Mạng và viễn thông P29

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Network Numbering and Addressing Plans Thenetworknumbering or addressingplanis an important part ofthenetworkrouting plan, because the network address is the identification used by a caller to identify the customer or network port to which he wishes to be connected. Based on the network address, switched connectionswithinalltypesofnetwork are established.Inthischapterwediscussthefive basicnumbering and addressing schemes, and the principles that goalongwiththem

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  1. Networks and Telecommunications: Design and Operation, Second Edition. Martin P. Clark Copyright © 1991, 1997 John Wiley & Sons Ltd ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic) 29 Network Numbering and Addressing Plans Thenetworknumbering or addressingplanis an important part ofthenetworkrouting plan, because the network address is the identification used by a caller to identify the customer or network port to which he wishes to be connected. Based on the network address, switched connectionswithinalltypesofnetwork are established.Inthischapterwediscussthefive basicnumbering and addressing schemes, and the principles that goalongwiththem.These schemes are 0 international telephone service/ISDN numbering plan according to ITU-T recommendations E.163 and E.164 (recently combined into one recommendation, E.164) 0 international public data networknumberingschemeaccording to ITU-T recommendation x.121 0 international telex service numbering according to ITU-T recommendation F.69 0 addressing scheme for the message handling service (ITU-T recommendations X.500) 0 Internetaddressingscheme 29.1 THE INTERNATIONAL TELEPHONE NUMBERING PLAN The international telephone numbering plan was originally defined in 1964 by ITU-T’s recommendationE.163,whichlaiddowntheprinciples of numberingpertinentto publictelephonenetworks.Itremainssubstantiallythesame,buthasrecently been combined with the subsequent recommendation E.164 ‘numbering for the ISDN era’ into a single recommendation E.164. Recommendation E.164 defines the recommended prefixes for international calls(00) and trunk calls (0), the allocation of country codes, and the maximum number length excluding international prefix (15 digits). Figure 29.1 illustrates an E. 164 number or network address. 513
  2. 514 NETWORK NUMBERING AND ADDRESSING PLANS international country national significant number prefix code NSN 00 cc trunk area code + subscriber number 14 maximum 15 digits 4 - structure of an international teleohone number trunk national significant number prefix NSN 0 trunk area code + subscriber number structure of a national teleohone number Figure 29.1 E.164 format of international telephone numbers The E. 164 numbering plan ensures the allocation of a unique number (string of digits) to identify each individual telephone connected to the worldwide telephone network. line These numbers are analysed by telephone exchanges to determine the appropriate call routing and the appropriate call charging rate. Theydesigned to allow exchanges to are select an economical and satisfactory onward connection analysing only a minimum by number of digits.Therecommendationdoesnotcontroleachindividualcountry’s numbering plan, but allocates instead a large of numbers use in each individual series for national network. This flexibility allows each national network operator to prepare a national numbering plan, optimized for their own particular purposes. Most network operators choose to adopt a three-tier numbering plan. The three tiers correspond to overseas (i.e. international) calls, long distance (i.e. toll or trunk) calls and local calls, and the procedures for each of these types will be discussed in order. To place an international call over the automatic telephone network, a customer must dial first the international prefix code (to indicate that the digits immediatelyfollowing indicate a destination overseas). The next digits be a 1,2 or will 3-digit country code ( C C ) to indicate the particular country required, then the area code and destination cus- tomer number. Figure 29.1 illustrates the component parts an example international of number. The example of Figure 29.2 shows a London, UK, telephone number, when dialled from Switzerland. The ITU-T recommended international prefix ‘00’ is followed by country code digits ‘44’ to signify the United Kingdom, digits ‘171’ to identify Central London, digits ‘234’ to specify the destination exchangeand digits‘5678’ to earmark the customer. Successive exchanges within the connection gradually discard the early digits and analyse progressively more of the later ones to determine the required routing. The standard ‘00’ prefix is used in many countries, including Switzerland, but some countries for historical reasons currently use other prefixes. For example, the inter- national prefix for calls made from USA is currently ‘01 l’, and from France it is ‘19’. ITU-T recommends that all countries eventually migrate to the common prefix, to ‘00’ ease travelling customers’ dialling difficulties.
