3 Internet Draft Tom McGarry
4 Document: <draft-ietf-enum-e164-gstn-np-05.txt> James Yu
6 Category: Informational June 24, 2002
9 Number Portability in the GSTN: An Overview
14 This document is an Internet-Draft and is in full conformance with
15 all provisions of Section 10 of RFC2026 [RFC].
17 Internet-Drafts are working documents of the Internet Engineering
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35 Copyright (C) The Internet Society (2002). All rights reserved.
40 This document provides an overview of E.164 telephone number
41 portability (NP) in the Global Switched Telephone Network (GSTN).
42 NP is a regulatory imperative seeking to liberalize local telephony
43 service competition, by enabling end-users to retain telephone
44 numbers while changing service providers. NP changes the
45 fundamental nature of a dialed E.164 number from a hierarchical
46 physical routing address to a virtual address, thereby requiring the
47 transparent translation of the later to the former. In addition,
48 there are various regulatory constraints that establish relevant
49 parameters for NP implementation, most of which are not network
50 technology specific. Consequently, the implementation of NP
51 behavior consistent with applicable regulatory constraints, as well
52 as the need for interoperation with the existing GSTN NP
53 implementations, are relevant topics for numerous areas of IP
54 telephony work-in-progress at IETF.
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58 Number Portability in the GSTN: An Overview June 24, 2002
63 1. Introduction ............................................... 2
64 2. Abbreviations and Acronyms ................................. 4
65 3. Types of Number Portability ................................ 5
66 4. Service Provider Number Portability Schemes ................ 7
67 4.1 All Call Query (ACQ) .................................. 7
68 4.2 Query on Release (QoR) ................................ 8
69 4.3 Call Dropback ......................................... 9
70 4.4 Onward Routing (OR) ................................... 9
71 4.5 Comparisons of the Four Schemes ....................... 10
72 5. Database Queries in the NP Environment ..................... 11
73 5.1 U.S. and Canada ....................................... 12
74 5.2 Europe ................................................ 13
75 6. Call Routing in the NP Environment ......................... 14
76 6.1 U.S. and Canada ....................................... 14
77 6.2 Europe ................................................ 15
78 7. NP Implementations for Geographic E.164 Numbers ............ 17
79 8. Number Conservation Method Enabled By NP ................... 20
80 8.1 Block Pooling ......................................... 20
81 8.2 ITN Pooling ........................................... 21
82 9. Potential Implications ..................................... 21
83 10. Security Considerations .................................... 24
84 11. IANA Considerations ........................................ 24
85 12. Normative References ....................................... 24
86 13. Informative References ..................................... 25
87 14. Acknowledgement ............................................ 25
88 15. AuthorsË Addresses ......................................... 25
94 This document provides an overview of E.164 telephone number
95 portability in the Global Switched Telephone Network (GSTN). There
96 are considered to be three types of number portability (NP): service
97 provider portability (SPNP), location portability (not to be
98 confused with terminal mobility), and service portability.
100 Service provider portability (SPNP), the focus of the present draft,
101 is a regulatory imperative in many countries seeking to liberalize
102 telephony service competition, especially local service.
103 Historically, local telephony service (as compared to long distance
104 or international service) has been regulated as a utility-like form
105 of service. While a number of countries had begun liberalization
106 (e.g. privatization, de-regulation, or re-regulation) some years
107 ago, the advent of NP is relatively recent (since ~1995).
109 E.164 numbers can be non-geographic and geographic numbers. Non-
110 geographic numbers do not reveal the locations information of those
111 numbers. Geographic E.164 numbers were intentionally designed as
112 hierarchical routing addresses which could systematically be digit-
113 analyzed to ascertain the country, serving network provider, serving
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117 Number Portability in the GSTN: An Overview June 24, 2002
119 end-office switch, and specific line of the called party. As such,
120 without NP a subscriber wishing to change service providers would
121 incur a number change as a consequence of being served off of a
122 different end-office switch operated by the new service provider.
123 The cost and convenience impact to the subscriber of changing
124 numbers is seen as barrier to competition. Hence NP has become
125 associated with GSTN infrastructure enhancements associated with a
126 competitive environment driven by regulatory directives.
128 Forms of SPNP have been deployed or are being deployed widely in the
129 GSTN in various parts of the world, including the U.S., Canada,
130 Western Europe, Australia, and the Pacific Rim (e.g. Hong Kong).
131 Other regions, such as South America (e.g. Brazil) are actively
134 Implementation of NP within a national telephony infrastructure
135 entails potentially significant changes to numbering administration,
136 network element signaling, call routing and processing, billing,
137 service management, and other functions.
139 NP changes the fundamental nature of a dialed E.164 number from a
140 hierarchical physical routing address to a virtual address. NP
141 implementations attempt to encapsulate the impacts to the GSTN and
142 make NP transparent to subscribers by incorporating a translation
143 function to map a dialed, potentially ported E.164 address, into a
144 network routing address (either a number prefix or another E.164
145 address) which can be hierarchically routed.
147 This is roughly analogous to the use of network address translation
148 on IP addresses to enable IP address portability by containing the
149 impact of the address change to the edge of the network and retain
150 the use of CIDR blocks in the core which can be route aggregated by
151 the network service provider to the rest of the internet.
153 NP bifurcates the historical role of a subscriberËs E.164 address
154 into two or more data elements (a dialed or virtual address, and a
155 network routing address) that must be made available to network
156 elements through an NP translations database, carried by forward
157 call signaling, and recorded on call detail records. Not only is
158 call processing and routing affected, but also so is SS7/C7
159 messaging. A number of TCAP-based SS7 messaging sets utilize an
160 E.164 address as an application-level network element address in the
161 global title address (GTA) field of the SCCP message header.
162 Consequently, SS7/C7 signaling transfer points (STPs) and gateways
163 need to be able to perform n-digit global title translation (GTT) to
164 translate a dialed E.164 address into its network address
165 counterpart via the NP database.
167 In addition, there are various national regulatory constraints that
168 establish relevant parameters for NP implementation, most of which
169 are not network technology specific. Consequently, implementations
170 of NP behavior in IP telephony consistent with applicable regulatory
171 constraints, as well as the need for interoperation with the
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176 Number Portability in the GSTN: An Overview June 24, 2002
178 existing GSTN NP implementations, are relevant topics for numerous
179 areas of IP telephony work-in-progress at IETF.
181 This document describes three types of number portability and the
182 four schemes that have been standardized to support SPNP for
183 geographic E.164 numbersspecifically. Following that, specific
184 information regarding the call routing and database query
185 implementations are described for several regions (North American
186 and Europe) and industries (wireless vs. wireline). The Number
187 Portability Database (NPDB) interfaces and the call routing schemes
188 that are used in the North America and Europe are described to show
189 the variety of standards that may be implemented worldwide. A
190 glance of the NP implementations worldwide is provided. Number
191 pooling is briefly discussed to show how NP is being enhanced in the
192 U.S. to conserve North American area codes. The conclusion briefly
193 touches the potential impacts of NP on IP & Telecommunications
194 Interoperability. Appendix A provides some specific technical and
195 regulatory information on NP in North America. Appendix B describes
196 the number portability administration process that manages the
197 number portability database in North America.
