InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/6_4_04.tro

Text File | 1991-12-13 | 160.8 KB | 5,190 lines

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.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 4
.ce 0
.sp 1P
.ce 1000
\fBINTERREGISTER\ SIGNALLING\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.440\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.1\ GENERAL\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.440''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.440    %'
.ce 0
.sp 1P
.PP
Interregister signals are of the multifrequency type using a
2\(hyout\(hyof\(hy6 in\(hyband code in both directions. The multifrequency
combinations are sent and received by multifrequency signalling equipment
which is assumed to be associated with the registers used to control the
switching equipment at both ends of the inter\(hyexchange link.
.sp 1P
.RT
.LP
.sp 1P
.LP
4.1.1
    \fIEnd\(hyto\(hyend signalling method\fR
.sp 9p
.RT
.PP
In System R2 interregister signalling is generally performed
end\(hyto\(hyend by a compelled procedure between the outgoing register and the
incoming registers which come into action one after another. Signalling
takes place over one or more links in tandem without signal regeneration
in
intermediate exchanges. With this signalling method only the address
information needed for routing the call through an intermediate exchange is
transferred from the outgoing register to the incoming registers. In an
intermediate exchange the speech path is immediately through\(hyconnected
and the incoming register released, then the outgoing register can exchange
information directly with the incoming register of the next exchange (see
Figure\ 11/Q.440). If any intermediate exchange has to carry out charging
operations, additional address information can be transferred from the
outgoing register to the
incoming register of that exchange as required.
.RT
.LP
.rs
.sp 14P
.ad r
\fBFIGURE\ 11/Q.440, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
In circumstances where transmission conditions do not comply with the requirements
specified for System\ R2 (see Recommendation\ Q.457) or where
System\ R2 is used in a satellite link, and thus the exchange of the
interregister signals over the complete System\ R2 connection is not permitted,
the overall multi\(hylink connection is divided into end\(hyto\(hyend signalling
sections. When the number of multifrequency combinations available is not
the same on all parts of the connection, the division should be made at
an exchange between links having different numbers of multifrequency combinations
to
improve the transfer of information.
.bp
.PP
The outgoing R2 register is situated at the outgoing end of a
signalling section on which System\ R2 interregister signalling according
to the present specifications is used. It controls the call set\(hyup over
the whole
signalling section. It sends forward interregister signals and receives
backward interregister signals.
.PP
The outgoing R2 register receives information via the preceding links of
the connection in a form used by the signalling system applied over the
last of these links; this system may be System\ R2, a decadic pulse system,
or any
other system. The preceding link may also be a subscriber's line. When an R2
register in a transit exchange is working according to this definition,
it is also called an \fIoutgoing\ R2 register.\fR
.PP
Special cases of the outgoing R2 register are the outgoing
international\ R2 register (see \(sc\ 4.1.2) and the outgoing R2 register
at the
incoming end of a satellite link.
.PP
The incoming R2 register is situated at the incoming end of a link on which
System\ R2 multifrequency interregister signalling according to the
present specification is used. It receives forward interregister signals via
the preceding link(s) and sends backward interregister signals. The
information received is used completely or in part for the control of selection
stages and may be sent in its entirety or in part to the succeeding equipment,
in which case the signalling used for retransmission is never System\ R2.
Interworking then takes place between System\ R2 and the other system. Thus
every register not situated at the outgoing end of a System\ R2 signalling
section is called an \fIincoming\ R2 register\fR independently of the exchange
type.
.PP
The term \fIincoming R2 register\fR  | ay be applied also to devices
controlling one or more selection stages, for example \fImarkers\fR etc.
It should be noted that in such equipment no provision is made for further
transfer of
the information received.
.RT
.sp 1P
.LP
4.1.2
    \fIInternational end\(hyto\(hyend working\fR
.sp 9p
.RT
.PP
The inclusion of a special \fIoutgoing international R2 register\fR  | s
shown in Figure\ 11/Q.440 is dictated by a number of considerations. An
outgoing international R2 register is an outgoing R2 register which controls
the call
set\(hyup on a signalling section which comprises at least one international
link and possibly national links in tandem.
