed extensions to the "tel" URL to support
NP and freephone service. Those extensions to the "tel" and "fax"
URLs will be automatically supported by SIP because they can be
carried as the optional parameters in the user portion of the "sip"
URL.
For a called directory number that belongs to a country that
supports NP, and if the IP-based network is to perform the NPDB
query, the logical step is to perform the NPDB dip first to retrieve
the routing number and use that routing number to select the correct
IP telephony gateways that can reach the serving switch that serves
the called directory number. Therefore, if the "rn" parameter is
present in the "tel" URL in the SIP INVITE message, it instead of
the called directory number should be used for making routing
decisions. If "rn" is not present, then the dialed directory number
can be used as the routing number for making routing decisions.
Telephony Routing Information Protocol (TRIP) [TRIP] is a policy
driven inter-administrative domain protocol for advertising the
reachability of telephony destinations between location servers, and
for advertising attributes of the routes to those destinations.
With the NP in mind, it is very important to know that it is the
routing number, if present, not the called directory number that
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 22
Number Portability in the GSTN: An Overview February 9, 2000
should be used to check against the TRIP tables for making the
routing decisions.
Overlap signaling exists in the GSTN today. For a call routing from
the originating GSTN to the IP-based network that involves overlap
signaling, NP will impact the call processing within the IP-based
networks if they must deal with the overlap signaling. The entities
in the IP-based networks that are to retrieve the NP information
(e.g., the routing number) must collect a complete called directory
number information before retrieving the NP information for a ported
number. Otherwise, the information retrieval won't be successful.
This is an issue for the IP-based networks if the originating GSTN
does not handle the overlap signaling and collect the complete
called directory number.
The IETF enum working group is defining the use of Domain Name
System (DNS) for identifying available services associated with a
particular E.164 number [ENUM]. [ENUMPO] outlines the principles
for the operation of a telephone number service that resolves
telephone numbers into Internet domain name addresses and service-
specific directory discovery. [ENUMPO] implements a three-level
approach where the first level is the mapping of the telephone
number delegation tree to the authority to which the number has been
delegated, the second level is the provision of the requested DNS
resource records from a service registrar, and the third level is
the provision of service specific data from the service provider
itself. NP certainly must be considered at the first level because
the telephony service providers do not "own" or control the
telephone numbers under the NP environment; therefore, they may not
be the proper entities to have the authority for a given E.164
number. Not only that, the donor network should not be relied on to
reach the delegated authority during the DNS process because there
is a regulatory requirement on NP in some countries. The delegated
authority for a given E.164 number is likely to be an entity
designated by the end user that owns/controls a specific telephone
number or a third-party designated by the end-user or by the
industry.
The IP-based networks also may need to support some forms of number
portability in the future if E.164 numbers [E164] are assigned to
the IP-based end users. One method is to assign a GSTN routing
number for each IP-based network domain or entity in a NP-capable
country. This may increase the number of digits in the routing
number to incorporate the IP entities and impact the existing
routing in the GSTN. Another method is to associate each IP entity
with a particular GSTN gateway. At that particular GSTN gateway,
the called directory number then is used to locate the IP-entity
that serves that dialed directory number. Yet, another method can
be to assign a special routing number so that the call to an end
user currently served by an IP entity is routed to the nearest GSTN
gateway. The called directory number then is used to locate the IP-
entity that serves that dialed directory number. Then a mechanism
is developed for the IP-based network to locate the IP entity that
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 23
Number Portability in the GSTN: An Overview February 9, 2000
serves a particular dialed directory number. Many other types of
networks use E.164 numbers to identify the end users or terminals in
those networks. Number portability among GSTN, IP-based network and
those various types of networks may also need to be supported in the
future.
11. References
[ANSI OSS] ANSI Technical Requirements No. 1, "Number Portability -
Operator Services Switching Systems," April 1999.
[ANSI SS] ANSI Technical Requirements No. 2, "Number Portability -
Switching Systems," April 1999.
[ANSI DB] ANSI Technical Requirements No. 3, "Number Portability
Database and Global Title Translation," April 1999.
[CS1] ITU-T Q-series Recommendations - Supplement 4, "Number
portability Capability set 1 requirements for service provider
portability (All call query and onward routing)," May 1998.
[CS2] ITU-T Q-series Recommendations - Supplement 5, "Number
portability -Capability set 2 requirements for service provider
portability (Query on release and Dropback)," March 1999.
[E164] ITU-T Recommendation E.164, "The International Public
Telecommunications Numbering Plan," 1997.
[ENUM] P. Falstrom, "E.164 number and DNS," RFC 2916.
[ENUMPO] A. Brown and G. Vaudreuil, "ENUM Service Specific
Provisioning: Principles of Operations," April 27, 2000.
[GSM] GSM 09.02: "Digital cellular telecommunications system (Phase
2+); Mobile Application Part (MAP) specification".
[IS41] TIA/EIA IS-756 Rev. A, "TIA/EIA-41-D Enhancements for
Wireless Number Portability Phase II (December 1998)"Number
Portability Network Support," April 1998.
[ISUP] ITU-T COM 11-R 162-E, Draft Recommendation Q.769.1,
"Signaling System No. 7 - ISDN User Part Enhancements for the
Support of Number Portability," May 1999.
[MNP] Draft GSM 03.66 V7.2.0 (1999-11) European Standard
(Telecommunications series) Digital cellular telecommunications
system (Phase 2+); Support of Mobile Number Portability (MNP);
Technical Realisation; Stage 2; (GSM 03.66 Version 7.2.0
Release 1998).
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 24
Number Portability in the GSTN: An Overview February 9, 2000
[RFC] Scott Bradner, RFC2026, "The Internet Standards Process --
Revision 3," October 1996.
[TEL] A. Vaha-Sipila, RFC2806, "URLs for Telephone Calls," April
2000.
[TELNP] J. Yu, draft-yu-tel-url-02.txt, "Extensions to the "tel" and
"fax" URLs to support Number Portability and Freephone
Service," February 9, 2001.
[SIP] M. Handley, H. Schulzrinne, E. Schooler and J. Rosenberg, RFC
2543, "SIP: Session Initiation Protocl," March 1999.
[TRIP] J. Rosenberg, H. Salama and M. Squire, draft-ietf-iptel-trip-
02.txt, "Telephony Routing Information Protocol (TRIP)," May
2000.
12. Acknowledgments
The authors would like to thank Monika Muench for providing
reference information on ISUP and MNP.
13. Author's Addresses
Mark D. Foster
NeuStar, Inc.
1120 Vermont Avenue, NW,
Suite 550
Washington, D.C. 20005
United States
Phone: +1-202-533-2800
Fax: +1-202-533-2976
Email: mark.foster@neustar.com
Tom McGarry
NeuStar, Inc.
1120 Vermont Avenue, NW,
Suite 550
Washington, D.C. 20005
United States
Phone: +1-202-533-2810
Fax: +1-202-533-2987
James Yu
NeuStar, Inc.
1120 Vermont Avenue, NW,
Suite 550
<Foster,McGarry,Yu> Informational - Expiration in August 9, 2001 25
Number Portability in the GSTN: An Overview February 9, 2000
Washington, D.C. 20005
United States
Phone: +1-202-533-2814
Fax: +1-202-533-2987
Email: james.yu@neustar.com
Full Copyright Statement
"Copyright (C) The Internet Society (date). 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.
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