[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-foster-e164-gstn-np) 00 01 02 03 04 05 RFC 3482

                                                            Mark Foster
Internet Draft                                              Tom McGarry
Document: <draft-ietf-enum-e164-gstn-np-05.txt>                James Yu
                                                          NeuStar, Inc.
Category: Informational                                   June 24, 2002


              Number Portability in the GSTN: An Overview


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [RFC].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


   Copyright Notice

      Copyright (C) The Internet Society (2002).  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 work-in-progress at IETF.

Foster,McGarry,Yu         Expired on December 23, 2002        [Page 1]


Number Portability in the GSTN: An Overview               June 24, 2002


   Table of Contents

    1.  Introduction ...............................................  2
    2.  Abbreviations and Acronyms .................................  4
    3.  Types of Number Portability ................................  5
    4.  Service Provider Number Portability Schemes ................  7
       4.1   All Call Query (ACQ) ..................................  7
       4.2   Query on Release (QoR) ................................  8
       4.3   Call Dropback .........................................  9
       4.4   Onward Routing (OR) ...................................  9
       4.5   Comparisons of the Four Schemes ....................... 10
    5.  Database Queries in the NP Environment ..................... 11
       5.1   U.S. and Canada ....................................... 12
       5.2   Europe ................................................ 13
    6.  Call Routing in the NP Environment ......................... 14
       6.1   U.S. and Canada ....................................... 14
       6.2   Europe ................................................ 15
    7.  NP Implementations for Geographic E.164 Numbers ............ 17
    8.  Number Conservation Method Enabled By NP ................... 20
       8.1   Block Pooling ......................................... 20
       8.2   ITN Pooling ........................................... 21
    9.  Potential Implications ..................................... 21
   10.  Security Considerations .................................... 24
   11.  IANA Considerations ........................................ 24
   12.  Normative References ....................................... 24
   13.  Informative References ..................................... 25
   14.  Acknowledgement ............................................ 25
   15.  AuthorsË Addresses ......................................... 25



1. 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

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 2]


Number Portability in the GSTN: An Overview               June 24, 2002

   end-office switch, and specific line of the called party.  As such,
   without NP a subscriber wishing to change service providers would
   incur a number change as a consequence of being served off of a
   different end-office switch operated by the new service provider.
   The cost and convenience impact to the subscriber of changing
   numbers is seen as barrier to competition.  Hence NP has become
   associated with GSTN infrastructure enhancements associated with a
   competitive environment driven by regulatory directives.

   Forms of SPNP have been deployed or are being deployed widely in the
   GSTN in various parts of the world, including the U.S., Canada,
   Western Europe, Australia, and the Pacific Rim (e.g. Hong Kong).
   Other regions, such as South America (e.g. Brazil) are actively
   considering it.

   Implementation of NP within a national telephony infrastructure
   entails potentially significant changes to numbering administration,
   network element signaling, call routing and processing, billing,
   service management, and other functions.

   NP changes the fundamental nature of a dialed E.164 number from a
   hierarchical physical routing address to a virtual address.  NP
   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 subscriberËs 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


Foster,McGarry,Yu           Expired on December 23, 2002      [Page 3]


Number Portability in the GSTN: An Overview               June 24, 2002

   existing GSTN NP implementations, are relevant topics for numerous
   areas of IP telephony work-in-progress at IETF.

   This document describes three types of number portability and the
   four schemes that have been standardized to support SPNP for
   geographic E.164 numbersspecifically.  Following that, specific
   information regarding the call routing and database query
   implementations are described for several regions (North American
   and Europe) and industries (wireless vs. wireline). The Number
   Portability Database (NPDB) interfaces and the call routing schemes
   that are used in the North America and Europe are described to show
   the variety of standards that may be implemented worldwide.  A
   glance of the NP implementations worldwide is provided.  Number
   pooling is briefly discussed to show how NP is being enhanced in the
   U.S. to conserve North American area codes.  The conclusion briefly
   touches the potential impacts of NP on IP & Telecommunications
   Interoperability.  Appendix A provides some specific technical and
   regulatory information on NP in North America.  Appendix B describes
   the number portability administration process that manages the
   number portability database in North America.