  3. THE INTERNATIONAL TELEPHONE NUMBERING PLAN 515 Generalinternational number - structure Digits dialled, 00 cc code CustomerlocalnumberArea in sequence (International + (Country + v (National number) prefix) code ) Example for a UK (London) 00 11 I 71 1 23L 5678 I dialled in (Identifies (Prefix) (Identifies (Identifies (Identifies Switzerland UK) central London) exchange) Customer) Figure 29.2 International telephone number Thecountry codes of E.164numbers,identifyingeachindividualcountry,are allocated by ITU-T, and the same country code is used to identify a particular country no matter where in the world the telephone caller is situated. Figure 29.3 illustrates the demographic location of world numbering zones. The entire list of country code allocations is given in Table 29.1. The North Americancountrycode is only one digit.This is becausethere is an integrated area code scheme, called the North American dial plan ( N A D P ) or number plan of America ( N P A ) . This plan covers the whole of the United States, Canada and the Caribbean islands. Telephone calls placed within this area need only be dialled as toll numbers. The table of Figure 28.4 shows the allocation of the three-digit area, or correctly number plan of America ( N P A ) , codes which identify the various regions. A typical New York, USA number is thus + l 212 345 6789. Recommendation E.164 sets the maximum number of digits allowed in an inter- national number at 15 digits plus the international prefix. This limits each national numbering plan (area code plus customer number) to a maximum length- n digits, of 15 where n is the length in digits of the corresponding countrycode. Limiting the number length in this way ensures that each network in the world canbe designed to cope with the maximum number length. The recommendation also states that it should not be necessary for an outgoing internationalexchange to analyse more than four digits after the international prefix to determine the routing and charging information for any call. (Four digits correspond to the country code and part orall of the area code). Returning to the example shown in Figure 29.2, Figure 29.5 illustrates the different digit strings for dialling the same London customer from either Switzerland (i.e. overseas calling), Birmingham, UK (i.e. trunk calling), or from a local customer in London. Note how thetrunk numbercomprises onlythe latter part the full international number, the of international prefix and country codehaving been replaced with a simpler trunk prefix. The standard ITU-T trunk prefix ‘0’ is used in the UK, but as is the case with the international prefix, some countries have not yet moved on to the use of the standard trunk prefix, for various historical reasons. (Example: the trunk prefix used in North America is ‘l’.) Finally, for local calling the customer’s number is normally dialled without prefix, as Figure 29.5 shows.
  4. 516 NUMBERING NETWORK AND ADDRESSING PLANS Figure 29.3 World telephone numbering zones (CCITT Recommendations E163/E164) Four key features of the E.164 ‘numbering plan for the ISDN era’ mark it out from its predecessor, E.163, the telephone numbering plan 0 Extended international numbers (up to 15 digits rather than only 12 following the international prefix). This has expanded 1000-fold the quantity of numbers available in each country and so caters for the needs of the foreseeable future. 0 The concept of direct dialling-in (DDZ). In DD1 the last few digits at the end of the ISDN subscriber number are transferred to the customer’s PBX or other equipment, so enabling the call to be completed direct to the recipient’s desk telephone without the assistance of a human PBX ‘switchboard’ operator. 0 The concept of sub-addressing (also called network address extension, N A E ) . A sub- address comprises up to 40 additional decimal digits on top of the ISDN number, allowing routing with established local area networks on customer premises at the distant end of a public ISDN. 0 Theconcept of two-stagecallset-up forthesupport of interworking.The very nature ofintegrated services digitalnetworks(ISDNs)demandsthatdifferent services can interwork over a common network. Sometimes, however, this is not possible without the use of a specialised interworking unit between the ISDN and As the dedicated network. Figure 29.6 shows, two-stage dialling can be invaluable in this case.
