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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Mark Foster 2 Internet Draft Tom McGarry 3 Document: James Yu 4 NeuStar, Inc. 5 Category: Informational June 24, 2002 7 Number Portability in the GSTN: An Overview 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026 [RFC]. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. Internet-Drafts are draft documents valid for a maximum of 18 six months and may be updated, replaced, or obsoleted by other 19 documents at any time. It is inappropriate to use Internet- Drafts 20 as reference material or to cite them other than as "work in 21 progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt. 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 Copyright Notice 31 Copyright (C) The Internet Society (2002). All rights reserved. 33 Abstract 35 This document provides an overview of E.164 telephone number 36 portability (NP) in the Global Switched Telephone Network (GSTN). 37 NP is a regulatory imperative seeking to liberalize local telephony 38 service competition, by enabling end-users to retain telephone 39 numbers while changing service providers. NP changes the 40 fundamental nature of a dialed E.164 number from a hierarchical 41 physical routing address to a virtual address, thereby requiring the 42 transparent translation of the later to the former. In addition, 43 there are various regulatory constraints that establish relevant 44 parameters for NP implementation, most of which are not network 45 technology specific. Consequently, the implementation of NP 46 behavior consistent with applicable regulatory constraints, as well 47 as the need for interoperation with the existing GSTN NP 48 implementations, are relevant topics for numerous areas of IP 49 telephony work-in-progress at IETF. 51 Number Portability in the GSTN: An Overview June 24, 2002 53 Table of Contents 55 1. Introduction ............................................... 2 56 2. Abbreviations and Acronyms ................................. 4 57 3. Types of Number Portability ................................ 5 58 4. Service Provider Number Portability Schemes ................ 7 59 4.1 All Call Query (ACQ) .................................. 7 60 4.2 Query on Release (QoR) ................................ 8 61 4.3 Call Dropback ......................................... 9 62 4.4 Onward Routing (OR) ................................... 9 63 4.5 Comparisons of the Four Schemes ....................... 10 64 5. Database Queries in the NP Environment ..................... 11 65 5.1 U.S. and Canada ....................................... 12 66 5.2 Europe ................................................ 13 67 6. Call Routing in the NP Environment ......................... 14 68 6.1 U.S. and Canada ....................................... 14 69 6.2 Europe ................................................ 15 70 7. NP Implementations for Geographic E.164 Numbers ............ 17 71 8. Number Conservation Method Enabled By NP ................... 20 72 8.1 Block Pooling ......................................... 20 73 8.2 ITN Pooling ........................................... 21 74 9. Potential Implications ..................................... 21 75 10. Security Considerations .................................... 24 76 11. IANA Considerations ........................................ 24 77 12. Normative References ....................................... 24 78 13. Informative References ..................................... 25 79 14. Acknowledgement ............................................ 25 80 15. Authors� Addresses ......................................... 25 82 1. Introduction 84 This document provides an overview of E.164 telephone number 85 portability in the Global Switched Telephone Network (GSTN). There 86 are considered to be three types of number portability (NP): service 87 provider portability (SPNP), location portability (not to be 88 confused with terminal mobility), and service portability. 90 Service provider portability (SPNP), the focus of the present draft, 91 is a regulatory imperative in many countries seeking to liberalize 92 telephony service competition, especially local service. 93 Historically, local telephony service (as compared to long distance 94 or international service) has been regulated as a utility-like form 95 of service. While a number of countries had begun liberalization 96 (e.g. privatization, de-regulation, or re-regulation) some years 97 ago, the advent of NP is relatively recent (since ~1995). 99 E.164 numbers can be non-geographic and geographic numbers. Non- 100 geographic numbers do not reveal the locations information of those 101 numbers. Geographic E.164 numbers were intentionally designed as 102 hierarchical routing addresses which could systematically be digit- 103 analyzed to ascertain the country, serving network provider, serving 105 Number Portability in the GSTN: An Overview June 24, 2002 107 end-office switch, and specific line of the called party. As such, 108 without NP a subscriber wishing to change service providers would 109 incur a number change as a consequence of being served off of a 110 different end-office switch operated by the new service provider. 111 The cost and convenience impact to the subscriber of changing 112 numbers is seen as barrier to competition. Hence NP has become 113 associated with GSTN infrastructure enhancements associated with a 114 competitive environment driven by regulatory directives. 116 Forms of SPNP have been deployed or are being deployed widely in the 117 GSTN in various parts of the world, including the U.S., Canada, 118 Western Europe, Australia, and the Pacific Rim (e.g. Hong Kong). 119 Other regions, such as South America (e.g. Brazil) are actively 120 considering it. 122 Implementation of NP within a national telephony infrastructure 123 entails potentially significant changes to numbering administration, 124 network element signaling, call routing and processing, billing, 125 service management, and other functions. 127 NP changes the fundamental nature of a dialed E.164 number from a 128 hierarchical physical routing address to a virtual address. NP 129 implementations attempt to encapsulate the impacts to the GSTN and 130 make NP transparent to subscribers by incorporating a translation 131 function to map a dialed, potentially ported E.164 address, into a 132 network routing address (either a number prefix or another E.164 133 address) which can be hierarchically routed. 135 This is roughly analogous to the use of network address translation 136 on IP addresses to enable IP address portability by containing the 137 impact of the address change to the edge of the network and retain 138 the use of CIDR blocks in the core which can be route aggregated by 139 the network service provider to the rest of the internet. 141 NP bifurcates the historical role of a subscriber�s E.164 address 142 into two or more data elements (a dialed or virtual address, and a 143 network routing address) that must be made available to network 144 elements through an NP translations database, carried by forward 145 call signaling, and recorded on call detail records. Not only is 146 call processing and routing affected, but also so is SS7/C7 147 messaging. A number of TCAP-based SS7 messaging sets utilize an 148 E.164 address as an application-level network element address in the 149 global title address (GTA) field of the SCCP message header. 150 Consequently, SS7/C7 signaling transfer points (STPs) and gateways 151 need to be able to perform n-digit global title translation (GTT) to 152 translate a dialed E.164 address into its network address 153 counterpart via the NP database. 155 In addition, there are various national regulatory constraints that 156 establish relevant parameters for NP implementation, most of which 157 are not network technology specific. Consequently, implementations 158 of NP behavior in IP telephony consistent with applicable regulatory 159 constraints, as well as the need for interoperation with the 161 Number Portability in the GSTN: An Overview June 24, 2002 163 existing GSTN NP implementations, are relevant topics for numerous 164 areas of IP telephony work-in-progress at IETF. 166 This document describes three types of number portability and the 167 four schemes that have been standardized to support SPNP for 168 geographic E.164 numbersspecifically. Following that, specific 169 information regarding the call routing and database query 170 implementations are described for several regions (North American 171 and Europe) and industries (wireless vs. wireline). The Number 172 Portability Database (NPDB) interfaces and the call routing schemes 173 that are used in the North America and Europe are described to show 174 the variety of standards that may be implemented worldwide. A 175 glance of the NP implementations worldwide is provided. Number 176 pooling is briefly discussed to show how NP is being enhanced in the 177 U.S. to conserve North American area codes. The conclusion briefly 178 touches the potential impacts of NP on IP & Telecommunications 179 Interoperability. Appendix A provides some specific technical and 180 regulatory information on NP in North America. Appendix B describes 181 the number portability administration process that manages the 182 number portability database in North America. 