200 2. Abbreviations and Acronyms
203 AIN Advanced Intelligent Network
204 AMPS Advanced Mobile Phone System
205 ANSI American National Standards Institute
206 CDMA Code Division Multiple Access
207 CdPA Called Party Address
208 CdPN Called Party Number
210 CMIP Common Management Information Protocol
214 DNS Domain Name System
215 ETSI European Technical Standards Institute
216 FCI Forward Call Indicator
217 GAP Generic Address Parameter
218 GMSC Gateway Mobile Services Switching Center or Gateway Mobile
220 GSM Global System for Mobile Communications
221 GSTN Global Switched Telephone Network
223 HLR Home Location Register
224 IAM Initial Address Message
225 IETF Internet Engineering Task Force
227 IN Intelligent Network
228 INAP Intelligent Network Application Part
231 IS-41 Interim Standards Number 41
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235 Number Portability in the GSTN: An Overview June 24, 2002
237 ISDN Integrated Services Digital Network
239 ITN Individual Telephony Number
240 ITU International Telecommunication Union
241 ITU-TS ITU-Telecommunication Sector
242 LDAP Lightweight Directory Access Protocol
243 LEC Local Exchange Carrier
244 LERG Local Exchange Routing Guide
245 LNP Local Number Portability
246 LRN Location Routing Number
247 MAP Mobile Application Part
248 MNP Mobile Number Portability
249 MSRN Mobile Station Roaming Number
250 MTP Message Transfer Part
251 NANP North American Numbering Plan
252 NP Number Portability
253 NPDB Number Portability Database
254 NRN Network Routing Number
256 OSS Operation Support System
257 PCS Personal Communication Services
258 PNTI Ported Number Translation Indicator
259 PODP Public Office Dialing Plan
260 PUC Public Utility Commission
264 SCCP Signaling Connection Control Part
265 SCP Service Control Point
266 SIP Session Initiation Protocol
267 SMR Special Mobile Radio
268 SMS Service Management System
269 SPNP Service Provider Number Portability
270 SRF Signaling Relaying Function
271 SRI Send Routing Information
272 SS7 Signaling System Number 7
273 STP Signaling Transfer Point
274 TCAP Transaction Capabilities Application Part
275 TDMA Time Division Multiple Access
277 TRIP Telephony Routing Information Protocol
278 URL Universal Resource Locator
282 3. Types of Number Portability
284 As there are several types of E.164 numbers (telephone numbers, or
285 just TN) in the GSTN, there are correspondingly several types of
286 E.164 NP in the GSTN. First there are so-call non-geographic E.164
287 numbers, commonly used for service-specific applications such as
288 freephone (800 or 0800). Portability of these numbers is called
289 non-geographic number portability (NGNP). NGNP, for example, was
290 deployed in the U.S. in 1986-92.
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294 Number Portability in the GSTN: An Overview June 24, 2002
297 Geographic number portability, which includes traditional fixed or
298 wireline numbers as well as mobile numbers which are allocated out
299 of geographic number range prefixes, is called NP or GNP or in the
300 U.S. local number portability (LNP).
302 Number portability allows the telephony subscribers in the Global
303 Switched Telephone Network (GSTN) to keep their phone numbers when
304 they change their service providers or subscribed services, or when
305 they move to a new location.
307 The ability to change the service provider while keeping the same
308 phone number is called service provider portability (SPNP) also
309 known as "operator portability."
311 The ability to change the subscriberËs fixed service location while
312 keeping the same phone number is called location portability.
314 The ability to change the subscribed services (e.g., from the plain
315 old telephone service to Integrated Services Digital Network (ISDN)
316 services) while keeping the same phone number is called service
317 portability. Another aspect of service portability is to allow the
318 subscribers to enjoy the subscribed services in the same way when
319 they roam outside their home networks as is supported by the
320 cellular/wireless networks.
322 In addition, mobile number portability (MNP) refers to specific NP
323 implementation in mobile networks either as part of a broader NP
324 implementation in the GSTN or on a stand-alone basis. Where
325 interoperation of LNP and MNP is supported, service portability
326 between fixed and mobile service types is possible.
328 At present, SPNP has been the primary form of NP deployed due to its
329 relevance in enabling local service competition.
331 Also in use in the GSTN are the terms interim NP (INP) or Interim
332 LNP (ILNP) and true NP. Interim NP usually refers to the use of
333 remote call forwarding-like measures to forward calls to ported
334 numbers through the donor network to the new service network. These
335 are considered interim relative to true NP, which seeks to remove
336 the donor network or old service provider from the call or signaling
337 path altogether. Often the distinction between interim and true NP
338 is a national regulatory matter relative to the
339 technical/operational requirements imposed on NP in that country.
341 Implementations of true NP in certain countries (e.g. U.S., Canada,
342 Spain, Belgium, Denmark) may pose specific requirements for IP
343 telephony implementations as a result of regulatory and industry
344 requirements for providing call routing and signaling independent of
345 the donor network or last previous serving network.
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353 Number Portability in the GSTN: An Overview June 24, 2002
356 4. Service Provider Number Portability Schemes
358 Four schemes can be used to support service provider portability and
359 are briefly described below. But first, some further terms are
362 The donor network is the network that first assigned a telephone
363 number (e.g., TN +1-202-533-1234) to a subscriber, out of a number
364 range administratively (e.g., +1 202-533) assigned to it. The
365 current service provider (new SP) or new serving network is the
366 network that currently serves the ported number. The old serving
367 network (or old SP) is the network that previously served the ported
368 number before the number was ported to the new serving network.
369 Since a TN can port a number of times, the old SP is not necessarily
370 the same as the donor network, except for the first time the TN
371 ports away, or if the TN ports back into the donor network and away
372 again. While the new SP and old SP roles are transitory as a TN
373 ports around, the donor network is always the same for any
374 particular TN based on the service provider to whom the subtending
375 number range was administratively assigned. See the discussion
376 below on number pooling, as this enhancement to NP further
377 bifurcates the role of donor network into two (the number range or
378 code holder network, and the block holder network).
380 To simplify the illustration, all the transit networks are ignored,
381 the originating or donor network is the one that performs the
382 database queries or call redirection, and the dialed directory
383 number (TN) has been ported out of the donor network before.
385 It is assumed that the old serving network, the new serving network
386 and the donor network are different networks so as to show which
387 networks are involved in call handling and routing and database
388 queries in each of four schemes. Please note that the port of the
389 number (process of moving it from one network to another) happened
390 prior to the call setup and is not included in the call steps.
391 Information carried in the signaling messages to support each of the
392 four schemes is not discussed to simplify the explanation.
395 4.1 All Call Query (ACQ)
397 Figure 1 shows the call steps for the ACQ scheme. Those call steps
400 (1) The Originating Network receives a call from the caller and
401 sends a query to a centrally administered Number Portability
402 Database (NPDB), a copy of which is usually resident on a
403 network element within its network or through a third party
405 (2) The NPDB returns the routing number associated with the dialed
406 directory number. The routing number is discussed later in
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412 Number Portability in the GSTN: An Overview June 24, 2002
414 (3) The Originating Network uses the routing number to route the
415 call to the new serving network.
418 +-------------+ +-----------+ Number +-----------+
419 | Centralized | | New Serv. | ported | Old Serv. |
420 | NPDB | +-------->| Network |<------------| Network |
421 +-------------+ | +-----------+ +-----------+
428 +----------+ | +----------+ +----------+
429 | Orig. |------+ | Donor | | Internal |
430 | Network | | Network | | NPDB |
431 +----------+ +----------+ +----------+
434 Figure 1 - All Call Query (ACQ) Scheme.
437 4.2 Query on Release (QoR)
439 Figure 2 shows the call steps for the QoR scheme. Those call steps
443 +-------------+ +-----------+ Number +-----------+
444 | Centralized | | New Serv. | ported | Old Serv. |
445 | NPDB | | Network |<------------| Network |
446 +-------------+ +-----------+ +-----------+
450 | | +----------------------+
453 +----------+ 2. +----------+ +----------+
454 | Orig. |<---------------| Donor | | Internal |
455 | Network |--------------->| Network | | NPDB |
456 +----------+ 1. +----------+ +----------+
459 Figure 2 - Query on Release (QoR) Scheme.
461 (1) The Originating Network receives a call from the caller and
462 routes the call to the donor network.