  5. UMBERING THE INTERNATIONAL TELEPHONE 517 Table 29.1 Country codes according to ITU-T recommendation E.164 Country code Country code Country code Country 1 Canada 23 1 Liberia 27 South Africa 1 United States of America 232 Sierra Leone 290 Saint Helena 1809 Anguilla 233 Ghana 295 San Marino 1809 Antigua and Barbuda 234 Nigeria 296 Trinidad and Tobago 1809 Bahamas 235 Chad 297 Aruba 1809 Barbados 236 Central African Republic 298 Faroe Islands 1809 Bermuda 237 Cameroon 299 Greenland 1809 British Virgin Islands 238 Cape Verde 30 Greece 1809 Cayman Islands 239 Sao Tome and Principe 31 Netherlands 1809 Dominican Republic 240 Equatorial Guinea 32 Belgium 1809 Grenada 24 1 Gabonese Republic 33 France and Monaco 1809 Jamaica 242 Congo 34 Spain 1809 Montserrat 243 Zaire 350 Gibraltar 1809 Saint Kitts and Nevis 244 Angola 35 1 Portugal 1809 Saint Lucia 245 Guinea-Bissau 352 Luxembourg 1809 Saint Vincent and the 246 Diego Garcia 353 Ireland Grenadines 247 Ascension 354 Iceland 1809 Turks and Caicos Islands 248 Seychelles 355 Albania 20 Egypt 249 Sudan 356 Malta 210 Morocco 250 Rwanda 357 Cyprus 21 1 Morocco 25 1 Ethiopia 358 Finland 212 Morocco 252 Somali Democratic 359 Bulgaria 213 Algeria Republic 36 Hungary 214 Algeria 253 Djibouti 38 Yugoslavia 215 Algeria 254 Kenya 39 Italy 216 Tunisia 255 Tanzania 40 Romania 217 Tunisia 256 Uganda 41 Switzerland and 218 Libya 257 Burundi Liechtenstein 219 Libya 258 Mozambique 42 Czech and Slovak 220 Gambia 259 Zanzibar Republics 22 1 Senegal 260 Zambia 43 Austria 222 Mauritania 26 1 Madagascar 44 United Kingdom 223 Mali 262 Reunion 45 Denmark 224 Guinea 263 Zimbabwe 46 Sweden 225 CBte d’Ivoire 264 Namibia 47 Norway 226 Burkino Faso 265 Malawi 48 Poland 227 Niger 266 Lesotho 49 Germany 228 Togolese Republic 267 Botswana 500 Falkland Islands 229 Benin 268 Swaziland 50 1 Belize 230 Mauritius 269 Comoros 502 Guatemala
  6. 518 PLANS ADDRESSINGAND NUMBERING NETWORK Table 29.1 (continued) Country untry code 503 El Salvador 670 Mariana Islands 855 Kampuchea 504 Honduras 67 1 Guam 856 Lao People’s Democratic 505 Nicaragua 672 Australian External Republic 506 Costa Rica Territories 86 China 507 Panama 673 Brunei Darussalam 87 Maritime Mobile Service 508 St Pierre and Miquelon 674 Nauru 880 Bangladesh 509 Haiti 675 Papua New Guinea 90 Turkey 51 Peru 676 Tonga 91 India 52 Mexico 677 Solomon Islands 92 Pakistan 53 Cuba 678 Vanuatu 93 Afghanistan 54 Argentina 679 Fiji 94 Sri Lanka 55 Brazil 680 Palau 95 Myanmar 56 Chile 68 1 Wallis and Futuna Islands 960 Maldives 57 Colombia 682 Cook Islands 96 1 Lebanon 58 Venezuela 683 Niue Island 962 Jordan 590 Guadeloupe 684 American Samoa 963 Syria 59 1 Bolivia 685 Western Samoa 964 Iraq 592 Guyana 686 Kiribati 965 Kuwait 593 Ecuador 687 New Caledonia and 966 Saudi Arabia 594 Guiana Dependencies 967 Yemen Arab Republic 595 Paraguay 688 Tuvalu 968 Oman 596 Martinique 689 French Polynesia 969 Yemen, People’s 597 Suriname 690 Tokelan Democratic Republic 598 Uruguay 69 1 Freestate of Micronesia 971 United Arab Emirates 599 Netherlands Antilles 692 Marshall Islands 972 Israel 60 Malaysia 7 USSR 973 Bahrain 61 Australia 81 Japan 974 Qatar 62 Indonesia 82 South Korea 975 Kingdom of Bhutan 63 Philippines 84 Vietnam 976 Mongolian People’s 64 New Zealand 850 North Korea Republic 65 Singapore 852 Hong Kong 977 Nepal 66 Thailand 853 Macao 98 Iran
