Internet DRAFT - draft-enum-e164-gstn-np

draft-enum-e164-gstn-np




Internet Draft						Mark Foster
Document: <draft-ietf-enum-e164-gstn-np-01.txt>		Tom McGarry
Category: Informational					  James Yu 
						      NeuStar, Inc.
					              November 2000

		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]. 

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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 


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the later to the former.  In addition, there are various regulatory 
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, 



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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 
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'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 

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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.


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
CRTC    Canadian Radio and Television Commission
CS1	   Capability Set 1
CS2	   Capability Set 2
DN	   Directory Number
DNS     Domain Name System
ETSI    European Technical Standards Institute
FCC     Federal Communications Commission
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
ICC	   Illinois Commerce Commission
IETF    Internet Engineering Task Force
IN	   Intelligent Network
INAP    Intelligent Network Application Part
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 

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LEC     Local Exchange Carrier
LLC	   Limited Liability Corporation
LNP	   Local Number Portability
LRN	   Location Routing Number
LSMS    Local Service Management System
MAP	   Mobile Application Part
MNP	   Mobile Number Portability
MSRN    Mobile Station Roaming Number
MTP	   Message Transfer Part
NANC    North American Numbering Council
NANP    North American Numbering Plan
NP	   Number Portability
NPAC    Number Portability Administration Center
NPDB    Number Portability Database
NPRM    Notice of Proposed Rulemaking
NRN     Network Routing Number
OR	   Onward Routing
OSS     Operation Support System
PCS	   Personal Communication Services
PNTI    Ported Number Translation Indicator
PODP    Public Office Dialing Plan
PUC	   Public Utility Commission
QoR	   Query on Release
RBOC    Regional Bell Operating Company
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
SOA	   Service Order Administration
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 


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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'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 
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 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.


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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 
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:


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+-------------+              +-----------+    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.


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. 






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(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.
(5) The Originating Network uses the routing number to route the 
call to the new serving network.









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+-------------+              +-----------+    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.














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+-------------+              +-----------+    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.



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


 
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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 
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" 


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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 
LRN implementation of LNP 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 
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 

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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 theUnited 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:

(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 


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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 
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 "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. 
 

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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.

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 


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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 
in the draft ITU-T Recommendation Q.769.1 [ISUP].   Those 
enhancements in the ISUP to support number portability are briefly 
described below.  



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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.

If MNP-SRF is supported, the Gateway Mobile Services Switching 
Center (GMSC) at the wireless donor network, when receiving a call 


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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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+-------------+----------------------------------------------------+
+   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.      +
+-------------+----------------------------------------------------+


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+  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.     +
+             + 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.                                           +



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+-------------+----------------------------------------------------+
+  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.                                         +
+-------------+----------------------------------------------------+

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 


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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 
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. NP implementation or emulation in IP telephony
2. Interoperation between NP in GSTN and 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 and 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 

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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).

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.

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 

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the called directory number.  Therefor, 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 
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 


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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 
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.


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INTERNET DRAFT 	NP IN THE GSTN : AN OVERVIEW      November 17,2000


[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".


[ICC] ICC, "Generic Switching & Signaling Requirements for Number 
Portability, Issue 1.05," August 1, 1997.

[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).

[RFC] Scott Bradner, RFC2026, "The Internet Standards Process -- 
Revision 3," October 1996.

[TEL] A. Vaha-Sipila, RFC2806, "URLs for Telephone Calls," April 
2000.

[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.





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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:   +1-202-533-2975
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:   +1-202-533-2975


James Yu
NeuStar, Inc.
1120 Vermont Avenue, NW, 
Suite 550
Washington, D.C. 20005
United States

Phone: +1-202-533-2814
Fax:   +1-202-533-2975
Email: james.yu@neustar.com




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Number Portability in the GSTN: An Overview	      November 2000