463 (2) The donor network releases the call and indicates that the
464 dialed directory number has been ported out of that switch.
465 (3) The Originating Network sends a query to its copy of the
466 centrally administered NPDB.
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471 Number Portability in the GSTN: An Overview June 24, 2002
473 (4) The NPDB returns the routing number associated with the dialed
475 (5) The Originating Network uses the routing number to route the
476 call to the new serving network.
481 Figure 3 shows the call steps for the Dropback scheme. This scheme
482 is also known as "Return to Pivot (RTP)." Those call steps are as
485 (1) The Originating Network receives a call from the caller and
486 routes the call to the donor network.
487 (2) The donor network detects that the dialed directory number has
488 been ported out of the donor switch and checks with an internal
489 network-specific NPDB.
490 (3) The internal NPDB returns the routing number associated with the
491 dialed directory number.
492 (4) The donor network releases the call by providing the routing
494 (5) The Originating Network uses the routing number to route the
495 call to the new serving network.
497 +-------------+ +-----------+ Number +-----------+
498 | Centralized | | New Serv. | porting | Old Serv. |
499 | NPDB | | Network |<------------| Network |
500 +-------------+ +-----------+ +-----------+
504 +------------------------+
507 +----------+ 4. +----------+ 3. +----------+
508 | Orig. |<---------------| Donor |<----------| Internal |
509 | Network |--------------->| Network |---------->| NPDB |
510 +----------+ 1. +----------+ 2. +----------+
513 Figure 3 - Dropback Scheme.
516 4.4 Onward Routing (OR)
518 Figure 4 shows the call steps for the OR scheme. Those call steps
521 (1) The Originating Network receives a call from the caller and
522 routes the call to the donor network.
523 (2) The donor network detects that the dialed directory number has
524 been ported out of the donor switch and checks with an internal
525 network-specific NPDB.
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530 Number Portability in the GSTN: An Overview June 24, 2002
532 (3) The internal NPDB returns the routing number associated with the
533 dialed directory number.
534 (4) The donor network uses the routing number to route the call to
535 the new serving network.
538 +-------------+ +-----------+ Number +-----------+
539 | Centralized | | New Serv. | porting | Old Serv. |
540 | NPDB | | Network |<------------| Network |
541 +-------------+ +-----------+ +-----------+
546 +----------+ +----------+ 3. +----------+
547 | Orig. | | Donor |<----------| Internal |
548 | Network |--------------->| Network |---------->| NPDB |
549 +----------+ 1. +----------+ 2. +----------+
552 Figure 4 - Onward Routing (OR) Scheme.
554 4.5 Comparisons of the Four Schemes
556 Only the ACQ scheme does not involve the donor network when routing
557 the call to the new serving network of the dialed ported number.
558 The other three schemes involve call setup to or signaling with the
561 Only the OR scheme requires the setup of two physical call segments,
562 one from the Originating Network to the donor network and the other
563 from the donor network to the new serving network. The OR scheme is
564 the least efficient in terms of using the network transmission
565 facilities. The QoR and Dropback schemes set up calls to the donor
566 network first but release the call back to the Originating Network
567 that then initiates a new call to the Current Serving Network. For
568 the QoR and Dropback schemes, circuits are still reserved one by one
569 between the Originating Network and the donor network when the
570 Originating Network sets up the call towards the donor network.
571 Those circuits are released one by one when the call is released
572 from the donor network back to the Originating Network. The ACQ
573 scheme is the most efficient in terms of using the switching and
574 transmission facilities for the call.
576 Both the ACQ and QoR schemes involve Centralized NPDBs for the
577 Originating Network to retrieve the routing information.
578 Centralized NPDB means that the NPDB contains ported number
579 information from multiple networks. This is in contrast to the
580 internal network-specific NPDB that is used for the Dropback and OR
581 schemes. The internal NPDB only contains information about the
582 numbers that were ported out of the donor network. The internal
583 NPDB can be a stand-alone database that contains information about
584 all or some ported-out numbers from the donor network. It can also
585 reside on the donor switch and only contains information about those
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589 Number Portability in the GSTN: An Overview June 24, 2002
591 numbers ported out of the donor switch. In that case, no query to a
592 stand-alone internal NPDB is required. The donor switch for a
593 particular phone number is the switch to which the number range is
594 assigned from which that phone number was originally assigned.
596 For example, number ranges in the North American Numbering Plan
597 (NANP) are usually assigned in the form of central office codes (CO
598 codes) comprising a six-digit prefix formatted as a NPA+NXX. Thus a
599 switch serving +1-202-533 would typically serve +1-202-533-0000
600 through +1-202-533-9999. In major cities, switches usually host
601 several CO codes. NPA stands for Numbering Plan Area that is also
602 known as the area code. It is three-digit long and has the format
603 of NXX where N is any digit from 2 to 9 and X is any digit from 0 to
604 9. NXX in the NPA+NXX format is known as the office code that has
605 the same format as the NPA. When a NPA+NXX code is set as
606 \9fportable÷ in the Local Exchange Routing Guide (LERG), it becomes a
607 "portable NPA+NXX" code.
609 Similarly, in other national E.164 numbering plans, number ranges
610 cover a contiguous range of numbers within that range. Once a
611 number within that range has ported away from the donor network, all
612 numbers in that range are considered potentially ported and should
613 be queried in the NPDB.
615 The ACQ scheme has two versions. One version is for the Originating
616 Network to always query the NPDB when a call is received from the
617 caller regardless whether the dialed directory number belongs to any
618 number range that is portable or has at least one number ported out.
619 The other version is to check whether the dialed directory number
620 belongs to any number range that is portable or has at least one
621 number ported out. If yes, an NPDB query is sent. If not, no NPDB
622 query is sent. The former performs better when there are many
623 portable number ranges. The latter performs better when there are
624 not too many portable number ranges at the expense of checking every
625 call to see whether NPDB query is needed. The latter ACQ scheme is
626 similar to the QoR scheme except that the QoR scheme uses call setup
627 and relies on the donor network to indicate "number ported out"
628 before launching the NPDB query.
631 5. Database Queries in the NP Environment
633 As indicated earlier, the ACQ and QoR schemes require that a switch
634 query the NPDB for routing information. Various standards have been
635 defined for the switch-to-NPDB interface. Those interfaces with
636 their protocol stacks are briefly described below. The term "NPDB"
637 is used for a stand-alone database that may support just one or some
638 or all of the interfaces mentioned below. The NPDB query contains
639 the dialed directory number and the NPDB response contains the
640 routing number. There are certainly other information that is sent
641 in the query and response. The primary interest is to get the
642 routing number from the NPDB to the switch for call routing.