  7. PLAN INTERNATIONAL THE TELEPHONE NUMBERING 519 ~ ~~ ~~~ ~~ ~ 201 New Jersey 202 Washington DC 203 Connecticut 204 Manitoba (Canada) 205 Alabama 206 Washington 207 Maine 208 Idaho 209 California New 2 21 3 York City 21 Los Angeles 214 Dallas 5 21 Pennsylvania 216 Ohio Illinois 21 7 8 21 301 Maryland 302 Delaware 303 Colorado Virginia 4 West 30 305 Florida 306 Saskatchewan (Canada) Wyoming 307 308 Nebraska 309 Illinois (311 Calling Card Service) 31 2 Chicago 31 Detroit31 3 4 Missouri York New 31 5 316 Kansas lndianapolis 7 31 Louisiana31 8 Iowa 319 Rhode Island 402 Nebraska 403 Alberta (Canada) 404 Georgia 405 Oklahoma City 406 Montana 408 San Jose Pittsburgh 2 41 Springfield, 41 3 Mass. Milwaukee 41 4 41 5 San Francisco (Canada) Toronto 41 6 Missouri 41 7 418 (Canada) Quebec 419 Ohio 501 Arkansas 502 Kentucky 503 Oregon 504 Louisiana Mexico New 505 swick New 506 510TWX (USA) Row 4 " 512 Texas 513 Ohio 51 4 (Canada) New 516 Iowa 515 Montreal York Michigan 1 7 51 York 51 9(Canada) Ontario 601 Mississippi 602 Arizona New 603 Hampshire 604 British Columbia (Canada) 6 0 5 Dakota South Kentucky 606 New 607 York 608 Wisconsin New 609 Jersey 6 1 0 (Canada)" 4 Row TWX 612 Minneapolis Ottawa 613 (Canada) 6 1 4 Columbus, Ohio Tennessee 61 5 61 6 Michigan 61 7 Massachusetts 618 Illinois (700 Value Services) Added 701 North Dakota 702 Nevada 703 Virginia 7 0 4 North Carolina (Canada) 705 Ontario 707 California Newfoundland 709 713 717124 Row Iowa TWX (USA)" 0 Houston, Texas 71 4 San Diego 71 5 Wisconsin 716 New York Pennsylvania 71 7 New 8 71 York City 800800 Service$ Utah 801 Vermont South 803 Carolina 8 0 4 Virginia 805 California 806 Texas (Canada) 807 Ontario 808 Hawaii 809 Caribbean 8 1 0 4TWX 1 (USA)" 8 Row Florida 1 Indiana 3 2 8 814 Pennsylvania 81 5 Illinois 816 Kansas City Worth,7 Texas Fort 81 819 Quebec (Canada) 900 900-Service 3 901 Memphis (Canada) 9Scotia 0 2 Nova Mexico903 9 0 4 Florida 905 Mexico City 906 Michigan 907 Alaska 91 0 4 Row TWX (USA)" 91 Georgia2 Kansas 91 3 York New 914 5 91 Texas 91 6 Sacrament0 91 8 Oklahoma North 9 91 Carolina T W X is the American equivalent of the Telex service, introduced by the Bell company in 1931. Telex was not available until Western Union introduced it in the 1950s. $ 800 and 900 service are described in Chapter 26. Figure 29.4 The number plan of America
  8. 520 NETWORK NUMBERING AND ADDRESSING PLANS Internattonal Country Dref ix code ~~ ~ ~ 00 CC Area code Customernumber (Central London, ; International number 3 dlalled from eg. 00 44 71 234 5G78 Switzerland) trunk prefix 0 (Centra' Customer number Area code Trunk dialled dialled from number 0 71 234 5G78 Birmingham, UK) (Central London, UK customer customercalls another number Local I 2% 5678 I in London,UK) Figure 29.5 International, trunk and local numbers Two-stage dialling may require the return a second dial toneand the sending of extra of digits after the completionof the first stage, and it can often be necessary calls passing on betweentwo normal telephone network, either from or into someotherspecialized network. 