.PP
Even when System R2 is used in the national network of the originating
country an outgoing international\ R2 register must always be provided
in the
country of origin to divide the connection into two signalling sections
for the following reasons:
.RT
.LP
    \(em
    to prevent the maximum number of links in a signalling
section over which System\ R2 can function from being exceeded on
international calls;
.LP
    \(em
    to permit the use of fewer signalling frequencies in the
country of origin (e.g. 5\ forward and 5 or 4\ backward signalling
frequencies);
.LP
    \(em
    to enable non\(hystandardized meanings to be allocated to the
spare national multifrequency combinations for use solely in the
country of origin;
.LP
    \(em
    to provide criteria for distinction, at the incoming end,
between national and international calls;
.LP
    \(em
    to have the facilities for routing and charging of
international calls concentrated in one place if it is more economical
than to equip every normal outgoing\ R2 register to perform
these functions.
.PP
In general the outgoing international R2 register is situated at the outgoing
international exchange. However, it may be situated in a national exchange
preceding the international exchange provided that the transmission
requirements specified are fulfilled.
.PP
End\(hyto\(hyend signalling from the outgoing international R2 register
can be extended beyond the incoming international exchange even if a reduced
number of signalling frequencies is used. However, such international/national
.PP
end\(hyto\(hyend signalling requires:
.RT
.LP
    \(em
     that the transmission conditions in the national destination network
comply with the System\ R2 specifications, and
.LP
    \(em
    that the routing principles employed in the national
destination network are compatible with the System\ R2 signalling
procedures for end\(hyto\(hyend transmission of address digits
from the outgoing international\ R2 register to an
incoming\ R2 register in a national exchange.
.sp 1P
.LP
4.1.3
    \fIRegister requirements\fR
.sp 9p
.RT
.PP
Apart from signalling procedures specified in Section\ 5 the
following characteristics of R2\ registers are specified.
.bp
.RT
.sp 1P
.LP
4.1.3.1
    \fIOutgoing R2 registers\fR
.sp 9p
.RT
.PP
The multifrequency signalling equipment associated with outgoing\ R2 registers
in national exchanges may be of the 2\(hywire or 4\(hywire\ type (see
Recommendation\ Q.451).
.PP
The multifrequency signalling equipment associated with outgoing
international\ R2 registers must be of the 4\(hywire\ type. This is dictated by
transmission constraints (see Recommendation\ Q.452).
.PP
The outgoing R2 register controlling a given multi\(hylink signalling
section must be able to recognize at least all the backward signals used on
that section.
.PP
The outgoing international R2 register must be able to send all
15\ forward multifrequency combinations with the meanings specified for
international working. It must be able to receive all 15\ backward
multifrequency combinations and act upon the received information in the
specified manner. In the case when System\ R2 is used on the preceding
link the calling party's category signals have to be translated by the
outgoing
international\ R2 register as specified (see Recommendation\ Q.480).
.PP
The outgoing\ R2 register must start call set\(hyup as soon as it has
received the minimum requisite information. Therefore signal transfer starts
before the complete address information is received, i.e.\ before the caller
finishes dialling. This \fIoverlapping interregister signalling\fR particularly
applies at an outgoing\ R2 register where the complete address information
from a subscriber or operator is stored (e.g.\ local registers). This is
in contrast to \fIen bloc register signalling\fR i.e.\ the transmission
of all the address
information as a whole in one sequence starting only after the complete
reception of the address information.
.RT
.sp 1P
.LP
4.1.3.2
    \fIIncoming\ R2 registers\fR
.sp 9p
.RT
.PP
The multifrequency signalling equipment associated with incoming R2 registers
may be of the 2\(hywire or 4\(hywire type (see Recommendation\ Q.451).
.PP
The multifrequency signalling equipment associated with the incoming R2
register in an international exchange must be of the 4\(hywire\ type and
equipped to send and receive all 15\ multifrequency combinations.
.PP
Every incoming R2 register in a multi\(hylink signalling section must be
able to recognize at least the forward signals used on that section and
directed to that register.
.RT
.sp 1P
.LP
4.1.4
    \fISystem\ R2 compelled signalling method\fR
.sp 9p
.RT
.PP
The compelled signalling operates as follows (see
Figure\ 12/Q.440):
.RT
.LP
    \(em
     on seizure of a link, the outgoing R2 register automatically starts sending
the first forward interregister signal;
.LP
    \(em
     as soon as the incoming R2 register recognizes this signal, it starts
sending a backward interregister signal which has its own
meaning and at the same time serves as an acknowledgement
signal;
.LP
    \(em
    as soon as the outgoing R2 register recognizes the
acknowledging signal, it stops sending the forward interregister signal;
.LP
    \(em
     as soon as the incoming R2 register recognizes the cessation of the forward
interregister signal, it stops sending the backward
interregister signal;
.LP
    \(em
     as soon as the outgoing R2 register recognizes the cessation of the acknowledging
backward interregister signal it may, if
necessary, start sending the appropriate next forward
interregister signal.
