29
Network Numbering and
Addressing Plans
The network numbering
or
addressing plan is an important part of the network routing
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
connections within all types of network are established. In this chapter we discuss the five
basic numbering and addressing schemes, and the principles that go along with them. 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 network numbering scheme according 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
Internet addressing scheme
29.1
THE INTERNATIONAL TELEPHONE NUMBERING PLAN
The international telephone numbering plan was originally defined in 1964 by ITU-T’s
recommendation E.163, which laid down the principles of numbering pertinent to
public telephone networks. It remains substantially the same, but has recently 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
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)
514
NETWORK NUMBERING AND ADDRESSING PLANS
international
national significant number
country
prefix
NSN
code
00
trunk area code
+
subscriber number
cc
14
maximum
15
digits
-4
structure of an international teleohone number
trunk
NSN
prefix
national significant number
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 line connected to the worldwide telephone network.
These numbers are analysed by telephone exchanges to determine the appropriate call
routing and the appropriate call charging rate. They are designed to allow exchanges to
select an economical and satisfactory onward connection by analysing only a minimum
number of digits. The recommendation does not control each individual country’s
numbering plan, but allocates instead a large series of numbers for use in each individual
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 immediately following
indicate a destination overseas). The next digits will be a 1,2 or 3-digit
country code
(CC)
to indicate the particular country required, then the area code and destination cus-
tomer number. Figure 29.1 illustrates the component parts of an example international
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 exchange and 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
‘00’ prefix, to
ease travelling customers’ dialling difficulties.
THE INTERNATIONAL TELEPHONE NUMBERING PLAN
515
General international number
-
structure
Digits
dialled,
Customer local number Area code
in sequence
cc
00
v
(International
+
(Country
+
(National number)
prefix) code
)
Example
for
a
UK
(London)
00
11
I
71
1
23L
5678
I
Switzerland
dialled in
(Prefix) (Identifies (Identifies (Identifies (Identifies
UK)
central London) exchange) Customer)
Figure
29.2
International telephone
number
The country codes of E.164 numbers, identifying each individual country, 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 American country code is only one digit. This is because there is an
integrated area code scheme, called the
North American dial plan (NADP)
or
number
plan
of
America (NPA).
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 (NPA),
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 of 15
-
n
digits,
where
n
is the length in digits of the corresponding country code. Limiting the number
length in this way ensures that each network in the world can be designed to cope with
the maximum number length. The recommendation also states that it should not be
necessary for an outgoing international exchange 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 or all 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 the trunk number comprises only the latter part of the full international number, the
international prefix and country code having 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
NETWORK NUMBERING 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,
NAE).
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
The concept of two-stage call set-up for the support of interworking. The very
nature of integrated services digital networks (ISDNs) demands that different
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
the dedicated network.
As
Figure 29.6 shows, two-stage dialling can be invaluable in
this case.
THE INTERNATIONAL TELEPHONE NUMBERING PLAN
517
Table
29.1
Country codes according to ITU-T recommendation E.164
Country Country Country
code Country code Country code Country
1
1
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
1809
20
210
21
1
212
213
214
215
216
217
218
219
220
22
1
222
223
224
225
226
227
228
229
230
Canada
United States of America
Anguilla
Antigua and Barbuda
Bahamas
Barbados
Bermuda
British Virgin Islands
Cayman Islands
Dominican Republic
Grenada
Jamaica
Montserrat
Saint Kitts and Nevis
Saint Lucia
Saint Vincent and the
Grenadines
Turks and Caicos Islands
Egypt
Morocco
Morocco
Morocco
Algeria
Algeria
Algeria
Tunisia
Tunisia
Libya
Libya
Gambia
Senegal
Mauritania
Mali
Guinea