29.2 INTERNATIONAL PUBLIC DATA NETWORK ADDRESS SCHEME Network addresses in public data networks conform to the format set out in ITU-T recommendation X.121. These are used by the layer 3 protocol (OS1 layer 3 , e.g. X.25 packet level protocol) to identify customer or device connections to the network as we saw in Chapter 9. The X.121 address format is as shown in Figure 29.7. AnX.121number (datanetworkaddress)hasamaximumlength of 14 decimal digits, composed of a data network identEfication code (DNZC) and a network terminal ISDN Interworking Called party calling unit on dedicated party network Figure 29.6 Two-stagecallset-up
  9. ESCAPE CODES 521 . . DCC = data country code DNlC data network identification code NN = national (data) number NTN = network terminal number maximum length 14 decimal digits, each international data number digit coded as 4 bits binary coded decimal Figure 29.7 X.121 format for public data network addresses number ( N T N ) . The DNZC identifies a particular network and operator within a given country. This is composed of a three-digit data country code ( D C C ) and a one-digit network identijication code (NZC). Following the DNIC is the network terminal number ( N T N ) . Data country codes ( D C C ) are listed Table 29.2. The national data number ( N N ) comprises the network identification digit (fourth digit) and the network terminal number ( N T N ) . In some countries and networks it is only necessary to dial the national number for calls made within the network or country. However, for calls made to other data networks, the full international data number (DNZC plus N T N ) must be dialled from the customer DTE. The X.121 address of the destination port is carried in the call setup packet of the X.25 packet level interface (OSI layer 3, or network layer protocol) as we discussed in Chapter 18. It uniquely identifies a port connected to a public data network. The digit values of the address are always decimal, to ease their carriage across ISDN and other network types, but are coded in the X.25 packet level interface as four-bit, binary coded decimal ( B C D ) characters (Figure 18.9 of Chapter 18). 29.3 ESCAPE CODES In some cases itis necessary when setting up calls across a networkto identify the called address as belonging to a different numbering scheme than that usually used. Thus, for example, we learned inChapter 10 how ITU-T recommendation X.3 1 defines the method- ologyforaccessing data terminalsconnected toISDNsfromaportonapacket- switched public data network. In such cases, it is necessary to identify the ISDN port address as being an E. 164-format (i.e. ISDN network) address. This is not the usual address format used within a public data network. The normal format is the X.121 format. Recommendation X.121, however, makes provision for the conversion of an E. 164-format address to an X. 121-format address. Thisis made simply by the addition of an escape code prefix. Thus the prefix ‘0’ (when an X.121-format address is normally expected) signifies an E.164 number and a call requiring escape from the public data networktotheISDN usingadigitalconnection. The prefix ‘9’ signifies an E.164 number and acall requiring analogue escape from the public data network to the ISDN or telephone network. A further escape code ‘8’ is also available within X.121 for an as yet undefined use.