2. Abbreviations and Acronyms

   ACQ     All Call Query
   AIN     Advanced Intelligent Network
   AMPS    Advanced Mobile Phone System
   ANSI    American National Standards Institute
   CDMA    Code Division Multiple Access
   CdPA    Called Party Address
   CdPN    Called Party Number
   CH      Code Holder
   CMIP    Common Management Information Protocol
   CS1     Capability Set 1
   CS2     Capability Set 2
   DN      Directory Number
   DNS     Domain Name System
   ETSI    European Technical Standards Institute
   FCI     Forward Call Indicator
   GAP     Generic Address Parameter
   GMSC    Gateway Mobile Services Switching Center or Gateway Mobile
           Switching Center
   GSM     Global System for Mobile Communications
   GSTN    Global Switched Telephone Network
   GW      Gateways
   HLR     Home Location Register
   IAM     Initial Address Message
   IETF    Internet Engineering Task Force
   ILNP    Interim LNP
   IN      Intelligent Network
   INAP    Intelligent Network Application Part
   INP     Interim NP
   IP      Internet Protocol
   IS-41   Interim Standards Number 41

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 4]


Number Portability in the GSTN: An Overview               June 24, 2002

   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
   NP      Number Portability
   NPDB    Number Portability Database
   NRN     Network Routing Number
   OR      Onward Routing
   OSS     Operation Support System
   PCS     Personal Communication Services
   PNTI    Ported Number Translation Indicator
   PODP    Public Office Dialing Plan
   PUC     Public Utility Commission
   QoR     Query on Release
   RN      Routing Number
   RTP     Return to Pivot
   SCCP    Signaling Connection Control Part
   SCP     Service Control Point
   SIP     Session Initiation Protocol
   SMR     Special Mobile Radio
   SMS     Service Management System
   SPNP    Service Provider Number Portability
   SRF     Signaling Relaying Function
   SRI     Send Routing Information
   SS7     Signaling System Number 7
   STP     Signaling Transfer Point
   TCAP    Transaction Capabilities Application Part
   TDMA    Time Division Multiple Access
   TN      Telephone Number
   TRIP    Telephony Routing Information Protocol
   URL     Universal Resource Locator
   U.S.    United States


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-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.

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 5]


Number Portability in the GSTN: An Overview               June 24, 2002


   Geographic number portability, which includes traditional fixed or
   wireline numbers as well as mobile numbers which are allocated out
   of geographic number range prefixes, is called NP or GNP or in the
   U.S. local number portability (LNP).

   Number portability allows the telephony subscribers in the Global
   Switched Telephone Network (GSTN) to keep their phone numbers when
   they change their service providers or subscribed services, or when
   they move to a new location.

   The ability to change the service provider while keeping the same
   phone number is called service provider portability (SPNP) also
   known as "operator portability."

   The ability to change the subscriberËs 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 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.





Foster,McGarry,Yu           Expired on December 23, 2002      [Page 6]


Number Portability in the GSTN: An Overview               June 24, 2002


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 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.


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.


Foster,McGarry,Yu           Expired on December 23, 2002      [Page 7]


Number Portability in the GSTN: An Overview               June 24, 2002

   (3) 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  |
   +-------------+    |         +-----------+             +-----------+
       ^  |           |
       |  |           |
      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,McGarry,Yu           Expired on December 23, 2002      [Page 8]


Number Portability in the GSTN: An Overview               June 24, 2002

   (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.


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.


Foster,McGarry,Yu           Expired on December 23, 2002      [Page 9]


Number Portability in the GSTN: An Overview               June 24, 2002

   (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
   between the Originating Network and the donor network when the
   Originating Network sets up the call towards the donor network.
   Those circuits are released one by one when the call is released
   from the donor network back to the Originating Network.  The ACQ
   scheme is the most efficient in terms of using the switching and
   transmission facilities for the call.

