InfoMagic Standards 1994 January/InfoMagic Standards - January 1994.iso/ccitt/1988/troff/6_1_04.tro

Text File | 1991-12-13 | 131KB | 5,186 lines

.rs
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.nr LL 40.5P
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.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 2
.ce 0
.sp 1P
.ce 1000
\fBNUMBERING\ PLAN\ AND\ DIALLING\ PROCEDURES\fR
.ce 0
.sp 1P
.ce 1000
\fBIN\ THE\ INTERNATIONAL\ SERVICE\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.10\fR
.RT
.sp 2P
.ce 1000
\fBDEFINITIONS\ RELATING\ TO\ NATIONAL\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.10''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.10    %'
.ce 0
.sp 1P
.ce 1000
\fBAND\ INTERNATIONAL\ NUMBERING\ PLANS\fR
.FS
This
Recommendation is an extract of Recommendation E.160 [1]. For the
examples relating to \(sc\(sc\ 1 to\ 11, see\ Fascicle\ II.2.
.FE
.ce 0
.sp 1P
.LP
\fB1\fR     \fBprefix\fR
.sp 1P
.RT
.LP
    \fIF:\ pr\*'efixe\fR
.LP
    \fIS:\ prefijo\fR
.PP
A prefix is an indicator consisting of one or more digits, that
allows the selection of different types of number formats (e.g.,\ local,
national or international), transit networks and/or the service.
.PP
Prefixes are not part of the number and are not signalled over
internetwork or international boundaries.
.PP
\fINote\fR \ \(em\ When prefixes are used, they are always entered by the
user or automatic calling equipment.
.RT
.sp 2P
.LP
\fB2\fR     \fBinternational prefix\fR
.sp 1P
.RT
.LP
    \fIF:\ pr\*'efixe international\fR
.LP
    \fIS:\ prefijo internacional\fR
.PP
The combination of digits to be dialled by a calling subscriber
making a call to a subscriber in another country to obtain access to the
automatic outgoing international equipment.
.RT
.sp 2P
.LP
\fB3\fR     \fBnational (trunk) prefix\fR
.sp 1P
.RT
.LP
    \fIF:\ pr\*'efixe (interurbain) national\fR
.LP
    \fIS:\ prefijo (interurbano) nacional\fR
.PP
A digit or combination of digits to be dialled by a calling
subscriber, making a call to a subscriber in his own country but outside his
own numbering area. It provides access to the automatic outgoing trunk
equipment.
.RT
.sp 2P
.LP
\fB4\fR     \fBescape code\fR
.sp 1P
.RT
.LP
    \fIF:\ code d'\*'echappement\fR
.LP
    \fIS:\ c\*'odigo de escape\fR
.PP
An escape code is an indicator consisting of one or more digits
which is defined in a given numbering plan and is used to indicate that the
digits that follow are from a specific numbering plan which is different
from the given numbering plan.
.bp
.PP
For example, escape codes are currently used within the X.121
numbering plan to interwork with E.164 (ISDN) and F.69 (Telex) numbering
plans.
.PP
An escape code can be carried forward through the originating network and
can be carried across internetwork and international boundaries. Therefore
the digits used for escape codes should be standardized.
.RT
.sp 2P
.LP
\fB5\fR     \fBcountry code\fR
.sp 1P
.RT
.LP
    \fIF:\ indicatif de pays\fR
.LP
    \fIS:\ indicativo de pa\*'is\fR
.PP
The combination of one, two or three digits characterizing the
called country.
.RT
.sp 2P
.LP
\fB6\fR     \fBtrunk code\fR
.sp 1P
.RT
.LP
    \fIF:\ indicatif interurbain\fR
.LP
    \fIS:\ indicativo interurbano\fR
.PP
A digit or combination of digits [not including the national (trunk) prefix]
characterizing the called numbering area within a country (or group of
countries included in one integrated numbering plan).
.PP
The trunk code has to be dialled before the called subscriber's number
where the calling and called subscribers are in different numbering
areas.
.RT
.sp 2P
.LP
\fB7\fR     \fBsubscriber number\fR
.FS
Care should be taken not to use
the term \*Qlocal number\*U instead of \*Qsubscriber number\*U.
.FE
.sp 1P
.RT
.LP
    \fIF:\ num\*'ero d'abonn\*'e\fR
.LP
    \fIS:\ n\*'umero de abonado\fR
.PP
The number to be dialled or called to reach a subscriber in the same local
network or numbering area.
.PP
This number is the one usually listed in the directory against the name
of the subscriber.
.RT
.sp 2P
.LP
\fB8\fR     \fBnational (significant) number\fR
.sp 1P
.RT
.LP
    \fIF:\ num\*'ero national (significatif)\fR
.LP
    \fIS:\ n\*'umero nacional (significativo)\fR
.PP
The number to be dialled following the national (trunk) prefix to
obtain a subscriber in the same country (or group of countries included
in one integrated numbering plan) but outside the same local network or
numbering
area.
.PP
The national (significant) number consists of the trunk code followed by
the subscriber number.
.PP
It should be noted that, in some countries, it is customary to
consider \fIfor national purposes\fR  | that the national (trunk) prefix
is included in the national number [which is then not the national (significant)
number]. A careful distinction must therefore be made between such national
definition or practice and the CCITT definition, which is internationally
valid. In order to avoid misunderstanding, the CCITT definition includes
the word \*Qsignificant\*U
between brackets, reading as follows:\ \*Qnational (significant) number\*U.
.RT
.sp 2P
.LP
\fB9\fR     \fBinternational number\fR
.sp 1P
.RT
.LP
    \fIF:\ num\*'ero international\fR
.LP
    \fIS:\ n\*'umero internacional\fR
.PP
The number to be dialled following the international prefix to
obtain a subscriber in another country.
.PP
The international number consists of the country code of the required
country followed by the national (significant) number of the called
subscriber.
.bp
.RT
.sp 2P
.LP
\fB10\fR     \fBnational destination code (NDC)\fR
.sp 1P
.RT
.LP
    \fIF:\ indicatif national de destination (IND)\fR
.LP
    \fIS:\ indicativo nacional de destino (IND)\fR
.PP
A code field, within the E.164 numbering plan, which combined with the
subscriber's number (SN) will constitute the national (significant) number
of the international ISDN number. The NDC will have a network and/or trunk
code selection function.
.PP
The NDC can be a decimal digit or a combination of decimal digits (not
including any prefix) characterizing a numbering area within a country
(or
group of countries included in one integrated numbering plan).
.PP
The NDC has to be inserted before the called subscriber's number when the
calling and called parties are located in different number areas.
.PP
NDC assignments are a national responsibility and therefore the NDC
structure varies from one country to another. It may take a trunk code
format or serve for selection of a destination network.
.PP
The NDC can in some instances, provide a combination of both the above
functions.
.RT
.sp 2P
.LP
\fB11\fR     \fBdestination network (DN) code\fR
.sp 1P
.RT
.LP
    \fIF:\ indicatif de r\*'eseau de destination (RD)\fR
.LP
    \fIS:\ indicativo de red de destino (RD)\fR
.PP
An optional code field within the E.164 numbering plan which
identifies the destination network serving the destination subscriber. It
performs the destination network selection function of the NDC. In some
instances it can be combined with a trunk code to form the NDC. The DN\
code can be a decimal digit or a combination of decimal digits (not including
any
prefix).
.RT
.sp 2P
.LP
    \fBReference\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIDefinitions relating to national and\fR
\fIinternational numbering plans\fR , Vol.\ II, Fascicle\ II.2, Rec.\ E.160.
.sp 2P
.LP
\fBRecommendation\ Q.11\fR
.FS
This Recommendation is also included in the
Series\ E Recommendations under the number E.163.
.FE
.RT
.sp 2P
.sp 1P
.ce 1000
\fBNUMBERING\ PLAN\ FOR\ THE\ INTERNATIONAL\ TELEPHONE\ SERVICE\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.11''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.11    %'
.ce 0
.sp 1P
.LP
    \fBIntroduction\fR
.sp 1P
.RT
.PP
This Recommendation describes the numbering plan for the
International Telephone Service. Recommendation\ E.164 describes the numbering
plan for the ISDN era. It is for each Administration to choose the method
of application from the two Recommendations which would provide the optimum
approach to meeting their future national numbering plan needs. Evolution
between the plans is for further study. However, for new equipment, it is
recommended that E.164\ [2] be adopted.
.RT
.sp 2P
.LP
\fB1\fR     \fBNational numbering plan\fR
.sp 1P
.RT
.PP
1.1
Each telephone Administration should give the most careful
consideration to the preparation of a \fInational numbering plan\fR
.FS
See the
CCITT manual cited in [1] for a comprehensive study of national numbering
plans from the national point of view.
.FE
for its own network. This plan should be designed so that a subscriber
is always called by the same number in the trunk service. It should be
applicable to all incoming international calls.
.bp
.sp 9p
.RT
.PP
Administrations are strongly urged to advise the ITU or CCITT of national
numbering plan changes well in advance of the event, so that this
information can be published in the ITU \fIOperational Bulletin\fR .
.sp 2P
.LP
1.2
    \fINumber analysis\fR
.sp 1P
.RT
.PP
1.2.1
The national numbering plan of a country should be such that an
analysis of a minimum number of digits of the national (significant) number
(see definitions in Recommendation\ E.160\ [3]):
.sp 9p
.RT
.LP
    a)
    gives routing that reflects economic and other appropriate   network factors;
.LP
    b)
    indicates the charging area in those countries where there   are several.
.PP
1.2.2
In the case of a country with a two\(hy or three\(hydigit country
code, not more than two digits of the national (significant) number need be
analyzed for these purposes.
.PP
In the case of a country with a one\(hydigit country code, not more than
the three digits of the national (significant) number need be analyzed
for these purposes.
.PP
1.2.3
In the case where an integrated numbering plan covers a group
of countries, the digit analysis specified
in \(sc\ 1.2.2 should also determine  the country of destination.
.PP
1.2.4
For the requirements relating to frontier traffic, see
Recommendation\ D.390\ R\ [4].
.sp 2P
.LP
\fB2\fR     \fBLimitation of the number of digits to be dialled by subscribers\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIInternational number\fR
.sp 9p
.RT
.PP
The CCITT recommended in 1964 that the number of digits to be
dialled by subscribers in the automatic international service should not be
more than\ 12 (excluding the international prefix). It is emphasized that
this is the maximum number of digits and Administrations are invited to
do their
utmost to limit the digits to be dialled to the smallest possible number.
.RT
.sp 1P
.LP
2.2
    \fINational (significant) number\fR
.sp 9p
.RT
.PP
Noting that:
.RT
.LP
    a)
    the international number (excluding the international
prefix) consists of the country code followed by the national
(significant) number;
.LP
    b)
     the smallest possible number of digits to be dialled in the automatic
international service is achieved by limiting the
number of digits of the country code and/or of the national
(significant) number;
.LP
    c)
     in some countries where telephony is already developed to an advanced
stage, the national numbering plans in force enable
the number of digits of the international number to be limited
to less than\ 12;
.LP
    d)
     some other countries which drew up their national numbering plans some
time before 1964 have taken steps to ensure that the
number of digits of the international number will not exceed\ 12
and may even be less;
.LP
the CCITT recommends that the number of digits of the national (significant)
number should be equal to a maximum of 12\ \(em\ \fIn\fR , where \fIn\fR
is the number of
digits of the country code.
.sp 2P
.LP
\fB3\fR     \fBDigit capacity of international registers\fR
.sp 1P
.RT
.PP
The CCITT considers it advisable to recommend that the digit
capacity of registers dealing with international traffic should allow for
future conditions that may arise, but not possible to specify at the present
time. In this regard, registers dealing with international traffic should
have a digit capacity, or a capacity that can be expanded, to cater for
more than
the maximum 12\(hydigit international number envisaged at present. The
increase in the number of digits above\ 12 is left as a matter of decision
to be taken by
individual Administrations. However, for new applications, a minimum digit
capacity of 15\ digits is recommended (see Recommendation\ E.164\ [2]).
Administrations are recommended, when making such a decision, to take account
of the new applications likely to be introduced in the international service,
and which are now being studied by the CCITT.
.bp
.RT
.sp 2P
.LP
\fB4\fR     \fBPrefixes and codes\fR
.sp 1P
.RT
.sp 1P
.LP
See definitions in Recommendation\ E.160\ [3].
.FE
4.1
    \fIInternational prefix\fR  |
.sp 9p
.RT
.PP
It is recommended by the CCITT that the Administrations of
countries that have not yet introduced automatic international operation, or
Administrations that are, for various reasons, revising their numbering
plans should adopt an international prefix (a code for access to the international
automatic network) composed of the two digits\ 00.
.PP
The reasons for this recommendation are:
.RT
.LP
    \(em
    to provide a maximum degree of standardization such that
dialling is made as easy as possible for a person travelling in different
countries (many countries already use the code\ 00),
.LP
    \(em
     to minimize the number of digits to be dialled in automatic international
operation,
.LP
    \(em
    to simplify, for a future time when the use of the
international prefix might have become a universal international standard,
the format for writing an international telephone number.
.LP
.sp 2P
.LP
4.2
    \fICountry code\fR  |
\u,\d |
.FS
A \*Qcountry code\*U may be assigned
either to an individual country or to a geographical area.
.FE
.sp 1P
.RT
.PP
4.2.1
Country codes will be used:
.sp 9p
.RT
.LP
    \(em
    in semiautomatic operation, to route calls to the required country
when the calls are transit calls or when, on the outgoing
positions, there is common dialling access to all the outgoing
routes;
.LP
    \(em
    in automatic operation.
.PP
4.2.2
A list of country codes was prepared by the CCITT
within the framework of a worldwide automatic telephone numbering plan.
.PP
This list was set up according to the following
principles:
.LP
    a)
    The number of digits of the country code is one, two or
three according to the foreseeable telephonic and demographic
development of the country concerned.
.LP
    b)
    The nine digits from\ 1 to\ 9 have been allocated as the
country code or as the first digit of the country code. These digits
define \fIworld numbering zones\fR .
.LP
    c)
    In the case of Europe, owing to the large number of
countries requiring two\(hydigit codes, the two digits\ 3 and\ 4 have been
allocated as the first digit of the country codes.
.PP
4.2.3
The list of country codes already assigned is given in
Annex\ A.
.sp 2P
.LP
4.3
    \fIAssignment of country codes\fR
.sp 1P
.RT
.PP
4.3.1
The existing world numbering plan should be maintained and
codes presently assigned should not be changed, unless consolidation of an
existing numbered area yields an advantage in terms of code usage.
.sp 9p
.RT
.PP
4.3.2
All spare country codes will be assigned on a 3\(hydigit basis, as
detailed in Annex\ B. The list of spare country codes
for the international semiautomatic and automatic service is given in
Annex\ C.
.PP
4.3.3
In the case where all the country codes in a world numbering
zone have been assigned and an additional code is required in that zone, a
spare country code from another world numbering zone can be used in accordance
with the following rules:
.PP
4.3.3.1
Preference should be given to the assignment of a spare country
code from an adjacent world numbering zone.
.PP
4.3.3.2
If spare codes are not available from an adjacent world
numbering zone, assignments will be made from the zones with the most
spare codes.
.sp 1P
.LP
4.4
    \fICodes for new international services\fR
.sp 9p
.RT
.PP
The introduction of some international services requires the
allocation of a country code. In such cases, the assignment of a country
code will be determined by the rules detailed in Annex\ B.
.bp
.RT
.sp 2P
.LP
4.5
    \fITrunk prefix\fR  |
.sp 1P
.RT
.PP
4.5.1
The \fInational (significant) number\fR (see definition\ 8 of
Recommendation\ E.160\ [3]) does not include the trunk prefix. Accordingly, in
the international service, the trunk prefix of the country of destination
must not be dialled.
.sp 9p
.RT
.PP
It should be noted that, in some countries, it is customary to
consider \fIfor national purposes\fR that the trunk prefix is included in the
national number [which is then not the national (significant) number]. A
.LP
careful distinction must therefore be made between such national definition
or practice and the CCITT definition, which is internationally valid. In
order to avoid misunderstanding, the CCITT definition includes the word
\*Qsignificant\*U
between brackets, reading as follows: \*Qnational (significant) number\*U.