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648 Number Portability in the GSTN: An Overview June 24, 2002
652 One of the following five NPDB interfaces can be used to query an
655 (a) Advanced Intelligent Network (AIN) using the American National
656 Standards Institute (ANSI) version of the Intelligent Network
657 Application Part (INAP) [ANSI SS] [ANSI DB]. The INAP is
658 carried on top of the protocol stack that includes the (ANSI)
659 Message Transfer Part (MTP) Levels 1 through 3, ANSI Signaling
660 Connection Control Part (SCCP), and ANSI Transaction
661 Capabilities Application Part (TCAP). This interface can be
662 used by the wireline or wireless switches, is specific to the NP
663 implementation in North America, and is modeled on the Public
664 Office Dialing Plan (PODP) trigger defined in the Advanced
665 Intelligent Network (AIN) 0.1 call model.
667 (b) Intelligent Network (IN), which is similar to the one used for
668 querying the 800 databases. The IN protocol is carried on top
669 of the protocol stack that includes the ANSI MTP Levels 1
670 through 3, ANSI SCCP, and ANSI TCAP. This interface can be used
671 by the wireline or wireless switches.
673 (c) ANSI IS-41 [IS41] [ISNP], which is carried on top of the
674 protocol stack that includes the ANSI MTP Levels 1 through 3,
675 ANSI SCCP, and ANSI TCAP. This interface can be used by the IS-
676 41 based cellular/Personal Communication Services (PCS) wireless
677 switches (e.g., AMPS, TDMA and CDMA). Cellular systems use
678 spectrum at 800 MHz range and PCS systems use spectrum at 1900
681 (d) Global System for Mobile Communication Mobile Application Part
682 (GSM MAP) [GSM], which is carried on top of the protocol stack
683 that includes the ANSI MTP Levels 1 through 3, ANSI SCCP, and
684 International Telecommunication Union - Telecommunication Sector
685 (ITU-TS) TCAP. It can be used by the PCS1900 wireless switches
686 that are based on the GSM technologies. GSM is a series of
687 wireless standards defined by the European Telecommunications
688 Standards Institute (ETSI).
690 (e) ISUP triggerless translation. NP translations are performed
691 transparently to the switching network by the signaling network
692 (e.g. Signaling Transfer Points (STPs) or signaling gateways).
693 ISUP IAM messages are examined to determine if the CdPN field
694 has already been translated, and if not, an NPDB query is
695 performed, and the appropriate parameters in the IAM message
696 modified to reflect the results of the translation. The
697 modified IAM message is forwarded by the signaling node on to
698 the designated DPC in a transparent manner to continue call
699 setup. The NPDB can be integrated with the signaling node or be
700 accessed via an API locally or by a query to a remote NPDB using
701 a proprietary protocol or the schemes described above.
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707 Number Portability in the GSTN: An Overview June 24, 2002
709 Wireline switches have the choice of using either (a), (b), or (e).
710 IS-41 based wireless switches have the choice of using (a), (b),
711 (c), or (e). PCS1900 wireless switches have the choice of using
712 (a), (b), (d), or (e). In the United States, service provider
713 portability will be supported by both the wireline and wireless
714 systems, not only within the wireline or wireless domain but also
715 across the wireline/wireless boundary. However, this is not true in
716 Europe where service provider portability is usually supported only
717 within the wireline or wireless domain, not across the
718 wireline/wireless boundary due to explicit use of service-specific
719 number range prefixes. The reason is to avoid caller confusion
720 about the call charge. GSM systems in Europe are assigned
721 distinctive destination network codes, and the caller pays a higher
722 charge when calling a GSM directory number.
727 One of the following two interfaces can be used to query an NPDB:
729 (a) Capability Set 1 (CS1) of the ITU-TS INAP [CS1], which is
730 carried on top of the protocol stack that includes the ITU-TS
731 MTP Levels 1 through 3, ITU-TS SCCP, and ITU-TS TCAP.
733 (b) Capability Set 2 (CS2) of the ITU-TS INAP [CS2], which is
734 carried on top of the protocol stack that includes the ITU-TS
735 MTP Levels 1 through ITU-TS MTP Levels 1 through 3, ITU-TS SCCP,
738 Wireline switches have the choice of using either (a) or (b);
739 however, all the implementations in Europe so far are based on CS1.
740 As indicated earlier that number portability in Europe does not go
741 across the wireline/wireless boundary. The wireless switches can
742 also use (a) or (b) to query the NPDBs if those NPDBs contains
743 ported wireless directory numbers. The term "Mobile Number
744 Portability (MNP)" is used for the support of service provider
745 portability by the GSM networks in Europe.
747 In most, if not all, cases in Europe, the calls to the wireless
748 directory numbers are routed to the wireless donor network first.
749 Over there, an internal NPDB is queried to determine whether the
750 dialed wireless directory number has been ported out or not. In
751 this case, the interface to the internal NPDB is not subject to
754 MNP in Europe can also be supported via MNP Signaling Relay Function
755 (MNP-SRF). Again, an internal NPDB or a database integrated at the
756 MNP-SRF is used to modify the SCCP Called Party Address parameter in
757 the GSM MAP messages so that they can be re-directed to the wireless
758 serving network. Call routing involving MNP will be explained in
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766 Number Portability in the GSTN: An Overview June 24, 2002
768 6. Call Routing in the NP Environment
770 This section discusses the call routing after the routing
771 information has been retrieved either through an NPDB query or an
772 internal database lookup at the donor switch, or from the Integrated
773 Services Digital Network User Part (ISUP) signaling message (e.g.,
774 for the Dropback scheme). For the ACQ, QoR and Dropback schemes, it
775 is the Originating Network that has the routing information and is
776 ready to route the call. For the OR scheme, it is the donor network
777 that has the routing information and is ready to route the call.
779 A number of triggering schemes may be employed that determine where
780 in the call path the NPDB query is performed. In the U.S. an
\9fN-1÷
781 policy is used, which essentially says that for domestic calls, the
782 originating local carriers performs the query, otherwise, the long
783 distance carrier is expected to. To ensure independence of the
784 actual trigger policy employed in any one carrier, forward call
785 signaling is used to flag that an NPDB query has already been
786 performed and to therefore suppress any subsequent NP triggers that
787 may be encountered in downstream switches, in downstream networks.
788 This allows the earliest able network in the call path to perform
789 the query without introducing additional costs and call setup delays
790 were redundant queries performed downstream.
795 In the U.S. and Canada, a ten-digit North American Numbering Plan
796 (NANP) number called Location Routing Number (LRN) is assigned to
797 every switch involved in NP. In the NANP, a switch is not reachable
798 unless it has a unique number range (CO code) assigned to it.
799 Consequently, the LRN for a switch is always assigned out of a CO
800 code that is assigned to that switch.
802 The LRN assigned to a switch currently serving a particular ported
803 telephone number is returned as the network routing address in the
804 NPDB response. The service portability scheme that was adopted in
805 the North America is very often referred to as the LRN scheme or
808 LRN serves as a network address for terminating calls served off
809 that switch using ported numbers. The LRN is assigned by the switch
810 operator using any of the unique CO codes (NPA+NXX) assigned to that
811 switch. The LRN is considered a non-dialable address, as the same
812 10-digit number value may be assigned to a line on that switch. A
813 switch may have more than one LRN.
815 During call routing/processing, a switch performs an NPDB query to
816 obtain the LRN associated with the dialed directory number. NPDB
817 queries are performed for all the dialed directory numbers whose
818 NPA+NXX codes are marked as portable NPA+NXX at that switch. When
819 formulating the ISUP Initial Address Message (IAM) to be sent to the
820 next switch, the switch puts the ten-digit LRN in the ISUP Called
821 Party Number (CdPN) parameter and the originally dialed directory
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825 Number Portability in the GSTN: An Overview June 24, 2002
827 number in the ISUP Generic Address parameter (GAP). A new code in
828 the GAP was defined to indicate that the address information in the
829 GAP is the dialed directory number. A new bit in the ISUP Forward
830 Call Indicator (FCI) parameter, the Ported Number Translation
831 Indicator (PNTI) bit, is set to imply that NPDB query has already
832 been performed. All the switches in the downstream will not perform
833 the NPDB query if the PNTI bit is set.