.PP
When the duration of the forward and backward signals is not
controlled by the compelling mechanism described above, it is either limited
by the time\(hyout delay for release of the register or determined by the
nature of the pulse imposed on them (see Recommendation\ Q.442).
.PP
Figure\ 12/Q.440 shows a basic compelled signalling cycle.
.PP
Figure\ 18/Q.457 shows in detail the build\(hyup and time sequence of a
compelled signalling cycle, including the operating and release times of
multifrequency signalling equipment and other internal operating times of
exchange equipment.
.RT
.LP
.PP
Besides being a functional part of the compelled procedure, the
acknowledging backward signals serve to convey special information concerning
the required forward signals, to indicate certain conditions encountered
during call set\(hyup or to announce switchover to changed meanings of
subsequent
backward signals. Changeover to secondary meanings allows information
concerning the state of the called subscriber's line to be transferred (see
Recommendation\ Q.441, \(sc\ 4.2.4). Therefore a choice of acknowledging
backward
signals is provided.
.bp
.LP
.rs
.sp 22P
.ad r
\fBFigure 12/Q.440 p.2\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fBRecommendation\ Q.441\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.2\ SIGNALLING\ CODE\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.441''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.441    %'
.ce 0
.sp 1P
.LP
4.2.1
    \fIMultifrequency combinations\fR
.sp 1P
.RT
.PP
Each interregister signal consists of the simultaneous sending of 2 out
of a range of 6, 5 or 4\ in\(hyband frequencies (multifrequency combination).
The band of the interregister signalling frequencies does not overlap with
the frequency band generally used for line\(hysignalling.
.PP
This \fI2\(hyout\(hyof\(hyn\fR  | ode allows erroneous signals consisting
of less or more than two frequencies to be detected and identified as faulty.
.PP
To make the system suitable for application on 2\(hywire links, two
different sets of 6\ frequencies are defined for the composition of the
forward and the backward signals.
.PP
Table\ 5/Q.441 shows all multifrequency combinations which can be
derived from the maximum of 6\ signalling frequencies per direction provided
by the system. For reference purposes each multifrequency combination of
a given direction is identified by a serial number. The numerical value
of this serial number can be calculated by adding the respective index
and weight allocated to the two frequencies making up the combination.
.PP
The number of multifrequency combinations depends upon the number of signalling
frequencies used. When the maximum of 6\ signalling frequencies are used,
15\ multifrequency combinations are available.
.RT
.PP
System R2 is designed for operation on international links with
15\ multifrequency combinations in each direction. However, it can be used in
national networks with a reduced number of signalling frequencies and still
permit international/national end\(hyto\(hyend working of System\ R2 signalling
in the case of incoming international traffic (see Figure\ 13/Q.441).
.PP
The reduction naturally cuts the number of multifrequency combinations
available but has the economic advantage of effecting savings in equipment.
The resulting reduction in facilities is of less importance in automatic
than
semi\(hyautomatic service.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBTableau 5/Q.441 p.3\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 19P
.ad r
\fBFigure 13/Q.441 p.4\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.2.2
    \fIAllocation of interregister signals\fR
.sp 9p
.RT
.PP
The signal coding consists of the association of the defined
meaning of interregister telephone signals to the multifrequency combinations
transmitted over the links. Certain combinations are left spare for the
allocation of national or international signals. (For signalling procedures,
see Recommendations\ Q.460 to\ Q.480.)
.RT
.sp 1P
.LP
4.2.2.1
    \fIMultiple meaning\fR
.sp 9p
.RT
.PP
The meaning of both the forward and backward multifrequency
combinations can change after transmission of certain backward signals. The
changed meaning is specific to the signal which caused or announced the
change. In certain cases a change back to the original meaning is possible.
The meaning of certain forward multifrequency combinations may also vary
depending on their position in the signalling sequence.