.PP
4.5.2
It is recommended by the CCITT that the Administrations of
countries that have not yet adopted a trunk prefix for access to their
national automatic trunk network should adopt a prefix composed of a single
digit,
preferably\ 0. Irrespective of what digit is adopted as a trunk prefix, this
digit should be precluded from being used also as a first digit of the trunk
codes.
.PP
The reasons for this recommendation are:
.LP
    \(em
     to provide the maximum degree of standardization of the trunk prefixes
used in different countries, so that dialling is made
as easy as possible for a person travelling from one country
to another,
.LP
    \(em
    to minimize the number of digits to be dialled in the
automatic national service,
.LP
    \(em
    to reduce user problems which arise because of the
requirement, in automatic international operation, that the trunk prefix of
the country of destination must not be dialled.
.PP
4.5.3
In the automatic international service, following the
international prefix and country code of the called country, the caller
should dial the national (significant) number of the called subscriber
(i.e.\ without dialling the trunk prefix).
.PP
4.5.4
The use and printing of symbols and separators in national and
international telephone numbers is detailed in Recommendation\ E.123\ [5].
.sp 1P
.LP
4.6
    \fIUse of zero as an\fR
\fIescape code\fR
.sp 9p
.RT
.PP
The use of the digit \*Q0\*U (zero) as an escape code for numbering
plan interworking is described in Recommendation\ E.166.
.RT
.LP
.sp 2
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.11)
.sp 9p
.RT
.ce 0
.ce 1000
\fBList of country codes\fR \fB incorporating amendments proposed\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBby the World Plan Committee, 1988\fR
.ce 0
.sp 1P
.ce 1000
\fBWorld numbering ZONE 1\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Anguilla
    1 | ua\d\u)\d
.LP
Canada
    1 | ua\d\u)\d
.LP
United\ States\ of\ America,\ including
.LP
\ \ Puerto\ Rico\ and\ the\ Virgin\ Islands
    1 | ua\d\u)\d
.LP
Jamaica
    1 | ua\d\u)\d
.LP
Barbados
    1 | ua\d\u)\d
.LP
Antigua and Barbuda
    1 | ua\d\u)\d
.LP
Cayman\ Islands
    1 | ua\d\u)\d
.LP
British\ Virgin\ Islands
    1 | ua\d\u)\d
.LP
Bermuda
    1 | ua\d\u)\d
.LP
Bahamas (Commonwealth of the)
    1 | ua\d\u)\d
.LP
Dominican Republic
    1 | ua\d\u)\d
.LP
Grenada
    1 | ua\d\u)\d
.LP
Montserrat
    1 | ua\d\u)\d
.LP
Saint Kitts and Nevis
    1 | ua\d\u)\d
.LP
Saint Lucia
    1 | ua\d\u)\d
.LP
Saint Vincent and the Grenadines
    1 | ua\d\u)\d
.LP
Turks and Caicos (Islands)
    1 | ua\d\u)\d
.LP
\ua\d\u)\d
    Integrated numbering area.
.bp
.LP
.PS 10
.sp 1P
.ce 1000
\fBWorld numbering ZONE 2\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Egypt\ (Arab\ Republic\ of)
    \ 20
.LP
Morocco\ (Kingdom\ of)
    \ 21 | ua\d\u)\d
.LP
Algeria\ (People's\ Democratic
.LP
\ \ Republic of)
    \ 21 | ua\d\u)\d
.LP
\fR Tunisia
    \ 21 | ua\d\u)\d
.LP
Libya\ (Socialist\ People's Libyan
.LP
\ \ Arab\ Jamahiriya)
    \ 21 | ua\d\u)\d
.LP
Gambia\ (Republic\ of\ the)
    220
.LP
Senegal\ (Republic\ of)
    221
.LP
Mauritania\ (Islamic\ Republic\ of)
    222
.LP
Mali\ (Republic\ of)
    223
.LP
Guinea\ (Republic\ of)
    224
.LP
C\* | te\ d'Ivoire\ (Republic\ of)
    225
.LP
Burkina\ Faso
    226
.LP
Niger\ (Republic\ of\ the)
    227
.LP
Togolese\ Republic
    228
.LP
Benin\ (People's\ Republic\ of)
    229
.LP
Mauritius
    230
.LP
Liberia\ (Republic\ of)
    231
.LP
Sierra\ Leone
    232
.LP
Ghana
    233
.LP
Nigeria\ (Federal\ Republic\ of)
    234
.LP
Chad\ (Republic\ of)
    235
.LP
Central\ African\ Republic
    236
.LP
Cameroon\ (Republic\ of)
    237
.LP
Cape\ Verde\ (Republic\ of)
    238
.LP
Sao\ Tome\ and\ Principe
.LP
\ \ Democratic\ Republic\ of)
    239
.LP
Equatorial\ Guinea\ (Republic\ of)
    240
.LP
Gabonese Republic
    241
.LP
Congo (People's Republic of the)
    242
.LP
Zaire (Republic of)
    243
.LP
Angola (People's Republic of)
    244
.LP
Guinea\(hyBissau (Republic of)
    245
.LP
Diego Garcia
    246
.LP
Ascension
    247
.LP
Seychelles (Republic of)
    248
.LP
Sudan (Republic of the)
    249
.LP
Rwandese Republic
    250
.LP
Ethiopia
    251
.LP
Somali Democratic Republic
    252
.LP
Djibouti (Republic of)
    253
.LP
Kenya (Republic of)
    254
.LP
Tanzania (United Republic of)
    255
.LP
Uganda (Republic of)
    256
.LP
Burundi (Republic of)
    257
.LP
Mozambique (People's Republic of)
    258
.LP
Zanzibar (Tanzania)
    259
.LP
Zambia (Republic of)
    260
.LP
Madagascar (Democratic Republic of)
    261
.LP
Reunion (French Department of)
    262
.LP
Zimbabwe (Republic of)
    263
.LP
Namibia
    264
.LP
Malawi
    265
.LP
Lesotho (Kingdom of)
    266
.LP
Botswana (Republic of)
    267
.LP
Swaziland (Kingdom of)
    268
.LP
Comoros (Islamic Federal
.LP
\ \ Republic of the)
    269
.LP
South Africa (Republic of)
    \ 27
.LP
San\ Marino\ (Republic\ of)
    295
.LP
Trinidad\ and\ Tobago
    296
.LP
Aruba
    297
.LP
Faroe Islands (Denmark)
    298
.LP
Greenland (Denmark)
    299
\v'3p'
.LP
\fISpare\ codes\fR
.LP
280, 281, 282, 283, 284, 285, 286, 287, 288, 289
.LP
290, 291, 292, 293, 294
.LP
\ua\d\u)\d
    \fIIntegrated numbering area with subdivisions:\fR
.LP
    \(em\ Morocco:\ 210, 211, 212 (212 in service);
.LP
    \(em\ Algeria:\ 213, 214, 215;
.LP
    \(em\ Tunisia:\ 216, 217;
.LP
    \(em\ Libya:\ 218, 219.
.LP
.PS 10
.sp 1P
.ce 1000
\fBWorld numbering ZONES 3 and 4\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Greece
    \ 30
.LP
Netherlands\ (Kingdom\ of\ the)
    \ 31
.LP
Belgium
    \ 32
.LP
France
    \ 33 | ua\d\u)\d
.LP
Monaco
    \ 33 | ua\d\u)\d
.LP
Spain
    \ 34
.LP
Gibraltar
    350
.LP
Portugal
    351
.LP
Luxembourg
    352
.LP
Ireland
    353
.LP
Iceland
    354
.LP
Albania (Socialist People's Republic of)
    355
.LP
Malta (Republic of)
    356
.LP
Cyprus (Republic of)
    357
.LP
Finland
    358
.LP
Bulgaria (People's Republic of)
    359
.LP
\ua\d\u)\d
    Integrated numbering plan.
.bp
.LP
Hungarian\ People's\ Republic
    36
.LP
German\ Democratic\ Republic
    37
.LP
Yugoslavia\ (Socialist\ Federal\ Republic\ of)
    38
.LP
Italy
    39
.LP
Romania\ (Socialist\ Republic\ of)
    40
.LP
Switzerland\ (Confederation\ of)
    41\ua\d\u)\d
.LP
Liechtenstein\ (Principality\ of)
    41\ua\d\u)\d
.LP
Czechoslovak\ Socialist\ Republic
    42
.LP
Austria
    43
.LP
United\ Kingdom\ of\ Great\ Britain\ and
.LP
\ \ Northern\ Ireland
    44
.LP
Denmark
    45
.LP
Sweden
    46
.LP
Norway
    47
.LP
Poland (People's Republic of)
    48
.LP
Germany (Federal Republic of)
    49
.LP
.rs
.sp 1P
.ad r
BLANC\fR
.ad b
.RT
.LP
\ua\d\u)\d
    Integrated numbering plan.
.LP
.PS 10
.bp
.sp 1P
.ce 1000
\fBWorld numbering ZONE 5\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Falkland Islands (Malvinas)
    500
.LP
Belize
    501
.LP
Guatemala\ (Republic\ of)
    502
.LP
El\ Salvador\ (Republic\ of)
    503
.LP
Honduras\ (Republic\ of)
    504
.LP
Nicaragua
    505
.LP
Costa\ Rica
    506
.LP
Panama\ (Republic\ of)
    507
.LP
St. Pierre and Miquelon (French Department of)
    508
.LP
Haiti\ (Republic\ of)
    509
.LP
Peru
    \ 51
.LP
Mexico
    \ 52
.LP
Cuba
    \ 53
.LP
Argentine\ Republic
    \ 54
.LP
Brazil (Federative\ Republic\ of)
    \ 55
.LP
Chile
    \ 56
.LP
Colombia (Republic of)
    \ 57
.LP
Venezuela (Republic of)
    \ 58
.LP
Guadeloupe (French Department of)
    590
.LP
Bolivia (Republic of)
    591
.LP
Guyana
    592
.LP
Ecuador
    593
.LP
Guiana (French Department of)
    594
.LP
Paraguay (Republic of)
    595
.LP
Martinique (French Department of)
    596
.LP
Suriname (Republic of)
    597
.LP
Uruguay (Eastern Republic of)
    598
.LP
Netherlands Antilles
    599
\v'1p'
.sp 1P
.ce 1000
\fBWorld numbering ZONE 6\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Malaysia
    \ 60
.LP
Australia
    \ 61
.LP
Indonesia\ (Republic\ of)
    \ 62
.LP
Philippines\ (Republic\ of\ the)
    \ 63
.LP
New\ Zealand
    \ 64
.LP
Singapore\ (Republic\ of)
    \ 65
.LP
Thailand
    \ 66
.LP
Mariana Islands
    670
.LP
Guam
    671
.LP
Australian External Territories
    672
.LP
Brunei Darussalam
    673
.LP
Nauru\ (Republic\ of)
    674
.LP
Papua\ New\ Guinea
    675
.LP
Tonga\ (Kingdom\ of)
    676
.LP
Solomon Islands
    677
.LP
Vanuatu\ (Republic\ of)
    678
.LP
Fiji
    679
.LP
Palau
    680
.LP
Wallis and Futuna Islands
    681
.LP
Cook Islands
    682
.LP
Niue Island
    683
.LP
American Samoa
    684
.LP
Western Samoa (Independent State of)
    685
.LP
Kiribati (Republic of)
    686
.LP
New Caledonia and Dependencies
    687
.LP
Tuvalu
    688
.LP
French Polynesia
    689
.LP
Tokelan
    690
.LP
F.S. of Micronesia
    691
.LP
Marshall Islands
    692
\v'3p'
.LP
\fISpare codes\fR     693, 694, 695, 696, 697, 698, 699
.LP
.PS 10
.sp 1P
.ce 1000
\fBWorld numbering ZONE 7\fR
.ce 0
.sp 1P
.ce 1000
Union of Soviet Socialist Republics\ \ 7
.ce 0
.sp 1P
.ce 1000
\fBWorld numbering ZONE 8\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Japan
    \ 81
.LP
Korea\ (Republic\ of)
    \ 82
.LP
Viet\ Nam\ (Socialist\ Republic\ of)
    \ 84
.LP
Democratic People's Republic of Korea
    850
.LP
Hong\(hyKong
    852
.LP
Macao
    853
.LP
Democratic Kampuchea
    855
.LP
Lao People's Democratic Republic
    856
.LP
China (People's Republic of)
    \ 86 | ua\d\u)\d
.LP
Maritime Mobile Service
    \ 87 | ub\d\u)\d
.LP
Bangladesh (People's Republic of)
    880 | uc\d\u)\d
\v'3p'
.LP
\fISpare\ codes\fR     800, 801, 802, 803, 804, 805, 806, 807, 808, 809
.LP
830, 831, 832, 833, 834, 835, 836, 837, 838, 839
.LP
851, 854, 857, 858, 859
.LP
890, 891, 892, 893, 894, 895, 896, 897, 898, 899
.LP
\ua\d\u)\d
    Within this national code, the Telecommunications
Administration of the People's Republic of China has notified that the
code\ 866 has been allocated to the province of Taiwan.
(Reference: Notification No. 1157 of 10 December 1980.)
.LP
    \ub\d\u)\d
    The country code 87 is reserved for the Maritime Mobile
Service. The following three digit country codes are assigned:\ 871 INMARSAT
(Atlantic), 872 INMARSAT (Pacific), 873 INMARSAT (Indian Ocean).
.LP
    \uc\d\u)\d
     The remaining combinations in series 88 will not be allocated until the
stock of spare 3\(hydigit codes for the region is
exhausted.
.bp
.LP
.PS 10
.sp 1P
.ce 1000
\fBWorld numbering ZONE 9\fR
.ce 0
.sp 1P
.ce 1000
2 col
.ce 0
.LP
Turkey
    \ 90
.LP
India\ (Republic\ of)
    \ 91
.LP
Pakistan\ (Islamic\ Republic\ of)
    \ 92
.LP
Afghanistan\ (Democratic\ Republic\ of)
    \ 93
.LP
Sri\ Lanka\ (Democratic
.LP
\ \ Socialist\ Republic\ of)
    \ 94
.LP
Burma\ (Socialist\ Republic
.LP
\ \ of\ the\ Union\ of)
    \ 95
.LP
Maldives\ (Republic\ of)
    960
.LP
Lebanon
    961
.LP
Jordan\ (Hashemite\ Kingdom\ of)
    962
.LP
Syrian\ Arab\ Republic
    963
.LP
Iraq\ (Republic\ of)
    964
.LP
Kuwait (State of)
    965
.LP
Saudi Arabia (Kingdom of)
    966
.LP
Yemen Arab Republic
    967
.LP
Oman (Sultanate of)
    968
.LP
Yemen (People's
.LP
\ \ Democratic Republic of)
    969
.LP
United Arab Emirates | ua\d\u)\d
    971
.LP
Israel (State of)
    972
.LP
Bahrain (State of)
    973
.LP
Qatar (State of)
    974
.LP
Kingdom of Bhutan
    975
.LP
Mongolian People's Republic
    976
.LP
Nepal
    977
.LP
Iran
    \ 98
\v'3p'
.LP
\fISpare codes\fR     970, 978, 979
.LP
990, 991, 992, 993, 994, 995, 996, 997, 998, 999
.LP
\ua\d\u)\d
    E.A.U: Abu Dhabi, Ajman, Dubai, Fujeirah, Ras Al Khaimah,
Sharjah, Umm Al Qaiwain.
\v'2P'
.LP
.PS 10
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation Q.11)
.sp 9p
.RT
.ce 0
.ce 1000
\fBRules for the\fR
\fBassignment of spare country codes\fR
.sp 1P
.RT
.ce 0
.PP
The rules listed in this Annex are provided as a basis for the most effective
utilization of the spare country codes.
.sp 1P
.RT
.PP
B.1
Single isolated 3\(hydigit codes should be assigned prior to the
assignment
of any 3\(hydigit code which is part of a series of more than two consecutive
3\(hydigit codes.