835 When the terminating switch receives the IAM and sees the PNTI bit
836 in the FCI parameter set and its own LRN in the CdPN parameter, it
837 retrieves the originally dialed directory number from the GAP and
838 uses the dialed directory number to terminate the call.
840 A dialed directory number with a portable NPA+NXX does not imply
841 that directory number has been ported. The NPDBs currently do not
842 store records for non-ported directory numbers. In that case, the
843 NPDB will return the same dialed directory number instead of the
844 LRN. The switch will then set the PNTI bit but keep the dialed
845 directory number in the CdPN parameter.
847 In the real world environment, the Originating Network is not always
848 the one that performs the NPDB query. For example, it is usually
849 the long distance carriers that query the NPDBs for long distance
850 calls. In that case, the Originating Network operated by the local
851 exchange carrier (LEC) simply routes the call to the long distance
852 carrier that is to handle that call. A wireless network acting as
853 the Originating Network can also route the call to the
854 interconnected local exchange carrier network if it does not want to
855 support the NPDB interface at its mobile switches.
860 In some European countries, a routing number is prefixed to the
861 dialed directory number. The ISUP CdPN parameter in the IAM will
862 contain the routing prefix and the dialed directory number. For
863 example, United Kingdom uses routing prefixes with the format of
864 5XXXXX and Italy uses C600XXXXX as the routing prefix. The networks
865 use the information in the ISUP CdPN parameter to route the call to
866 the New/Current Serving Network.
868 The routing prefix can identify the Current Serving Network or the
869 Current Serving Switch of a ported number. For the former case,
870 another query to the "internal" NPDB at the Current Serving Network
871 is required to identify the Current Serving Switch before routing
872 the call to that switch. This shields the Current Serving Switch
873 information for a ported number from the other networks at the
874 expense of an additional NPDB query. Another routing number, may be
875 meaningful within the Current Serving Network, will replace the
876 previously prefixed routing number in the ISUP CdPN parameter. For
877 the latter case, the call is routed to the Current Serving Switch
878 without an additional NPDB query.
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884 Number Portability in the GSTN: An Overview June 24, 2002
886 When the terminating switch receives the IAM and sees its own
887 routing prefix in the CdPN parameter, it retrieves the originally
888 dialed directory number after the routing prefix, and uses the
889 dialed directory number to terminate the call.
891 The call routing example described above shows one of the three
892 methods that can be used to transport the Directory Number (DN) and
893 the Routing Number (RN) in the ISUP IAM message. In addition, some
894 other information may be added/modified as is listed in the ETSI 302
895 097 document [ETSIISUP], which is based on the ITU-T Recommendation
896 Q.769.1 [ITUISUP]. The three methods and the enhancements in the
897 ISUP to support number portability are briefly described below
899 (a) Two separate parameters with the CdPN parameter containing the
900 RN and a new Called Directory Number (CdDN) parameter containing
901 the DN. A new value for the Nature of Address (NOA) indicator in
902 the CdPN parameter is defined to indicate that the RN is in the
903 CdPN parameter. The switches use the CdPN parameter to route the
904 call as is done today.
906 (b) Two separate parameters with the CdPN parameter containing the
907 DN and a new Network Routing Number (NRN) parameter containing
908 the RN. This method requires that the switches use the NRN
909 parameter to route the call.
911 (c) Concatenated parameter with the CdPN parameter containing the RN
912 plus the DN. A new Nature of Address (NOA) indicator in the CdPN
913 parameter is defined to indicate that the RN is concatenated with
914 the DN in the CdPN parameter. Some countries may not use new NOA
915 value because the routing prefix does not overlap with the dialed
916 directory numbers. But if the routing prefix overlaps with the
917 dialed directory numbers, a new NOA value must be assigned. For
918 example, Spain uses "XXXXXX" as the routing prefix to identify
919 the new serving network and uses a new NOA value of 126.
921 There is also a network option to add a new ISUP parameter called
922 Number Portability Forwarding Information parameter. This parameter
923 has a four-bit Number Portability Status Indicator field that can
924 provide an indication whether number portability query is done for
925 the called directory number and whether the called directory number
926 is ported or not if the number portability query is done.
928 Please note that all those NP enhancements for a ported number can
929 only be used in the country that defined them. This is because
930 number portability is supported within a nation. Within each
931 nation, the telecommunications industry or the regulatory bodies can
932 decide which method or methods to use. Number portability related
933 parameters and coding are usually not passed across the national
934 boundaries unless the interconnection agreements allow that. For
935 example, a UK routing prefix can only be used in UK, and would cause
936 routing problem if it appears outside UK.
941 Foster,McGarry,Yu Expired on December 23, 2002 [Page 16]
943 Number Portability in the GSTN: An Overview June 24, 2002
945 As indicated earlier, an originating wireless network can query the
946 NPDB and concatenate the RN with DN in the CdPN parameter and route
947 the call directly to the Current Serving Network.
949 If NPDBs do not contain information about the wireless directory
950 numbers, the call, originated from either a wireline or a wireless
951 network, will be routed to the Wireless donor network. Over there,
952 an internal NPDB is queried to retrieve the RN that then is
953 concatenated with the DN in the CdPN parameter.
955 There are several ways of realizing MNP. When MNP-SRF is supported,
956 the Gateway Mobile Services Switching Center (GMSC) at the wireless
957 donor network, when receiving a call from the wireline network, can
958 send the GSM MAP Send Routing Information (SRI) message to the MNP-
959 SRF. The MNP-SRF interrogates an internal or integrated NPDB for
960 the RN of the MNP-SRF of the wireless Current Serving Network and
961 prefixes the RN to the dialed wireless directory number in the
962 global title address information in the SCCP Called Party Address
963 (CdPA) parameter. This SRI message will be routed to the MNP-SRF of
964 the wireless Current Serving Network, which then responds with an
965 acknowledgement by providing the RN plus the dialed wireless
966 directory number as the Mobile Station Roaming Number (MSRN). The
967 GMSC of the wireless donor network formulates the ISUP IAM with the
968 RN plus the dialed wireless directory number in the CdPN parameter
969 and routes the call to the wireless Current Serving Network. A GMSC
970 of the wireless Current Serving Network receives the call and sends
971 an SRI message to the associated MNP-SRF where the global title
972 address information of the SCCP CdPA parameter contains only the
973 dialed wireless directory number. The MNP-SRF then replaces the
974 global title address information in the SCCP CdPA parameter with the
975 address information associated with a Home Location Register (HLR)
976 that hosts the dialed wireless directory number and forwards the
977 message to that HLR after verifying that the dialed wireless
978 directory number is a ported-in number. The HLR then returns an
979 acknowledgement by providing an MSRN for the GMSC to route the call
980 to the MSC that currently serves the mobile station that is
981 associated with the dialed wireless directory number. Please see
982 [MNP] for details and additional scenarios.
