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+Network Working Group                                          M. Foster
+Request for Comments: 3482                                    T. McGarry
+Category: Informational                                            J. Yu
+                                                           NeuStar, Inc.
+                                                           February 2003
+
+
+  Number Portability in the Global Switched Telephone Network (GSTN):
+                              An Overview
+
+Status of this Memo
+
+   This memo provides information for the Internet community.  It does
+   not specify an Internet standard of any kind.  Distribution of this
+   memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+Abstract
+
+   This document provides an overview of E.164 telephone number
+   portability (NP) in the Global Switched Telephone Network (GSTN).
+   NP is a regulatory imperative seeking to liberalize local telephony
+   service competition, by enabling end-users to retain telephone
+   numbers while changing service providers.  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 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 works-in-progress
+   with the IETF.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Foster, et al.               Informational                      [Page 1]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+Table of Contents
+
+   1.  Introduction .................................................  2
+   2.  Abbreviations and Acronyms ...................................  4
+   3.  Types of Number Portability ..................................  6
+   4.  Service Provider Number Portability Schemes ..................  7
+       4.1   All Call Query (ACQ) ...................................  8
+       4.2   Query on Release (QoR) .................................  9
+       4.3   Call Dropback .......................................... 10
+       4.4   Onward Routing (OR) .................................... 11
+       4.5   Comparisons of the Four Schemes ........................ 11
+   5.  Database Queries in the NP Environment ....................... 13
+       5.1   U.S. and Canada ........................................ 13
+       5.2   Europe ................................................. 14
+   6.  Call Routing in the NP Environment ........................... 15
+       6.1   U.S. and Canada ........................................ 16
+       6.2   Europe ................................................. 17
+   7.  NP Implementations for Geographic E.164 Numbers .............. 19
+   8.  Number Conservation Method Enabled By NP ..................... 22
+       8.1   Block Pooling .......................................... 22
+       8.2   ITN Pooling ............................................ 23
+   9.  Potential Implications ....................................... 23
+   10. Security Considerations ...................................... 27
+   11. IANA Considerations .......................................... 27
+   12. Normative References ......................................... 27
+   13. Informative References ....................................... 28
+   14. Acknowledgement .............................................. 29
+   15. Authors' Addresses ........................................... 29
+   16. Full Copyright Statement ..................................... 30
+
+1. Introduction
+
+   This document provides an overview of E.164 telephone number [E164]
+   portability in the Global Switched Telephone Network (GSTN).  There
+   are considered to be three types of number portability (NP): service
+   provider number portability (SPNP), location portability (not to be
+   confused with terminal mobility), and service portability.
+
+   SPNP, the focus of the present document, 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).
+
+
+
+
+
+Foster, et al.               Informational                      [Page 2]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   E.164 numbers can be non-geographic and geographic numbers.  Non-
+   geographic numbers do not reveal the location 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 impact in cost and convenience to the subscriber of changing
+   numbers is seen as a 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
+   implementations attempt to encapsulate the impact 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 is that enables IP address portability by containing the
+   address change to the edge of the network and retain the use of
+   Classless Inter-Domain Routing (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 translation database, carried by forward call
+   signaling, and recorded on call detail records.  Not only is call
+   processing and routing affected, but also Signaling System Number 7
+   (SS7)/Common Channel Signaling System Number 7 (C7) messaging.  A
+   number of Transaction Capabilities Application Part (TCAP)-based SS7
+
+
+
+Foster, et al.               Informational                      [Page 3]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   messaging sets utilize an E.164 address as an application-level
+   network element address in the global title address (GTA) field of
+   the Signaling Connection Control Part (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 works-in-progress with the IETF.
+
+   This document describes three types of number portability and the
+   four schemes that have been standardized to support SPNP for
+   geographic E.164 numbers specifically.  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 North America and Europe are described to show the
+   variety of standards that may be implemented worldwide.  A glance at
+   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 and Telecommunications
+   Interoperability.