   Both the ACQ and QoR schemes involve Centralized NPDBs for the
   Originating Network to retrieve the routing information.
   Centralized NPDB means that the NPDB contains ported number
   information from multiple networks.  This is in contrast to the
   internal network-specific NPDB that is used for the Dropback and OR
   schemes.  The internal NPDB only contains information about the
   numbers that were ported out of the donor network.  The internal
   NPDB can be a stand-alone database that contains information about
   all or some ported-out numbers from the donor network.  It can also
   reside on the donor switch and only contains information about those

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 10]


Number Portability in the GSTN: An Overview               June 24, 2002

   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 a NPA+NXX code is set as
   Ÿportable÷ 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 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 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 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.



Foster,McGarry,Yu           Expired on December 23, 2002      [Page 11]


Number Portability in the GSTN: An Overview               June 24, 2002

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 Signaling
       Connection Control Part (SCCP), and ANSI Transaction
       Capabilities Application Part (TCAP).  This interface can be
       used by the wireline or wireless switches, is specific to the NP
       implementation in North America, and is modeled on the Public
       Office Dialing Plan (PODP) trigger defined in the Advanced
       Intelligent Network (AIN) 0.1 call model.

   (b) Intelligent Network (IN), which is similar to the one used for
       querying the 800 databases.  The IN protocol is carried on top
       of the protocol stack that includes the ANSI MTP Levels 1
       through 3, ANSI SCCP, and ANSI TCAP.  This interface can be used
       by the wireline or wireless switches.

   (c) ANSI IS-41 [IS41] [ISNP], which is carried on top of the
       protocol stack that includes the ANSI MTP Levels 1 through 3,
       ANSI SCCP, and ANSI TCAP.  This interface can be used by the IS-
       41 based cellular/Personal Communication Services (PCS) wireless
       switches (e.g., AMPS, TDMA and CDMA).  Cellular systems use
       spectrum at 800 MHz range and PCS systems use spectrum at 1900
       MHz range.

   (d) Global System for Mobile Communication Mobile Application Part
       (GSM MAP) [GSM], which is carried on top of the protocol stack
       that includes the ANSI MTP Levels 1 through 3, ANSI SCCP, and
       International Telecommunication Union - Telecommunication Sector
       (ITU-TS) TCAP.  It can be used by the PCS1900 wireless switches
       that are based on the GSM technologies.  GSM is a series of
       wireless standards defined by the European Telecommunications
       Standards Institute (ETSI).

   (e) ISUP triggerless translation.  NP translations are performed
       transparently to the switching network by the signaling network
       (e.g. Signaling Transfer Points (STPs) or signaling gateways).
       ISUP IAM messages are examined to determine if the CdPN field
       has already been translated, and if not, an NPDB query is
       performed, and the appropriate parameters in the IAM message
       modified to reflect the results of the translation.   The
       modified IAM message is forwarded by the signaling node on to
       the designated DPC in a transparent manner to continue call
       setup.  The NPDB can be integrated with the signaling node or be
       accessed via an API locally or by a query to a remote NPDB using
       a proprietary protocol or the schemes described above.



Foster,McGarry,Yu           Expired on December 23, 2002      [Page 12]


Number Portability in the GSTN: An Overview               June 24, 2002

   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 ITU-TS MTP Levels 1 through 3, ITU-TS SCCP,
       and ITU-TS TCAP.

   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 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.




Foster,McGarry,Yu           Expired on December 23, 2002      [Page 13]


Number Portability in the GSTN: An Overview               June 24, 2002

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. an ŸN-1÷
   policy is used, which essentially says that for domestic calls, the
   originating local carriers performs the query, otherwise, the long
   distance carrier is expected to.  To ensure independence of the
   actual trigger policy employed in any one carrier, forward call
   signaling is used to flag that an NPDB query has already been
   performed and to therefore suppress any subsequent NP triggers that
   may be encountered in downstream switches, in downstream networks.
   This allows the earliest able network in the call path to perform
   the query without introducing additional costs and call setup delays
   were redundant queries performed downstream.