.RT
.sp 1P
.LP
4.2.2.2
    \fIMeanings of the forward multifrequency combinations\fR
.sp 9p
.RT
.PP
There are two groups of meanings allocated to the forward
multifrequency combinations. The Group\ I meanings are indicated in
.PP
Table\ 6/Q.441 and the Group\ II meanings in Table\ 7/Q.441\fR . The change
from
Group\ I to Group\ II meanings takes place when requested by the backward
signals\ A\(hy3 or A\(hy5. Change back to Group\ I meanings is only possible
when the change to Group\ II meanings was in response to signal\ A\(hy5.
.PP
The first forward signal transmitted in international working is used for
additional routing information. It enables a distinction to be made between
terminal and transit calls. In the case of terminal calls it carries the
language or discriminating digit whereas, for transit calls, it serves
the dual purpose of providing a country code indicator and to indicate
whether an echo suppressor is required or not.
.PP
The above arrangements obviate the need for two different seizing
signals (line signals) to distinguish between transit and terminal traffic
on links terminated in a transit exchange.
.RT
.LP
.sp 1P
.LP
4.2.2.3
    \fIMeanings of the backward multifrequency combinations\fR
.sp 9p
.RT
.PP
There are two groups of meanings allocated to the backward
multifrequency combinations. The Group\ A meanings are indicated in
Table\ 8/Q.441 and the Group\ B meanings in Table\ 9/Q.441. The change
to Group\ B meanings is announced by the backward signal\ A\(hy3. No change
back is possible
once a change to the Group\ B meanings of the backward multifrequency
combinations has been indicated.
.bp
.RT
.sp 1P
.LP
4.2.2.4
    \fIIntegration of national and international\fR \fIsignalling codes\fR
.sp 9p
.RT
.PP
The utilization of Signalling System R2 in national networks is
facilitated by the provision, in the specified signalling code, of signals
specially assigned for national use. Under the specified code, specific
national meanings are allocated to some of these signals, others are available
for the allocation of national meanings at the discretion of each
Administration.
.PP
National allocations must not conflict with the present specifications
in order to ensure end\(hyto\(hyend interregister signalling i.e.\ the
direct dialogue between the outgoing international\ R2 register (in the
originating country) and incoming\ R2 registers, in the national network
of the destination country.
.PP
The specified signalling code allows for a reduction of signalling
frequencies in national networks (see \(sc\ 4.2.1\ above).
.RT
.sp 2P
.LP
4.2.3
    \fIForward signals\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.3.1
    \fIGroup\ I forward signals\fR
.sp 9p
.RT
.PP
Compelled interregister signalling must always begin with a Group\ I forward
signal. For the signal codes see Table\ 6/Q.441.
.RT
.LP
.rs
.sp 36P
.ad r
\fBTABLE 6/Q.441, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The \fIsignals I\(hy1 to I\(hy10\fR  | re numerical signals indicating:
.LP
     \fIa)\fR the \fIaddress\fR  | equired for setting up the call (country
code, national significant number); such address signals are sent by
an outgoing\ R2 register or an outgoing international\ R2 register,
either spontaneously and immediately after the seizure of the
link or in response to one of the backward signals\ A\(hy1, A\(hy2,
A\(hy7 or\ A\(hy8;
.LP
     \fIb)\fR the country code (and possibly the area code as well) of the
\fIlocation of the outgoing international\ R2 register\fR , in response
to signals requesting the origin of the call. For national
traffic, the telephone number of the calling subscriber's line
(see Recommendation\ Q.480);
.LP
     \fIc)\fR for automatic working the \fIdiscriminating digit\fR  | r, in
the case of semi\(hyautomatic working, the service language to be used
by the operator (i.e.\ \fIlanguage digit\fR ).
.LP
.PP
The \fIsignal\ I\(hy11\fR  | s a non\(hynumerical address signal. The meaning
of the signal is dependent on its position within the sequence of address
signals specified in Recommendation\ Q.107.
\v'3p'
.LP
\fI\fR     a)
    \fICountry code indicator, outgoing half\(hyecho suppressor\fR
\fIrequired\fR
.PP
When signal\ I\(hy11 is transmitted as the first forward signal it
indicates that:
.RT
.LP
    i)
    a country code will follow (international transit);
.LP
    ii)
    the call requires echo suppressors;
.LP
    iii)
    the outgoing half\(hyecho suppressor has to be
inserted.
.PP
The use of this signal in international working is subject to
bilateral agreement and is made in conformity with Recommendation\ Q.479.