+
+2. Abbreviations and Acronyms
+
+   ACQ     All Call Query
+   AIN     Advanced Intelligent Network
+   AMPS    Advanced Mobile Phone System
+   ANSI    American National Standards Institute
+   API     Application Programming Interface
+   C7      Common Channel Signaling System Number 7
+   CDMA    Code Division Multiple Access
+   CdPA    Called Party Address
+   CdPN    Called Party Number
+   CH      Code Holder
+   CIC     Carrier Identification Code
+   CIDR    Classless Inter-Domain Routing
+   CMIP    Common Management Information Protocol
+   CO      Central Office
+   CS1     Capability Set 1
+
+
+
+Foster, et al.               Informational                      [Page 4]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   CS2     Capability Set 2
+   DN      Directory Number
+   DNS     Domain Name System
+   ENUM    Telephone Number Mapping
+   ETSI    European Tecommunications Standards Institute
+   FCI     Forward Call Indicator
+   GAP     Generic Address Parameter
+   GMSC    Gateway Mobile Services Switching Center or Gateway Mobile
+           Switching Center
+   GNP     Geographic Number Portability
+   GSM     Global System for Mobile Communications
+   GSTN    Global Switched Telephone Network
+   GTT     Global Title Translation
+   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
+   LERG    Local Exchange Routing Guide
+   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
+   NGNP    Non-Geographic Number Portability
+   NOA     Nature of Address
+   NP      Number Portability
+   NPA     Numbering Plan Area
+   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, et al.               Informational                      [Page 5]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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
+   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
+
+3. 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-called 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 (GNP), 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 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
+
+
+
+Foster, et al.               Informational                      [Page 6]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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 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.
+
+4. 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 when the TN ports back into the donor network and away
+
+
+
+Foster, et al.               Informational                      [Page 7]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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 of NP further bifurcates the role of the
+   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 previously been ported out of the donor network.
+
+   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 the 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.
+
+4.1 All Call Query (ACQ)
+
+   Figure 1 shows the call steps for the ACQ scheme.  Those call steps
+   are as follows:
+
+   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 6.
+
+   3) The Originating Network uses the routing number to route the call
+      to the new serving network.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Foster, et al.               Informational                      [Page 8]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   +-------------+              +-----------+    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.
+
+4.2 Query on Release (QoR)
+
+   Figure 2 shows the call steps for the QoR scheme.  Those call steps
+   are as follows:
+
+   +-------------+              +-----------+    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.
+
+   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.
+
+
+
+
+Foster, et al.               Informational                      [Page 9]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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.
+
+4.3 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.
+
+   +-------------+              +-----------+    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.
+
+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 10]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+4.4 Onward Routing (OR)
+
+   Figure 4 shows the call steps for the OR 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 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.
+
+4.5 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 transmission
+   facilities.  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
+
+
+
+Foster, et al.               Informational                     [Page 11]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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 contain 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, which is also
+   known as the area code.  It is three-digits 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 a NPA+NXX code is set as "portable"
+   in the Local Exchange Routing Guide (LERG), it becomes a "portable
+   NPA+NXX" code.
+
+   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 of whether the dialed directory number belongs to
+   any number range that is portable or has at least one number ported
+   out.  The other version is to check whether the dialed directory
+   number belongs to any number range that is portable or has at least
+   one number ported out.  If yes, an NPDB query is sent.  If not, no
+
+
+
+Foster, et al.               Informational                     [Page 12]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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.
+
+5. 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 is 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.
+
+5.1 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 SCCP and ANSI 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 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.
+
+
+
+Foster, et al.               Informational                     [Page 13]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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, accessed via an Application
+      Programming Interface (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.
+
+5.2 Europe
+
+   One of the following two 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 3, ITU-TS SCCP, and ITU-TS TCAP.
+
+
+
+Foster, et al.               Informational                     [Page 14]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   Wireline switches have the choice of using either (a) or (b);
+   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 the 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 6.2.
+
+6. 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. a "N-1"
+   policy is used, which essentially says that for local calls, the
+   originating local carriers performs the query.  Otherwise, the long
+   distance carrier is expected to follow through with the query.  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 when redundant queries are performed
+   downstream.
+
+
+
+
+Foster, et al.               Informational                     [Page 15]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+6.1 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
+   a 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.
+
+
+
+Foster, et al.               Informational                     [Page 16]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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.
+
+6.2 Europe
+
+   In some European countries, 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, that 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.
+
+   The call routing example described above shows one of the three
+   methods that can be used to transport the Directory Number (DN) and
+   the Routing Number (RN) in the ISUP IAM message.  In addition, some
+   other information may be added/modified as is listed in the ETSI 302
+   097 document [ETSIISUP], which is based on the ITU-T Recommendation
+   Q.769.1 [ITUISUP].  The three methods and the enhancements in ISUP to
+   support number portability are briefly described below:
+
+   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
+
+
+
+Foster, et al.               Informational                     [Page 17]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+      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.  For
+      example, 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 of the NP enhancements for a ported number can
+   only be used in the country that defined them.  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 usually not passed across the national
+   boundaries unless the interconnection agreements allow it.  For
+   example, a UK routing prefix can only be used in the UK, and would
+   cause a routing problem if it appears outside the UK.
+
+   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.