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

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 14]


Number Portability in the GSTN: An Overview               June 24, 2002

   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
   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.


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, 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.



Foster,McGarry,Yu           Expired on December 23, 2002      [Page 15]


Number Portability in the GSTN: An Overview               June 24, 2002

   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 the
   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 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 those 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 that.  For
   example, a UK routing prefix can only be used in UK, and would cause
   routing problem if it appears outside UK.




Foster,McGarry,Yu           Expired on December 23, 2002      [Page 16]


Number Portability in the GSTN: An Overview               June 24, 2002

   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.  When MNP-SRF is supported,
   the Gateway Mobile Services Switching Center (GMSC) at the wireless
   donor network, when receiving a call from the wireline network, can
   send the GSM MAP Send Routing Information (SRI) message to the MNP-
   SRF.  The MNP-SRF interrogates an internal or integrated NPDB for
   the RN of the MNP-SRF of the wireless Current Serving Network and
   prefixes the RN to the dialed wireless directory number in the
   global title address information in the SCCP Called Party Address
   (CdPA) parameter.  This SRI message will be routed to the MNP-SRF of
   the wireless Current Serving Network, which then responds with an
   acknowledgement by providing the RN plus the dialed wireless
   directory number as the Mobile Station Roaming Number (MSRN).  The
   GMSC of the wireless donor network formulates the ISUP IAM with the
   RN plus the dialed wireless directory number in the CdPN parameter
   and routes the call to the wireless Current Serving Network.  A GMSC
   of the wireless Current Serving Network receives the call and sends
   an SRI message to the associated MNP-SRF where the global title
   address information of the SCCP CdPA parameter contains only the
   dialed wireless directory number.  The MNP-SRF then replaces the
   global title address information in the SCCP CdPA parameter with the
   address information associated with a Home Location Register (HLR)
   that hosts the dialed wireless directory number and forwards the
   message to that HLR after verifying that the dialed wireless
   directory number is a ported-in number.   The HLR then returns an
   acknowledgement by providing an MSRN for the GMSC to route the call
   to the MSC that currently serves the mobile station that is
   associated with the dialed wireless directory number.  Please see
   [MNP] for details and additional scenarios.


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,   +


Foster,McGarry,Yu           Expired on December 23, 2002      [Page 17]


Number Portability in the GSTN: An Overview               June 24, 2002

   +             + 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.                                +
   +-------------+----------------------------------------------------+
   +   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.      +
   +-------------+----------------------------------------------------+
   +  Ireland    + Operators choose their own solution but use onward +
   +             + routing now. Routing prefix is "1750" as the intra-+

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 18]


Number Portability in the GSTN: An Overview               June 24, 2002

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

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 19]


Number Portability in the GSTN: An Overview               June 24, 2002

   +             + 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.

   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.




Foster,McGarry,Yu           Expired on December 23, 2002      [Page 20]


Number Portability in the GSTN: An Overview               June 24, 2002

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 work-in-
   progress at 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.  Not only that, 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 impractical, if not an impossible, job for that entity
   to support all those interface standards to access the NPDBs in many
   countries.