CBte d’Ivoire
Burkino Faso
Niger
Togolese Republic
Benin
Mauritius
23
1
232
233
234
235
236
237
238
239
240
24
1
242
243
244
245
246
247
248
249
250
25 1
252
253
254
255
256
257
258
259
260
26
1
262
263
264
265
266
267
268
269
Liberia
Sierra Leone
Ghana
Nigeria
Chad
Central African Republic
Cameroon
Cape Verde
Sao Tome and Principe
Equatorial Guinea
Gabonese Republic
Congo
Zaire
Angola
Guinea-Bissau
Diego Garcia
Ascension
Seychelles
Sudan
Rwanda
Ethiopia
Somali Democratic
Republic
Djibouti
Kenya
Tanzania
Uganda
Burundi
Mozambique
Zanzibar
Zambia
Madagascar
Reunion
Zimbabwe
Namibia
Malawi
Lesotho
Botswana
Swaziland
Comoros
27
290
295
296
297
298
299
30
31
32
33
34
350
35
1
352
353
3 54
355
356
357
358
359
36
38
39
40
41
42
43
44
45
46
47
48
49
500
50
1
502
South Africa
Saint Helena
San Marino
Trinidad and Tobago
Aruba
Faroe Islands
Greenland
Greece
Netherlands
Belgium
France and Monaco
Spain
Gibraltar
Portugal
Luxembourg
Ireland
Iceland
Albania
Malta
Cyprus
Finland
Bulgaria
Hungary
Yugoslavia
Italy
Romania
Switzerland and
Liechtenstein
Czech and Slovak
Republics
Austria
United Kingdom
Denmark
Sweden
Norway
Poland
Germany
Falkland Islands
Belize
Guatemala
518
NETWORK NUMBERING AND ADDRESSING PLANS
Table
29.1
(continued)
Country Country Country
code Country code Country code Country
503
504
505
506
507
508
509
51
52
53
54
55
56
57
58
590
59 1
592
593
594
595
596
597
598
599
60
61
62
63
64
65
66
El Salvador
Honduras
Nicaragua
Costa Rica
Panama
St Pierre and Miquelon
Haiti
Peru
Mexico
Cuba
Argentina
Brazil
Chile
Colombia
Venezuela
Guadeloupe
Bolivia
Guyana
Ecuador
Guiana
Paraguay
Martinique
Suriname
Uruguay
Netherlands Antilles
Malaysia
Australia
Indonesia
Philippines
New Zealand
Singapore
Thailand
670
67 1
672
673
674
675
676
677
678
679
680
68
1
682
683
684
685
686
687
688
689
690
69 1
692
7
81
82
84
850
852
853
Mariana Islands
Guam
Australian External
Territories
Brunei Darussalam
Nauru
Papua New Guinea
Tonga
Solomon Islands
Vanuatu
Fiji
Palau
Wallis and Futuna Islands
Cook Islands
Niue Island
American Samoa
Western Samoa
Kiribati
New Caledonia and
Dependencies
Tuvalu
French Polynesia
Tokelan
Freestate
of
Micronesia
Marshall Islands
USSR
Japan
South Korea
Vietnam
North Korea
Hong Kong
Macao
855
856
86
87
880
90
91
92
93
94
95
960
96
1
962
963
964
965
966
967
968
969
971
972
973
974
975
976
977
98
Kampuchea
Lao People’s Democratic
Republic
China
Maritime Mobile Service
Bangladesh
Turkey
India
Pakistan
Afghanistan
Sri Lanka
Myanmar
Maldives
Lebanon
Jordan
Syria
Iraq
Kuwait
Saudi Arabia
Yemen Arab Republic
Oman
Yemen, People’s
Democratic Republic
United Arab Emirates
Israel
Bahrain
Qatar
Kingdom
of
Bhutan
Mongolian People’s
Republic
Nepal
Iran
THE INTERNATIONAL TELEPHONE NUMBERING PLAN
519
~
201 New Jersey
203 Connecticut
204 Manitoba (Canada) 205 Alabama 206 Washington
207 Maine 208 Idaho 209 California
21 2 New York City 21 3 Los Angeles 214 Dallas
21 5 Pennsylvania 216 Ohio 21 7 Illinois
21 8 Minnosota 21 9 Indiana 301 Maryland
302 Delaware 303 Colorado 304 West Virginia
305 Florida 306 Saskatchewan (Canada) 307 Wyoming
308 Nebraska
309
Illinois
(31
1
Calling Card Service) 31
2
Chicago
31 3 Detroit 31
4
Missouri 31 5 New York
316 Kansas 31 7 lndianapolis 31 8 Louisiana
319 Iowa 401 Rhode Island 402 Nebraska
403 Alberta (Canada) 404 Georgia 405 Oklahoma City
406 Montana 408 San Jose 41 2 Pittsburgh
41 3 Springfield, Mass. 41 4 Milwaukee 41 5 San Francisco
41 6 Toronto (Canada) 41 7 Missouri 418 Quebec (Canada)
419 Ohio 501 Arkansas 502 Kentucky
503 Oregon 504 Louisiana 505 New Mexico
506 New Brunswick 507 Minnesota 509 Washington
510
4
Row TWX (USA)
"
512 Texas 513 Ohio
51
4
Montreal (Canada) 515 Iowa 516 New York
51 7 Michigan 51 8 New York 51
9
Ontario (Canada)
601 Mississippi 602 Arizona 603 New Hampshire
604
British
Columbia (Canada) 605 South Dakota 606 Kentucky
607 New York 608 Wisconsin 609 New Jersey
610
4
Row TWX (Canada)" 612 Minneapolis 613 Ottawa (Canada)
614 Columbus, Ohio
61
5 Tennessee
61
6
Michigan
61 7 Massachusetts 618 Illinois (700 Value Added Services) 701
North
Dakota
702 Nevada 703 Virginia 704 North Carolina
705 Ontario (Canada) 707 California 709 Newfoundland
71
0
4
Row TWX (USA)" 712 Iowa 713 Houston, Texas
71
4 San Diego 71
5
Wisconsin 716 New York
71 7 Pennsylvania 71 8 New York City 800 800 Service$
801 Utah 802 Vermont 803 South Carolina
804 Virginia 805 California 806 Texas
807 Ontario (Canada) 808 Hawaii 809 Caribbean
810
4
Row TWX (USA)" 8 1
2
Indiana 8 1 3 Florida
81
4
Pennsylvania 81 5 Illinois 816 Kansas City
81 7 Fort Worth, Texas 819 Quebec (Canada) 900 900-Service
3
901 Memphis 902 Nova Scotia (Canada) 903 Mexico
904 Florida 905 Mexico
City
906 Michigan
907 Alaska 91
0
4
Row TWX (USA)" 91 2 Georgia
91 3 Kansas 914 New York 91 5 Texas
91
6
Sacrament0 91
8
Oklahoma 91 9 North Carolina
TWX
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.
