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diff --git a/doc/draft/draft-ietf-enum-e164-gstn-np-05.txt b/doc/draft/draft-ietf-enum-e164-gstn-np-05.txt new file mode 100644 index 0000000..3353b3b --- /dev/null +++ b/doc/draft/draft-ietf-enum-e164-gstn-np-05.txt @@ -0,0 +1,1588 @@ + + 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). 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