985 7. NP Implementations for Geographic E.164 Numbers
987 This section shows the known SPNP implementations worldwide.
989 +-------------+----------------------------------------------------+
990 + Country + SPNP Implementation +
991 +-------------+----------------------------------------------------+
992 + Argentina + Analyzing operative viability now. Will determine +
993 + + whether portability should be made obligatory +
994 + + after a technical solution has been determined. +
995 +-------------+----------------------------------------------------+
996 + Australia + NP supported by wireline operators since 11/30/99. +
997 + + NP among wireless operators in March/April 2000, +
1000 Foster,McGarry,Yu Expired on December 23, 2002 [Page 17]
1002 Number Portability in the GSTN: An Overview June 24, 2002
1004 + + but may be delayed to 1Q01. The access provider +
1005 + + or long distance provider has the obligation to +
1006 + + route the call to the correct destination. The +
1007 + + donor network is obligated to maintain and make +
1008 + + available a register of numbers ported away from +
1009 + + its network. Telstra uses onward routing via an +
1010 + + on-switch solution. +
1011 +-------------+----------------------------------------------------+
1012 + Austria + Uses onward routing at the donor network. Routing +
1013 + + prefix is "86xx" where "xx" identifies the +
1014 + + recipient network. +
1015 +-------------+----------------------------------------------------+
1016 + Belgium + ACQ selected by the industry. Routing prefix is +
1017 + + "Cxxxx" where "xxxx" identifies the recipient +
1018 + + switch. Another routing prefix is "C00xx" with "xx"+
1019 + + identifying the recipient network. Plan to use NOA+
1020 + + to identify concatenated numbers and abandon the +
1021 + + hexadecimal routing prefix. +
1022 +-------------+----------------------------------------------------+
1023 + Brazil + Considering NP for wireless users. +
1024 +-------------+----------------------------------------------------+
1025 + Chile + There has been discussions lately on NP. +
1026 +-------------+----------------------------------------------------+
1027 + Colombia + There was an Article 3.1 on NP to support NP prior +
1028 + + to December 31, 1999 when NP became technically +
1029 + + possible. Regulator has not yet issued regulations +
1030 + + concerning this matter. +
1031 +-------------+----------------------------------------------------+
1032 + Denmark + Uses ACQ. Routing number not passed between +
1033 + + operators; however, NOA is set to "112" to +
1034 + + indicate "ported number." QoR can be used based +
1035 + + on bilateral agreements. +
1036 +-------------+----------------------------------------------------+
1037 + Finland + Uses ACQ. Routing prefix is "1Dxxy" where "xxy" +
1038 + + identifies the recipient network and service type. +
1039 +-------------+----------------------------------------------------+
1040 + France + Uses onward routing. Routing prefix is "Z0xxx" +
1041 + + where "xxx" identifies the recipient switch. +
1042 +-------------+----------------------------------------------------+
1043 + Germany + The originating network needs to do necessary +
1044 + + rerouting. Operators decide their own solution(s).+
1045 + + Deutsche Telekom uses ACQ. Routing prefix is +
1046 + + "Dxxx" where "xxx" identifies the recipient +
1048 +-------------+----------------------------------------------------+
1049 + Hong Kong + Recipient network informs other networks about +
1050 + + ported-in numbers. Routing prefix is "14x" where +
1051 + + "14x" identifies the recipient network, or a +
1052 + + routing number of "4x" plus 7 or 8 digits is used +
1053 + + where "4x" identifies the recipient network and +
1054 + + the rest of digits identify the called party. +
1055 +-------------+----------------------------------------------------+
1056 + Ireland + Operators choose their own solution but use onward +
1057 + + routing now. Routing prefix is "1750" as the intra-+
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1061 Number Portability in the GSTN: An Overview June 24, 2002
1063 + + network routing code (network-specific) and +
1064 + + "1752xxx" to "1759xxx" for GNP where "xxx" +
1065 + + identifies the recipient switch. +
1066 +-------------+----------------------------------------------------+
1067 + Italy + Uses onward routing. Routing prefix is "C600xxxxx" +
1068 + + where "xxxxx" identifies the recipient switch. +
1069 + + Telecom Italia uses IN solution and other operators+
1070 + + use on-switch solution. +
1071 +-------------+----------------------------------------------------+
1072 + Japan + Uses onward routing. Donor switch uses IN to get +
1073 + + routing number. +
1074 +-------------+----------------------------------------------------+
1075 + Mexico + NP is considered in the Telecom law; however, the +
1076 + + regulator (Cofetel) or the new local entrants have +
1077 + + started no initiatives on this process. +
1078 +-------------+----------------------------------------------------+
1079 + Netherlands + Operators decide NP scheme to use. Operators have +
1080 + + chosen ACQ or QoR. KPN implemented IN solution +
1081 + + similar to U.S. solution. Routing prefix is not +
1082 + + passed between operators. +
1083 +-------------+----------------------------------------------------+
1084 + Norway + OR for short-term and ACQ for long-term. QoR is +
1085 + + optional. Routing prefix can be "xxx" with NOA=8, +
1086 + + or "142xx" with NOA=3 where "xxx" or "xx" +
1087 + + identifies the recipient network. +
1088 +------------ +----------------------------------------------------+
1089 + Peru + Wireline NP may be supported in 2001. +
1090 +-------------+----------------------------------------------------+
1091 + Portugal + No NP today. +
1092 +-------------+----------------------------------------------------+
1093 + Spain + Uses ACQ. Telefonica uses QoR within its network. +
1094 + + Routing prefix is "xxyyzz" where "xxyyzz" +
1095 + + identifies the recipient network. NOA is set to +
1097 +-------------+----------------------------------------------------+
1098 + Sweden + Standardized the ACQ but OR for operators without +
1099 + + IN. Routing prefix is "xxx" with NOA=8 or "394xxx" +
1100 + + with NOA=3 where "xxx" identifies the recipient +
1101 + + network. But operators decide NP scheme to use. +
1102 + + Telia uses onward routing between operators. +
1103 +-------------+----------------------------------------------------+
1104 + Switzerland + Uses OR now and QoR in 2001. Routing prefix is +
1105 + + "980xxx" where "xxx" identifies the recipient +
1107 +-------------+----------------------------------------------------+
1108 + UK + Uses onward routing. Routing prefix is "5xxxxx" +
1109 + + where "xxxxx" identifies the recipient switch. NOA +
1110 + + is 126. BT uses the dropback scheme in some parts +
1111 + + of its network. +
1112 +-------------+----------------------------------------------------+
1113 + US + Uses ACQ. "Location Routing Number (LRN)" is used +
1114 + + in the Called Party Number parameter. Called party+
1115 + + number is carried in the Generic Address Parameter +
1116 + + Use a PNTI indicator in the Forward Call Indicator +
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1120 Number Portability in the GSTN: An Overview June 24, 2002
1122 + + parameter to indicate that NPDB dip has been +
1124 +-------------+----------------------------------------------------+
1127 8. Number Conservation Methods Enabled by NP
1129 In addition to porting numbers NP provides the ability for number
1130 administrators to assign numbering resources to operators in smaller
1131 increments. Today it is common for numbering resources to be
1132 assigned to telephone operators in a large block of consecutive
1133 telephone numbers (TNs). For example, in North America each of
1134 these blocks contains 10,000 TNs and is of the format NXX+0000 to
1135 NXX+9999. Operators are assigned a specific NXX, or block. That
1136 operator is referred to as the block holder. In that block there
1137 are 10,000 TNs with line numbers ranging from 0000 to 9999.
1139 Instead of assigning an entire block to the operator NP allows the
1140 administrator to assign a sub-block or even an individual telephone
1141 number. This is referred to as block pooling and individual
1142 telephone number (ITN) pooling, respectively.