~~
202 Washington DC
~~~ ~~ ~
Figure
29.4 The number plan
of
America
520
NETWORK NUMBERING AND ADDRESSING PLANS
Internattonal Country
Dref
ix
code
~~ ~ ~
International
Switzerland)
234
5G78
71
44
00
eg.
number
(Central
London,
;
Customer number
Area code
CC
00
3
dlalled from
trunk
prefix
Trunk dialled
number
(Centra'
Customer number Area code
0
dialled from
0
Birmingham,
UK)
234
5G78
71
(Central London,
UK
customer
Local number calls another customer
I
2%
5678
I
in
London,UK)
Figure
29.5
International, trunk and local numbers
Two-stage dialling may require the return of a second dial tone and the sending
of
extra
digits after the completion
of
the first stage, and it can often be necessary on calls passing
between two normal telephone network, either from or into some other specialized
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.
An X.121 number (data network address) has a maximum length 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-stage call set-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 (NTN).
The
DNZC
identifies a particular network and operator within a given
country. This is composed of a three-digit
data country code (DCC)
and a one-digit
network identijication code (NZC).
Following the DNIC is the
network terminal number
(NTN). Data country codes (DCC)
are listed Table 29.2.
The
national data number (NN)
comprises the network identification digit (fourth
digit) and the
network terminal number (NTN).
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
NTN)
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 (BCD)
characters (Figure 18.9 of Chapter 18).
29.3
ESCAPE CODES
In some cases it is necessary when setting up calls across a network to identify the called
address as belonging to a different numbering scheme than that usually used. Thus, for
example, we learned in Chapter 10 how ITU-T recommendation X.3
1
defines the method-
ology for accessing data terminals connected to ISDNs from a port on a packet-
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. This is 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
network to the ISDN using a digital connection. The prefix ‘9’ signifies an E.164
number and a call 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
NETWORK NUMBERING AND ADDRESSING PLANS
Table
29.2 Data Country Code (DCC) values defined by ITU-T recommendation X.121
Data Data Data
country country country
code code code
(DCC) Country (DCC) Country WC) Country
202
204, 205
206
208, 209
212
214
216
220
222
225
226
228
230
232
234-231
238
240
242
244
246
241
248
250, 251
255
251
259
260
262-265
266
268
270
212
274
276
278
280
Greece
Netherlands
Belgium
France
Monaco
Spain
Hungary
Yugoslavia
Italy
Vatican City
Romania
Switzerland
Czech and Slovak
Republics
Austria
United Kingdom
Denmark
Sweden
Norway
Finland
Lithuania
Latvia
Estonia
Russian Federation
Ukraine
Belarus
Moldova
Poland
Germany
Gibraltar
Portugal
Luxembourg
Ireland
Iceland
Albania
Malta
Cyprus
282
283
284
286
288
290
292
302
303
308
310-316
330
332
334
338
340
342
344
346
348
3
50
352
354
356
358
360
362
3 64
366
368
370
312
374
376
400
Georgia
Armenia
Bulgaria
Turkey
Faroe Islands
Greenland
San Marino
Canada
Canada
St Pierre and Miquelon
USA
Puerto Rico
Virgin Islands
Mexico
Jamaica
French Antilles
Barbados
Antigua and Barbuda
Cayman Islands
British Virgin Islands
Bermuda
Grenada
Montserrat
St.