184 2. Abbreviations and Acronyms 186 ACQ All Call Query 187 AIN Advanced Intelligent Network 188 AMPS Advanced Mobile Phone System 189 ANSI American National Standards Institute 190 CDMA Code Division Multiple Access 191 CdPA Called Party Address 192 CdPN Called Party Number 193 CH Code Holder 194 CMIP Common Management Information Protocol 195 CS1 Capability Set 1 196 CS2 Capability Set 2 197 DN Directory Number 198 DNS Domain Name System 199 ETSI European Technical Standards Institute 200 FCI Forward Call Indicator 201 GAP Generic Address Parameter 202 GMSC Gateway Mobile Services Switching Center or Gateway Mobile 203 Switching Center 204 GSM Global System for Mobile Communications 205 GSTN Global Switched Telephone Network 206 GW Gateways 207 HLR Home Location Register 208 IAM Initial Address Message 209 IETF Internet Engineering Task Force 210 ILNP Interim LNP 211 IN Intelligent Network 212 INAP Intelligent Network Application Part 213 INP Interim NP 214 IP Internet Protocol 215 IS-41 Interim Standards Number 41 217 Number Portability in the GSTN: An Overview June 24, 2002 219 ISDN Integrated Services Digital Network 220 ISUP ISDN User Part 221 ITN Individual Telephony Number 222 ITU International Telecommunication Union 223 ITU-TS ITU-Telecommunication Sector 224 LDAP Lightweight Directory Access Protocol 225 LEC Local Exchange Carrier 226 LERG Local Exchange Routing Guide 227 LNP Local Number Portability 228 LRN Location Routing Number 229 MAP Mobile Application Part 230 MNP Mobile Number Portability 231 MSRN Mobile Station Roaming Number 232 MTP Message Transfer Part 233 NANP North American Numbering Plan 234 NP Number Portability 235 NPDB Number Portability Database 236 NRN Network Routing Number 237 OR Onward Routing 238 OSS Operation Support System 239 PCS Personal Communication Services 240 PNTI Ported Number Translation Indicator 241 PODP Public Office Dialing Plan 242 PUC Public Utility Commission 243 QoR Query on Release 244 RN Routing Number 245 RTP Return to Pivot 246 SCCP Signaling Connection Control Part 247 SCP Service Control Point 248 SIP Session Initiation Protocol 249 SMR Special Mobile Radio 250 SMS Service Management System 251 SPNP Service Provider Number Portability 252 SRF Signaling Relaying Function 253 SRI Send Routing Information 254 SS7 Signaling System Number 7 255 STP Signaling Transfer Point 256 TCAP Transaction Capabilities Application Part 257 TDMA Time Division Multiple Access 258 TN Telephone Number 259 TRIP Telephony Routing Information Protocol 260 URL Universal Resource Locator 261 U.S. United States 263 3. Types of Number Portability 265 As there are several types of E.164 numbers (telephone numbers, or 266 just TN) in the GSTN, there are correspondingly several types of 267 E.164 NP in the GSTN. First there are so-call non-geographic E.164 268 numbers, commonly used for service-specific applications such as 269 freephone (800 or 0800). Portability of these numbers is called 270 non-geographic number portability (NGNP). NGNP, for example, was 271 deployed in the U.S. in 1986-92. 273 Number Portability in the GSTN: An Overview June 24, 2002 275 Geographic number portability, which includes traditional fixed or 276 wireline numbers as well as mobile numbers which are allocated out 277 of geographic number range prefixes, is called NP or GNP or in the 278 U.S. local number portability (LNP). 280 Number portability allows the telephony subscribers in the Global 281 Switched Telephone Network (GSTN) to keep their phone numbers when 282 they change their service providers or subscribed services, or when 283 they move to a new location. 285 The ability to change the service provider while keeping the same 286 phone number is called service provider portability (SPNP) also 287 known as "operator portability." 289 The ability to change the subscriber�s fixed service location while 290 keeping the same phone number is called location portability. 292 The ability to change the subscribed services (e.g., from the plain 293 old telephone service to Integrated Services Digital Network (ISDN) 294 services) while keeping the same phone number is called service 295 portability. Another aspect of service portability is to allow the 296 subscribers to enjoy the subscribed services in the same way when 297 they roam outside their home networks as is supported by the 298 cellular/wireless networks. 300 In addition, mobile number portability (MNP) refers to specific NP 301 implementation in mobile networks either as part of a broader NP 302 implementation in the GSTN or on a stand-alone basis. Where 303 interoperation of LNP and MNP is supported, service portability 304 between fixed and mobile service types is possible. 306 At present, SPNP has been the primary form of NP deployed due to its 307 relevance in enabling local service competition. 309 Also in use in the GSTN are the terms interim NP (INP) or Interim 310 LNP (ILNP) and true NP. Interim NP usually refers to the use of 311 remote call forwarding-like measures to forward calls to ported 312 numbers through the donor network to the new service network. These 313 are considered interim relative to true NP, which seeks to remove 314 the donor network or old service provider from the call or signaling 315 path altogether. Often the distinction between interim and true NP 316 is a national regulatory matter relative to the 317 technical/operational requirements imposed on NP in that country. 319 Implementations of true NP in certain countries (e.g. U.S., Canada, 320 Spain, Belgium, Denmark) may pose specific requirements for IP 321 telephony implementations as a result of regulatory and industry 322 requirements for providing call routing and signaling independent of 323 the donor network or last previous serving network. 325 Number Portability in the GSTN: An Overview June 24, 2002 327 4. Service Provider Number Portability Schemes 329 Four schemes can be used to support service provider portability and 330 are briefly described below. But first, some further terms are 331 introduced. 333 The donor network is the network that first assigned a telephone 334 number (e.g., TN +1-202-533-1234) to a subscriber, out of a number 335 range administratively (e.g., +1 202-533) assigned to it. The 336 current service provider (new SP) or new serving network is the 337 network that currently serves the ported number. The old serving 338 network (or old SP) is the network that previously served the ported 339 number before the number was ported to the new serving network. 340 Since a TN can port a number of times, the old SP is not necessarily 341 the same as the donor network, except for the first time the TN 342 ports away, or if the TN ports back into the donor network and away 343 again. While the new SP and old SP roles are transitory as a TN 344 ports around, the donor network is always the same for any 345 particular TN based on the service provider to whom the subtending 346 number range was administratively assigned. See the discussion 347 below on number pooling, as this enhancement to NP further 348 bifurcates the role of donor network into two (the number range or 349 code holder network, and the block holder network). 351 To simplify the illustration, all the transit networks are ignored, 352 the originating or donor network is the one that performs the 353 database queries or call redirection, and the dialed directory 354 number (TN) has been ported out of the donor network before. 356 It is assumed that the old serving network, the new serving network 357 and the donor network are different networks so as to show which 358 networks are involved in call handling and routing and database 359 queries in each of four schemes. Please note that the port of the 360 number (process of moving it from one network to another) happened 361 prior to the call setup and is not included in the call steps. 