1147 Block Pooling refers to the process whereby the number administrator
1148 assigns a range of numbers defined by a logical sub-block of the
1149 existing block. Using North America as an example, block pooling
1150 would allow the administrator to assign sub-blocks of 1,000 TNs to
1151 multiple operators. That is, NXX+0000 to NXX+0999 can be assigned
1152 to operator A, NXX+1000 to NXX+1999 can be assigned to operator B,
1153 NXX-2000 to 2999 can be assigned to operator C, etc. In this
1154 example block pooling divides one block of 10,000 TNs into ten
1155 blocks of 1,000 TNs.
1157 Porting the sub-blocks from the block holder enables block pooling.
1158 Using the example above operator A is the block holder, as well as,
1159 the holder of the first sub-block, NXX+0000 to NXX+0999. The second
1160 sub-block, NXX+1000 to NXX+1999, is ported from operator A to
1161 operator B. The third sub-block, NXX+2000 to NXX+2999, is ported
1162 from operator A to operator C, and so on. NP administrative
1163 processes and call processing will enable proper and efficient
1166 From a number administration and NP administration perspective block
1167 pooling introduces a new concept, that of the sub-block holder.
1168 Block pooling requires coordination between the number
1169 administrator, the NP administrator, the block holder, and the sub-
1170 block holder. Block pooling must be implemented in a manner that
1171 allows for NP within the sub-blocks. Each TN can have a different
1172 serving operator, sub-block holder, and block holder.
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1179 Number Portability in the GSTN: An Overview June 24, 2002
1183 ITN pooling refers to the process whereby the number administrator
1184 assigns individual telephone numbers to operators. Using the North
1185 American example, one block of 10,000 TNs can be divided into 10,000
1186 ITNs. ITN is more commonly deployed in freephone services.
1188 In ITN the block is not assigned to an operator but to a central
1189 administrator. The administrator then assigns ITNs to operators.
1190 NP administrative processes and call processing will enable proper
1191 and efficient routing.
1194 9. Potential Implications
1196 There are three general areas of impact to IP telephony work-in-
1199 - Interoperation between NP in GSTN and IP telephony
1200 - NP implementation or emulation in IP telephony
1201 - Interconnection to NP administrative environment
1203 A good understanding of how number portability is supported in the
1204 GSTN is important when addressing the interworking issues between
1205 IP-based networks and the GSTN. This is especially important when
1206 the IP-based network needs to route the calls to the GSTN. As shown
1207 in Section 5, there are a variety of standards with various protocol
1208 stacks for the switch-to-NPDB interface. Not only that, the
1209 national variations of the protocol standards make it very
1210 complicated to deal with in a global environment. If an entity in
1211 the IP-based network needs to query those existing NPDBs for routing
1212 number information to terminate the calls to the destination GSTN,
1213 it would be impractical, if not an impossible, job for that entity
1214 to support all those interface standards to access the NPDBs in many
1217 Several alternatives may address this particular problem. One
1218 alternative is to use certain entities in the IP-based networks for
1219 dealing with NP query, similar to the International Switches that
1220 are used in the GSTN to interwork different national ISUP
1221 variations. This will force signaling information associated with
1222 the calls to certain NP-capable networks in the terminating GSTN to
1223 be routed to those IP entities that support the NP functions. Those
1224 IP entities then query the NPDBs in the terminating country. This
1225 will limit the number of NPDB interfaces that certain IP entities
1226 need to support. Another alternative can be to define a "common"
1227 interface to be supported by all the NPDBs so that all the IP
1228 entities use that standardized protocol to query them. The
1229 existing NPDBs can support this additional interface, or new NPDBs
1230 can be deployed that contain the same information but support the
1231 common IP interface. The candidates for such a common interface
1232 include Lightweight Directory Access Protocol (LDAP) and SIP
1233 [SIP](e.g., using the SIP redirection capability). Certainly
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1238 Number Portability in the GSTN: An Overview June 24, 2002
1240 another possibility is to use interworking function to convert from
1241 one protocol to another.
1243 IP-based networks can handle the domestic calls between two GSTNs.
1244 If the originating GSTN has performed NPDB query, SIP will need to
1245 transport and make use of some of the ISUP signaling information
1246 even if ISUP signaling may be encapsulated in SIP. Also, IP-based
1247 networks may perform the NPDB queries, as the N-1 carrier. In that
1248 case, SIP also needs to transport the NP related information while
1249 the call is being routed to the destination GSTN. There are three
1250 pieces of NP related information that SIP needs to transport. They
1251 are 1) the called directory number, 2) a routing number, and 3) a
1252 NPDB dip indicator. The NPDB dip indicator is needed so that the
1253 terminating GSTN will not perform another NPDB dip. The routing
1254 number is needed so that it is used to route the call to the
1255 destination network or switch in the destination GSTN. The called
1256 directory number is needed so that the terminating GSTN switch can
1257 terminate the call. When the routing number is present, the NPDB
1258 dip indicator may not be present because there are cases where
1259 routing number is added for routing the call even if NP is not
1260 involved. One issue is how to transport the NP related information
1261 via SIP. The SIP Universal Resource Locator (URL) is one mechanism.
1262 Another better choice may be to add an extension to the "tel" URL
1263 [TEL] that is also supported by SIP. Please see [TELNP] for the
1264 proposed extensions to the "tel" URL to support NP and freephone
1265 service. Those extensions to the "tel" URL will be automatically
1266 supported by SIP because they can be carried as the optional
1267 parameters in the user portion of the "sip" URL.
1269 For a called directory number that belongs to a country that
1270 supports NP, and if the IP-based network is to perform the NPDB
1271 query, the logical step is to perform the NPDB dip first to retrieve
1272 the routing number and use that routing number to select the correct
1273 IP telephony gateways that can reach the serving switch that serves
1274 the called directory number. Therefore, if the "rn" parameter is
1275 present in the "tel" URL or sip URL in the SIP INVITE message, it
1276 instead of the called directory number should be used for making
1277 routing decisions assuming that no other higher priority routing-
1278 related parameters such as the
\9fcic÷ are present. If "rn" is not
1279 present, then the dialed directory number can be used as the routing
1280 number for making routing decisions.
1282 Telephony Routing Information Protocol (TRIP) [TRIP] is a policy
1283 driven inter-administrative domain protocol for advertising the
1284 reachability of telephony destinations between location servers, and
1285 for advertising attributes of the routes to those destinations.
1286 With the NP in mind, it is very important to know that it is the
1287 routing number, if present, not the called directory number that
1288 should be used to check against the TRIP tables for making the
1291 Overlap signaling exists in the GSTN today. For a call routing from
1292 the originating GSTN to the IP-based network that involves overlap
1293 signaling, NP will impact the call processing within the IP-based
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1297 Number Portability in the GSTN: An Overview June 24, 2002
1299 networks if they must deal with the overlap signaling. The entities
1300 in the IP-based networks that are to retrieve the NP information
1301 (e.g., the routing number) must collect a complete called directory
1302 number information before retrieving the NP information for a ported
1303 number. Otherwise, the information retrieval won't be successful.
1304 This is an issue for the IP-based networks if the originating GSTN
1305 does not handle the overlap signaling by collecting the complete
1306 called directory number.