.sp 1P
.RT
.PP
B.2
The assignment of spare codes of a zone, both within that zone and also
to another zone, will take place as follows:
.sp 9p
.RT
.LP
    a)
    When assigning a code to a country in the same zone:
.LP
\fR
    start with the lowest numbered 3\(hydigit codes in ascending order,
e.g.\ 670, 680\ . |  |
.LP
    b)
    When assigning a code to a country in another zone:
.LP
     start with the highest numbered 3\(hydigit codes in descending order,
e.g.\ 688, 685\ . |  |
.LP
    c)
     Within code 87 reserved for the Maritime Mobile Service a third digit
will be assigned to codes used for maritime satellite ocean area systems,
with the
restriction that codes\ 878 and\ 879 may not be touched because they are
reserved for national purposes.
.PP
B.3
Country codes for new international services or for the
automation of some existing services
should be taken from the world
numbering zone with the most spare codes.
.bp
.sp 9p
.RT
.ce 1000
ANNEX\ C
.ce 0
.ce 1000
(to Recommendation Q.11)
.sp 9p
.RT
.ce 0
.ce 1000
\fBList of spare country codes for the international\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBsemiautomatic and automatic service\fR
.ce 0
.LP
\fISpare\ codes\fR     280, 281, 282, 283, 284, 285, 286, 287, 288, 289
.sp 1P
.RT
.LP
290, 291, 292, 293, 294
.LP
693, 694, 695, 696, 697, 698, 699
.LP
800, 801, 802, 803, 804, 805, 806, 807, 808, 809
.LP
830, 831, 832, 833, 834, 835, 836, 837, 838, 839
.LP
851, 854, 857, 858, 859
.LP
890, 891, 892, 893, 894, 895, 896, 897, 898, 899
.LP
970, 975, 978, 979
.LP
990, 991, 992, 993, 994, 995, 996, 997, 998, 999
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT manual \fINational telephone networks for the automatic\fR
\fIservice\fR , ITU, Geneva, 1964, 1968, 1978.
.LP
[2]
    CCITT Recommendation \fINumbering plan for the ISDN era\fR , Vol.\ II,
Rec.\ E.164.
.LP
[3]
    CCITT Recommendation \fIDefinitions relating to national and\fR
\fIinternational numbering plans\fR , Vol.\ II, Rec.\ E.160.
.LP
[4]
    CCITT Recommendation \fIAccounting system in the international\fR
\fIautomatic telephone service\fR , Vol.\ II, Rec.\ D.390\ R.
.LP
[5]
     CCITT Recommendation \fIThe use and printing of symbols and separators\fR
\fIin national and international telephone numbers\fR , Vol.\ II,
Rec.\ E.123.
.sp 2P
.LP
\fBRecommendation Q.11 | fR \fIbis\fR
.FS
This Recommendation appears in
the Series E Recommendations as Recommendation\ E.164 and in the I
series Recommendations as I.331.
.FE
.RT
.sp 2P
.sp 1P
.ce 1000
\fBNUMBERING\ PLAN\ FOR\ THE\ ISDN\ ERA\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.11^bis''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.11^bis    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
The rapid advances in telecommunications technology coupled with
increased diversification of customer demands served by a number of different
types of dedicated public switched networks (telephone, telex, data,\ etc.)
have created a need to provide a uniform customer access and network structure.
Such a structure is called the Integrated Services Digital Network (ISDN).
Implementation of ISDNs have begun in a number of countries and eventually
these will carry all existing and new services.
.PP
To facilitate ISDN evolution internationally, this Recommendation
defines the numbering arrangements for an ISDN. The timetable for
implementation of this numbering plan is described in
Recommendation\ E.165.
.RT
.sp 2P
.LP
\fB2\fR     \fBDefinitions\fR
.sp 1P
.RT
.PP
Within the integrated service environment, the terms used for all
networks and services must be compatible and consistent. A list of
terms and their definitions relating to numbering are contained in
Recommendation\ E.160.
.bp
.RT
.sp 2P
.LP
\fB3\fR     \fBISDN numbering plan principles\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The ISDN numbering and addressing principles are described in
Recommendation\ I.330. The ISDN numbering plan will be based on and evolve
from the existing numbering plans applicable to national and international
public
telephone networks.
.PP
In view of the evolutionary nature of ISDN, the international numbering
plan should provide for substantial capacity to accommodate future network
requirements.
.RT
.PP
Country or geographical area.
.FE
Where multiple destinations (i.e., RPOAs/networks) serve the called party's
geographic area, the national ISDN numbering arrangement in the
country
of destination shall provide for discrimination between these
RPOAs/networks. The procedure for discrimination between multiple
transit\(hyRPOAs/networks is not considered to be a destination address
requirement and shall therefore be excluded from the ISDN numbering
arrangements.
.PP
Before the ISDN numbering arrangement attains global penetration, it must
allow for interworking between the ISDN and other public networks. Such
arrangements are discussed in Recommendation\ E.166. Interworking with
private networks shall also be taken into account. The definition of private
networks and the methods of interworking are for further study and will
be covered in
future Series\ E Recommendations.
.PP
The 10\ digit decimal character set\ 0\(hy9 is used throughout the ISDN
numbering plan format including subscriber number, national (significant)
number and the country code.
.PP
Prefixes and other information concerned with identifying selection
procedures or network service parameters (such as quality of service or
transit delay) do not form part of the ISDN number.
.PP
The ISDN numbering plan shall include an unambiguous identification of
a particular country
. In addition, the ISDN number will identify
networks and/or ISDNs within these countries
, if required. In doing so, it shall retain the integrity of the telephone
country code as defined in
Recommendations\ E.160 and\ E.163.
.RT
.sp 1P
.LP
3.2
    \fIStructure of the international ISDN number\fR
.sp 9p
.RT
.PP
The international ISDN number is composed of a variable
length of decimal digits arranged in specific code fields. The international
ISDN number code fields are the country code (CC) and the national
(significant) number.
.PP
The country code (CC) is used to select the destination
country
and varies in length as outlined in Recommendation\ E.163.
.PP
The national (significant) number N(S)N is used to select the
destination subscriber. In selecting the destination subscriber, however, it
may be necessary to select a destination network. To accomplish this selection,
the national (significant) number N(S)N code field comprises a national
destination code (NDC)
.FS
See definitions in Recommendation\ E.160.
.FE
followed by the subscribers number (SN).
.PP
The NDC field will be variable in length depending upon the
requirements of the destination country. Each NDC may have one of the following
structures:
.RT
.LP
    a)
     a Destination Network (DN) code, which can be used to select a destination
network serving the destination subscribers;
.LP
    b)
    a Trunk Code (TC), the format of which is defined in
Recommendation\ E.160;
.LP
    c)
    any combination of Destination Network (DN) code and Trunk   Code (TC).
.PP
The NDCs of an Administration may consist of any of the above
structures.
.PP
\fINote\fR \ \(em\ The sequences DN\(hyTC and TC\(hyDN are a national matter.
This is a subject for further study.
.PP
The subscriber's number (SN) varies in length depending on
the requirements of the destination country
and is in accordance with
Recommendation\ E.160.
.bp
.PP
Figure\ 1/Q.11 | fIbis\fR shows the number structure.
.PP
Where appropriate, identification of an ISDN within the
destination country
shall be through the use of a national destination
code (NDC) incorporated in the ISDN number.
.RT
.LP
.rs
.sp 15P
.ad r
\fBFigura 1/Q.11 | is, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
3.3
    \fINumber length\fR
.sp 9p
.RT
.PP
The
international number
may be of variable length. The
maximum number length shall be 15\ digits. However, some Administrations may
wish to increase their register capacity to 16\ or 17\ digits. The decision on
register capacity is left as a matter to be taken by individual
Administrations.
.PP
The length does not include prefixes,
language digit
, address delimiters (e.g.,\ end of pulsing signals,\ etc.) since these
items are not
considered as part of the international ISDN number.
.RT
.sp 1P
.LP
3.4
    \fINumber analysis\fR
.sp 9p
.RT
.PP
In order to determine:
.RT
.LP
    \(em
    the country
of destination,
.LP
    \(em
    the most appropriate network routing,
.LP
    \(em
    the proper charging,
.LP
the originating country
must analyse a number of digits of the
international number. The national destination code (NDC) increases the
potential requirement for number analysis because it provides for a combination
of either a
trunk code (TC)
and/or a network identification function. Careful consideration should
be given to the preparation of the national
destination code (NDC) assignments.
.PP
On international calls the number analysis performed at the
originating country
need not be more than the country code and:
.LP
    \(em
     three digits of the NSN in the case of a country with a three digit country
code,
.LP
    \(em
    four digits of the NSN in the case of a country with a two
digit country code,
.LP
    \(em
    five digits of the NSN in the case of a country with a one
digit country code.
.PP
(Translation beyond this requirement could be arranged by
bilateral agreement if required, e.g.,\ countries assigned a 1\ digit country
code may require analysis of up to 6\ digits beyond the country code.)
.bp
.sp 2P
.LP
\fB4\fR     \fBNumber allocation principles\fR
.sp 1P
.RT
.PP
The assignment of country codes is administered by the CCITT,
while NSN (NDC plus SN) code assignments are a national responsibility.
.PP
ISDN subscriber numbers
may be allocated from the range of
subscriber numbers available in the local ISDN exchange. These will be
assigned to customers who subscribe only to the telephone service, customers
with one or more data services and customers with a mixture of telephony
and data
services.
.PP
Subscribers equipped with
basic access
(the definition of ISDN basic access is given in the Series\ I Recommendations)
should normally be
allocated one unique number.
.RT
.sp 2P
.LP
\fB5\fR     \fBNetwork identification\fR
.sp 1P
.RT
.PP
In countries
served by more than one ISDN and/or Public
Switched Telephone Network (PSTN) the network identification of each is a
national matter.
.PP
Network identification within the national (significant) number shall be
such that:
.RT
.LP
    \(em
    in a country
all destination ISDN and PSTN networks
shall operate under a single Recommendation\ E.163 country
code,
.LP
    \(em
    the international number maximum length of 15\ digits shall
not be exceeded, nor shall it be necessary for the number of
digits for number analysis to exceed that specified in \(sc\ 3.4,
.LP
    \(em
    provision of network identification is not mandatory for
countries using a single integrated numbering plan arrangement
for their ISDNs and PSTNs.
.sp 2P
.LP
\fB6\fR     \fBService identification\fR
.sp 1P
.RT
.PP
The ISDN number by itself will not identify the particular nature of the
service, type of connection or quality of service required. An
indication of parameters describing the service required by the calling
terminal will be included in a service identifier in the signalling
information. This service identifier is not considered to be part of the
numbering plan.
.RT
.sp 2P
.LP
\fB7\fR     \fBCalling/called line identity\fR
.FS
This termiminology needs  further study.
.FE
.sp 1P
.RT
.PP
Calling/called line identity (CLI/CDLI) is address information
which is passed across the network to provide supplementary services such as
calling (or called) line identification presentation. The format of the
CLI and CDLI for international calls should be the full international number,
i.e.,\ Country Code (CC), National Destination Code (NDC) and Subscriber
Number (SN). No other information, such as prefixes or symbols (e.g.\ \*Q+\*U),
should be included, although a subaddress may be associated with the
CLI/CDLI.
.RT
.sp 2P
.LP
\fB8\fR     \fBDialling procedures\fR
.sp 1P
.RT
.PP
The subscriber dialling procedures for local, national and
international calls shall be in accordance with Recommendation\ E.163.
However, subscribers' control procedures for
supplementary services
will be as defined in Recommendation\ E.131 or in separate Recommendations
for each
service.
.PP
ISDN subscribers will always be called by the same subscriber number irrespective
of where in the network the call originates. For calls in the same numbering
area or local network the subscriber number alone is dialled. For
national calls between numbering areas or local networks the subscriber
number may be preceded by the
national prefix
and the national destination
code.
.PP
The addressing procedures for calls using sub\(hyaddressing are
described in \(sc\ 11.
.bp
.RT
.sp 2P
.LP
\fB9\fR     \fBPrefixes\fR
.sp 1P
.RT
.PP
The use of prefixes shall be in accordance with
Recommendations\ E.160, E.163 and E.166. Where necessary, prefixes can
also be used for network and service selection.
.RT
.sp 2P
.LP
\fB10\fR     \fBEscape code\fR
.sp 1P
.RT
.PP
The use of the digit \*Q0\*U as an escape code for numbering plan
interworking is described in Recommendation\ E.166.
.RT
.sp 2P
.LP
\fB11\fR     \fBAddress information\fR
.sp 1P
.RT
.PP
Identification within a subscriber's installation of a point beyond that
defined by the ISDN number requires the transfer of address information
from the public network to the subscriber's equipment. The following methods
apply:
.RT
.sp 1P
.LP
11.1
    \fIDirect dialling\(hyin\fR
.sp 9p
.RT
.PP
With direct\(hydialling\(hyin (DDI) the last few digits forming the end
of the ISDN subscriber number are transferred to the called subscriber's
installation (see Figure\ 2/Q.11 | fIbis\fR ). The number of digits used
varies and
depends upon the requirements of the called subscriber's equipment and the
capacity of the numbering plan used.
.PP
ISDN subscriber numbers used for DDI may be those published in the
public directory.
.RT
.LP
.rs
.sp 13P
.ad r
\fBFigure 2/Q.11 | is, p.
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
11.2
    \fISub\(hyaddressing (network address extension)\fR
.sp 9p
.RT
.PP
Sub\(hyaddressing provides a separate additional addressing capacity outside
the ISDN numbering plan but constitutes an intrinsic part of the ISDN addressing
capabilities. As shown in Figure\ 2/Q.11 | fIbis\fR up to 20\ octets (or
40\ digits) may follow the ISDN number and form the ISDN sub\(hyaddress,
which is transferred to the equipment at the subscriber's premises.
.PP
When required, the sub\(hyaddress is sent by the calling party within the
call set\(hyup procedure and is passed transparently through the network
as a
separate entity from both the ISDN number and user\(hyto\(hyuser information.
Sub\(hyaddress information is not required to be processed within the public
network.
.PP
Sub\(hyaddressing procedures are the subject of a separate
Recommendation.
.bp
.RT
.sp 1P
.LP
11.3
    \fICombination of sub\(hyaddressing and direct dialling\(hyin\fR
.sp 9p
.RT
.PP
Sub\(hyaddressing may be used separately or in combination with DDI
(see Figure 2/Q.11 | fIbis\fR ).
.RT
.sp 1P
.LP
11.4
    \fIAddress delimiters\fR
.sp 9p
.RT
.PP
DDI address information may contain an \*Qend of address\*U (e.g.,\ ST)
delimiter. In the case of sub\(hyaddressing, an \*Qend of subscriber
number/beginning of sub\(hyaddress\*U delimiter and the \*Qend of address\*U
delimiter are required.
.PP
(The use of an address delimiter at the end of an ISDN address is for further
study.)
.RT
.sp 2P
.LP
\fBRecommendation\ Q.11 | fR \fIter\fR
.FS
This Recommendation es also included in the series E Recommendations under
the number E.165.
.FE
.RT
.sp 2P
.ce 1000
\fBTIMETABLE\ FOR\ COORDINATED\ IMPLEMENTATION\ OF\ THE\ FULL\ CAPABILITY\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.11^ter''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.11^ter    %'
.ce 0
.sp 1P
.ce 1000
\fBOF\ THE\ NUMBERING\ PLAN\ FOR\ THE\ ISDN\ ERA\ (RECOMMENDATION\ E.164)\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
Recommendation I.330 describes ISDN numbering and addressing
principles, while Recommendation\ E.164 describes the numbering plan for the
ISDN era. Recommendation\ E.164 also identifies the need for interworking
arrangements between ISDN and present dedicated networks.
.PP
This Recommendation sets a specific time (Time \fIT\fR ), after which all
ISDNs and PSTNs can use the full capability of Recommendation\ E.164, \*QNumbering
plan for the ISDN era\*U, and identifies the numbering requirements on
ISDNs and on dedicated networks intending to interwork with ISDNs, before
and after
Time\ \fIT\fR .
.PP
Among the significant principles which form the basis for this
Recommendation, the following are considered especially useful for ready
reference:
.RT
.LP
    \(em
    An E.163/E.164 telephony subscriber may become an ISDN
subscriber without a number change.
.LP
    \(em
     Numbers according to Recommendation E.164 apply to both PSTN and ISDN
subscribers in the ISDN era. A mixture of PSTN and ISDN terminations on
the same exchange is allowed.
.LP
    \(em
    E.164 numbering arrangements may be used to distinguish
between ISDN and PSTN subscribers. This is not necessary but is allowed,
provided that possible effects on routing and digit analysis remain
within the limits of Recommendation\ E.164.