362 Information carried in the signaling messages to support each of the 363 four schemes is not discussed to simplify the explanation. 365 4.1 All Call Query (ACQ) 367 Figure 1 shows the call steps for the ACQ scheme. Those call steps 368 are as follows: 370 (1) The Originating Network receives a call from the caller and 371 sends a query to a centrally administered Number Portability 372 Database (NPDB), a copy of which is usually resident on a 373 network element within its network or through a third party 374 provider. 375 (2) The NPDB returns the routing number associated with the dialed 376 directory number. The routing number is discussed later in 377 Section 6. 379 Number Portability in the GSTN: An Overview June 24, 2002 381 (3) The Originating Network uses the routing number to route the 382 call to the new serving network. 384 +-------------+ +-----------+ Number +-----------+ 385 | Centralized | | New Serv. | ported | Old Serv. | 386 | NPDB | +-------->| Network |<------------| Network | 387 +-------------+ | +-----------+ +-----------+ 388 ^ | | 389 | | | 390 1| | 3.| 391 | | 2. | 392 | | | 393 | v | 394 +----------+ | +----------+ +----------+ 395 | Orig. |------+ | Donor | | Internal | 396 | Network | | Network | | NPDB | 397 +----------+ +----------+ +----------+ 399 Figure 1 - All Call Query (ACQ) Scheme. 401 4.2 Query on Release (QoR) 403 Figure 2 shows the call steps for the QoR scheme. Those call steps 404 are as follows: 406 +-------------+ +-----------+ Number +-----------+ 407 | Centralized | | New Serv. | ported | Old Serv. | 408 | NPDB | | Network |<------------| Network | 409 +-------------+ +-----------+ +-----------+ 410 ^ | ^ 411 | | 4. | 412 3.| | 5. | 413 | | +----------------------+ 414 | | | 415 | v | 416 +----------+ 2. +----------+ +----------+ 417 | Orig. |<---------------| Donor | | Internal | 418 | Network |--------------->| Network | | NPDB | 419 +----------+ 1. +----------+ +----------+ 421 Figure 2 - Query on Release (QoR) Scheme. 423 (1) The Originating Network receives a call from the caller and 424 routes the call to the donor network. 425 (2) The donor network releases the call and indicates that the 426 dialed directory number has been ported out of that switch. 427 (3) The Originating Network sends a query to its copy of the 428 centrally administered NPDB. 430 Number Portability in the GSTN: An Overview June 24, 2002 432 (4) The NPDB returns the routing number associated with the dialed 433 directory number. 434 (5) The Originating Network uses the routing number to route the 435 call to the new serving network. 437 4.3 Call Dropback 439 Figure 3 shows the call steps for the Dropback scheme. This scheme 440 is also known as "Return to Pivot (RTP)." Those call steps are as 441 follows: 443 (1) The Originating Network receives a call from the caller and 444 routes the call to the donor network. 445 (2) The donor network detects that the dialed directory number has 446 been ported out of the donor switch and checks with an internal 447 network-specific NPDB. 448 (3) The internal NPDB returns the routing number associated with the 449 dialed directory number. 450 (4) The donor network releases the call by providing the routing 451 number. 452 (5) The Originating Network uses the routing number to route the 453 call to the new serving network. 455 +-------------+ +-----------+ Number +-----------+ 456 | Centralized | | New Serv. | porting | Old Serv. | 457 | NPDB | | Network |<------------| Network | 458 +-------------+ +-----------+ +-----------+ 459 /\ 460 | 461 5. | 462 +------------------------+ 463 | 464 | 465 +----------+ 4. +----------+ 3. +----------+ 466 | Orig. |<---------------| Donor |<----------| Internal | 467 | Network |--------------->| Network |---------->| NPDB | 468 +----------+ 1. +----------+ 2. +----------+ 470 Figure 3 - Dropback Scheme. 472 4.4 Onward Routing (OR) 474 Figure 4 shows the call steps for the OR scheme. Those call steps 475 are as follows: 477 (1) The Originating Network receives a call from the caller and 478 routes the call to the donor network. 479 (2) The donor network detects that the dialed directory number has 480 been ported out of the donor switch and checks with an internal 481 network-specific NPDB. 483 Number Portability in the GSTN: An Overview June 24, 2002 485 (3) The internal NPDB returns the routing number associated with the 486 dialed directory number. 487 (4) The donor network uses the routing number to route the call to 488 the new serving network. 490 +-------------+ +-----------+ Number +-----------+ 491 | Centralized | | New Serv. | porting | Old Serv. | 492 | NPDB | | Network |<------------| Network | 493 +-------------+ +-----------+ +-----------+ 494 /\ 495 | 496 4.| 497 | 498 +----------+ +----------+ 3. +----------+ 499 | Orig. | | Donor |<----------| Internal | 500 | Network |--------------->| Network |---------->| NPDB | 501 +----------+ 1. +----------+ 2. +----------+ 503 Figure 4 - Onward Routing (OR) Scheme. 505 4.5 Comparisons of the Four Schemes 507 Only the ACQ scheme does not involve the donor network when routing 508 the call to the new serving network of the dialed ported number. 509 The other three schemes involve call setup to or signaling with the 510 donor network. 512 Only the OR scheme requires the setup of two physical call segments, 513 one from the Originating Network to the donor network and the other 514 from the donor network to the new serving network. The OR scheme is 515 the least efficient in terms of using the network transmission 516 facilities. The QoR and Dropback schemes set up calls to the donor 517 network first but release the call back to the Originating Network 518 that then initiates a new call to the Current Serving Network. For 519 the QoR and Dropback schemes, circuits are still reserved one by one 520 between the Originating Network and the donor network when the 521 Originating Network sets up the call towards the donor network. 522 Those circuits are released one by one when the call is released 523 from the donor network back to the Originating Network. The ACQ 524 scheme is the most efficient in terms of using the switching and 525 transmission facilities for the call. 527 Both the ACQ and QoR schemes involve Centralized NPDBs for the 528 Originating Network to retrieve the routing information. 529 Centralized NPDB means that the NPDB contains ported number 530 information from multiple networks. This is in contrast to the 531 internal network-specific NPDB that is used for the Dropback and OR 532 schemes. The internal NPDB only contains information about the 533 numbers that were ported out of the donor network. The internal 534 NPDB can be a stand-alone database that contains information about 535 all or some ported-out numbers from the donor network. It can also 536 reside on the donor switch and only contains information about those 538 Number Portability in the GSTN: An Overview June 24, 2002 540 numbers ported out of the donor switch. In that case, no query to a 541 stand-alone internal NPDB is required. The donor switch for a 542 particular phone number is the switch to which the number range is 543 assigned from which that phone number was originally assigned. 545 For example, number ranges in the North American Numbering Plan 546 (NANP) are usually assigned in the form of central office codes (CO 547 codes) comprising a six-digit prefix formatted as a NPA+NXX. Thus a 548 switch serving +1-202-533 would typically serve +1-202-533-0000 549 through +1-202-533-9999. In major cities, switches usually host 550 several CO codes. NPA stands for Numbering Plan Area that is also 551 known as the area code. It is three-digit long and has the format 552 of NXX where N is any digit from 2 to 9 and X is any digit from 0 to 553 9. NXX in the NPA+NXX format is known as the office code that has 554 the same format as the NPA. When a NPA+NXX code is set as 555 �portable� in the Local Exchange Routing Guide (LERG), it becomes a 556 "portable NPA+NXX" code. 558 Similarly, in other national E.164 numbering plans, number ranges 559 cover a contiguous range of numbers within that range. Once a 560 number within that range has ported away from the donor network, all 561 numbers in that range are considered potentially ported and should 562 be queried in the NPDB. 564 The ACQ scheme has two versions. One version is for the Originating 565 Network to always query the NPDB when a call is received from the 566 caller regardless whether the dialed directory number belongs to any 567 number range that is portable or has at least one number ported out. 568 The other version is to check whether the dialed directory number 569 belongs to any number range that is portable or has at least one 570 number ported out. If yes, an NPDB query is sent. If not, no NPDB 571 query is sent. The former performs better when there are many 572 portable number ranges. The latter performs better when there are 573 not too many portable number ranges at the expense of checking every 574 call to see whether NPDB query is needed. The latter ACQ scheme is 575 similar to the QoR scheme except that the QoR scheme uses call setup 576 and relies on the donor network to indicate "number ported out" 577 before launching the NPDB query. 