\v'3p'
.LP
    b)\fR     \fIAccess to incoming operator (code\ 11)\fR
.PP
When signal\ I\(hy11 is preceded by the language digit (and possibly
by one further address digit) it indicates the address of the incoming
operator's position and is then always followed by signal\ I\(hy15 alone.
.PP
For international working this signal is to be used only in conformity
with Recommendation\ Q.107 | fIbis\fR . It can be used in national traffic
only if the incoming\ R2 registers are equipped to receive all six forward
frequencies. The necessary specifications are then the responsibility of
the Administration
concerned.
.PP
The \fIsignal\ I\(hy12\fR  | s a non\(hynumerical address signal. The meaning
of the signal is dependent on its position in the sequence of address signals
specified in Recommendation\ Q.107.
\v'3p'
.RT
.LP
    a)
    \fICountry code indicator, no echo suppressor required\fR
.PP
When signal\ I\(hy12 is transmitted as the first forward signal it
indicates that:
.RT
.LP
    i)
    a country code will follow (international transit);
.LP
    ii)
    the call may not require any echo suppressor (see
Recommendation\ Q.479).
\v'3p'
.LP
    b)
    \fIAccess to delay operator (code\ 12)\fR
.LP
.PP
When signal\ I\(hy12 is preceded by the language digit (and possibly
by one further address digit) it indicates that the call must be routed
to the delay operator's position, either to a particular operator, or one
of those
operating a particular group of positions. It is then followed by further
digits and the signal\ I\(hy15 or by the signal\ I\(hy15 alone.
.PP
In international working this signal is to be used in conformity with Recommendation\
Q.107 | fIbis\fR . It can be used in national traffic only if the
incoming\ R2 registers are equipped to receive all six forward frequencies.
The necessary specifications are then the responsibility of the Administrations
concerned.
\v'3p'
.RT
.LP
    c)
    \fIRequest not accepted\fR
.PP
An outgoing international R2 register which receives a signal A\(hy9 or
A\(hy10, the use of which is exclusively national, or which receives by
signal\ A\(hy13 a request to which it is unable to reply, should
indicate by transmitting signal\ I\(hy12 that it cannot answer the query (see
Recommendation\ Q.480). This signal may be similarly used in national traffic
to indicate that response to signal\ A\(hy9 or A\(hy10 is not possible.
.PP
The meaning of the non\(hynumerical signal I\(hy13 is dependent on its
position in the sequence of address signals specified in
Recommendation\ Q.107.
\v'3p'
.RT
.LP
    a)
    \fITest call indicator\fR
.PP
When in international working the signal I\(hy13 is transmitted as
the first forward signal it occupies the position of the language or
discriminating digit. It serves then as a test call indicator and must be
followed by the complete test equipment address information as specified
in b) below.
.bp
.RT
.LP
    b)
    \fIAccess to test equipment (code\ 13)\fR
.PP
To access automatic test equipment the second signal I\(hy13 (the
address digit) must be followed by two digits \fIxy\fR and the
signal\ I\(hy15.
\v'3p'
.RT
.LP
    c)
    \fISatellite link not included\fR
.PP
In response to signal A\(hy13, the meaning of the signal I\(hy13 is that
up to the outgoing\ R2 register no satellite link is included.
.PP
The meaning of the non\(hynumerical \fIsignal I\(hy14\fR  | s dependent on its
position in the sequence of address signals specified in
Recommendation\ Q.107.
\v'3p'
.RT
.LP
    a)
    \fICountry code indicator, outgoing half\(hyecho suppressor\fR
\fIinserted\fR
.PP
When signal I\(hy14 is transmitted as the first forward signal it
indicates that:
.RT
.LP
    i)
    a country code will follow (international transit);
.LP
    ii)
    the call requires echo suppressors;
.LP
    iii)
    the outgoing half\(hyecho suppressor has already been
inserted.
.PP
This signal is to be used in international working and only in
conformity with Recommendation\ Q.479.
\v'3p'
.LP
    b)
    \fIIncoming half\(hyecho suppressor required\fR
.PP
In response to signal A\(hy14, the meaning of the signal\ I\(hy14 is that
an incoming half\(hyecho suppressor is necessary.
\v'3p'
.RT
.LP
    c)
    \fISatellite link included\fR
.PP
In response to signal A\(hy13, the meaning of the signal I\(hy14 is that
up to the outgoing\ R2 register a satellite link is included in the connection.