1308 The IETF enum working group is defining the use of Domain Name
1309 System (DNS) for identifying available services associated with a
1310 particular E.164 number [ENUM]. [ENUMPO] outlines the principles
1311 for the operation of a telephone number service that resolves
1312 telephone numbers into Internet domain name addresses and service-
1313 specific directory discovery. [ENUMPO] implements a three-level
1314 approach where the first level is the mapping of the telephone
1315 number delegation tree to the authority to which the number has been
1316 delegated, the second level is the provision of the requested DNS
1317 resource records from a service registrar, and the third level is
1318 the provision of service specific data from the service provider
1319 itself. NP certainly must be considered at the first level because
1320 the telephony service providers do not "own" or control the
1321 telephone numbers under the NP environment; therefore, they may not
1322 be the proper entities to have the authority for a given E.164
1323 number. Not only that, there is a regulatory requirement on NP in
1324 some countries that the donor network should not be relied on to
1325 reach the delegated authority during the DNS process . The
1326 delegated authority for a given E.164 number is likely to be an
1327 entity designated by the end user that owns/controls a specific
1328 telephone number or one that is designated by the service registrar.
1330 Since the telephony service providers may have the need to use ENUM
1331 for their network-related services (e.g., map an E.164 number to a
1332 HLR Identifier in the wireless networks), their ENUM records must be
1333 collocated with those of the telephony subscribers. If that is the
1334 case, NP will impact ENUM when a telephony subscriber who has ENUM
1335 service changes the telephony service provider. This is because
1336 that the ENUM records from the new telephony service provider must
1337 replace those from the old telephony service provider. To avoid the
1338 NP impact on ENUM, it is recommended that the telephony service
1339 providers use a different domain tree for their network-related
1340 service. For example, if e164.arpa is chosen for
\9fend user÷ ENUM, a
1341 domain tree different from e164.arpa should be used for
\9fcarrier÷
1344 The IP-based networks also may need to support some forms of number
1345 portability in the future if E.164 numbers [E164] are assigned to
1346 the IP-based end users. One method is to assign a GSTN routing
1347 number for each IP-based network domain or entity in a NP-capable
1348 country. This may increase the number of digits in the routing
1349 number to incorporate the IP entities and impact the existing
1350 routing in the GSTN. Another method is to associate each IP entity
1351 with a particular GSTN gateway. At that particular GSTN gateway,
1352 the called directory number then is used to locate the IP-entity
1354 Foster,McGarry,Yu Expired on December 23, 2002 [Page 23]
1356 Number Portability in the GSTN: An Overview June 24, 2002
1358 that serves that dialed directory number. Yet, another method can
1359 be to assign a special routing number so that the call to an end
1360 user currently served by an IP entity is routed to the nearest GSTN
1361 gateway. The called directory number then is used to locate the IP-
1362 entity that serves that dialed directory number. A mechanism can be
1363 developed or used for the IP-based network to locate the IP entity
1364 that serves a particular dialed directory number. Many other types
1365 of networks use E.164 numbers to identify the end users or terminals
1366 in those networks. Number portability among GSTN, IP-based network
1367 and those various types of networks may also need to be supported in
1371 10. Security Considerations
1373 This document does not raise any security issues.
1376 11. IANA Considerations
1378 This document introduces no new values for IANA registration.
1381 12. Normative References
1383 [ANSI OSS] ANSI Technical Requirements No. 1, "Number Portability -
1384 Operator Services Switching Systems," April 1999.
1386 [ANSI SS] ANSI Technical Requirements No. 2, "Number Portability -
1387 Switching Systems," April 1999.
1389 [ANSI DB] ANSI Technical Requirements No. 3, "Number Portability
1390 Database and Global Title Translation," April 1999.
1392 [CS1] ITU-T Q-series Recommendations - Supplement 4, "Number
1393 portability Capability set 1 requirements for service provider
1394 portability (All call query and onward routing)," May 1998.
1396 [CS2] ITU-T Q-series Recommendations - Supplement 5, "Number
1397 portability -Capability set 2 requirements for service provider
1398 portability (Query on release and Dropback)," March 1999.
1400 [E164] ITU-T Recommendation E.164, "The International Public
1401 Telecommunications Numbering Plan," 1997.
1403 [ENUM] P. Falstrom, "E.164 number and DNS," RFC 2916.
1405 [ETSIISUP] ETSI EN 302 097 V.1.2.2,
\9fIntegrated Services Digital
1406 Network (ISDN); Signalling System No.7 (SS7); ISDN User Part
1407 (ISUP); Enhancement for support of Number Portability (NP)
1408 [ITU-T Recommendation Q.769.1 (2000), modified]
1410 [GSM] GSM 09.02: "Digital cellular telecommunications system (Phase
1411 2+); Mobile Application Part (MAP) specification".
1413 Foster,McGarry,Yu Expired on December 23, 2002 [Page 24]
1415 Number Portability in the GSTN: An Overview March 1, 2002
1419 [IS41] TIA/EIA IS-756 Rev. A, "TIA/EIA-41-D Enhancements for
1420 Wireless Number Portability Phase II (December 1998)"Number
1421 Portability Network Support," April 1998.
1423 [ITUISUP] ITU-T Recommendation Q.769.1, "Signaling System No. 7 -
1424 ISDN User Part Enhancements for the Support of Number
1425 Portability," December 1999.
1427 [MNP] ETSI EN 301 716 (2000-10) European Standard
1428 (Telecommunications series) Digital cellular telecommunications
1429 system (Phase 2+); Support of Mobile Number Portability (MNP);
1430 Technical Realisation; Stage 2; (GSM 03.66 Version 7.2.0
1433 [RFC] Scott Bradner, RFC2026, "The Internet Standards Process --
1434 Revision 3," October 1996.
1437 13. Informative References
1439 [ENUMPO] A. Brown and G. Vaudreuil, "ENUM Service Specific
1440 Provisioning: Principles of Operations," draft-ietf-enum-
1441 operation-02.txt, February 23, 2001.
1443 [SIP] J. Rosenberg, et al., draft-ietf-sip-rfc2543bis-09.txt, "SIP:
1444 Session Initiation Protocol," February 27, 2002.
1446 [TEL] H. Schulzrinne and A. Vaha-Sipila, draft-antti-rfc2806bis-
1447 04.txt, "URIs for Telephone Calls," May 24, 2002.
1449 [TELNP] J. Yu, draft-yu-tel-url-05.txt, "Extensions to the "tel" URL
1450 to support Number Portability and Freephone Service," June 14,
1453 [TRIP] J. Rosenberg, H. Salama and M. Squire, RFC 3219, "Telephony
1454 Routing Information Protocol (TRIP)," January 2002.
1459 The authors would like to thank Monika Muench for providing
1460 information on ISUP and MNP.
1463 15. Authors' Addresses
1467 1120 Vermont Avenue, NW,
1469 Washington, D.C. 20005
1472 Foster,McGarry,Yu Expired on August 31, 2002 [Page 25]
1474 Number Portability in the GSTN: An Overview March 1, 2002
1478 Phone: +1-202-533-2800
1479 Fax: +1-202-533-2987
1480 Email: mark.foster@neustar.biz
1484 1120 Vermont Avenue, NW,
1486 Washington, D.C. 20005
1489 Phone: +1-202-533-2810
1490 Fax: +1-202-533-2987
1491 Email: tom.mcgarry@neustar.biz
1495 1120 Vermont Avenue, NW,
1497 Washington, D.C. 20005
1500 Phone: +1-202-533-2814
1501 Fax: +1-202-533-2987
1502 Email: james.yu@neustar.biz
1506 Full Copyright Statement
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1514 kind, provided that the above copyright notice and this paragraph
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1529 Foster,McGarry,Yu Expired on August 31, 2002 [Page 26]
1531 Number Portability in the GSTN: An Overview March 1, 2002
1534 This document and the information contained herein is provided on an
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1544 Funding for the RFC Editor function is currently provided by the
1587 Foster,McGarry,Yu Expired on August 31, 2002 [Page 27]
projects / FreeBSD / releng / 7.2.git / blob