579 5. Database Queries in the NP Environment 581 As indicated earlier, the ACQ and QoR schemes require that a switch 582 query the NPDB for routing information. Various standards have been 583 defined for the switch-to-NPDB interface. Those interfaces with 584 their protocol stacks are briefly described below. The term "NPDB" 585 is used for a stand-alone database that may support just one or some 586 or all of the interfaces mentioned below. The NPDB query contains 587 the dialed directory number and the NPDB response contains the 588 routing number. There are certainly other information that is sent 589 in the query and response. The primary interest is to get the 590 routing number from the NPDB to the switch for call routing. 592 Number Portability in the GSTN: An Overview June 24, 2002 594 5.1 U.S. and Canada 596 One of the following five NPDB interfaces can be used to query an 597 NPDB: 599 (a) Advanced Intelligent Network (AIN) using the American National 600 Standards Institute (ANSI) version of the Intelligent Network 601 Application Part (INAP) [ANSI SS] [ANSI DB]. The INAP is 602 carried on top of the protocol stack that includes the (ANSI) 603 Message Transfer Part (MTP) Levels 1 through 3, ANSI Signaling 604 Connection Control Part (SCCP), and ANSI Transaction 605 Capabilities Application Part (TCAP). This interface can be 606 used by the wireline or wireless switches, is specific to the NP 607 implementation in North America, and is modeled on the Public 608 Office Dialing Plan (PODP) trigger defined in the Advanced 609 Intelligent Network (AIN) 0.1 call model. 611 (b) Intelligent Network (IN), which is similar to the one used for 612 querying the 800 databases. The IN protocol is carried on top 613 of the protocol stack that includes the ANSI MTP Levels 1 614 through 3, ANSI SCCP, and ANSI TCAP. This interface can be used 615 by the wireline or wireless switches. 617 (c) ANSI IS-41 [IS41] [ISNP], which is carried on top of the 618 protocol stack that includes the ANSI MTP Levels 1 through 3, 619 ANSI SCCP, and ANSI TCAP. This interface can be used by the IS- 620 41 based cellular/Personal Communication Services (PCS) wireless 621 switches (e.g., AMPS, TDMA and CDMA). Cellular systems use 622 spectrum at 800 MHz range and PCS systems use spectrum at 1900 623 MHz range. 625 (d) Global System for Mobile Communication Mobile Application Part 626 (GSM MAP) [GSM], which is carried on top of the protocol stack 627 that includes the ANSI MTP Levels 1 through 3, ANSI SCCP, and 628 International Telecommunication Union - Telecommunication Sector 629 (ITU-TS) TCAP. It can be used by the PCS1900 wireless switches 630 that are based on the GSM technologies. GSM is a series of 631 wireless standards defined by the European Telecommunications 632 Standards Institute (ETSI). 634 (e) ISUP triggerless translation. NP translations are performed 635 transparently to the switching network by the signaling network 636 (e.g. Signaling Transfer Points (STPs) or signaling gateways). 637 ISUP IAM messages are examined to determine if the CdPN field 638 has already been translated, and if not, an NPDB query is 639 performed, and the appropriate parameters in the IAM message 640 modified to reflect the results of the translation. The 641 modified IAM message is forwarded by the signaling node on to 642 the designated DPC in a transparent manner to continue call 643 setup. The NPDB can be integrated with the signaling node or be 644 accessed via an API locally or by a query to a remote NPDB using 645 a proprietary protocol or the schemes described above. 647 Number Portability in the GSTN: An Overview June 24, 2002 649 Wireline switches have the choice of using either (a), (b), or (e). 650 IS-41 based wireless switches have the choice of using (a), (b), 651 (c), or (e). PCS1900 wireless switches have the choice of using 652 (a), (b), (d), or (e). In the United States, service provider 653 portability will be supported by both the wireline and wireless 654 systems, not only within the wireline or wireless domain but also 655 across the wireline/wireless boundary. However, this is not true in 656 Europe where service provider portability is usually supported only 657 within the wireline or wireless domain, not across the 658 wireline/wireless boundary due to explicit use of service-specific 659 number range prefixes. The reason is to avoid caller confusion 660 about the call charge. GSM systems in Europe are assigned 661 distinctive destination network codes, and the caller pays a higher 662 charge when calling a GSM directory number. 664 5.2 Europe 666 One of the following two interfaces can be used to query an NPDB: 668 (a) Capability Set 1 (CS1) of the ITU-TS INAP [CS1], which is 669 carried on top of the protocol stack that includes the ITU-TS 670 MTP Levels 1 through 3, ITU-TS SCCP, and ITU-TS TCAP. 672 (b) Capability Set 2 (CS2) of the ITU-TS INAP [CS2], which is 673 carried on top of the protocol stack that includes the ITU-TS 674 MTP Levels 1 through ITU-TS MTP Levels 1 through 3, ITU-TS SCCP, 675 and ITU-TS TCAP. 677 Wireline switches have the choice of using either (a) or (b); 678 however, all the implementations in Europe so far are based on CS1. 679 As indicated earlier that number portability in Europe does not go 680 across the wireline/wireless boundary. The wireless switches can 681 also use (a) or (b) to query the NPDBs if those NPDBs contains 682 ported wireless directory numbers. The term "Mobile Number 683 Portability (MNP)" is used for the support of service provider 684 portability by the GSM networks in Europe. 686 In most, if not all, cases in Europe, the calls to the wireless 687 directory numbers are routed to the wireless donor network first. 688 Over there, an internal NPDB is queried to determine whether the 689 dialed wireless directory number has been ported out or not. In 690 this case, the interface to the internal NPDB is not subject to 691 standardization. 693 MNP in Europe can also be supported via MNP Signaling Relay Function 694 (MNP-SRF). Again, an internal NPDB or a database integrated at the 695 MNP-SRF is used to modify the SCCP Called Party Address parameter in 696 the GSM MAP messages so that they can be re-directed to the wireless 697 serving network. Call routing involving MNP will be explained in 698 Section 6.2. 700 Number Portability in the GSTN: An Overview June 24, 2002 702 6. Call Routing in the NP Environment 704 This section discusses the call routing after the routing 705 information has been retrieved either through an NPDB query or an 706 internal database lookup at the donor switch, or from the Integrated 707 Services Digital Network User Part (ISUP) signaling message (e.g., 708 for the Dropback scheme). For the ACQ, QoR and Dropback schemes, it 709 is the Originating Network that has the routing information and is 710 ready to route the call. For the OR scheme, it is the donor network 711 that has the routing information and is ready to route the call. 713 A number of triggering schemes may be employed that determine where 714 in the call path the NPDB query is performed. In the U.S. an �N-1� 715 policy is used, which essentially says that for domestic calls, the 716 originating local carriers performs the query, otherwise, the long 717 distance carrier is expected to. To ensure independence of the 718 actual trigger policy employed in any one carrier, forward call 719 signaling is used to flag that an NPDB query has already been 720 performed and to therefore suppress any subsequent NP triggers that 721 may be encountered in downstream switches, in downstream networks. 722 This allows the earliest able network in the call path to perform 723 the query without introducing additional costs and call setup delays 724 were redundant queries performed downstream. 