+
+   There are several ways of realizing MNP.  If MNP-SRF is supported,
+   the Gateway Mobile Services Switching Center (GMSC) at the wireless
+
+
+
+Foster, et al.               Informational                     [Page 18]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   donor network can send the GSM MAP Send Routing Information (SRI)
+   message to the MNP-SRF when receiving a call from the wireline
+   network.  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.
+
+7. 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.                                +
+   +-------------+----------------------------------------------------+
+
+
+
+Foster, et al.               Informational                     [Page 19]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   +-------------+----------------------------------------------------+
+   +   Country   +             SPNP Implementation                    +
+   +-------------+----------------------------------------------------+
+   +   Austria   + Uses onward routing at the donor network.  Routing +
+   +             + prefix is "86xx" where "xx" identifies the         +
+   +             + recipient network.                                 +
+   +-------------+----------------------------------------------------+
+   +  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 became 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.      +
+   +-------------+----------------------------------------------------+
+
+
+
+
+Foster, et al.               Informational                     [Page 20]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   +-------------+----------------------------------------------------+
+   +   Country   +             SPNP Implementation                    +
+   +-------------+----------------------------------------------------+
+   +  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.       +
+   +-------------+----------------------------------------------------+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 21]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   +-------------+----------------------------------------------------+
+   +   Country   +             SPNP Implementation                    +
+   +-------------+----------------------------------------------------+
+   + 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.                                         +
+   +-------------+----------------------------------------------------+
+
+8. 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.
+
+8.1 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.
+
+
+
+Foster, et al.               Informational                     [Page 22]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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.
+
+8.2 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.
+
+9. Potential Implications
+
+   There are three general areas of impact to IP telephony works-in-
+   progress with the IETF:
+
+   - Interoperation between NP in GSTN and IP telephony
+   - NP implementation or emulation in IP telephony
+   - 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 5, there are a variety of standards with various protocol
+   stacks for the switch-to-NPDB interface.  Furthermore, the national
+   variations of the protocol standards make it very complicated 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 an
+
+
+
+Foster, et al.               Informational                     [Page 23]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   impractical, if not 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 that contain the same
+   information but support the common IP interface can be deployed.  The
+   candidates for such a common interface include ENUM (telephone number
+   mapping) [ENUM], Lightweight Directory Access Protocol (LDAP) and SIP
+   [SIP] (e.g., using the SIP redirection capability).  Certainly
+   another possibility is to use an interworking function to convert
+   from one protocol to another.
+
+   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 the
+   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.  Please see [TELNP] for the
+   proposed extensions to the "tel" URL to support NP and freephone
+   service.  Those extensions to the "tel" URL will be automatically
+   supported by SIP because they can be carried as the optional
+   parameters in the user portion of the "sip" URL.
+
+
+
+Foster, et al.               Informational                     [Page 24]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   For a called directory number that belongs to a country that supports
+   NP, and if the IP-based network is expected 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 or sip URL in the SIP INVITE message, it,
+   instead of the called directory number, should be used for making
+   routing decisions assuming that no other higher priority routing-
+   related parameters such as the "cic" (Carrier Identification Code)
+   are present.  If "rn" (Routing Number) 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 if present, it is
+   the routing number, 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 by collecting the complete
+   called directory number.
+
+   The IETF enum working group is defining the use of the Domain Name
+   System (DNS) for identifying available services and/or Internet
+   resources associated with a particular E.164 number.  [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
+
+
+
+Foster, et al.               Informational                     [Page 25]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   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, there is a
+   regulatory requirement on NP in some countries that the donor network
+   should not be relied on to reach the delegated authority during the
+   DNS process.  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 one that is designated by the service
+   registrar.
+
+   Since the telephony service providers may have the need to use ENUM
+   for their network-related services (e.g., map an E.164 number to a
+   HLR Identifier in the wireless networks), their ENUM records must be
+   collocated with those of the telephony subscribers.  If that is the
+   case, NP will impact ENUM when a telephony subscriber who has ENUM
+   service changes the telephony service provider.  This is because that
+   the ENUM records from the new telephony service provider must replace
+   those from the old telephony service provider.  To avoid the NP
+   impact on ENUM, it is recommended that the telephony service
+   providers use a different domain tree for their network-related
+   service.  For example, if e164.arpa is chosen for "end user" ENUM, a
+   domain tree different from e164.arpa should be used for "carrier"
+   ENUM.
+
+   The IP-based networks also may need to support some forms of number
+   portability in the future if E.164 numbers 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 is then 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.  A mechanism can be developed or
+   used 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.
