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- 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
- 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.
- 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.
- 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.
- 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
- 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
- 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
- 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
- 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.
- 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
- 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
- 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
- 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 252.158.32.195.
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.
- 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 167.23.1.146 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
- 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)
- 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.).
nguon tai.lieu . vn