.PP
The non\(hynumerical \fIsignal\ I\(hy15\fR  | ndicates the end of a sequence of
forward interregister signals. It is never sent as the first signal on an
international link.
\v'3p'
.RT
.LP
    a)
    \fIEnd\(hyof\(hypulsing\fR
.PP
In international working, signal I\(hy15 is used to indicate that
there are no more address signals to follow (see Recommendations\ Q.107
and\ Q.473).
\v'3p'
.RT
.LP
    b)
    \fIEnd of identification\fR
.PP
In national traffic, signal I\(hy15 may be used to indicate that
transmission of the sequence identifying the calling subscribers line is
terminated (see Recommendation\ Q.480, \(sc\ 5.8.2).
.RT
.sp 1P
.LP
4.2.3.2
    \fIGroup\ II forward signals\fR
.sp 9p
.RT
.PP
The Group\ II forward signals are calling party's category signals sent
by outgoing\ R2 registers or by outgoing international\ R2 registers in
reply to the backward signals\ A\(hy3 or A\(hy5 and give information whether
national or international working applies. For the signal codes see Table\
5/Q.441.
.PP
It is useful to identify calls according to type or
function:
.RT
.LP
    i)
    to indicate whether the forward transfer facility is
required in international traffic;
.LP
    ii)
    for adequate control of switching operations;
.LP
    iii)
     to enable any additional meanings for the signals A\(hy5 used in a national
network but not internationally accepted (for example,
to change the meanings of one or more following signals,
forward or backward) to be made inoperative for incoming
international calls;
.LP
    iv)
    for maintenance purposes.
.PP
The meanings of the calling party's category signals are detailed  below:
.PP
a)
The \fIsignal\ II\(hy1, subscriber without priority\fR  | ndicates that
the call is set up from a subscriber's line and is non\(hypriority.
.LP
.PP
b)
The \fIsignals\ II\(hy2 and II\(hy9, subscriber with priority\fR
 | ndicate that the call is set up from a subscriber's line to which priority
treatment of calls has been accorded. Signal\ II\(hy2 is specified for national
working only since there are no Recommendations regarding priority calls in
automatic international working (see Recommendation\ Q.480).
.bp
.PP
c)
The \fIsignal\ II\(hy3, maintenance equipment\fR  | ndicates that the call
comes from maintenance equipment.
.PP
d)
The \fIsignal\ II\(hy5, operator\fR  | ndicates that the call is set up
from an operator's position.
.PP
e)
The \fIsignals\ II\(hy6 and II\(hy8, data transmission\fR  | ndicate that
the call will be used for data transmission.
.PP
f
)
The \fIsignal\ II\(hy7, subscriber\fR  | ndicates that the
call is set up from a subscriber's line, an operator's position or from
maintenance equipment and that no forward transfer signal will be used.
.PP
g)
The \fIsignal\ II\(hy10, operator with forward transfer facility\fR  | ndicates
that the call is set up from an operator's position with possibility of
recourse to the forward transfer facility. Its use must be subject to
bilateral agreement (see Annex\ A to the present Specifications).
.LP
.PP
The signal\ II\(hy4 and the signals\ II\(hy11 to II\(hy15 are spare. The
meaning of signal\ II\(hy4 will be decided later by international agreement.
.LP
.rs
.sp 25P
.ad r
\fBTABLE 7/Q.441, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
4.2.4
    \fIBackward signals\fR
.sp 1P
.RT
.sp 1P
.LP
4.2.4.1
    \fIGroup\ A backward signals\fR
.sp 9p
.RT
.LP
.PP
Group\ A backward signals (for signal codes see Table\ 8/Q.441) are required
to acknowledge Group\ I forward signals and under certain conditions, Group\
II forward signals. Besides that functional part of the compelled
procedure, the Group\ A signals convey signalling information as detailed
below:
.RT
.LP
    a)
    The \fIsignal\ A\(hy1, send next digit (n\ +\ 1)\fR  | equests
transmission of the next digit (\fIn\fR \ +\ 1) after reception of digit\
\fIn\fR . The
latest address signal sent is assumed to have the rank \fIn\fR within the
signal
sequence specified in Recommendation\ Q.107.