  10. 522 PLANS ADDRESSINGAND NUMBERING NETWORK Table 29.2 Data Country Code (DCC) values defined by ITU-T recommendation X.121 Data country code code Country (DCC) W C ) Country 202 Greece 282 Georgia 40 1 Kazakhstan 204, 205 Netherlands 283 Armenia 404 India 206 Belgium 284 Bulgaria 410 Pakistan 208, 209 France 286 Turkey 412 Afghanistan 212 Monaco 288 Faroe Islands 413 Sri Lanka 214 Spain 290 Greenland 414 Myanmar 216 Hungary 292 San Marino 415 Lebanon 220 Yugoslavia 302 Canada 416 Jordan 222 Italy 303 Canada 411 Syria 225 Vatican City 308 St Pierre and Miquelon 418 Iraq 226 Romania 310-316 USA 419 Kuwait 228 Switzerland 330 Puerto Rico 420 Saudi Arabia 230 Czech and Slovak 332 Virgin Islands 42 1 Yemen (Republic of) Republics 334 Mexico 422 Oman 232 Austria 338 Jamaica 423 Yemen (Republic of) 234-231 United Kingdom 340 French Antilles 424 United Arab Emirates 238 Denmark 342 Barbados 425 Israel 240 Sweden 344 Antigua and Barbuda 426 Bahrain 242 Norway 346 Cayman Islands 421 Qatar 244 Finland 348 British Virgin Islands 428 Mongolia 246 Lithuania 350 Bermuda 429 Nepal 241 Latvia 352 Grenada 430, 431 United Arab Emirates 248 Estonia 354 Montserrat 432 Iran 250, 251 Russian Federation 356 St. Kitts 434 Uzbekistan 255 Ukraine 358 St. Lucia 436 Tajikistan 251 Belarus 360 St. Vincent & the 431 Kyrgyztan 259 Moldova Grenadines 438 Turmenistan 260 Poland 362 Netherlands Antilles 440-443 Japan 262-265 Germany 364 Bahamas 450 South Korea 266 Gibraltar 366 Dominica 452 Vietnam 268 Portugal 368 Cuba 453, 454 Hong Kong 270 Luxembourg 370 Dominican Republic 455 Macao 212 Ireland 312 Haiti 456 Cambodia 274 Iceland 374 Trinidad and Tobago 451 Lao People’s 276 Albania 376 Turks and Caicos Democratic Republic 278 Malta Islands 460 China 280 Cyprus 400 Azerbaijan 466 Taiwan
  11. ESCAPE CODES 523 Table 29.2 (continued) Data Data country country country code code Country ) W C (DCC) Country Country (DCC) 467 North Korea 608 Senegal 64 1 Uganda 470 Bangladesh 609 Mauritania 642 Burundi 472 Maldives 610 Mali 643 Mozambique 480. 481 South Korea 61 1 Guinea 645 Zambia 502 Malaysia 612 C8te d’Ivoire 646 Madagascar 505 Australia 613 Burkino Faso 647 Reunion 510 Indonesia 614 Niger 648 Zimbabwe 515 Philippines 615 Togolese Republic 649 Namibia 520 Thailand 616 Benin 650 Malawi 525 Singapore 617 Mauritius 65 1 Lesotho 528 Brunei Darussalam 618 Liberia 6.52 Botswana 530 New Zealand 619 Sierra Leone 653 Swaziland 534 Northern Marianas 620 Ghana 654 Comoros 535 Guam 62 1 Nigeria 655 South Africa 536 Nauru 622 Chad 702 Belize 537 Papua New Guinea 623 Central African 704 Guatemala 539 Tonga Republic 706 El Salvador 540 Solomon Islands 624 Cameroon 708 Honduras 54 1 Vanuatu 625 Cape Verde 710 Nicaragua 542 Fiji 626 Sao Tome and Principe 712 Costa Rica 543 Wallis and Futuna 627 Equatorial Guinea 714 Panama Islands 628 Gabon 716 Peru 544 American Samoa 629 Congo 722 Argentina 545 Kiribati 630 Zaire 724 Brazil 546 New Caledonia 63 1 Angola 730 Chile 547 French Polynesia 632 Guinea-Bissau 732 Colombia 548 Cook Islands 633 Seychelles 734 Venezuala 549 Western Samoa 634 Sudan 736 Bolivia 550 Micronesia 635 Rwanda 738 Guyana 602 Egypt 636 Ethiopia 140 Ecuador 603 Algeria 637 Somali Democratic 742 Guiana 604 Morocco Republic 744 Paraguay 605 Tunisia 638 Djibouti 746 Suriname 606 Libya 639 Kenya 748 Uruguay 607 Gambia 640 Tanzania