.sp 2P
.LP
\fB2\fR     \fBApplication and evolution of Time \fI\fBT\fR
.sp 1P
.RT
.PP
ISDNs are expected to interwork with dedicated networks. However, due to
the different addressing capabilities between the ISDN and existing
numbering plans, some temporary constraints need to be imposed on the
number length and digit analysis required to access the user network interfaces
of the ISDNs before Time\ \fIT\fR .
.RT
.sp 2P
.LP
2.1
    \fINumbering constraints before Time T\fR
.sp 1P
.RT
.sp 1P
.LP
2.1.1
    \fIISDNs\fR
\fIinterworking with dedicated networks\fR
.sp 9p
.RT
.PP
To allow numbering plan interworking with dedicated networks before Time\
\fIT\fR , an ISDN will not assign international E.164 numbers longer than
12\ digits to its
user network interfaces
capable of receiving calls
from dedicated networks.
.PP
In addition, for ISDNs and PSTNs, digit analysis as defined in
Recommendation\ E.163 will apply.
.bp
.RT
.sp 1P
.LP
2.1.2
    \fIISDNs which do not interwork with dedicated networks\fR
.sp 9p
.RT
.PP
These ISDNs are allowed to assign numbers to user network
interfaces
according to the full capability of the numbering plan for the ISDN era.
.PP
Digit analysis according to Recommendation E.164 may be required to
access user network interfaces connected to these networks.
.RT
.sp 1P
.LP
2.2
    \fIEvolution after Time T\fR
.sp 9p
.RT
.PP
After Time\ \fIT\fR , ISDNs and PSTNs can make use of the full capability
of E.164 numbers to identify their user network interfaces and terminals
respectively. In addition, for routing purposes, the ISDNs and PSTNs conforming
to Recommendation\ E.164 must be capable of analysing the ISDN international
number to the extent required in that Recommendation.
.PP
\fINote\fR \ \(em\ Digit analysis for other dedicated networks is for further
study.
.RT
.sp 2P
.LP
\fB3\fR     \fBDate of Time \fI\fBT\fR
.sp 1P
.RT
.PP
The date for Time\ \fIT\fR has been set for 31 December 1996 at 23h59m
Coordinated Universal Time (UTC).
.RT
.sp 2P
.LP
\fB4\fR     \fBNetwork requirements at Time \fI\fBT\fR
.sp 1P
.RT
.PP
ISDNs and PSTNs supporting number length and digit analysis as
described in Recommendation\ E.164 are said to be \*QE.164\(hyconforming\*U
networks.
.PP
All ISDNs must be E.164\(hyconforming networks. Functions associated with
E\(hy164\(hyconforming networks are:
.RT
.LP
    a)
    for calls originated within such a network, provision for
carrying E.164\ numbers of up to 15\ digits to interfacing
networks;
.LP
    b)
    comparable treatment for transit calls;
.LP
    c)
    capability for conducting digit analysis for ISDNs and
PSTNs as indicated in Recommendation\ E.164;
.LP
    d)
    screening to ensure that, taking into account agreements
between the networks concerned, no transit calls are offered
to non\(hyconforming networks incapable of handling number lengths
as defined in Recommendation\ E.164;
.LP
    e)
    provision of interim procedures, such as two\(hystage
selection, for internal network sources, e.g.,\ local exchanges,
not equipped to handle 15\ digits, so that all internal network
sources can originate calls to all E.164 addresses.
.PP
\fINote\ 1\fR \ \(em\ Other requirements on conforming networks are for
further study. Non\(hyconforming networks may seek bilateral agreements with
conforming networks, or adopt intra\(hynetwork procedures to provide means by
which subscribers of the non\(hyconforming networks may originate calls to
subscribers connected to ISDNs and PSTNs requiring a number length or analysis
in excess of the capabilities of the non\(hyconforming network.
.PP
\fINote\ 2\fR \ \(em\ Limitations of non\(hyconforming networks and interworking
procedures are for further study.
.RT
.LP
.rs
.sp 12P
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 3
.ce 0
.sp 1P
.ce 1000
\fBROUTING\ PLAN\ FOR\ INTERNATIONAL\ SERVICE\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.12\fR
.RT
.sp 2P
.ce 1000
\fBOVERFLOW\ \(em\ ALTERNATIVE\ ROUTING\ \(em\ REROUTING\ \(em\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.12''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.12    %'
.ce 0
.sp 1P
.ce 1000
\fBAUTOMATIC\ REPEAT\ ATTEMPT\fR
.ce 0
.sp 1P
.PP
\fB1\fR
When a call cannot find a free circuit in one group of circuits (first
choice), technical arrangements can be made to route the call
automatically via another group of circuits (second choice), at the same
.sp 1P
.RT
.LP
exchange; this process is called \fIoverflow\fR . There may also be overflow,
at the same exchange, from a second choice group of circuits to a third
choice group of circuits, etc.
.PP
\fB2\fR
When the group of circuits over which the overflow traffic is
routed
involves at least one exchange not involved in the previous choice route,
the process is called \fIalternative routing\fR .
.sp 9p
.RT
.PP
\fB3\fR
It should be noted that overflow can occur without alternative routing
for cases such as, when there are in one relation two groups of
circuits, one group reserved for one\(hyway operation and the other group
used for both\(hyway operation. In this case, when all one\(hyway circuits
are busy, the call can overflow to the both\(hyway circuit group.
.sp 9p
.RT
.PP
\fB4\fR
When congestion occurs at a transit exchange, arrangements can be made
in some signalling systems, at the outgoing international exchange on receipt
of a busy\(hyflash signal or a congestion signal sent by the transit
exchange, to reroute the call automatically from the outgoing international
exchange over another route. This process is called \fIre\(hyrouting\fR
. The use of
rerouting is not envisaged in the International Routing Plan.
.sp 9p
.RT
.sp 1P
.LP
.
.sp 9p
.RT
.PP
\fB5\fR
When a difficulty is encountered in the setting\(hyup of a
connection\ \(em\ such as double seizure on both\(hyway circuits or error
detection\ \(em\ arrangements can be provided to make another attempt to
set up
.sp 9p
.RT
.LP
the connection for that call from the point where the first attempt took
place. This process is called \fIautomatic repeat attempt\fR .
.PP
An automatic repeat attempt may take place:
.LP
    \(em
    on the same circuit; or
.LP
    \(em
    on another circuit of the same group of circuits; or
.LP
    \(em
    on a circuit in another group of
circuits.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.13\fR
.FS
This Recommendation is also included in the
E\ Series Recommendations under the number E.171
.FE
.RT
.sp 2P
.sp 1P
.ce 1000
\fBINTERNATIONAL\ TELEPHONE\ ROUTING\ PLAN\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.13''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.13    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
1.1
This Plan describes an international telephone routing plan
designed to enable Administrations to select routings for their traffic
which will result in a satisfactory connection between any two telephone
stations in the world. The Plan relates to automatic and semi\(hyautomatic
telephone traffic from fixed and mobile (both land and maritime) stations.
The Plan is necessary to allow the objective to be achieved with maximum
economy by the most
efficient use of costly circuits and switching centres while safeguarding
the grade of service and quality of transmission.
.sp 9p
.RT
.PP
1.2
The Plan is one of the basic CCITT Recommendations which
influence many other Recommendations, for example the transmission plan
(Recommendation\ G.101).
.PP
1.3
In practice the large majority of
international telephone
traffic
is routed on
direct circuits
(i.e.\ no intermediate
switching point)
between International Switching Centres (ISCs). It should be noted that
it is the rules governing the routing of connections consisting of a number
of
circuits in tandem that this Recommendation primarily addresses. These
connections have an importance in the network because:
.LP
    \(em
    they are used as
alternate routes
to carry
overflow
traffic
in busy periods to increase network efficiency,
.LP
    \(em
    they can provide a degree of service protection in the event
of failures of other routes,
.LP
    \(em
    they can facilitate
network management
when
associated with ISCs having temporary alternative routing capabilities.
.PP
1.4
This Plan replaces the previous one established in 1964 and it
can be applied to all existing switching equipment and signalling systems
and is intended to be flexible enough to incorporate new switching and
signalling developments.
.PP
Nevertheless, it is recognized that the Plan, which is
complementary to the plan contained in Recommendation\ E.172, will have to be
reviewed and revised to take account of developments in telecommunications.
.PP
1.5
The Plan accomplishes its basic purposes unconstrained by, and
requiring no changes to, the
numbering plan
, the rules for charging the calling
subscriber and the rules for the apportionment of charges (
international
accounting
).
.sp 2P
.LP
\fB2\fR     \fBPrinciples\fR
.sp 1P
.RT
.PP
2.1
The Plan preserves the freedom of Administrations:
.sp 9p
.RT
.LP
    a)
    to route their originating traffic directly or via any
transit Administration they choose;
.LP
    b)
    to offer transit capabilities to as wide a range of
destinations as possible in accordance with the guidelines which
it provides.
.PP
2.2
The Plan provides guidance on possible international routings.
Any routing chosen must be subject to agreements between the Administrations
involved before implementation.
.PP
The freedom of Administrations to choose the routing of their
terminal and transit traffic may be limited by technical, commercial and
administrative considerations including:
.LP
    \(em
    the capability of precisely measuring traffic volumes
for accounting purposes,
.LP
    \(em
    the need to maximize route profitability,
.LP
    \(em
    the desirability of simplicity in international
accounting.
.PP
2.3
The governing features of this Plan are:
.LP
    a)
    it is not hierarchical;
.LP
    b)
    Administrations are free to offer whatever transit
capabilities they wish, providing they conform to this
Recommendation;
.LP
    c)
    direct traffic should be routed over final (fully provided)
or high usage circuit groups;
.bp
.LP
    d)
    no more than 4 international circuits in tandem should be
involved between the originating and terminating ISCs;
.LP
    e)
    advantage should be taken of the non\(hycoincidence of
international traffic by the use of alternative routings to
effect circuit economies and provide route diversity
(Recommendation\ E.523);
.LP
    f
)
    the routing of transit switched traffic should be
planned to avoid the possibility of
circular routings
;
.LP
    g)
    when a circuit group has both terrestrial and satellite
circuits the choice of routing should be governed by:
.LP
    \(em
    the guidance given in Recommendation\ G.114,
.LP
    \(em
    the number of satellite circuits likely to be utilized in the
overall connection,
.LP
    \(em
    the circuit which provides the better transmission and
overall service quality
.FS
When there are circuits between
ISCs using different
geographical routes with different transmission means, preference should be
given to those circuits which provide better transmission quality as
long as this is not conflicting with any other part of this
Recommendation.
.FE
;
.LP
    h)
    the inclusion of two or more satellite circuits in the same
connection should be avoided in all but exceptional cases.
Annex\ A contains details on the effects of satellite
communications.
.LP
    Recommendation\ Q.14 defines the means to control
the number of satellite links in an international telephone
connection;
.LP
    i)
    both originating and transit traffic should be routed over
the minimum number of international circuits in tandem unless
this is in conflict with one of the above\(hymentioned features.
.sp 2P
.LP
\fB3\fR     \fBNumber of circuits in tandem\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIInternational circuits\fR
.sp 9p
.RT
.PP
For reasons of transmission quality as well as the minimization of post\(hydialling
and answer signal delays and the avoidance of signalling
time\(hyouts, it is desirable to limit the number of
circuits in tandem
in an overall
connection (Recommendations\ G.101 and G.114, \(sc\ 1). Recommendation\
Q.7 gives
signalling considerations on tandem routings.
.PP
In this Plan the number of international circuits in a connection is limited
to a maximum of\ 4. (See \(sc\ 3.3.2 for a special case with multiple ISCs
within the area of one Administration.)
.RT
.sp 1P
.LP
3.2
    \fINational circuits\fR
.sp 9p
.RT
.PP
Limitations in the national section of the international connection are
given in Recommendation\ G.101, \(sc\ 3.1.
.PP
Many Administrations have fulfilled the requirements of
Recommendation\ G.101, \(sc\ 3.1 by establishing a national routing plan
based on a theoretical final route structure with low\(hyloss\(hyprobability
circuit groups
between switching centres of different categories.
.PP
The actual structure in many cases involves direct routes which bypass
the theoretical final route or part of it, the structure being rather similar
to the former international routing plan.
.PP
\fINote\fR \ \(em\ The former international routing plan was last published
in the \fIOrange Book\fR , Volume\ II.2, Recommendation\ E.171.
.RT
.sp 2P
.LP
3.3
    \fIMultiple ISCs in a country\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.1
    \fIIn the originating or terminating country\fR
.sp 9p
.RT
.PP
Administrations may find it advantageous for technical or economic reasons,
or for the protection of service, or to use multiple
originating and/or terminating
.PP
ISCs. In some cases this could result in a routing for a call which includes
a circuit between two ISCs in the originating or terminating country. Such
circuits may be regarded as national circuits in applying this Plan and
as such should be included in the national link allocation (see
Recommendation\ E.172).
.bp
.RT
.sp 1P
.LP
3.3.2
    \fIIn a transit country\fR
.sp 9p
.RT
.PP
Some Administrations may find it desirable to route transit traffic between
two ISCs in their own country. In this case the allowable number of
international circuits in tandem may be increased from 4 to 5 (this is
the only exception to \(sc\ 3.1 above).
.RT
.sp 2P
.LP
\fB4\fR     \fBRouting techniques\fR
.sp 1P
.RT
.PP
With advanced SPC exchanges and enhanced signalling systems new
routing techniques are emerging (see Recommendation\ E.170). These techniques
can be used nationally as found necessary by individual Administrations or
bilaterally between Administrations.
.RT
.sp 2P
.LP
\fB5\fR     \fBBasic routing rules\fR
.sp 1P
.RT
.sp 1P
.LP
5.1
    \fIOriginating traffic\fR \v'3p'
.sp 9p
.RT
.PP
5.1.1
Originating traffic at an ISC may be offered to any route,
taking into account all factors in this Plan, and the following guiding
principles, to ensure good overall service quality for the call
connection:
.LP
    a)
    an originating ISC should first select the direct route to
the destination, if it is available;
.LP
    b)
    if the direct route is unavailable (because all circuits are
busy or because no direct route is provided) then the
originating ISC may select the route to any transit ISC which
conforms to the principles in \(sc\ 5.2 below. An agreement should
first be reached between the originating, terminating and
transit Administrations involved, for the use of this transit
route.
.PP
5.1.2
A circuit group may be designed as a
high usage circuit
group
(see Recommendation\ E.522) or as a
final circuit group
(see   Recommendations\ E.520 or\ E.521).
.PP
5.1.3
Examples of some possible routings are given in Annex\ B.
.sp 2P
.LP
5.2
    \fITransit traffic\fR
.sp 1P
.RT
.sp 1P
.LP
5.2.1
    \fITwo and three international circuits in tandem\fR
.sp 9p
.RT
.LP
.PP
An Administration offering transit capabilities may do so without special
arrangements or restrictions to all destinations served by:
.RT
.LP
    a)
    direct circuit groups, or
.LP
    b)
    switching via an additional transit ISC that has a direct
final circuit group to the destination, or
.LP
    c)
    a combination of a) and b).
.PP
Examples of two and three international circuits in tandem are
given in b) to e) of Figure\ B\(hy1/Q.13.
.sp 1P
.LP
5.2.2
    \fIFour international circuits in tandem\fR
.sp 9p
.RT
.PP
If an Administration has provided a routing for its originating
traffic that involves a maximum of 3 international circuits in tandem to a
destination, it may offer this capability to other Administrations for
transit traffic. In this case, these other Administrations must not themselves
offer
transit capabilities to the same destination as this would exceed
4\ international circuits in tandem.
.PP
Examples of 4 international circuits in tandem are given in f
)   and g) of Figure\ B\(hy1/Q.13.
.RT
.LP
.PP
5.2.3
A circuit group may be designed as a high usage circuit group
(see Recommendation\ E.522) or as a final circuit group (see
Recommendations\ E.520 or\ E.521).
.sp 1P
.LP
5.2.4
    \fISpecial arrangements\fR
.sp 9p
.RT
.PP
Some Administrations may route transit traffic differently from
their own originating traffic to a given destination. These routings will in
some cases involve offering transit traffic to direct routes, but not to
overflow routes via alternative transit ISCs. On the other hand, originating
traffic offered to the same direct routes is given access to overflow routes.