726 6.1 U.S. and Canada 728 In the U.S. and Canada, a ten-digit North American Numbering Plan 729 (NANP) number called Location Routing Number (LRN) is assigned to 730 every switch involved in NP. In the NANP, a switch is not reachable 731 unless it has a unique number range (CO code) assigned to it. 732 Consequently, the LRN for a switch is always assigned out of a CO 733 code that is assigned to that switch. 735 The LRN assigned to a switch currently serving a particular ported 736 telephone number is returned as the network routing address in the 737 NPDB response. The service portability scheme that was adopted in 738 the North America is very often referred to as the LRN scheme or 739 method. 741 LRN serves as a network address for terminating calls served off 742 that switch using ported numbers. The LRN is assigned by the switch 743 operator using any of the unique CO codes (NPA+NXX) assigned to that 744 switch. The LRN is considered a non-dialable address, as the same 745 10-digit number value may be assigned to a line on that switch. A 746 switch may have more than one LRN. 748 During call routing/processing, a switch performs an NPDB query to 749 obtain the LRN associated with the dialed directory number. NPDB 750 queries are performed for all the dialed directory numbers whose 751 NPA+NXX codes are marked as portable NPA+NXX at that switch. When 752 formulating the ISUP Initial Address Message (IAM) to be sent to the 753 next switch, the switch puts the ten-digit LRN in the ISUP Called 754 Party Number (CdPN) parameter and the originally dialed directory 756 Number Portability in the GSTN: An Overview June 24, 2002 758 number in the ISUP Generic Address parameter (GAP). A new code in 759 the GAP was defined to indicate that the address information in the 760 GAP is the dialed directory number. A new bit in the ISUP Forward 761 Call Indicator (FCI) parameter, the Ported Number Translation 762 Indicator (PNTI) bit, is set to imply that NPDB query has already 763 been performed. All the switches in the downstream will not perform 764 the NPDB query if the PNTI bit is set. 766 When the terminating switch receives the IAM and sees the PNTI bit 767 in the FCI parameter set and its own LRN in the CdPN parameter, it 768 retrieves the originally dialed directory number from the GAP and 769 uses the dialed directory number to terminate the call. 771 A dialed directory number with a portable NPA+NXX does not imply 772 that directory number has been ported. The NPDBs currently do not 773 store records for non-ported directory numbers. In that case, the 774 NPDB will return the same dialed directory number instead of the 775 LRN. The switch will then set the PNTI bit but keep the dialed 776 directory number in the CdPN parameter. 778 In the real world environment, the Originating Network is not always 779 the one that performs the NPDB query. For example, it is usually 780 the long distance carriers that query the NPDBs for long distance 781 calls. In that case, the Originating Network operated by the local 782 exchange carrier (LEC) simply routes the call to the long distance 783 carrier that is to handle that call. A wireless network acting as 784 the Originating Network can also route the call to the 785 interconnected local exchange carrier network if it does not want to 786 support the NPDB interface at its mobile switches. 788 6.2 Europe 790 In some European countries, a routing number is prefixed to the 791 dialed directory number. The ISUP CdPN parameter in the IAM will 792 contain the routing prefix and the dialed directory number. For 793 example, United Kingdom uses routing prefixes with the format of 794 5XXXXX and Italy uses C600XXXXX as the routing prefix. The networks 795 use the information in the ISUP CdPN parameter to route the call to 796 the New/Current Serving Network. 798 The routing prefix can identify the Current Serving Network or the 799 Current Serving Switch of a ported number. For the former case, 800 another query to the "internal" NPDB at the Current Serving Network 801 is required to identify the Current Serving Switch before routing 802 the call to that switch. This shields the Current Serving Switch 803 information for a ported number from the other networks at the 804 expense of an additional NPDB query. Another routing number, may be 805 meaningful within the Current Serving Network, will replace the 806 previously prefixed routing number in the ISUP CdPN parameter. For 807 the latter case, the call is routed to the Current Serving Switch 808 without an additional NPDB query. 810 Number Portability in the GSTN: An Overview June 24, 2002 812 When the terminating switch receives the IAM and sees its own 813 routing prefix in the CdPN parameter, it retrieves the originally 814 dialed directory number after the routing prefix, and uses the 815 dialed directory number to terminate the call. 817 The call routing example described above shows one of the three 818 methods that can be used to transport the Directory Number (DN) and 819 the Routing Number (RN) in the ISUP IAM message. In addition, some 820 other information may be added/modified as is listed in the ETSI 302 821 097 document [ETSIISUP], which is based on the ITU-T Recommendation 822 Q.769.1 [ITUISUP]. The three methods and the enhancements in the 823 ISUP to support number portability are briefly described below 825 (a) Two separate parameters with the CdPN parameter containing the 826 RN and a new Called Directory Number (CdDN) parameter containing 827 the DN. A new value for the Nature of Address (NOA) indicator in 828 the CdPN parameter is defined to indicate that the RN is in the 829 CdPN parameter. The switches use the CdPN parameter to route the 830 call as is done today. 832 (b) Two separate parameters with the CdPN parameter containing the 833 DN and a new Network Routing Number (NRN) parameter containing 834 the RN. This method requires that the switches use the NRN 835 parameter to route the call. 837 (c) Concatenated parameter with the CdPN parameter containing the RN 838 plus the DN. A new Nature of Address (NOA) indicator in the CdPN 839 parameter is defined to indicate that the RN is concatenated with 840 the DN in the CdPN parameter. Some countries may not use new NOA 841 value because the routing prefix does not overlap with the dialed 842 directory numbers. But if the routing prefix overlaps with the 843 dialed directory numbers, a new NOA value must be assigned. For 844 example, Spain uses "XXXXXX" as the routing prefix to identify 845 the new serving network and uses a new NOA value of 126. 847 There is also a network option to add a new ISUP parameter called 848 Number Portability Forwarding Information parameter. This parameter 849 has a four-bit Number Portability Status Indicator field that can 850 provide an indication whether number portability query is done for 851 the called directory number and whether the called directory number 852 is ported or not if the number portability query is done. 854 Please note that all those NP enhancements for a ported number can 855 only be used in the country that defined them. This is because 856 number portability is supported within a nation. Within each 857 nation, the telecommunications industry or the regulatory bodies can 858 decide which method or methods to use. Number portability related 859 parameters and coding are usually not passed across the national 860 boundaries unless the interconnection agreements allow that. For 861 example, a UK routing prefix can only be used in UK, and would cause 862 routing problem if it appears outside UK. 864 Number Portability in the GSTN: An Overview June 24, 2002 866 As indicated earlier, an originating wireless network can query the 867 NPDB and concatenate the RN with DN in the CdPN parameter and route 868 the call directly to the Current Serving Network. 870 If NPDBs do not contain information about the wireless directory 871 numbers, the call, originated from either a wireline or a wireless 872 network, will be routed to the Wireless donor network. Over there, 873 an internal NPDB is queried to retrieve the RN that then is 874 concatenated with the DN in the CdPN parameter. 