  12. 524 NETWORK NUMBERING AND ADDRESSING PLANS 29.4 TELEXNETWORK NUMBERING PLAN (ITU-T F.69) ITU-T recommendation F.69 sets out the numbering plan for public telex networks. A telex number is used within the telex network in a similar manner to the use of telephone numbers withintelephone a network, to signal desired the telex port destination of calls at call setup time. Ainternational telex numberconforming to ITU-T F.69 has a maximum length of 12 decimal digits, of which the first two three comprise or the telex destination code, the telex equivalent of the data network identlJication code (DNZC) of recommendation X.121. The allocation of the codes is carried out by ITU according to the rough schedule of Table 29.3. As well as having a unique telex destination code, each telex network is allocated a unique or one two (alphabetic letter character) telex networkidentiJication code (TNZC). This code is used as part of the answerback procedure. It appears onat the top of a telex being sent, to confirm the network to which the connected line (as opposed to the dialled line) is attached. 29.5 X.500: THEADDRESSING PLAN FOR THEMESSAGE HANDLING SERVICE (MHS) The addresses used in the message handling service (X.400, Chapter 23) conform to the OS1 and I S 0 directory service, laid out in the ITU-T X.500 series of recommendations. of Recommendation X.500 lays out the general form standard addresses, conforming to a standard directory scheme. The addresses themselves are held in a directory informa- tion base (DZB) and they consist of a set of individual directory information trees(DZT). At the first layer of the tree is always the ISO-assigned two-digit country identiJication (‘C =’). At the next layer is the administrative domain (‘A =’). At the lower layers of individual trees, separate structures (correctly called directory schemas) may be used, as befitting the situation of the individual administrations. Figure 29.8 illustrates the actual X.500 address of the ETSI secretariat (located in Sophia Antipolis in France). Written out in full, the address is C = FR; A = ATLAS; P = ETSI; S = SECRETARIAT (country) (administration) (private domain) (section) Table 29.3 Allocation of telex destination codes (ITU-T F.69) First digit of code Region 2 North America 3 South America 4, 5 , 6 Europe maritime and services l Pacific 8 Middle East and Far East 9 Africa
  13. INTERNET ADDRESSING SCHEME 525 directory informationtree (DIT) A / \ \ I C=DE C=GB C=FR A=BT A=MCL S=SECRETARIAT Figure 29.8 ITU-T recommendation X.500: A directory information base (DIB) and directory information tree (DIT) Also shown in Figure 29.8 are other hypothetical addresses in Great Britain (GB) and Germany (DE). The imaginary British Telecom domain has been shown as if segregated first according to organization (0) rather than private domain ( P ) . 29.6 INTERNET ADDRESSING SCHEME Internet addresses are used to identify hardware ports and software applications within theworldwide Internet7 computernetwork.Theyare used andinterpreted by the Internet protocol (ZP). The addresses comprise 32 bits when coded in binary form, but when written are usually quoted in a decimal form of four numbers, each of values between 0 and 255 (corresponding to four 8 bit numbers), separated by dots. Thus a typical Internet address is written Internet addresses are classified into five different types as shown in Figure 29.9. The different types of class address are assigned by agencies worldwide who administer the address plan. Class A addresses comprise a 1 byte network address assigned by the Inter- net numbering authority. The three remaining bytes are for host addresses (i.e. com- left puter addresses), whichcan be assigned‘locally’ by the network operator (i.e. the A class address owner). Close to 17 million computers may be connectedto a class A network. Class A addresses are only available to major Internet network operators.