.bp
.PP
This arrangement may be used for:
.RT
.LP
    a)
    limiting the number of international circuits in tandem for
transit calls, yet allowing originating calls up to the maximum
of 4 international circuits in tandem.
.LP
    b)
    preventing transit traffic from overflowing from direct
routes, to minimize subsequent transit charges.
.LP
    c)
    minimizing transmission propagation delay for transit
calls.
.PP
In such cases, care must be exercised to avoid grade of service
problems. Consideration should be given to
:
.LP
    i)
    the analysis of
24\(hyhour traffic profiles
;
.LP
    ii)
    the exchange of network status information between
Administrations.
.PP
In implementing such arrangements, Administrations offering transit capability
should provide the necessary information on traffic profiles and
network status capabilities. Originating Administrations should evaluate
such information taking into account transmission costs, and call completion
factors. (See Recommendations\ E.522 and E.523.)
.PP
Examples of some routings involving special arrangements are given in a)
and b) of Figure\ B\(hy2/Q.13.
.RT
.sp 2P
.LP
\fB6\fR     \fBList of international transit capabilities\fR
.sp 1P
.RT
.PP
6.1
To aid in the application of transit routings, a list of
international transit capabilities via an Administration is desirable.
.sp 9p
.RT
.PP
6.2
Each Administration that wishes to offer transit capabilities
should develop and distribute its own list.
.LP
.PP
6.3
Annex C details the essential information that should be
contained in a list of international transit capabilities plus additional
information that might also be distributed by Administrations offering
transit capabilities or might be requested by Administrations seeking transit
routings.
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.13)
.sp 9p
.RT
.ce 0
.ce 1000
\fBThe\fR
\fBeffects of satellite communication\fR
.sp 1P
.RT
.ce 0
.PP
A.1
The use of
geostationary satellite circuits
does not call for
any alteration in the basic principles and rules of this Plan. However,
because of the mean propagation time on satellite circuits, the precautions
specified in Recommendation\ G.114 must be observed.
.sp 1P
.RT
.PP
A.2
At originating ISCs, calls which are to be transit switched
at another ISC and likely to use a
satellite circuit
elsewhere in the   connection should be routed using
terrestrial circuits
from the
originating ISC, if available.
.PP
A.3
At ISCs arrangements should be made to guard against the
inclusion of two or more satellite circuits in the same connection in all
but exceptional cases. (See \(sc\ A.6 below.)
.LP
.PP
Avoidance of two or more satellite circuits is made more feasible when
the signalling systems used have signals indicating whether the connection
already includes a satellite circuit. (See Recommendation\ Q.7.)
.PP
In those cases when the signalling system does not provide the
necessary information, bilateral agreement should be sought between the
Administrations involved to establish a special circuit group on which
traffic can be routed that has already one or more satellite circuits in
the
connections. (See Figure\ A\(hy1/Q.13.)
.RT
.PP
A.4
The use of
national satellite circuits
for
international
originating and terminating connections should be avoided to the extent
possible.
.PP
A.5
Connections (originating, terminating or transit) to and from
the
international maritime mobile satellite service should not, so far as possible,
comprise other satellite circuits. In the shore\(hyto\(hyship direction
the
country
codes
allocated to the
maritime mobile satellite service
should be  analysed in order to apply this provision.
.bp
.PP
A.6
There will be cases when the above provisions cannot be
fully applied. These are:
.LP
    a)
    routing to and from Administrations with exclusive or almost
exclusive use of satellite circuits for international service;
.LP
    b)
    routings containing more than one international circuit in
tandem in which the signalling systems used on one or more of
the circuits in the connection does not provide nature of
circuit indicators, or when no agreement can be reached with
respect to the special circuit group;
.LP
    c)
    when no other reliable means of communication is available;
then two
or more satellite circuits in one connection may be used.
.PP
\fINote\fR \ \(em\ When it is unavoidable to use more than one satellite
circuit in an international connection, attention to echo control as indicated
in
Notes\ 2 and\ 3 of Recommendation\ G.114 should be exercised.
.PP
A.7
Control methods for echo suppressors
.FS
Echo cancellers are
also now in use.
.FE
are given in Recommendation\ Q.115.
.PP
A.8
The use of demand assigned satellite systems in international
telephony (e.g.\ SPADE) is governed by the same general and special
considerations given above. The entirety of a demand assigned
system and its access circuits may be regarded as a single international
circuit for transmission purposes and as a transit ISC for routing purposes.
.LP
.rs
.sp 31P
.ad r
\fBFigure A\(hy1/Q.13, p. MONTAGE:\fR \
\(em 2cic.
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation Q.13)
.sp 9p
.RT
.ce 0
.ce 1000
\fBExamples of possible routings and special arrangements\fR
.sp 1P
.RT
.ce 0
.LP
.rs
.sp 49P
.ad r
\fBFigure B\(hy1/Q.13, p. 4\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure B\(hy1/Q.13, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX C
.ce 0
.ce 1000
(to Recommendation Q.13)
.sp 9p
.RT
.ce 0
.ce 1000
\fBList of international transit capabilities\fR
.sp 1P
.RT
.ce 0
.LP
C.1
    \fIEssential information on international transit capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
C.1.1
    \fIUse\fR
.sp 9p
.RT
.PP
Every Administration offering transit capabilities should compile and distribute
a list including at least the information shown below in order to enable
other Administrations to make a first choice of possible transit
routings.
.RT
.sp 1P
.LP
C.1.2
    \fISuggested format\fR
.sp 9p
.RT
.PP
See Figure C\(hy1/Q.13.
.RT
.LP
.rs
.sp 32P
.ad r
\fBFigure C\(hy1/Q.13 [T1.13], p. (\*`a traiter comme tableau MEP)\fR
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.bp
.sp 1P
.LP
C.1.3
    \fIInstructions for completing the list\fR \v'3p'
.sp 9p
.RT
.LP
    \fIItem A \(em Administration or RPOA\fR
.LP
    Enter the name of the Administration or recognized private
operating agency responsible for preparing this list.
\v'3p'
.LP
    \fIItem B \(em Date of information\fR
.LP
    Enter the date for which the information below applies.
\v'3p'
.LP
    \fIItem C \(em Address for inquiries\fR
.LP
    Enter the name, address, telex and telephone number of the
organizational unit or individual who will respond to enquiries
concerning transit capabilities.
\v'3p'
.LP
    \fIColumn 1 \(em Destination country or Administration\fR
.LP
    Enter the name of the destination country or Administration.
These destinations should be listed alphabetically within each World
Zone grouping. Only those destinations for which this ISC can carry
automatic transit traffic should be listed in this column. All
destinations for which transit capabilities are being offered should
be listed.
\v'3p'
.LP
    \fIColumn 2 \(em Transit ISCs\fR
.LP
    Enter the name or location that identifies the international
switching centre(s) that has automatic transit access to the
destinations in column\ 1. For multiple transit ISCs within the same
Administration list each ISC in sequence.
\v'3p'
.LP
    \fIColumn 3 \(em \fI
.LP
    Enter whether the transit route to the destination is either:
.LP
    DIR\ \(em
    If \*Qdirect\*U to the terminating ISC.
.LP
    IND\ \(em
    If \*Qindirectly\*U first routed via a further transit
ISC. The name of the further transit ISC should also be
entered.
.LP
    ALT\ \(em
    If either the \*QDIR\*U or \*QIND\*U route automatically
overflows to an \*Qalternative\*U transit ISC. The name of the
alternative transit ISC should also be entered.
\v'3p'
.LP
    \fIColumn 4 \(em Terrestrial possible\fR
.LP
    Enter YES if at least some transit calls to this destination can
obtain an all\(hyterrestrial route beyond the transit ISC.
.LP
    Enter NO if all transit calls to this destination will use a
satellite circuit in the route beyond the transit ISC.
\v'3p'
.LP
    \fIColumn 5 \(em Special restrictions\fR
.LP
    Enter YES if the transit traffic is subject to overflow
restrictions (see \(sc\ 5.2.4) that might
affect the grade of service achieved.
.LP
    Enter NO if no such restrictions apply.
.sp 2P
.LP
C.2
    \fIAdditional information on international transit capabilities\fR
.sp 1P
.RT
.sp 1P
.LP
C.2.1
    \fIUse\fR
.sp 9p
.RT
.PP
The information shown below is of value in comparing and selecting possible
transit routes.
Administrations offering transit capabilities might choose to compile
and distribute some or all of these items with their basic list of
international transit capabilities. Alternatively, Administrations selecting
a transit route may use the items shown below as a basis for enquiries.
.bp
.RT
.sp 1P
.LP
C.2.2
    \fIFormat\fR
.sp 9p
.RT
.PP
No particular format is suggested for this information. However, it is
recommended that both transit and originating Administrations use the
terminology and definitions given below.
.PP
If changes are planned in any of the items the change should be
indicated together with the effective date.
.RT
.sp 1P
.LP
C.2.3
    \fIDetails of additional items\fR \v'3p'
.sp 9p
.RT
.LP
    \fItraffic profile\fR
.LP
    Under this item the busy hour traffic on the circuit group used
beyond the transit ISC should be given together with an indication of
the traffic variations during the day. Preferably the variations
should be presented in the form of hourly traffic distributions as
shown in Recommendation\ E.523.
\v'3p'
.LP
    \fITransit charges\fR
.LP
    Under this item details of the applicable transit charges should
be given.
\v'3p'
.LP
    \fIGrade of service\fR
.LP
    The grade of service normally experienced to the destination
should be given. This may be supplemented by time of day variations.
If overflow restrictions for transit traffic apply, the information
must include at least the hours during which the grade of service is
1% or better.
\v'3p'
.LP
    \fICircuit quantities\fR
.LP
    The total circuit quantities available and subtotals for each type
of transmission medium should be given.
.LP
    If indirect routing is used this information should be given for
the circuit groups to the next transit ISC.
\v'3p'
.LP
    \fISignalling\fR
.LP
    The signalling systems used for the onward routing from the
transit ISC should be listed.
\v'3p'
.LP
    \fIRestoration\fR
.LP
    This item should outline the restoration policy in the case of a
major transmission facility outage in the onward routing.
\v'3p'
.LP
    \fIEcho control\fR
.LP
    This item should list the echo control capabilities at the transit
ISC.
\v'3p'
.LP
    \fIPrevention of two or more satellite circuits in tandem\fR
.LP
    This item should explain the capabilities at the transit ISC for
preventing the connection of two satellite circuits in tandem.
.LP
    Where indirect routing is used, this item should also identify
whether a specially designated circuit group has been agreed to allow
prevention of two satellite circuits in the same connection at a
subsequent ISC.
.LP
.rs
.sp 11P
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.14\fR
.RT
.sp 2P
.ce 1000
\fBMEANS\ TO\ CONTROL\ THE\ NUMBER\ OF\ SATELLITE\ LINKS\ IN\ AN\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.14''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.14    %'
.ce 0
.sp 1P
.ce 1000
\fBINTERNATIONAL\ TELEPHONE\ CONNECTION\fR
.ce 0
.sp 1P
.PP
Recommendation Q.41 states that connections with a mean one\(hyway
propagation time in excess of 400\ ms should be avoided apart from exceptional
circumstances. Means should therefore be provided in international switching
centres to prevent the multiple connection of satellite links whenever
possible.
.sp 1P
.RT
.PP
The following principles should apply in controlling such
connections:
.LP
    a)
     If an exchange can determine the prior connection of a satellite link
in a connection by:
.LP
    \(em
    information relating to the incoming circuit,
.LP
    \(em
    receipt of the Nature of Circuit Indicator: \*Qsatellite
included\*U,
.LP
     the exchange should forward the call on a terrestrial circuit. A satellite
circuit may be used in the following exceptional circumstances:
.LP
    \(em
    where no terrestrial circuits are provided to the required
destination,
.LP
    \(em
     where only a few terrestrial circuits are provided on a final route and
the loss of quality of service of a double satellite
connection (echo problems and \*Qdouble\(hytalk\*U) is preferable to the
degradation of grade of service that would be caused by the
exclusion of the satellite circuits.
.LP
    A Nature of Circuit Indicator \*Qsatellite included\*U should be
forwarded on the outgoing circuit where possible.
.LP
    b)
    If an exchange can determine by an analysis of the call destination   that
a satellite link will definitely or most probably be included at a later
point in the call connection, it should give priority to terrestrial links
in its
outgoing circuit selection. Special attention is drawn to the analysis of
country code\ 87S which may indicate that the call will include a maritime
satellite link. (For the use of the S\ digit, see Recommendations\ E.210\ [1]
and E.211\ [2].)
.
.PP
The above principles apply to all international exchanges and to all national
exchanges which may connect to circuits via domestic satellite
systems.
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIShip station identification for VHF/UHF and\fR
\fImaritime mobile\(hysatellite services\fR , Vol.\ II, Rec.\ E.210.
.LP
[2]
    CCITT Recommendation \fISelection procedures for VHF/UHF\fR
\fImaritime mobile services\fR , Vol.\ II, Rec.\ E.211.
.LP
.rs
.sp 16P
.LP
.bp
.ce 1000
ANNEX A
.ce 0
.ce 1000
(to Recommendation Q.14)
.sp 9p
.RT
.ce 0
.ce 1000
\fBCall processing logic \(em Nature of circuit indications\fR
.sp 1P
.RT
.ce 0
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy50650, p. 7\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE:\ \fR PAGE BLANCHE = PAGE PAIRE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 4
.ce 0
.sp 1P
.ce 1000
\fBGENERAL\ RECOMMENDATIONS\ RELATIVE\ TO\ SIGNALLING\ AND\ SWITCHING\
SYSTEMS\fR
.ce 0
.sp 1P
.ce 1000
\fB(NATIONAL\ OR\ INTERNATIONAL)\fR
.ce 0
.sp 1P
.IP
\fB4.1\fR     \fBPower limits of signals of a signalling system\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.15\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBNOMINAL\ MEAN\ POWER\ DURING\ THE\ BUSY\ HOUR\fR
.FS
This
Recommendation is, basically, an extract of Recommendation\ G.223 [1].
.FE
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.15''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.15    %'
.ce 0
.sp 1P
.ce 1000
\fI(Remark of Recommendation\ G.222, Volume\ III of the\fR  | Red Book,
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIamended at Geneva, 1964; further amended)\fR
.ce 0
.sp 1P
.LP
    \fBNominal \fR \fBmean power during the busy hour\fR
.sp 1P
.RT
.PP
To simplify calculations when designing carrier systems on cables or radio
links, the CCITT has adopted a \fIconventional\fR value to represent the
\fImean absolute power level\fR (at a zero relative level point) of the
speech plus signalling currents, etc., transmitted over a telephone channel
in one
direction of transmission during the busy hour.
.PP
The value adopted for this mean absolute power level corrected to a
zero relative level point is \(em15\ dBm0 (mean power\ =\ 31.6\ microwatts);
this is the mean with time and the mean for a large batch of circuits.
.PP
\fINote\ 1\fR \ \(em\ This conventional value was adopted by the CCIF in 1956
after a series of measurements and calculations had been carried out by
various Administrations between 1953 and 1955. The documentation assembled
at the time is indicated in\ [2]. The adopted value of about 32\ microwatts
was based on the following assumptions:
.RT
.LP
    i)
    mean power of 10\ microwatts for all signalling and tones
(Recommendation\ Q.15\ [2], gives information concerning
the apportionment on an energy basis of signals and tones);
.LP
    ii)
    mean power of 22\ microwatts for other currents,
namely:
.LP
    \(em
    speech currents, including echoes, assuming a mean
activity factor of 0.25 for one telephone channel
in one direction of transmission;
.LP
    \(em
    carrier leaks (see Recommendations\ G.232, \(sc\ 5\ [3];
G.233, \(sc\ 11\ [4]; G.235, \(sc\ 5\ [5]); and the Recommendations cited
in [6]
and\ [7];
.bp
.LP
    \(em
     telegraph signals, assuming that few telephone channels are used for
VF telegraphy systems (output signal power
135\ microwatts (the Recommendation cited in\ [8])) or phototelegraphy
(amplitude modulated signal with a maximum signal power of
about 1\ milliwatt (the Recommendation cited in\ [9])).