Kitts
St. Lucia
St. Vincent
&
the
Grenadines
Netherlands Antilles
Bahamas
Dominica
Cuba
Dominican Republic
Haiti
Trinidad and Tobago
Turks and Caicos
Islands
Azerbaijan
40
1
404
410
412
413
414
415
416
411
418
419
420
42 1
422
423
424
425
426
421
428
429
430, 431
432
434
436
431
438
440-443
450
452
453, 454
455
456
451
460
466
Kazakhstan
India
Pakistan
Afghanistan
Sri Lanka
Myanmar
Lebanon
Jordan
Syria
Iraq
Kuwait
Saudi Arabia
Yemen (Republic
of)
Oman
Yemen (Republic
of)
United Arab Emirates
Israel
Bahrain
Qatar
Mongolia
Nepal
United Arab Emirates
Iran
Uzbekistan
Tajikistan
Kyrgyztan
Turmenistan
Japan
South Korea
Vietnam
Hong Kong
Macao
Cambodia
Lao
People’s
Democratic Republic
China
Taiwan
ESCAPE CODES
523
Table
29.2
(continued)
Data
country
code
WC) Country
467 North Korea
470
Bangladesh
472 Maldives
480. 481
South Korea
502
505
510
515
520
525
528
530
534
535
536
537
539
540
54
1
542
543
544
545
546
547
548
549
550
602
603
604
605
606
607
Malaysia
Australia
Indonesia
Philippines
Thailand
Singapore
Brunei Darussalam
New Zealand
Northern Marianas
Guam
Nauru
Papua New Guinea
Tonga
Solomon Islands
Vanuatu
Fiji
Wallis and Futuna
Islands
American Samoa
Kiribati
New Caledonia
French Polynesia
Cook Islands
Western Samoa
Micronesia
Egypt
Algeria
Morocco
Tunisia
Libya
Gambia
Data Data
country country
code code
(DCC) Country (DCC) Country
608
609
610
61
1
612
613
614
615
616
617
618
619
620
62
1
622
623
624
625
626
627
628
629
630
63
1
632
633
634
635
636
637
638
639
640
Senegal
Mauritania
Mali
Guinea
C8te d’Ivoire
Burkino Faso
Niger
Togolese Republic
Benin
Mauritius
Liberia
Sierra Leone
Ghana
Nigeria
Chad
Central African
Republic
Cameroon
Cape Verde
Sao Tome and Principe
Equatorial Guinea
Gabon
Congo
Zaire
Angola
Guinea-Bissau
Seychelles
Sudan
Rwanda
Ethiopia
Somali Democratic
Republic
Djibouti
Kenya
Tanzania
64
1
642
643
645
646
647
648
649
650
65
1
6.52
653
654
655
702
704
706
708
710
712
714
716
722
724
730
732
734
736
738
140
742
744
746
748
Uganda
Burundi
Mozambique
Zambia
Madagascar
Reunion
Zimbabwe
Namibia
Malawi
Lesotho
Botswana
Swaziland
Comoros
South Africa
Belize
Guatemala
El
Salvador
Honduras
Nicaragua
Costa Rica
Panama
Peru
Argentina
Brazil
Chile
Colombia
Venezuala
Bolivia
Guyana
Ecuador
Guiana
Paraguay
Suriname
Uruguay
524
NETWORK
NUMBERING
AND
ADDRESSING
PLANS
29.4
TELEX NETWORK 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 within a telephone network,
to
signal the desired telex port
destination of calls at call setup time. A
international telex number
conforming to ITU-T
F.69 has a maximum length of 12 decimal digits, of which the first two or three comprise
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 one or two letter (alphabetic character)
telex network identiJication code
(TNZC).
This code is used as part of the
answerback
procedure. It appears on at 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: THE ADDRESSING PLAN
FOR
THE MESSAGE
HANDLING SERVICE (MHS)
The addresses used in the
message handling service
(X.400, Chapter 23) conform to the
OS1 and
IS0
directory service, laid out in the ITU-T
X.500
series of recommendations.
Recommendation X.500 lays out the general form
of
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 and maritime services
l
Pacific
8
Middle East
and
Far East
9
Africa
INTERNET ADDRESSING
SCHEME
525
directory
information
tree
(DIT)
A
/
\\
I
C=FR C=GB C=DE
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
the worldwide
Internet7
computer network. They are used and interpreted 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 left for host addresses (i.e. com-
puter addresses), which can be assigned ‘locally’ by the network operator (i.e. the
class
A
address owner). Close to
17
million computers may be connected to a class
A
network.
Class
A
addresses are only available to major Internet network operators.
526
NETWORK NUMBERING 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 65 536 computers may be connected to a
class
B
network. Class
B
addresses are
generally only available to 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. Such messages 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-network address.
This gives a huge scope 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
UNIX server
somewhere within the local network to convert the
alias address
to the 32 bit binary address. This file is called the ‘/etc/hosts’ file and is part of the set up
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
akin to the difference between an
MHS
(X.500) address and an X.25
Byte
1
Byte 2 Byte
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
Không có nhận xét nào:
Đăng nhận xét