876 There are several ways of realizing MNP. When MNP-SRF is supported, 877 the Gateway Mobile Services Switching Center (GMSC) at the wireless 878 donor network, when receiving a call from the wireline network, can 879 send the GSM MAP Send Routing Information (SRI) message to the MNP- 880 SRF. The MNP-SRF interrogates an internal or integrated NPDB for 881 the RN of the MNP-SRF of the wireless Current Serving Network and 882 prefixes the RN to the dialed wireless directory number in the 883 global title address information in the SCCP Called Party Address 884 (CdPA) parameter. This SRI message will be routed to the MNP-SRF of 885 the wireless Current Serving Network, which then responds with an 886 acknowledgement by providing the RN plus the dialed wireless 887 directory number as the Mobile Station Roaming Number (MSRN). The 888 GMSC of the wireless donor network formulates the ISUP IAM with the 889 RN plus the dialed wireless directory number in the CdPN parameter 890 and routes the call to the wireless Current Serving Network. A GMSC 891 of the wireless Current Serving Network receives the call and sends 892 an SRI message to the associated MNP-SRF where the global title 893 address information of the SCCP CdPA parameter contains only the 894 dialed wireless directory number. The MNP-SRF then replaces the 895 global title address information in the SCCP CdPA parameter with the 896 address information associated with a Home Location Register (HLR) 897 that hosts the dialed wireless directory number and forwards the 898 message to that HLR after verifying that the dialed wireless 899 directory number is a ported-in number. The HLR then returns an 900 acknowledgement by providing an MSRN for the GMSC to route the call 901 to the MSC that currently serves the mobile station that is 902 associated with the dialed wireless directory number. Please see 903 [MNP] for details and additional scenarios. 905 7. NP Implementations for Geographic E.164 Numbers 907 This section shows the known SPNP implementations worldwide. 909 +-------------+----------------------------------------------------+ 910 + Country + SPNP Implementation + 911 +-------------+----------------------------------------------------+ 912 + Argentina + Analyzing operative viability now. Will determine + 913 + + whether portability should be made obligatory + 914 + + after a technical solution has been determined. + 915 +-------------+----------------------------------------------------+ 916 + Australia + NP supported by wireline operators since 11/30/99. + 917 + + NP among wireless operators in March/April 2000, + 919 Number Portability in the GSTN: An Overview June 24, 2002 921 + + but may be delayed to 1Q01. The access provider + 922 + + or long distance provider has the obligation to + 923 + + route the call to the correct destination. The + 924 + + donor network is obligated to maintain and make + 925 + + available a register of numbers ported away from + 926 + + its network. Telstra uses onward routing via an + 927 + + on-switch solution. + 928 +-------------+----------------------------------------------------+ 929 + Austria + Uses onward routing at the donor network. Routing + 930 + + prefix is "86xx" where "xx" identifies the + 931 + + recipient network. + 932 +-------------+----------------------------------------------------+ 933 + Belgium + ACQ selected by the industry. Routing prefix is + 934 + + "Cxxxx" where "xxxx" identifies the recipient + 935 + + switch. Another routing prefix is "C00xx" with "xx"+ 936 + + identifying the recipient network. Plan to use NOA+ 937 + + to identify concatenated numbers and abandon the + 938 + + hexadecimal routing prefix. + 939 +-------------+----------------------------------------------------+ 940 + Brazil + Considering NP for wireless users. + 941 +-------------+----------------------------------------------------+ 942 + Chile + There has been discussions lately on NP. + 943 +-------------+----------------------------------------------------+ 944 + Colombia + There was an Article 3.1 on NP to support NP prior + 945 + + to December 31, 1999 when NP became technically + 946 + + possible. Regulator has not yet issued regulations + 947 + + concerning this matter. + 948 +-------------+----------------------------------------------------+ 949 + Denmark + Uses ACQ. Routing number not passed between + 950 + + operators; however, NOA is set to "112" to + 951 + + indicate "ported number." QoR can be used based + 952 + + on bilateral agreements. + 953 +-------------+----------------------------------------------------+ 954 + Finland + Uses ACQ. Routing prefix is "1Dxxy" where "xxy" + 955 + + identifies the recipient network and service type. + 956 +-------------+----------------------------------------------------+ 957 + France + Uses onward routing. Routing prefix is "Z0xxx" + 958 + + where "xxx" identifies the recipient switch. + 959 +-------------+----------------------------------------------------+ 960 + Germany + The originating network needs to do necessary + 961 + + rerouting. Operators decide their own solution(s).+ 962 + + Deutsche Telekom uses ACQ. Routing prefix is + 963 + + "Dxxx" where "xxx" identifies the recipient + 964 + + network. + 965 +-------------+----------------------------------------------------+ 966 + Hong Kong + Recipient network informs other networks about + 967 + + ported-in numbers. Routing prefix is "14x" where + 968 + + "14x" identifies the recipient network, or a + 969 + + routing number of "4x" plus 7 or 8 digits is used + 970 + + where "4x" identifies the recipient network and + 971 + + the rest of digits identify the called party. + 972 +-------------+----------------------------------------------------+ 973 + Ireland + Operators choose their own solution but use onward + 974 + + routing now. Routing prefix is "1750" as the intra-+ 976 Number Portability in the GSTN: An Overview June 24, 2002 978 + + network routing code (network-specific) and + 979 + + "1752xxx" to "1759xxx" for GNP where "xxx" + 980 + + identifies the recipient switch. + 981 +-------------+----------------------------------------------------+ 982 + Italy + Uses onward routing. Routing prefix is "C600xxxxx" + 983 + + where "xxxxx" identifies the recipient switch. + 984 + + Telecom Italia uses IN solution and other operators+ 985 + + use on-switch solution. + 986 +-------------+----------------------------------------------------+ 987 + Japan + Uses onward routing. Donor switch uses IN to get + 988 + + routing number. + 989 +-------------+----------------------------------------------------+ 990 + Mexico + NP is considered in the Telecom law; however, the + 991 + + regulator (Cofetel) or the new local entrants have + 992 + + started no initiatives on this process. + 993 +-------------+----------------------------------------------------+ 994 + Netherlands + Operators decide NP scheme to use. Operators have + 995 + + chosen ACQ or QoR. KPN implemented IN solution + 996 + + similar to U.S. solution. Routing prefix is not + 997 + + passed between operators. + 998 +-------------+----------------------------------------------------+ 999 + Norway + OR for short-term and ACQ for long-term. QoR is + 1000 + + optional. Routing prefix can be "xxx" with NOA=8, + 1001 + + or "142xx" with NOA=3 where "xxx" or "xx" + 1002 + + identifies the recipient network. + 1003 +------------ +----------------------------------------------------+ 1004 + Peru + Wireline NP may be supported in 2001. + 1005 +-------------+----------------------------------------------------+ 1006 + Portugal + No NP today. + 1007 +-------------+----------------------------------------------------+ 1008 + Spain + Uses ACQ. Telefonica uses QoR within its network. + 1009 + + Routing prefix is "xxyyzz" where "xxyyzz" + 1010 + + identifies the recipient network. NOA is set to + 1011 + + 126. + 1012 +-------------+----------------------------------------------------+ 1013 + Sweden + Standardized the ACQ but OR for operators without + 1014 + + IN. Routing prefix is "xxx" with NOA=8 or "394xxx" + 1015 + + with NOA=3 where "xxx" identifies the recipient + 1016 + + network. But operators decide NP scheme to use. + 1017 + + Telia uses onward routing between operators. + 1018 +-------------+----------------------------------------------------+ 1019 + Switzerland + Uses OR now and QoR in 2001. Routing prefix is + 1020 + + "980xxx" where "xxx" identifies the recipient + 1021 + + network. + 1022 +-------------+----------------------------------------------------+ 1023 + UK + Uses onward routing. Routing prefix is "5xxxxx" + 1024 + + where "xxxxx" identifies the recipient switch. NOA + 1025 + + is 126. BT uses the dropback scheme in some parts + 1026 + + of its network. + 1027 +-------------+----------------------------------------------------+ 1028 + US + Uses ACQ. "Location Routing Number (LRN)" is used + 1029 + + in the Called Party Number parameter. Called party+ 1030 + + number is carried in the Generic Address Parameter + 1031 + + Use a PNTI indicator in the Forward Call Indicator + 1033 Number Portability in the GSTN: An Overview June 24, 2002 1035 + + parameter to indicate that NPDB dip has been + 1036 + + performed. + 1037 +-------------+----------------------------------------------------+ 1039 8. Number Conservation Methods Enabled by NP 1041 In addition to porting numbers NP provides the ability for number 1042 administrators to assign numbering resources to operators in smaller 1043 increments. Today it is common for numbering resources to be 1044 assigned to telephone operators in a large block of consecutive 1045 telephone numbers (TNs). For example, in North America each of 1046 these blocks contains 10,000 TNs and is of the format NXX+0000 to 1047 NXX+9999. Operators are assigned a specific NXX, or block. That 1048 operator is referred to as the block holder. In that block there 1049 are 10,000 TNs with line numbers ranging from 0000 to 9999. 