.LP
    b)
    The \fIsignal\ A\(hy2, send last but one digit (n\ \(em\ 1)\fR  | equests
the transmission of digit\ (\fIn\fR \ \(em\ 1) after reception of digit\
\fIn\fR . The latest
address signal sent is assumed to have the rank\ \fIn\fR within the signal
sequence specified in Recommendation\ Q.107. This signal must not be used
on a satellite link.
.bp
.LP
.rs
.sp 20P
.ad r
\fBTABLE 8/Q.441, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
    c)
    The \fIsignal\ A\(hy3, address\(hycomplete, changeover to\fR
\fIreception of Group\ B signals\fR  | ndicates that the incoming\ R2 register
at the incoming end needs no additional address digit and is about to go
over to
transmission of a Group\ B signal conveying information about the condition
of the equipment at the incoming exchange or the condition of the called
subscriber's line (see Recommendation\ Q.442).
.LP
    d)
    The \fIsignal\ A\(hy4, congestion in the national network\fR
 | ndicates:
.LP
    i)
    congestion of national links;
.LP
    ii)
     congestion in selection stages of terminal international or national
exchanges;
.LP
    iii)
    occurrence of time\(hyout or abnormal release of a System\ R2
register produced for any reason.
.LP
    For exception to these rules see n) below. See also signal\ B\(hy4
and Recommendation\ Q.442.
.LP
    e)
    The \fIsignal\ A\(hy5, send calling party's category\fR  | equests
transmission of a Group\ II signal.
.LP
    f
)
    The \fIsignal\ A\(hy6, address\(hycomplete, charge \(em\fR
\fIset\(hyup speech conditions\fR  | ndicates that the R2 register at the
incoming end needs no additional digit, but will not send Group\ B signals.
The call has to be charged on answer (see Recommendation\ Q.442).
.LP
    g)
    The \fIsignal\ A\(hy7, send last but two digit\ (n\ \(em\ 2)\fR
 | equests the sending of digit (\fIn\fR \ \(em\ 2) after reception of
digit\ \fIn\fR . The
latest address signal sent is to have the rank\ \fIn\fR within the signal
sequence specified in Recommendation\ Q.107. This signal must not be used
on a satellite link.
.LP
    h)
    The \fIsignal\ A\(hy8, send last but three digit\ (n\ \(em\ 3)\fR
 | equests the sending of digit\ (\fIn\fR \ \(em\ 3) after reception of
digit\ \fIn\fR . The
latest address signal sent is to have the rank\ \fIn\fR within the signal
sequence specified in Recommendation\ Q.107. This signal must not be used
on a satellite link.
.LP
    i)
    The \fIsignals\ A\(hy9 to A\(hy10\fR  | re spares available for
allocation of national meanings. The use of signals\ A\(hy9 and A\(hy10
in national
networks can be decided by each Administration. These signals must not
be used on international satellite links.
.LP
    j)
     The \fIsignal\ A\(hy11, send country code indicator\fR  | equests the
country code indicator (transit indication) in acknowledgement of any
.LP
forward signal. The signal is used in international transit calls only (see
Recommendation\ Q.462). This signal must not be used on a satellite link.
.LP
    k)
    The \fIsignal\ A\(hy12, send language or discriminating digit\fR
 | equests the language digit or the discriminating digit in acknowledgement
of any forward signal. This signal must not be used on a satellite link.
.bp
.LP
    l)
    The \fIsignal\ A\(hy13, send nature of circuit\fR  | equests
information regarding the nature of the circuits involved in the
connection so far, i.e.\ satellite link (see Recommendation\ Q.480).
This signal should only be used on a satellite link by bilateral
agreement.
.LP
    m)
    The \fIsignal\ A\(hy14, request for information on use of echo\fR
\fIsuppressor\fR  | is an incoming half\(hyecho suppressor required?) indicates
that an incoming international exchange acknowledges the discrimination
digit or the
language digit and that it is possible to insert an incoming half\(hyecho
suppressor in that incoming international exchange if required. This signal
must not be used on a satellite link.
.LP
    n)
    The \fIsignal\ A\(hy15, congestion in an international exchange\fR
\fIor at its output\fR  | ndicates:
.LP
    i)
    congestion on international links;
.LP
    ii)
    congestion in selection stages at an international transit
exchange or at a terminal international exchange and/or its
outgoing links;
.LP
    iii)
    occurrence of time\(hyout or abnormal release of a System\ R2
register produced for any reason (see Recommendation\ Q.442).