.LP
On the other hand, the power of pilots in the load of modern carrier
systems has been treated as negligible.
.LP
The reference to \*Qthe busy hour\*U in \(sc\ 1 is to indicate that the
limit (of \(em15\ dBm0) applies when transmission systems and telephone
exchanges are at their busiest so that the various factors concerning occupancy
and
activity of the various services and signals are to be those appropriate to
such busy conditions.
.LP
It is not intended to suggest that an integrating period of one hour may
be used in the specification of the signals emitted by individual devices
connected to transmission systems. This could lead to insupportably high
short\(hyterm power levels being permitted which give rise to interference for
durations of significance to telephony and other services.
.PP
\fINote\ 2\fR \ \(em\ The question of reconsidering the assumptions leading
to this conventional value arose in 1968 for the following reasons:
.LP
    \(em
     changes in the r.m.s. power of speech signals, due to the use of more
modern telephone sets, to a different transmission plan,
and perhaps also to some change in subscriber habits;
.LP
    \(em
    change in the mean activity factor of a telephone channel
due, \fIinter alia\fR , to different operating methods;
.LP
    \(em
     increase in the number of VF telegraphy bearer circuits and sound\(hyprogramme
circuits;
.LP
    \(em
    introduction of circuits used for data transmission, and
rapid increase in their number.
.LP
During several Study Periods these points have been under study
and various Administrations carried out measurements of speech signal power
and loading of carrier systems. The results are shown in Supplement No.\
5. These
results indicate that there is no sufficiently firm information to justify
an alteration to the conventional mean value of \(em15\ dBm0 (32\ \(*mW0)
for the
long\(hyterm mean power level per channel.
.LP
Indeed, the steps envisaged by Administrations to control and reduce the
levels of non\(hyspeech signals indicate a tendency to limit the effect of
the increase in the non\(hyspeech services.
.LP
As regards the subdivision of the 32\ \(*mW into 10\ \(*mW signalling and
tones and 22\ \(*mW speech and echo, carrier leaks, and telegraphy, again
there is no evidence which would justify proposals to alter this subdivision.
.LP
As a general principle, it should always be the objective of
Administrations to ensure that the \fIactual\fR load carried by transmission
systems does not significantly differ from the \fIconventional\fR value
assumed in the design of such systems.
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIAssumptions for the calculation of noise on\fR
\fIhypothetical reference circuits for telephony\fR , Vol.\ III,
Rec.\ G.223.
.LP
[2]
     \fICCITT collected documents on the volume and power of speech currents\fR
\fItransmitted over international telephone circuits\fR , Blue Book, Vol.\
III,
Part\ 4, Annex\ 6, ITU, Geneva,\ 1965.
.LP
[3]
    CCITT Recommendation \fI12\(hychannel terminal equipments\fR , Vol.\ III,
Rec.\ G.232, \(sc\ 5.
.LP
[4]
    CCITT Recommendation \fIRecommendations concerning translating\fR
\fIequipments\fR , Vol.\ III, Rec.\ G.233, \(sc\ 11.
.LP
[5]
    CCITT Recommendation \fI16\(hychannel terminal equipments\fR , Vol.\ III,
Rec.\ G.235, \(sc\ 5.
.LP
[6]
    CCITT Recommendation \fICharacteristics of group links for the\fR
\fItransmission of wide\(hyspectrum signals\fR , Vol.\ III,
Rec.\ H.14, \(sc\ 2.3.
.LP
[7]
    CCITT Recommendation \fICharacteristics of supergroup links for the\fR
\fItransmission of wide\(hyspectrum signals\fR , Vol.\ III,
Rec.\ H.15, \(sc\ 2.3.
.LP
[8]
    CCITT Recommendation \fIBasic characteristics of telegraph equipments\fR
\fIused in international voice\(hyfrequency telegraph systems\fR , Vol.\ III,
Rec.\ H.23, \(sc\ 1.2.
.LP
[9]
    CCITT Recommendation \fIPhototelegraph transmission on telephone\(hytype\fR
\fIcircuits\fR , Vol.\ III, Rec.\ H.41, \(sc\ 2.3.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.16\fR  |
.FS
This Recommendation also appears as
Recommendation\ G.224\ [1].
.FE
.RT
.sp 2P
.ce 1000
\fBMAXIMUM\ PERMISSIBLE\ VALUE\ FOR\ THE\ ABSOLUTE\ POWER\ LEVEL\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.16''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.16    %'
.ce 0
.sp 1P
.ce 1000
\fBOF\ A\ SIGNALLING\ PULSE\fR
.ce 0
.sp 1P
.PP
The CCITT recommends that, for crosstalk reasons, the absolute power
level of each component of a short duration signal should not exceed the
values given in Table\ 1/Q.16.
.sp 1P
.RT
.PP
The values given in this table result from a compromise between the characteristics
of various existing channel filters.
.ce
\fBH.T. [T1.16]\fR
.ce
TABLE\ 1/Q.16
.ce
\fBMaximum permissible value of power at a zero relative\fR
.ce
\fBlevel point\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(80p) | cw(74p) | cw(74p) .
Signalling frequency (Hz)     {
Maximum permissible power
for a signal at a zero relative
level point (microwatts)
 }     {
Corresponding absolute
power level. Decibels
referred to 1 mW (dBm0)
 }
_
.T&
cw(80p) | cw(74p) | cw(74p) .
\ 800    750     \(em1
.T&
cw(80p) | cw(74p) | cw(74p) .
1200    500     \(em3
.T&
cw(80p) | cw(74p) | cw(74p) .
1600    400     \(em4
.T&
cw(80p) | cw(74p) | cw(74p) .
2000    300     \(em5
.T&
cw(80p) | cw(74p) | cw(74p) .
2400    250     \(em6
.T&
cw(80p) | cw(74p) | cw(74p) .
2800    150     \(em8
.T&
cw(80p) | cw(74p) | cw(74p) .
3200    150     \(em8
_
.T&
lw(228p) .
 {
If the signals are made up of two different frequency components,
transmitted simultaneously, the maximum permissible values for the
absolute power levels are 3\ decibels below the above figures
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTable\ 1/Q.16 [T1.16] p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
    \fBReference\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIMaximum permissible value for the absolute\fR
\fIpower level (power referred to one milliwatt) of a signalling pulse\fR ,
Vol.\ III, Rec.\ G.224.
\v'1P'
.IP
\fB4.2\fR \fBSignalling in the speech frequency band and outside the speech\fR
\fBfrequency band\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.20\fR
.RT
.sp 2P
.ce 1000
\fBCOMPARATIVE\ ADVANTAGES\ OF\ \*QIN\(hyBAND\*U\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.20''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.20    %'
.ce 0
.sp 1P
.ce 1000
\fBAND\ \*QOUT\(hyBAND\*U\ SYSTEMS\fR
.ce 0
.sp 1P
.PP
Signalling over telephone circuits may be effected \fIin\fR  | the frequency
band used for speech (\*Qin\(hyband\*U signalling), or \fIoutside\fR it
(\*Qout\(hyband\*U
signalling). In the latter case, the same channel carries both the signalling
and speech frequency bands, the signalling band being separate from the
speech band, and signalling equipment is an integral part of the carrier
system.
.bp
.sp 1P
.RT
.PP
In a further type of out\(hyband signalling, a circuit, not used for
speech, can be used to effect the signalling requirements of a number of
speech circuits. This may be termed \*Qseparate channel signalling\*U.
The separate
channel may be:
.LP
    a)
    a channel in a carrier system used to effect the signalling
requirements of the remaining channels in the same carrier
system which are used for speech, signalling equipment
being an integral part of the carrier system: this may be
termed \*Qbuilt\(hyin separate channel signalling\*U;
.LP
    b)
     completely separate, in which case signalling equipment is not an integral
part of the carrier system; this may be termed
\*Qcompletely separate channel signalling\*U.
.sp 2P
.LP
\fB1\fR     \fBAdvantages of in\(hyband signalling\fR
.sp 1P
.RT
.PP
1.1
In\(hyband signalling can be applied to any type of line plant. The application
of out\(hyband signalling, and built\(hyin separate channel signalling,
is limited to carrier systems.
.sp 9p
.RT
.PP
1.2
Through\(hysignalling can be employed at transit points, and at carrier
system terminals when a telephone circuit comprises two or more carrier
links. No direct current repetition and thus no delay and no distortion
of signals
arises at such points. Out\(hyband signalling and built\(hyin separate channel
signalling require a direct current repetition at such points.
.PP
1.3
Replacement of a faulty line section is easy. In the case of
completely separate channel signalling, replacement of a faulty line section
is based on security arrangements.
.PP
1.4
It is impossible to set up a connection on a faulty speech path. In
the case of completely separate channel signalling, a continuity check
of the speech path is required.
.PP
1.5
The full bandwidth of the speech channel is available for
signalling. This facilitates the use of more than one signalling frequency.
Normally the full bandwidth permits faster signalling than with a smaller
signalling bandwidth. With in\(hyband signalling, realization of this advantage
is limited to those signals not required to be protected against signal
imitation due to speech currents.
.sp 2P
.LP
\fB2\fR     \fBAdvantages of out\(hyband signalling\fR
.sp 1P
.RT
.PP
2.1
Relative freedom from disturbances due to speech currents;
freedom from disturbances due to echo\(hysuppressors; freedom from disturbances
which might arise from connections to other signalling systems. With in\(hyband
signalling it is necessary to take steps to guard against such disturbances.
.sp 9p
.RT
.PP
2.2
Possibility of signalling, during the setting\(hyup of the call, by
either discontinuous or continuous transmission, and the possibility of
transmitting those signals during speech. Signalling during speech is not
compatible with in\(hyband signalling.
.PP
2.3
Simplicity of terminal equipment due to \(sc\ 2.1 above and to the
possibility of continuous signalling.
.PP
Out\(hyband signalling (where the same channel carries both speech and
signalling) also has the advantage of \(sc\ 1.3 of in\(hyband signalling.
.PP
Built\(hyin separate channel signalling has the advantages of \(sc\(sc\
2.1, 2.2 and\ 2.3 of out\(hyband, and the advantage of \(sc\ 1.3 of in\(hyband
signalling.
.PP
Completely separate channel signalling has the advantages of \(sc\(sc\ 2.1
and\ 2.2
of out\(hyband signalling and, compared with out\(hyband signalling and
built\(hyin
separate channel signalling, has the additional advantages that no direct
current repetition is necessary, and no distortion of signals arises, at
carrier system terminals when a circuit comprises two or more carrier
links.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ Q.21\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSYSTEMS\ RECOMMENDED\ FOR\ OUT\(hyBAND\ SIGNALLING\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.21''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.21    %'
.ce 0
.sp 1P
.PP
When Administrations wish to make mutual agreements to use out\(hyband
signalling systems, the CCITT considers it desirable, from the transmission
viewpoint, for them to use one of the types of signalling systems (outside
the speech band) defined in the following annexes:
.sp 1P
.RT
.LP
    Annex\ A:\ Normal carrier systems with 12\ channels per group;
.LP
    Annex\ B
:\ Carrier systems with 8\ channels per group.
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.21)
.sp 9p
.RT
.ce 0
.ce 1000
\fBOut\(hyband signalling systems for\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBcarrier systems with 12 channels per group\fR
.ce 0
.PP
(The signal levels are quoted in terms of absolute power level at a
zero relative level point in dBm0.)
.sp 1P
.RT
.sp 1P
.LP
A.1
    \fIType I\fR \ (discontinuous signals)
.sp 9p
.RT
.LP
    Frequency: virtual carrier (zero frequency).
.LP
    Level: high,
.LP
    for example \(em3\ dBm0.
.sp 1P
.LP
A.2
    \fIType II\fR
.sp 9p
.RT
.LP
\fR     1)
    (discontinuous signals)
.LP
    Frequency: 3825\ Hz.
.LP
    Level: high,
.LP
    for example \(em5\ dBm0.
\v'2p'
.LP
    2)
    (semi\(hycontinuous signals)
.LP
    Frequency: 3825\ Hz
.LP
    Level: low,
.LP
    for example \(em20\ dBm0.
.PP
A.3
The \fIType\ I\fR signalling system is compatible with only those group
and supergroup reference pilots having a displacement from the virtual
carrier frequency (zero frequency) of 140\ Hz.
.PP
\fITypes\ II\(hy1 and II\(hy2\fR are compatible with only those group and
supergroup reference pilots having a displacement from the virtual carrier
frequency (zero frequency) of 80\ Hz.
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Recommendation Q.21)
.sp 9p
.RT
.ce 0
.ce 1000
\fBOut\(hyband signalling systems for\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBcarrier systems with 8\ channels per group\fR
.ce 0
.PP
[The signal levels are quoted in terms of absolute power level
(reference\ 1\ mW) at a zero relative level point.]
.sp 1P
.RT
.LP
    Frequency:\ 4.3\ kHz\ \(+-\ 10\ Hz.
.LP
    Level:
.LP
    \(em
    discontinuous signals:\ \(em6\ dBm0;
.LP
    \(em
    semi\(hycontinuous signals:\ value between \(em20\ dBm0 and
\(em17.4\ dBm0.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.22\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBFREQUENCIES\ TO\ BE\ USED\ FOR\ IN\(hyBAND\ SIGNALLING\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.22''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.22    %'
.ce 0
.sp 1P
.PP
To reduce the risk of signal imitation by speech currents, the
frequencies for an in\(hyband signalling system should be chosen from the
frequencies in the band in which speech signal power is lowest, i.e.
frequencies above 1500\ Hz.
.sp 1P
.RT
.PP
The desirability of this was confirmed by tests carried out in
London, Paris and Zurich in 1946 and 1948 to choose the signalling frequencies
of systems standardized by the CCITT. These tests led to the conclusion
that, if relative freedom from false signals was to be obtained other than
by undue increase in signal duration, frequencies of at least 2000\ Hz
would have to be used.
.IP
\fB4.3\fR     \fBSignalling frequencies for push\(hybutton telephone sets and
reception of those signals in exchanges\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.23\fR
.RT
.sp 2P
.LP
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.23''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.23    %'
.sp 1P
.ce 1000
\fBTECHNICAL\ FEATURES\ OF\ PUSH\(hyBUTTON\ TELEPHONE\ SETS\fR
.ce 0
.sp 1P
.PP
\fB1\fR
The introduction of push\(hybuttons on telephone sets may have an effect
on the operation of international circuits:
.sp 1P
.RT
.LP
    a)
    owing to the greater dialling speed, the post\(hydialling may
be longer, since national and international networks will only
be gradually adapted to allow for this greater speed;
.LP
    b)
    when pressing the buttons after an international call has
been set up, the signalling frequencies for push\(hybutton sets may
cause interference to foreign signalling systems on the
connection. However, the subscriber can be warned of the possible
disadvantages of touching the buttons in conditions different
from those prescribed.
.PP
\fB2\fR
There can be no doubt that, owing to the high dialling
speed which can be obtained with push\(hybutton sets, their use is bound
to spread widely and rapidly and it is desirable for the signalling methods
for such sets to be internationally standardized.
.sp 9p
.RT
.PP
One factor in favour of such standardization is the advantage it
offers for countries which have to import their equipments from various
other countries. This argument, admittedly, applies to any type of telephone
equipment.
.PP
Other advantages of standardization are:
.RT
.LP
    \(em
    the possibility of using the push\(hybutton of such sets for
signalling directly from one subscriber to another subscriber
via a national and/or international connection;
.LP
    \(em
    the standardized allocation of signalling frequencies for
push\(hybutton sets facilitates the choice of signalling frequencies
in the frequency band of a telephone circuit for any other use
(data transmission, telephone signalling system, etc.) for which
provision might have to be made. The risk of mutual interference
among the signalling systems (see Recommendation\ Q.25) makes it
necessary to have an orderly arrangement of the spectrum of
frequencies used for signalling.
.PP
\fB3\fR
The general use of push\(hybutton sets for purposes other than
telephone dialling is envisaged by some Administrations. However, some
Administrations observe that it would seem advisable to reserve such uses
for a network of relatively limited extent; in their view the reliability
of
standards for data transmission should not make any demands on the push\(hybutton
set system other than those required for the transmission of telephone
numerical information to the local exchange, if the design of push\(hybutton
sets is to remain within economical limits compatible with their widespread
use.