1051 Instead of assigning an entire block to the operator NP allows the 1052 administrator to assign a sub-block or even an individual telephone 1053 number. This is referred to as block pooling and individual 1054 telephone number (ITN) pooling, respectively. 1056 8.1 Block Pooling 1058 Block Pooling refers to the process whereby the number administrator 1059 assigns a range of numbers defined by a logical sub-block of the 1060 existing block. Using North America as an example, block pooling 1061 would allow the administrator to assign sub-blocks of 1,000 TNs to 1062 multiple operators. That is, NXX+0000 to NXX+0999 can be assigned 1063 to operator A, NXX+1000 to NXX+1999 can be assigned to operator B, 1064 NXX-2000 to 2999 can be assigned to operator C, etc. In this 1065 example block pooling divides one block of 10,000 TNs into ten 1066 blocks of 1,000 TNs. 1068 Porting the sub-blocks from the block holder enables block pooling. 1069 Using the example above operator A is the block holder, as well as, 1070 the holder of the first sub-block, NXX+0000 to NXX+0999. The second 1071 sub-block, NXX+1000 to NXX+1999, is ported from operator A to 1072 operator B. The third sub-block, NXX+2000 to NXX+2999, is ported 1073 from operator A to operator C, and so on. NP administrative 1074 processes and call processing will enable proper and efficient 1075 routing. 1077 From a number administration and NP administration perspective block 1078 pooling introduces a new concept, that of the sub-block holder. 1079 Block pooling requires coordination between the number 1080 administrator, the NP administrator, the block holder, and the sub- 1081 block holder. Block pooling must be implemented in a manner that 1082 allows for NP within the sub-blocks. Each TN can have a different 1083 serving operator, sub-block holder, and block holder. 1085 Number Portability in the GSTN: An Overview June 24, 2002 1087 8.2 ITN Pooling 1089 ITN pooling refers to the process whereby the number administrator 1090 assigns individual telephone numbers to operators. Using the North 1091 American example, one block of 10,000 TNs can be divided into 10,000 1092 ITNs. ITN is more commonly deployed in freephone services. 1094 In ITN the block is not assigned to an operator but to a central 1095 administrator. The administrator then assigns ITNs to operators. 1096 NP administrative processes and call processing will enable proper 1097 and efficient routing. 1099 9. Potential Implications 1101 There are three general areas of impact to IP telephony work-in- 1102 progress at IETF: 1104 - Interoperation between NP in GSTN and IP telephony 1105 - NP implementation or emulation in IP telephony 1106 - Interconnection to NP administrative environment 1108 A good understanding of how number portability is supported in the 1109 GSTN is important when addressing the interworking issues between 1110 IP-based networks and the GSTN. This is especially important when 1111 the IP-based network needs to route the calls to the GSTN. As shown 1112 in Section 5, there are a variety of standards with various protocol 1113 stacks for the switch-to-NPDB interface. Not only that, the 1114 national variations of the protocol standards make it very 1115 complicated to deal with in a global environment. If an entity in 1116 the IP-based network needs to query those existing NPDBs for routing 1117 number information to terminate the calls to the destination GSTN, 1118 it would be impractical, if not an impossible, job for that entity 1119 to support all those interface standards to access the NPDBs in many 1120 countries. 1122 Several alternatives may address this particular problem. One 1123 alternative is to use certain entities in the IP-based networks for 1124 dealing with NP query, similar to the International Switches that 1125 are used in the GSTN to interwork different national ISUP 1126 variations. This will force signaling information associated with 1127 the calls to certain NP-capable networks in the terminating GSTN to 1128 be routed to those IP entities that support the NP functions. Those 1129 IP entities then query the NPDBs in the terminating country. This 1130 will limit the number of NPDB interfaces that certain IP entities 1131 need to support. Another alternative can be to define a "common" 1132 interface to be supported by all the NPDBs so that all the IP 1133 entities use that standardized protocol to query them. The 1134 existing NPDBs can support this additional interface, or new NPDBs 1135 can be deployed that contain the same information but support the 1136 common IP interface. The candidates for such a common interface 1137 include Lightweight Directory Access Protocol (LDAP) and SIP 1138 [SIP](e.g., using the SIP redirection capability). Certainly 1140 Number Portability in the GSTN: An Overview June 24, 2002 1142 another possibility is to use interworking function to convert from 1143 one protocol to another. 1145 IP-based networks can handle the domestic calls between two GSTNs. 1146 If the originating GSTN has performed NPDB query, SIP will need to 1147 transport and make use of some of the ISUP signaling information 1148 even if ISUP signaling may be encapsulated in SIP. Also, IP-based 1149 networks may perform the NPDB queries, as the N-1 carrier. In that 1150 case, SIP also needs to transport the NP related information while 1151 the call is being routed to the destination GSTN. There are three 1152 pieces of NP related information that SIP needs to transport. They 1153 are 1) the called directory number, 2) a routing number, and 3) a 1154 NPDB dip indicator. The NPDB dip indicator is needed so that the 1155 terminating GSTN will not perform another NPDB dip. The routing 1156 number is needed so that it is used to route the call to the 1157 destination network or switch in the destination GSTN. The called 1158 directory number is needed so that the terminating GSTN switch can 1159 terminate the call. When the routing number is present, the NPDB 1160 dip indicator may not be present because there are cases where 1161 routing number is added for routing the call even if NP is not 1162 involved. One issue is how to transport the NP related information 1163 via SIP. The SIP Universal Resource Locator (URL) is one mechanism. 1164 Another better choice may be to add an extension to the "tel" URL 1165 [TEL] that is also supported by SIP. Please see [TELNP] for the 1166 proposed extensions to the "tel" URL to support NP and freephone 1167 service. Those extensions to the "tel" URL will be automatically 1168 supported by SIP because they can be carried as the optional 1169 parameters in the user portion of the "sip" URL. 1171 For a called directory number that belongs to a country that 1172 supports NP, and if the IP-based network is to perform the NPDB 1173 query, the logical step is to perform the NPDB dip first to retrieve 1174 the routing number and use that routing number to select the correct 1175 IP telephony gateways that can reach the serving switch that serves 1176 the called directory number. Therefore, if the "rn" parameter is 1177 present in the "tel" URL or sip URL in the SIP INVITE message, it 1178 instead of the called directory number should be used for making 1179 routing decisions assuming that no other higher priority routing- 1180 related parameters such as the �cic� are present. If "rn" is not 1181 present, then the dialed directory number can be used as the routing 1182 number for making routing decisions. 1184 Telephony Routing Information Protocol (TRIP) [TRIP] is a policy 1185 driven inter-administrative domain protocol for advertising the 1186 reachability of telephony destinations between location servers, and 1187 for advertising attributes of the routes to those destinations. 1188 With the NP in mind, it is very important to know that it is the 1189 routing number, if present, not the called directory number that 1190 should be used to check against the TRIP tables for making the 1191 routing decisions. 