   Several alternatives may address this particular problem.  One
   alternative is to use certain entities in the IP-based networks for
   dealing with NP query, similar to the International Switches that
   are used in the GSTN to interwork different national ISUP
   variations.  This will force signaling information associated with
   the calls to certain NP-capable networks in the terminating GSTN to
   be routed to those IP entities that support the NP functions.  Those
   IP entities then query the NPDBs in the terminating country.   This
   will limit the number of NPDB interfaces that certain IP entities
   need to support.  Another alternative can be to define a "common"
   interface to be supported by all the NPDBs so that all the IP
   entities use that standardized protocol to query them.   The
   existing NPDBs can support this additional interface, or new NPDBs
   can be deployed that contain the same information but support the
   common IP interface. The candidates for such a common interface
   include Lightweight Directory Access Protocol (LDAP) and SIP
   [SIP](e.g., using the SIP redirection capability).  Certainly


Foster,McGarry,Yu           Expired on December 23, 2002      [Page 21]


Number Portability in the GSTN: An Overview               June 24, 2002

   another possibility is to use 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
   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.

   For a called directory number that belongs to a country that
   supports NP, and if the IP-based network is to perform the NPDB
   query, the logical step is to perform the NPDB dip first to retrieve
   the routing number and use that routing number to select the correct
   IP telephony gateways that can reach the serving switch that serves
   the called directory number.  Therefore, if the "rn" parameter is
   present in the "tel" URL 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 Ÿcic÷ are present.  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

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 22]


Number Portability in the GSTN: An Overview               June 24, 2002

   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 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, 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 Ÿend user÷ ENUM, a
   domain tree different from e164.arpa should be used for Ÿcarrier÷
   ENUM.

   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

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 23]


Number Portability in the GSTN: An Overview               June 24, 2002

   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.


10. Security Considerations

   This document does not raise any security issues.


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] P. Falstrom, "E.164 number and DNS," RFC 2916.

   [ETSIISUP] ETSI EN 302 097 V.1.2.2, ŸIntegrated 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".

Foster,McGarry,Yu           Expired on December 23, 2002      [Page 24]


Number Portability in the GSTN: An Overview              March 1, 2002



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


13. Informative References

   [ENUMPO] A. Brown and G. Vaudreuil, "ENUM Service Specific
        Provisioning: Principles of Operations," draft-ietf-enum-
        operation-02.txt, February 23, 2001.

   [SIP] J. Rosenberg, et al., draft-ietf-sip-rfc2543bis-09.txt, "SIP:
        Session Initiation Protocol," February 27, 2002.

   [TEL] H. Schulzrinne and A. Vaha-Sipila, draft-antti-rfc2806bis-
        04.txt, "URIs for Telephone Calls," May 24, 2002.

   [TELNP] J. Yu, draft-yu-tel-url-05.txt, "Extensions to the "tel" URL
        to support Number Portability and Freephone Service," June 14,
        2002.

   [TRIP] J. Rosenberg, H. Salama and M. Squire, RFC 3219, "Telephony
        Routing Information Protocol (TRIP)," January 2002.


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.
   1120 Vermont Avenue, NW,
   Suite 400
   Washington, D.C. 20005
   United States

Foster,McGarry,Yu           Expired on August 31, 2002        [Page 25]


Number Portability in the GSTN: An Overview              March 1, 2002



   Phone: +1-202-533-2800
   Fax:   +1-202-533-2987
   Email: mark.foster@neustar.biz

   Tom McGarry
   NeuStar, Inc.
   1120 Vermont Avenue, NW,
   Suite 400
   Washington, D.C. 20005
   United States

   Phone: +1-202-533-2810
   Fax:   +1-202-533-2987
   Email: tom.mcgarry@neustar.biz

   James Yu
   NeuStar, Inc.
   1120 Vermont Avenue, NW,
   Suite 400
   Washington, D.C. 20005
   United States

   Phone: +1-202-533-2814
   Fax:   +1-202-533-2987
   Email: james.yu@neustar.biz



Full Copyright Statement

   "Copyright (C) The Internet Society (2002). 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.



Foster,McGarry,Yu           Expired on August 31, 2002        [Page 26]


Number Portability in the GSTN: An Overview              March 1, 2002


   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,McGarry,Yu           Expired on August 31, 2002        [Page 27]


Html markup produced by rfcmarkup 1.113, available from https://tools.ietf.org/tools/rfcmarkup/