.bp
.sp 9p
.RT
.PP
However, the CCITT considered, at Mar del Plata in 1968 that, even if the
transmission of data from a push\(hybutton telephone set is at present
to be envisaged in international traffic on a limited scale only, it would
nonetheless be wise not to rule out the possibility of such transmission of
data on a general scale.
.PP
\fB4\fR
In choosing a signalling system for push\(hybutton sets,
Administrations may be guided by conditions which vary considerably from one
country to another. Economic considerations may, for instance, lead them to
prefer a direct current system which might be less expensive than a
voice\(hyfrequency system. The numerical dialling information would then be
transmitted only as far as the telephone exchange to which the subscriber is
connected. There are no tones that could affect the connection after its
establishment. Data would not be transmitted from the push\(hybutton sets
unless a suitable converter were used in the exchange.
.sp 9p
.RT
.PP
Standardization of a direct current system for signalling from
push\(hybutton sets does not seem justified at the international level; it may
depend on the conditions peculiar to the local networks of the country
concerned.
.PP
\fB5\fR
The signalling system for push\(hybutton sets recommended by the
CCITT applies solely to voice\(hyfrequency signals.
.sp 9p
.RT
.PP
A multifrequency code for such signalling is recommended in which
the dialling signal is composed of two frequencies emitted simultaneously
when a button is pressed. It is planned to have 10\ decimal digits and
6\ reserve
signals, making 16\ signals in all. The two frequencies composing each signal
are taken from two mutually exclusive frequency groups of four frequencies
each, a code known as the \*Q2\ (1/4)\ code\*U.
.PP
\fB6\fR
The low group frequencies of this 2\ (1/4)\ code are:
.sp 9p
.RT
.sp 1P
.ce 1000
697, 770, 852, 941 Hz.
.ce 0
.sp 1P
.PP
The high group frequencies are:
.sp 1P
.ce 1000
1209, 1336, 1477 and 1633 Hz.
.ce 0
.sp 1P
.PP
The allocation of frequencies to the various digits and symbols of a push\(hybutton
set appears in Figure\ 1/Q.23.
.PP
\fB7\fR
The frequency variation tolerances and the permissible
intermodulation products are defined as follows:
.sp 9p
.RT
.PP
7.1
each transmitted frequency must be within \(+- | .8% of the
nominal frequency;
.PP
7.2
the total distortion products (resulting from harmonics or
intermodulation) must be at least 20\ dB below the fundamental
frequencies.
.PP
\fB8\fR
The CCITT determined, at Mar del Plata in 1968, that it was not practicable
to specify a standardization of the levels for the frequencies
transmitted when a push\(hybutton is pressed, as these level conditions depend
essentially on national transmission plans which are not the same in all
countries.
.sp 9p
.RT
.PP
However, the sending level conditions must be such that on an
international connection they do not exceed the values specified in
Recommendation\ Q.16 (maximum permissible value for the absolute power
level of a signalling pulse).
.LP
.rs
.sp 17P
.ad r
\fBFigure 1/Q.23 p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.24\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMULTIFREQUENCY\ PUSH\(hyBUTTON\ SIGNAL\ RECEPTION\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.24''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.24    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
Characteristics of multifrequency push\(hybutton (MFPB) telephone
sets using voice frequency signals are included in Recommendation\ Q.23. This
Recommendation\ Q.24 is intended primarily for application in local exchanges
for the reception of MFPB signals. Other MFPB signal receiving applications,
such as transit exchanges, would need to take into account the effects of
transmission impairments, such as signal clipping, that could be introduced
in long distance telephone networks. Since technical factors, such as transmission
loss, vary among national networks, varying national standards exist. Varying
.PP
standards may also exist, for example, to incorporate differences between
local and transit exchange applications. This Recommendation is not intended
to
supersede existing national standards nor is it intended to imply that
Administrations should modify those standards.
.RT
.sp 2P
.LP
\fB2\fR     \fBTechnical parameters\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The technical parameters identified herein are fundamental to the MFPB
receiving function and reasons are given for the importance of each
parameter. The parameters require operational values to be specified for
compatibility with the MFPB sending equipment (Recommendation\ Q.23) and the
network environment in which the receiving equipment must function. Annex\ A
contains a Table showing values for some of these parameters that have been
adopted by various Administrations and RPOAs. In addition to the fundamental
parameters covered by this Recommendation, Administrations should consider
whether other parameters need specification to account for operating conditions
found in their networks.
.RT
.sp 1P
.LP
2.2
    \fISignal frequencies\fR
.sp 9p
.RT
.PP
Each signal consists of two frequencies taken from two mutually
exclusive frequency groups (a high group and a low group) of four frequencies
each, as specified in Recommendation\ Q.23. These frequencies and their
allocation to form the various digits and symbols of the push\(hybutton
signalling code are defined in Recommendation\ Q.23. The exchange shall
provide a check for the simultaneous presence of one and only one frequency
from the high group and one and only one from the low group.
.RT
.sp 1P
.LP
2.3
    \fIFrequency tolerances\fR
.sp 9p
.RT
.PP
The exchange should respond to signals whose frequencies are within the
tolerances for MFPB sending. Somewhat wider tolerances may be appropriate,
for example to cater for transmission impairments encountered in subscriber
cables or FDM transmission facilities. However, wider limits may increase
susceptibility to noise and digit simulation by speech.
.RT
.sp 1P
.LP
2.4
    \fIPower levels\fR
.sp 9p
.RT
.PP
The exchange should provide proper reception of signals whose power levels
are determined by the amplitude of the sending equipment and loss that
may be introduced by the subscriber cables or other network elements. The
sending amplitude and transmission attenuation may be different for different
frequencies. The reception characteristics may take advantage of a limitation,
if specified, on the maximum difference in power level between the two
received frequencies forming a valid signal to facilitate improved overall
performance.
.RT
.sp 1P
.LP
2.5
    \fISignal reception timing\fR
.sp 9p
.RT
.PP
The exchange should recognize signals whose duration exceeds the
minimum expected value from subscribers. To guard against false signal
indications the exchange should not respond to signals whose duration is
less than a specified maximum value.
.bp
.PP
Similarly, pause intervals greater
than
a specified minimum value should be recognized by the exchange. To minimize
erroneous double\(hyregistration of a signal if reception is interrupted by a
short break in transmission or by a noise pulse, interruptions shorter
than a specified maximum value must not be recognized. The maximum rate
at which
signals can be received (signalling velocity) may be related to the above
minimum values. All of these values may also be determined by subscriber
feature requirements.
.RT
.sp 1P
.LP
2.6
    \fISignal simulation by speech\fR
.sp 9p
.RT
.PP
Because telephone set speech transmitters are normally connected in the
circuit during the push\(hybutton dialling interval, it is necessary for
the exchange to properly receive valid MFPB signals in the presence of
voice or
other disturbances. The nature of such disturbances may vary from one
geographical area to another. The number of calls affected by signal simulation
should not significantly degrade the overall telephone network performance
experienced by subscribers.
.PP
Since actual immunity to digit simulation may be difficult to measure,
a test environment using recorded speech, music, and other voice frequency
sounds may be utilized to verify design performance.
.RT
.sp 1P
.LP
2.7
    \fIInterference by dial tone\fR
.sp 9p
.RT
.PP
MFPB reception should not be adversely affected while dial tone is being
applied. Characteristics of dial tone such as frequencies, power levels
and spurious components are covered in Recommendation\ Q.35. These
characteristics are specified to minimize the interference between the dial
tone sending and the MFPB receiving functions. These functions are normally
provided by closely related exchange equipment which must be designed to
function properly over the entire range of signal characteristics and
transmission impairments to be encountered.
.RT
.sp 1P
.LP
2.8
    \fIInterference by echos\fR
.sp 9p
.RT
.PP
MFPB signal reception from extended subscriber lines having long
4\(hywire transmission sections must discriminate between a true signal
condition and an echo condition which may persist for a number of milliseconds.
Failure to provide such discrimination could result in signal reception
errors, for
example due to a reduction of the detected pause duration. Administrations
having such extended subscriber lines with MFPB signalling should therefore
specify the echo conditions under which the MFPB signalling function must
operate.
.RT
.sp 1P
.LP
2.9
    \fINoise immunity\fR
.sp 9p
.RT
.PP
Noise sources such as power lines, electric railways and
telecommunication circuits may induce electrical disturbances with various
characteristics into MFPB signalling paths. These disturbances may cause
MFPB signals to be missed, split (double signal registration) or cause
signal
simulation. The distortion products produced by the MFPB signalling source
should also be included in the noise environment. A realistic noise environment
specification and facilities for testing MFPB reception under the specified
conditions, e.g., using recorded test tapes, are important to ensure that
performance standards will be met under actual service conditions.
.RT
.LP
.rs
.sp 12P
.ad r
BLANC
.ad b
.RT
.LP
.bp
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation Q.24)
.sp 9p
.RT
.ce 0
.ce
\fBH.T. [T1.24]\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(330p) .
TABLE\ A\(hy1/Q.24
.T&
cw(330p) .
 {
\fBValues of multi\(hyfrequency push\(hybutton receiving parameters\fR
\fBadopted by various Administrations/RPOAs\fR
 }
.TE
.TS
cw(84p) | lw(48p) sw(48p) sw(54p) sw(48p) sw(48p) , ^  | l | l | l | l | l.
 {
Parameters
Values
NTT
AT&T
Danish Administration | ua\d\u)\d
Australian Administration
Brazilian Administration
 }

_
.T&
lw(42p) | cw(42p) | cw(48p) | lw(48p) | lw(54p) | lw(48p) | lw(48p) , ^  | c | c | ^ | ^ | ^ | ^ .
 {
Signal frequencies
Low group
697, 770, 852, 941 Hz
High group
1209, 1336, 1477, 1633 Hz
 }    same as left column    same as left column
    same as left column    same as left column
_
.T&
lw(42p) | lw(42p) | lw(48p) | lw(48p) | lw(54p) | lw(48p) | lw(48p) , ^  | l | l | l | l | l | l.
 {
Frequency tolerance
@ left | (*D\fIf\fR right | @
Operation
\(= 1.8%
\(= 1.5%
\(= (1.5% + 2 Hz)
\(= (1.5% + 4 Hz)
\(= 1.8%
Non\(hyoperation
\(>=" 3.0%
\(>=" 3.5%
.
\(>=" 7%
\(>=" 3%
 }

_
.T&
lw(42p) | lw(42p) | lw(48p) | lw(48p) | lw(54p) | lw(48p) | lw(48p) , ^  | l | l | l | l | l | l.
 {
Power levels per frequency
Operation
\(em3 to \(em24 dBm
0 to \(em25 dBm
(A + 25) to A dBm
\(em5 to \(em27 dBm
\(em3 to \(em25 dBm
Non\(hyoperation
Max. \(em29 dBm
Max. \(em55 dBm
Max. (A \(em 9) dBm (A = \(em27)
Max. \(em30 dBm
Max. \(em50 dBm
 }

_
.T&
lw(84p) | cw(48p) | cw(48p) | cw(54p) | cw(48p) | cw(48p) .
 {
Power level difference between frequencies
 }    Max. 5 dB    +4 dB to \(em8 dB | ub\d\u)\d    Max. 6 dB    Max. 10 dB    Max. 9 dB
_
Unable to convert table
.TE
.nr PS 9
.RT
.ad r
\fBTable A\(hy1/Q.24 [T1.24], p.  \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.IP
\fB4.4\fR \fBProtection of \*Qin\(hyband\*U signalling systems against
each\fR
\fBother\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.25\fR
.RT
.sp 2P
.LP
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.25''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.25    %'
.ce 1000
\fBSPLITTING\ ARRANGEMENTS\ AND\ SIGNAL\ RECOGNITION\ TIMES\fR
.ce 0
.sp 1P
.ce 1000
\fBIN\ \*QIN\(hyBAND\*U\ SIGNALLING\ SYSTEMS\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
In each \*Qin\(hyband\*U signalling system precautions should be taken so
that, when the signalling in that system is taking place:
.RT
.PP
1.1\fR no interference in the voice\(hyfrequency range from outside the
system can pass into the system (i.e. into the transmission path
between the sending end and the receiving end of the
voice\(hyfrequency signals), and
.PP
1.2
as far as possible, no signalling current used in the system can
pass into other systems, connected in tandem.\fR
.sp 2P
.LP
\fB2\fR     \fBSending\(hyend splitting arrangements\fR
.sp 1P
.RT
.PP
2.1
In order to satisfy the condition in \(sc\ 1.1\ above, care should be taken
that the correct operation of the signal receiver at the other end of the
circuit is not disturbed by:
.sp 9p
.RT
.LP
    \(em
     surges (transient currents) caused by the opening or closing of direct
current circuits connected to the speech wires of the
switching equipment, whether these surges precede or follow
the sending of a signal;
.LP
    \(em
    noise, speech currents, etc., coming from tandem switched
circuits, preceding or during the sending of a signal.
.PP
2.2
For this reason the following arrangements have been made in the
Signalling Systems No.\ 4 and No.\ 5 for the transmission of
voice\(hyfrequency signals on the international circuit:
.LP
    i)
     The exchange side of the circuit shall be disconnected 30 to 50\ ms before
a voice\(hyfrequency signal is sent over the circuit.
.LP
    ii)
     The exchange side of the circuit will not be reconnected for 30 to 50\
ms following the end of the sending of a voice\(hyfrequency
signal over the circuit.
.PP
2.3
Arrangements of the same type are required on System\ R1 and on
national \*Qin\(hyband\*U systems
[see\ \(sc\ 3.4.1\ b)\ below].
.sp 2P
.LP
\fB3\fR     \fBReceiving\(hyend splitting arrangements\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIGeneral\fR \v'3p'
.sp 9p
.RT
.PP
3.1.1
In order to satisfy the condition in \(sc\ 1.2\ above, the length of
the part
of a signal which passes into another system is limited by splitting the
speech wires beyond the signal receiver when a signal is received and detected
by this receiver.
.PP
The time during which the first part (sometimes called
\fIspillover\fR ) of a received signal passes into another system, until
the splitting becomes effective, is called \*Q
splitting time
\*U.
.PP
Too long a splitting time may result in interference to signalling on
a tandem system depending on the signal recognition time on the tandem system.
.PP
Too short a splitting time may result in an increase in the number of
false operations of the splitting device by speech currents (\fIsignal\fR
\fIimitation\fR ) and so impair speech transmission.
.bp
.PP
The splitting time must therefore be a compromise between the above two
factors.
.PP
The splitting device also serves to limit the duration of signals on
one path of the 4\(hywire circuit from returning over the other path by
reflections at the termination; these reflections may give rise to faulty
operation of signalling equipment on the other path.
.RT
.PP
3.1.2
The protection against mutual interference between in\(hyband
signalling systems in international service involves limitations of the
length of any part of:
.PP
3.1.2.1
the \fIinternational\fR signal that may be able to pass:
.LP
    a)
    from the international signalling system into a national
signalling system (protection of the national system);
.LP
    b)
    from one international signalling system into another
international signalling system, when they are switched in
tandem (protection of the international systems);
.LP
    c)
    from one international circuit into another international
circuit of the same system when they are switched in tandem in
the case of link\(hyby\(hylink signalling.
.PP
3.1.2.2
the \fInational\fR  | signal that may be able to pass:
.LP
    a)
    from the national signalling system into an international
signalling system (protection of the international system);
.LP
    b)
    from one national signalling system into the national
signalling system of another country via an international connection
(protection of the national system).
.sp 1P
.LP
3.2
    \fIProtection of national and international systems against\fR
\fIinternational systems\fR
.sp 9p
.RT
.PP
Conditions in \(sc\ 3.1.2.1 above are met because international
signalling
systems have a splitting device on each circuit. The splitting times of such
systems are:
.RT
.LP
    55\ milliseconds for the compound signal element in System\ No.\ 4;
.LP
    35\ milliseconds for a signal in System\ No.\ 5;
.LP
    20\ milliseconds for a signal in System\ R1.