  14. 526 NUMBERING NETWORK AND ADDRESSING PLANS Class B addresses comprise a two byte network address assigned by the numbering authority and a two byte host address space administered by the network operator. Up to 65536 computers may be connected to a class B network. Class B addresses are generally only availableto major corporations, who must be able to justify the extensive addressing allocation. Class C addresses comprise a three byte network address assigned by the numbering authority and a 1 byte host address space. Up to 256 devices may be connected to a class C network. These are the types of addresses allocated to most operators of small scale networks connected to the Internet. Class D addresses are used for broadcasting messages. Suchmessages will be received by all connected stations. Class E addresses are used only for experimental purposes. In addition to the 32 bit Internet address, some networks additionally use a further 32 bit address field known as the sub-networkaddress. This gives ahugescope for massively increasing the number of applications accessible within the connected end devices. Alias addressing is also possible. Thus a UNZXserver might have the Class B internet address and the alias RS6000. Where alias addressing is used a file must exist on a U N I X server somewhere within the local network to convert the alias address to the 32 bit binary address. This is called the ‘/etc/hosts’file and is part of the set up file configuration of the server. 29.7 INTERNET E-MAIL (SMTP) ADDRESSES Internet e-mail addresses should not be confused with ordinary Internet addresses. The difference is akintothedifference between an MHS (X.500)address and an X.25 Byte 1 ByteByte 2 3 Byte 4 Class A Network Address .Host Address .Host Address .Host Address Class B Network Address .Network Address .Host Address .Host Address Class C Network Address .Network Address .Network Address .Host Address Class D Broadcast Address .Broadcast Address .Broadcast Address .Broadcast Address Class E Experimental .Experimental .Experimental .Experimental Address type Value of byte 1 Class A 0-127 Class B 128-191 Class C 192-223 Class D 224-239 Class E 240-255 Figure 29.9 Internet address format and classification
  15. L INTERNET 527 networkaddress.e-mailaddressesarethoserecognized by the SMTP (simplemail transfer protocol). They typically have the form 0 1789748.34543@compuserve.com 0 martin.clark@onlineservice.de The first of these forms is the actual numerical address. The part of the address after the @ symbol identifies the mail server or postofice (theequivalentofa given mail operators ‘domain’). The second form given above (i.e. the name form) is actually an alias address.On reaching the mail server the partof the address preceding the symbol @ has tobe converted to the actual numerical address order that the in SMTP or local mail protocol can effect the final delivery. To perform the conversion a look-up table must exist at the destination mail server. 29.8 NETWORK ADDRESSING SCHEMES USED INSUPPORT OF BROADBAND-ISDN AND ATM Broadband-ISDN or ATM network addresses (correctly A T M logical network add- resses) consist of three general parts, comprising nine separate fields as illustrated in Figure 29.10. The three main parts are the AFI (authority and format identzjier), the IDI (initial domain identzjier) and the DSP (domain specijic part), where the AFI and IDP are known together as the IDP (initial domain part). The AFI allows for a number of differentcodingschemes to beused for the IDI, and determines which ofthese codings is in use. The N S A P (network service access point) format defined by I S 0 8348 and ITU-T recommendation X.213 allows the AFI to be set ‘to indicate one of three forms of the IDI. In the first, DCC form (AFI = 39) the ID1 is the data country code ( D C C ) as defined by I S 0 3166 (ITU-T recommendation X.121). In the second form (AFI = 47), the ICD or international code designator form, the ID1 identifies international organiza- IDP -- F - part domain specific (DSP) l AFI DCC DFI AA RSVD RD AREA ESI SEL I I I I I AA = administrative authority AFI = authority and format identifier DCC = data country code DFI = DSP format identifier DSP = domainspecificpart ESI = end system identifier ID1 = initial domainidentifier RD = routingdomain RSVD = reserved SEL = selector Figure 29.10 ATM addressing plans (conformant to OS1 NSAP format)
  16. 528 NUMBERING NETWORK AND ADDRESSING PLANS tions as defined by British Standards. In the third form (AFI = 4 9 , the ID1 takes the form of a full E.164 international ISDN or telephone number, and the separate fields DFI and AA do not appear. Maybe a fourth form appear using Internet addresses. will The DFZ (DSP format ident$er) defines the format (and therefore meaning) of the DSP (domain specific part). The administrative authority ( A A ) identifies the organiza- tionwhichadministratestheaddresses in this field (usuallythepublic orprivate networkoperator).The routing domain ( R D ) togetherwiththe area field indicate the destination sub-network and area. The ESI (end system identifier) indicates the end device. The selector field is an extension of the address not used for routing within the network, but may be required to indicate to the end system which local device (e.g. telephone extension) is to be connected or which mode of communication should be expected (e.g. telephone or fax, etc.).
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