+
+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 26]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+10. Security Considerations
+
+   In the PSTN, the NPDB queries are generated by the PSTN switches and
+   carried over the SS7 networks to reach the NPDBs and back to the
+   switches.  The SS7 networks are operated by telecommunications
+   operators and signaling transport service providers in such a closed
+   environment that make them difficult for the hackers to penetrate.
+   However, when VoIP operators need the NP information and have to
+   launch the NP queries from their softswitches, media gateway
+   controllers or call managers, there would be security concerns if the
+   NP queries and responses are transported over the Internet.  If the
+   routing number or routing prefix in the response is altered during
+   the message transport, the call will be routed to the wrong place.
+   It is recommended that the NPDB queries be transported via a secure
+   transport layer or with added security mechanisms to ensure the data
+   integrity.
+
+11. IANA Considerations
+
+   This document introduces no new values for IANA registration.
+
+12. Normative 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]     Falstrom, P., "E.164 number and DNS", RFC 2916, September
+              2000.
+
+
+
+
+Foster, et al.               Informational                     [Page 27]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+   [ETSIISUP] ETSI EN 302 097 V.1.2.2, Integrated Services Digital
+              Network (ISDN); Signalling System No.7 (SS7); ISDN User
+              Part (ISUP); Enhancement for support of Number Portability
+              (NP) [ITU-T Recommendation Q.769.1 (2000), modified]
+
+   [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.
+
+   [ITUISUP]  ITU-T Recommendation Q.769.1, "Signaling System No. 7 -
+              ISDN User Part Enhancements for the Support of Number
+              Portability," December 1999.
+
+   [MNP]      ETSI EN 301 716 (2000-10) 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]      Bradner, S., "The Internet Standards Process -- Revision
+              3", BCP 9, RFC 2026, October 1996.
+
+13. Informative References
+
+   [ENUMPO]   Brown A. and G. Vaudreuil, "ENUM Service Specific
+              Provisioning: Principles of Operations", Work in Progress.
+
+   [SIP]      Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
+              A., Peterson, J., Sparks, R., Handley, M. and E. Schooler,
+              "SIP:  Session Initiation Protocol", RFC 3461, June 2002.
+
+   [TEL]      Schulzrinne, H. and A. Vaha-Sipila, "URIs for Telephone
+              Calls", Work in Progress.
+
+   [TELNP]    Yu, J., "Extensions to the "tel" URL to support Number
+              Portability and Freephone Service", Work in Progress.
+
+   [TRIP]     Rosenberg, J., Salama, H. and M. Squire, "Telephony
+              Routing Information Protocol (TRIP)", RFC 3219, January
+              2002.
+
+
+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 28]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+14. Acknowledgment
+
+   The authors would like to thank Monika Muench for providing
+   information on ISUP and MNP.
+
+15. Authors' Addresses
+
+   Mark D. Foster
+   NeuStar, Inc.
+   46000 Center Oak Plaza
+   Sterling, VA 20166
+   United States
+
+   Phone: +1-571-434-5410
+   Fax:   +1-571-434-5401
+   EMail: mark.foster@neustar.biz
+
+
+   Tom McGarry
+   NeuStar, Inc.
+   46000 Center Oak Plaza
+   Sterling, VA 20166
+   United States
+
+   Phone: +1-571-434-5570
+   Fax:   +1-571-434-5401
+   EMail: tom.mcgarry@neustar.biz
+
+
+   James Yu
+   NeuStar, Inc.
+   46000 Center Oak Plaza
+   Sterling, VA 20166
+   United States
+
+   Phone: +1-571-434-5572
+   Fax:   +1-571-434-5401
+   EMail: james.yu@neustar.biz
+
+
+
+
+
+
+
+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 29]
+
+RFC 3482      Number Portability in the GSTN: An Overview  February 2003
+
+
+16. Full Copyright Statement
+
+   Copyright (C) The Internet Society (2003).  All Rights Reserved.
+
+   This document and translations of it may be copied and furnished to
+   others, and derivative works that comment on or otherwise explain it
+   or assist in its implementation may be prepared, copied, published
+   and distributed, in whole or in part, without restriction of any
+   kind, provided that the above copyright notice and this paragraph are
+   included on all such copies and derivative works.  However, this
+   document itself may not be modified in any way, such as by removing
+   the copyright notice or references to the Internet Society or other
+   Internet organizations, except as needed for the purpose of
+   developing Internet standards in which case the procedures for
+   copyrights defined in the Internet Standards process must be
+   followed, or as required to translate it into languages other than
+   English.
+
+   The limited permissions granted above are perpetual and will not be
+   revoked by the Internet Society or its successors or assigns.
+
+   This document and the information contained herein is provided on an
+   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Foster, et al.               Informational                     [Page 30]
+