.sp 1P
.LP
3.3
    \fIProtection of the international system against national systems\fR
.sp 9p
.RT
.PP
The condition in \(sc\ 3.1.2.2\ a) above is generally covered
because:
.RT
.LP
    \(em
    the values given in the specifications of the CCITT standard
systems as the minimum recognition time of a line signal are
.LP
in general greater than the splitting times of national systems
(see the tables giving the basic characteristics of national
signalling systems in Supplement\ No.\ 3 at the end of this
fascicle);
.LP
    \(em
    the signalling frequencies used in the international systems
are, in the majority of countries, different from those used in
national systems.
.PP
It may be necessary, if the splitting time of a national signalling system
is greater than the minimum signal recognition time
of an international system and the signalling frequencies
used in the national system and international system are
the same or nearly the same, to insert a device at the
international exchange which will prevent a part of the
national signal from passing into the international circuit
for longer than this recognition time.
.sp 1P
.LP
3.4
    \fIInterference between national signalling systems when they are\fR
\fIinterconnected via an international circuit\fR \v'3p'
.sp 9p
.RT
.PP
3.4.1
To ensure protection of national signalling systems one against
the other [protection defined under \(sc\ 3.1.2.2\ b) above], it has been
recommended by the CCITT since 1954 that new national \*Qin\(hyband\*U
signalling
systems should comply with the following two clauses:
.LP
    a)
     not more than 35\ milliseconds of a national signal should be able to
pass into another country;
.LP
    b)
    the connection between an international circuit and a
national circuit should be split on the national circuit at the
international exchange\ 30 to 50\ milliseconds before that exchange
sends any signal over the national signalling system.
.PP
\fINote\fR \ \(em\ The object of these two clauses is to avoid interference,
especially in conditions that may exist on international
automatic connections.
.bp
.PP
3.4.2
The requirement of \(sc\ 3.4.1\ a) permits the signalling
system used in country\ A to
have a minimum signal recognition time based on this value of
35\ milliseconds.
It will then be possible to ensure, without taking any other precautions
at the incoming end of an international circuit, that no fraction of a
signal coming from country\ B, and being of the same, or nearly the same,
frequency as that
used in country\ A, will be wrongly recognized as a signal in country\ A.
.PP
One method of meeting the requirement of \(sc\ 3.4.1\ a) is to adopt a
splitting time of less than 35\ milliseconds for the national systems.
.PP
Another method exists which does not involve such a limitation in the
splitting times of national systems, and which might be preferred when the
design of the national signalling system is such that a short splitting
time is not normally justified for that system alone. This second method
involves
.PP
the introduction, in the international exchange, of an arrangement for
limiting the length of national signals which are liable to pass into the
international circuit. Such an arrangement would be used only on circuits
to those countries where there is a danger that interference might arise.
.RT
.PP
3.4.3
The requirement of \(sc\ 3.4.1\ b) avoids the false operation of
the guard circuit
of a signal receiver situated at the distant end of a national circuit.
.IP
\fB4.5\fR     \fBMiscellaneous provisions\fR
.sp 1P
.RT
.sp 2P
.LP
    \fBRecommendation\ Q.26\fR
.RT
.sp 2P
.ce 1000
\fBDIRECT\ ACCESS\ TO\ THE\ INTERNATIONAL\ NETWORK\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.26''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.26    %'
.ce 0
.sp 1P
.ce 1000
\fBFROM\ THE\ NATIONAL\ NETWORK\fR
.ce 0
.sp 1P
.PP
The choice of the method of access to an outgoing international
exchange from the national network is a purely national matter. Nevertheless,
if an international connection is set up by automatic switching from an
.sp 1P
.RT
.LP
exchange other than the international exchange which is the outgoing point
of the international circuit used, arrangements should be made in the national
network to transmit over the international circuit at least the signals
required to ensure the satisfactory setting\(hyup, control and clearing\(hydown
of
the international connection.
.PP
In addition, where a group of national circuits used in the above
manner
carries both semi\(hyautomatic and automatic traffic, means should be provided
for distinguishing between these two classes of traffic for the purposes
of
international accounting\ [1].
.sp 2P
.LP
    \fBReference\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIBasic technical problems concerning the\fR
\fImeasurement and recording of call durations\fR , Vol.\ II,
Rec.\ E.260, \(sc\ 2.
.sp 2P
.LP
\fBRecommendation\ Q.27\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSMISSION\ OF\ THE\ ANSWER\ SIGNAL\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.27''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.27    %'
.ce 0
.sp 1P
.PP
It is essential for the answer signal to be transmitted with a
minimum of interference to the transmission of speech currents, because the
called subscriber may already be announcing his presence at this stage
of the call.
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.RT
.PP
On a connection which has been set up, the answer signal generally entails,
at a certain number of points:
.LP
    a)
    repetitions and conversions, which delay transmission; and
.LP
    b)
    splitting of the speech path, where in\(hyband signalling is
used.
.PP
It is therefore desirable to minimize the delays and the duration of the
interruption of the speech path. Minimization of the latter can be achieved
by:
.LP
    \(em
    short send line splitting;
.LP
    \(em
    short duration of the signal; and
.LP
    \(em
    fast termination of the sending and receiving splits on
cessation of the signal.
.bp
.sp 2P
.LP
\fBRecommendation\ Q.28\fR
.RT
.sp 2P
.ce 1000
\fBDETERMINATION\ OF\ THE\ MOMENT\ OF\ THE\ CALLED\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.28''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.28    %'
.ce 0
.sp 1P
.ce 1000
\fBSUBSCRIBER'S\ ANSWER\ IN\ THE\ AUTOMATIC\ SERVICE\fR
.ce 0
.sp 1P
.PP
\fB1\fR
Arrangements should be made in the national signalling system of
the incoming country to determine (in the outgoing international exchange)
the moment when the called subscriber replies; this information is necessary
in the international service for the purposes of:
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.RT
.LP
    \(em
    charging the calling subscriber [1];
.LP
    \(em
    measuring the call duration [2].
.PP
\fB2\fR
Where subscribers in an outgoing country have direct access
to an operator's position (in a manual exchange, for instance) in a public
exchange of an incoming country, arrangements should be made in the national
network of the incoming country to ensure that\ \(em in the outgoing country
\(em\ the calling subscriber is charged, and the call duration measured,
only from the
moment when the called subscriber replies. This means that an answer signal
is not sent when the operator in a public exchange of the incoming country
replies. These provisions are set out in detail for CCITT standardized
systems (see Recommendation\ Q.102).
.sp 9p
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIChargeable duration of calls\fR , Vol.\ II,
Rec.\ E.230.
.LP
[2]
    CCITT Recommendation \fIBasic technical problems concerning the\fR
\fImeasurement and recording of call durations\fR , Vol.\ II,
Rec.\ E.260.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ Q.29\fR
.RT
.sp 2P
.ce 1000
\fBCAUSES\ OF\ NOISE\ AND\ WAYS\ OF\ REDUCING\ \fR \fBNOISE\ IN\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.29''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.29    %'
.ce 0
.sp 1P
.ce 1000
\fBTELEPHONE\ EXCHANGES\fR
.ce 0
.sp 1P
.PP
Circuit noise may be classified as follows:
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.RT
.LP
    1)
    power supply noise,
.LP
    2)
    noise generated in the speech path circuit,
.LP
    3)
    noise induced in the speech path
circuit.
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.LP
\fB1\fR     \fBPower supply noise\fR
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.RT
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.LP
1.1
    \fIPower sources\fR
.sp 9p
.RT
.PP
The interference resulting from the harmonics, ripple and current
fluctuation of machines, rectifiers and batteries.
.PP
This noise may be reduced by d.c. generators with low harmonics and good
regulation and rectifiers with good regulation, effective filters, and
batteries with large capacity (i.e. with low internal impedance).
.RT
.sp 1P
.LP
1.2
    \fISupply leads\fR
.sp 9p
.RT
.PP
The interference in the speech circuits of an exchange due to power supply
equipment originates mainly in the common impedances of the supply paths
of speech and switching circuits, and is caused mainly by the sudden
fluctuation of the current resulting from the sudden operation and release
of the different relays, magnets and contacts.
.bp
.PP
These common impedances may be reduced by:
.RT
.LP
    a)
    the use of common power supply leads of sufficiently low
resistance, the use of large capacitors fitted at apparatus
ends of supply leads with minimum impedances, e.g. minimum
distance between bus bars, or coaxial feeders. Another
method employs close\(hyspaced cables with alternate polarity;
.LP
    b)
    the use of a common battery with separate power supply
leads for speech and switching circuits. Better results may
be obtained at an increased cost by independent batteries
adequately separated;
.LP
    c)
    the arrangement of the cells of the battery in a
U\ formation.
.sp 1P
.LP
1.3
    \fIEarth returns\fR
.sp 9p
.RT
.PP
Independent earth returns should be used for signalling\(hyfrequency
supply circuits.
.RT
.sp 2P
.LP
\fB2\fR     \fBNoise generated in the speech circuit\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIContact noise caused by vibration\fR
.sp 9p
.RT
.PP
This kind of noise is caused by contact resistance variations of the various
commutator, switch and relay contacts due to mechanical vibration.
.PP
This contact noise may be reduced by:
.RT
.LP
    a)
    the use of damping devices to reduce the generation of
vibration caused in particular by relay sets, mechanical
and electromagnetic clutches;
.LP
    b)
    the use of multiple brushes, spring or resilient mountings
to reduce the transmission of vibration;
.LP
    c)
    a suitable choice of contact materials;
.LP
    d)
    the use of the best contact shape and of twin contacts;
.LP
    e)
     maintaining atmospheric conditions at an appropriate relative humidity
and the use of air filters; use of dust covers on
equipment, arranging design of columns, window sills,
radiators and floor to avoid harbouring dust;
.LP
    f
)
    careful maintenance cleaning and lubrication in accordance
with specifications.
.sp 1P
.LP
2.2
    \fIFrying noise\fR
.sp 9p
.RT
.PP
In speech circuits some contact materials are liable to cause frying  noise.
.PP
This noise may be reduced by the use of suitable contact materials and
by keeping an appropriate relative humidity.
.RT
.sp 1P
.LP
2.3
    \fIContact noise caused by wetting currents\fR
.sp 9p
.RT
.PP
Speech circuits without d.c. currents are liable to fading due to
contact resistance fluctuations. Fading may be reduced by wetting. However,
wetting currents may introduce frying noise on the lines.
.RT
.sp 1P
.LP
2.4
    \fICharge and discharge clicks\fR
.sp 9p
.RT
.PP
Clicks may frequently be caused by the charging or discharging of
capacities (cable capacity) by switches when rotating over occupied and
non\(hyoccupied terminals.
.PP
Objectionable clicks are also likely to result from sudden battery
reversals, dialling and other abrupt changes in the current flowing in the
speech circuits.
.PP
These effects may be reduced:
.RT
.LP
    a)
    by disconnecting the speech circuits from the brushes during
the hunting period of the switch;
.LP
    b)
     by the use of twisted pairs, by limiting the length of cabling and also
by locating relays as close as possible to the
selectors they control.
.bp
.sp 1P
.LP
2.5
    \fIUnsound contacts\fR
.sp 9p
.RT
.PP
Objectionable noise may be due to unsound contacts on distribution
frames, particularly when work is in progress such as adding or changing
jumpers, etc. Such unsound contacts may be due to \*Qdry\*U contacts inadequately
soldered, poorly wrapped joints, or to the use of distribution frame equipment
having inadequate contact pressure. It is suspected that this type of trouble
is responsible for most of the \*Qhits\*U and \*Qmisses\*U and usually
for an increase in noise.
.RT
.sp 1P
.LP
2.6
    \fITapping losses\fR
.sp 9p
.RT
.PP
When lines are tapped for service interception, observation, etc.,
the tapping circuit should be designed to give the minimum of unbalance to
earth and the transmission loss introduced should be a minimum.
Semi\(hy
permanent
connections should be used in preference to base\(hymetal sliding connections
at the tapping point.
.RT
.sp 1P
.LP
2.7
    \fIReduction of the number of switching contacts\fR
.sp 9p
.RT
.PP
Circuits should be designed so that at each switching stage there is a
minimum number of contacts in the speech circuit in order to reduce the
risk of microphonic noise from \*Qdry\*U contacts.
.RT
.sp 2P
.LP
\fB3\fR     \fBNoise induced in the speech circuit\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fINoise induced in the speech circuit may be due to:\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    speech crosstalk;
.LP
    b)
    signalling frequency crosstalk;
.LP
    c)
    induction from tone supplies;
.LP
    d)
    direct current pulses;
.LP
    e)
    clicks caused by abrupt changes in inductive and
capacitive circuits.
.PP
Clicks may be reduced at the source by the use of spark quench
devices or other means to reduce the steepness of the interfering wave\(hyfront
concerned. In addition, noise may be reduced by balancing, by using twisted
pairs and/or by screening.
.sp 1P
.LP
3.2
    \fINoises due to unbalanced transmission bridge circuits\fR
.sp 9p
.RT
.PP
A well\(hybalanced circuit is necessary for the transmission bridge to
avoid noise interference. This can be achieved by:
.RT
.LP
    a)
    the use of balanced components;
.LP
    b)
    the separation of components used for speech from those
used for control and switching;
.LP
    c)
    the separation of individual transmission bridges by
screening or spacing;
.LP
    d)
    the addition of balancing components, e.g. balancing
transformers of retardation coils;
.LP
    e)
    taking the precautions listed at the end of \(sc\ 3.1\ above.
.sp 1P
.LP
3.3
    \fILow\(hylevel speech circuits\fR
.sp 9p
.RT
.PP
Low\(hylevel electronic speech circuits are particularly susceptible to
noise induction and should therefore be screened.
.RT
.sp 1P
.LP
3.4
    \fILongitudinal interference\fR
.sp 9p
.RT
.PP
Such noise may be induced into the speech circuit from the line by
power distribution systems and traction circuits or by earth potential
differences.
.PP
These may be reduced by balancing the line or by the addition of
transformers.
.PP
\fINote\fR \ \(em\ Interference which is sufficiently severe to cause unwanted
operation of relays, etc., may be overcome by the use of loop circuits which
should also reduce noise.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ Q.30\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBIMPROVING\ THE\ RELIABILITY\ OF\ CONTACTS\ IN\
SPEECH\ CIRCUITS\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.30''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.30    %'
.ce 0
.sp 1P
.PP
The following methods can be used for improving the reliability of
contacts in speech circuits:
.sp 1P
.RT
.LP
    a)
    use of precious metals such as platinum, palladium, gold,
silver, or alloys of these metals. If, for one reason or another,
it is not desired to \*Qwet\*U the contacts, or if enough contact
pressure cannot be provided, it is preferable to use the metals
or alloys mentioned above, with the exception of pure silver;
.LP
    b)
    use of high contact pressure;
.LP
    c)
    double contacts;
.LP
    d)
     lubrication (with suitable oils) of certain non\(hyprecious metal contacts
in the case of sliding contacts;
.LP
    e)
    direct current \*Qwetting\*U of contacts, care being taken to
avoid the introduction of noise due to transients when the
contacts are made or broken;
.LP
    f
)
    air filtration or other protective measures to avoid
dust;
.LP
    g)
    the maintenance of suitable humidity;
.LP
    h)
    the use of protective covers;
.LP
    i)
    protection against fumes, vapours and gases;
.LP
    j
)
     avoidance of the use, near contacts, of materials likely to be detrimentral
to the contacts.
.PP
When voice\(hyfrequency signals are sent over a transmission path, as it
is not possible to use direct current wetting for the voice\(hyfrequency
signal transmitting contacts due to the surges which occur on closing and
opening the contact, it is preferable to use static modulators with rectifier
elements.
.sp 2P
.LP
\fBRecommendation\ Q.31\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBNOISE\ IN\ A\ NATIONAL\ 4\(hyWIRE\ AUTOMATIC\ EXCHANGE\fR
.EF '%    Fascicle\ VI.1\ \(em\ Rec.\ Q.31''
.OF '''Fascicle\ VI.1\ \(em\ Rec.\ Q.31    %'
.ce 0
.sp 1P
.PP
It is desirable that the requirements concerning noise conditions for a
national 4\(hywire automatic exchange be the same as for an international
exchange (see Recommendation\ Q.45, \(sc\ 5).
.sp 1P
.RT
.LP
.rs
.sp 20P
.LP
\fBMONTAGE:\ \fR DEBUT REC. Q.32 A LA FIN DE CETTE PAGE
.sp 1P
.RT
.LP
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