1193 Overlap signaling exists in the GSTN today. For a call routing from 1194 the originating GSTN to the IP-based network that involves overlap 1195 signaling, NP will impact the call processing within the IP-based 1197 Number Portability in the GSTN: An Overview June 24, 2002 1199 networks if they must deal with the overlap signaling. The entities 1200 in the IP-based networks that are to retrieve the NP information 1201 (e.g., the routing number) must collect a complete called directory 1202 number information before retrieving the NP information for a ported 1203 number. Otherwise, the information retrieval won't be successful. 1204 This is an issue for the IP-based networks if the originating GSTN 1205 does not handle the overlap signaling by collecting the complete 1206 called directory number. 1208 The IETF enum working group is defining the use of Domain Name 1209 System (DNS) for identifying available services associated with a 1210 particular E.164 number [ENUM]. [ENUMPO] outlines the principles 1211 for the operation of a telephone number service that resolves 1212 telephone numbers into Internet domain name addresses and service- 1213 specific directory discovery. [ENUMPO] implements a three-level 1214 approach where the first level is the mapping of the telephone 1215 number delegation tree to the authority to which the number has been 1216 delegated, the second level is the provision of the requested DNS 1217 resource records from a service registrar, and the third level is 1218 the provision of service specific data from the service provider 1219 itself. NP certainly must be considered at the first level because 1220 the telephony service providers do not "own" or control the 1221 telephone numbers under the NP environment; therefore, they may not 1222 be the proper entities to have the authority for a given E.164 1223 number. Not only that, there is a regulatory requirement on NP in 1224 some countries that the donor network should not be relied on to 1225 reach the delegated authority during the DNS process . The 1226 delegated authority for a given E.164 number is likely to be an 1227 entity designated by the end user that owns/controls a specific 1228 telephone number or one that is designated by the service registrar. 1230 Since the telephony service providers may have the need to use ENUM 1231 for their network-related services (e.g., map an E.164 number to a 1232 HLR Identifier in the wireless networks), their ENUM records must be 1233 collocated with those of the telephony subscribers. If that is the 1234 case, NP will impact ENUM when a telephony subscriber who has ENUM 1235 service changes the telephony service provider. This is because 1236 that the ENUM records from the new telephony service provider must 1237 replace those from the old telephony service provider. To avoid the 1238 NP impact on ENUM, it is recommended that the telephony service 1239 providers use a different domain tree for their network-related 1240 service. For example, if e164.arpa is chosen for �end user� ENUM, a 1241 domain tree different from e164.arpa should be used for �carrier� 1242 ENUM. 1244 The IP-based networks also may need to support some forms of number 1245 portability in the future if E.164 numbers [E164] are assigned to 1246 the IP-based end users. One method is to assign a GSTN routing 1247 number for each IP-based network domain or entity in a NP-capable 1248 country. This may increase the number of digits in the routing 1249 number to incorporate the IP entities and impact the existing 1250 routing in the GSTN. Another method is to associate each IP entity 1251 with a particular GSTN gateway. At that particular GSTN gateway, 1252 the called directory number then is used to locate the IP-entity 1254 Number Portability in the GSTN: An Overview June 24, 2002 1256 that serves that dialed directory number. Yet, another method can 1257 be to assign a special routing number so that the call to an end 1258 user currently served by an IP entity is routed to the nearest GSTN 1259 gateway. The called directory number then is used to locate the IP- 1260 entity that serves that dialed directory number. A mechanism can be 1261 developed or used for the IP-based network to locate the IP entity 1262 that serves a particular dialed directory number. Many other types 1263 of networks use E.164 numbers to identify the end users or terminals 1264 in those networks. Number portability among GSTN, IP-based network 1265 and those various types of networks may also need to be supported in 1266 the future. 1268 10. Security Considerations 1270 This document does not raise any security issues. 1272 11. IANA Considerations 1274 This document introduces no new values for IANA registration. 1276 12. Normative References 1278 [ANSI OSS] ANSI Technical Requirements No. 1, "Number Portability - 1279 Operator Services Switching Systems," April 1999. 1281 [ANSI SS] ANSI Technical Requirements No. 2, "Number Portability - 1282 Switching Systems," April 1999. 1284 [ANSI DB] ANSI Technical Requirements No. 3, "Number Portability 1285 Database and Global Title Translation," April 1999. 1287 [CS1] ITU-T Q-series Recommendations - Supplement 4, "Number 1288 portability Capability set 1 requirements for service provider 1289 portability (All call query and onward routing)," May 1998. 1291 [CS2] ITU-T Q-series Recommendations - Supplement 5, "Number 1292 portability -Capability set 2 requirements for service provider 1293 portability (Query on release and Dropback)," March 1999. 1295 [E164] ITU-T Recommendation E.164, "The International Public 1296 Telecommunications Numbering Plan," 1997. 1298 [ENUM] P. Falstrom, "E.164 number and DNS," RFC 2916. 1300 [ETSIISUP] ETSI EN 302 097 V.1.2.2, �Integrated Services Digital 1301 Network (ISDN); Signalling System No.7 (SS7); ISDN User Part 1302 (ISUP); Enhancement for support of Number Portability (NP) 1303 [ITU-T Recommendation Q.769.1 (2000), modified] 1305 [GSM] GSM 09.02: "Digital cellular telecommunications system (Phase 1306 2+); Mobile Application Part (MAP) specification". 1308 Number Portability in the GSTN: An Overview March 1, 2002 1310 [IS41] TIA/EIA IS-756 Rev. A, "TIA/EIA-41-D Enhancements for 1311 Wireless Number Portability Phase II (December 1998)"Number 1312 Portability Network Support," April 1998. 1314 [ITUISUP] ITU-T Recommendation Q.769.1, "Signaling System No. 7 - 1315 ISDN User Part Enhancements for the Support of Number 1316 Portability," December 1999. 1318 [MNP] ETSI EN 301 716 (2000-10) European Standard 1319 (Telecommunications series) Digital cellular telecommunications 1320 system (Phase 2+); Support of Mobile Number Portability (MNP); 1321 Technical Realisation; Stage 2; (GSM 03.66 Version 7.2.0 1322 Release 1998). 1324 [RFC] Scott Bradner, RFC2026, "The Internet Standards Process -- 1325 Revision 3," October 1996. 1327 13. Informative References 1329 [ENUMPO] A. Brown and G. Vaudreuil, "ENUM Service Specific 1330 Provisioning: Principles of Operations," draft-ietf-enum- 1331 operation-02.txt, February 23, 2001. 1333 [SIP] J. Rosenberg, et al., draft-ietf-sip-rfc2543bis-09.txt, "SIP: 1334 Session Initiation Protocol," February 27, 2002. 1336 [TEL] H. Schulzrinne and A. Vaha-Sipila, draft-antti-rfc2806bis- 1337 04.txt, "URIs for Telephone Calls," May 24, 2002. 1339 [TELNP] J. Yu, draft-yu-tel-url-05.txt, "Extensions to the "tel" URL 1340 to support Number Portability and Freephone Service," June 14, 1341 2002. 1343 [TRIP] J. Rosenberg, H. Salama and M. Squire, RFC 3219, "Telephony 1344 Routing Information Protocol (TRIP)," January 2002. 1346 14. Acknowledgment 1348 The authors would like to thank Monika Muench for providing 1349 information on ISUP and MNP. 1351 15. Authors' Addresses 1353 Mark D. Foster 1354 NeuStar, Inc. 1355 1120 Vermont Avenue, NW, 1356 Suite 400 1357 Washington, D.C. 20005 1358 United States 1360 Number Portability in the GSTN: An Overview March 1, 2002 1362 Phone: +1-202-533-2800 1363 Fax: +1-202-533-2987 1364 Email: mark.foster@neustar.biz 1366 Tom McGarry 1367 NeuStar, Inc. 1368 1120 Vermont Avenue, NW, 1369 Suite 400 1370 Washington, D.C. 20005 1371 United States 1373 Phone: +1-202-533-2810 1374 Fax: +1-202-533-2987 1375 Email: tom.mcgarry@neustar.biz 1377 James Yu 1378 NeuStar, Inc. 1379 1120 Vermont Avenue, NW, 1380 Suite 400 1381 Washington, D.C. 20005 1382 United States 1384 Phone: +1-202-533-2814 1385 Fax: +1-202-533-2987 1386 Email: james.yu@neustar.biz 1388 Full Copyright Statement 1390 "Copyright (C) The Internet Society (2002). 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