.sp 1P
.LP
4.2.4.2
    \fIGroup\ B backward signals\fR
.sp 9p
.RT
.PP
Any Group\ B backward signal (for signal codes see Table\ 9/Q.441)
acknowledges a Group\ II forward signal and is always preceded by the
address\(hycomplete signal\ A\(hy3 which indicates that the incoming\ R2
register has received all the Group\ I forward signals it requires from
the outgoing
international\ R2 register. Besides that functional part of the compelled
procedure the Group\ B signals convey information about the condition of
switching equipment in the incoming exchange, or about the condition of the
called subscriber's line, to the outgoing international\ R2 register which
can then take the necessary action as specified in Recommendation\ Q.474.
.RT
.LP
.rs
.sp 23P
.ad r
\fBTABLE 9/Q.441, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
The following Group\ B signals are specified:
.LP
    a)
    The \fIsignal\ B\(hy1 is spare\fR  | or national use and its
meaning must be compatible with that of signal\ B\(hy6 (see Recommendation\
Q.474).
.LP
    b)
     The \fIsignal\ B\(hy2, send special information tone\fR  | ndicates that
the special information tone should be returned to the calling party. This
tone indicates that the called number cannot be reached for reasons not
covered by other specific signals and that the unavailability is of a long
term nature (see also Recommendation\ Q.35).
.bp
.LP
    c)
    The \fIsignal\ B\(hy3, subscriber's line busy\fR  | ndicates that
the line or lines connecting the called subscriber to the exchange are
engaged.
.LP
    d)
    The \fIsignal\ B\(hy4, congestion\fR  | ndicates that congestion
condition is encountered after the changeover from Group\ A signals to
Group\ B signals. The signal\ B\(hy4 shall be sent in the conditions specified
for
signal\ A\(hy4 [see \(sc\ 4.2.4.1,\ d) and Recommendation\ Q.474, \(sc\
5.3.5.1].
.LP
    e)
    The \fIsignal\ B\(hy5, unallocated number\fR  | ndicates that the
number received is not in use (e.g.\ an unused country code, an unused trunk
code or subscriber number that has not been allocated).
.LP
    f
)
    The \fIsignal\ B\(hy6, subscriber's line free, charge\fR
 | ndicates that the called party's line is free and that the call has to be
charged on answer.
.LP
    g)
    The \fIsignal\ B\(hy7, subscriber's line free, no\fR
\fIcharge\fR  | ndicates that the called party's line is free but is
not to be charged on answer. This signal permits non\(hychargeable
calls without the need for transferring \*Qno charge\*U information
by line signals.
.LP
    h)
    The \fIsignal\ B\(hy8, subscriber's line out of order\fR
 | ndicates that the subscriber's line is out\(hyof\(hyservice or faulty.
.LP
    i)
    \fISignals\ B\(hy9 and B\(hy10\fR  | re spare for national use. Their
meaning must not be incompatible with the sending of special
information tone to the calling party (see Recommendation\ Q.474).
.LP
    j)
    \fISignals B\(hy11 to B\(hy15\fR  | re spare for national use. Their
meaning can be allocated as required. Sending of these signals into the
international network must be prevented.
.LP
     To deviate from this rule will result in the actions defined in Recommendation\
Q.474.
.sp 2P
.LP
\fBRecommendation\ Q.442\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.3\ \fR \fBPULSE\ TRANSMISSION\ OF\ BACKWARD\ SIGNALS\ A\(hy3,\fR \fBA\(hy4,\
A\(hy6\ OR\ A\(hy15\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.442''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.442    %'
.ce 0
.sp 1P
.PP
Under certain conditions it may prove necessary or desirable
to send one of the \fIsignals\ A\(hy3, A\(hy4, A\(hy6 or A\(hy15\fR without
prior reception of a forward signal. This can occur when the incoming\
R2 register, after
acknowledging a recognized forward signal, is unable to complete the call
(for example during congestion) and the next forward signal does not appear
on the line; or when the address\(hycomplete signal must be sent after
the last forward address signal has been acknowledged. It may be desirable
to deliberately
suspend compelled signalling by acknowledging the last address digit, and
signal\ I\(hy15 if received, with signal A\(hy1 to avoid prolonging the
transmission
.sp 1P
.RT
.LP
time of certain interregister signals. Such a
course should certainly be considered when there is a possibility that a
relatively long period may elapse between reception of the last digit and
detection of the condition of the called subscriber's line. The average
duration of such periods during the busy hour must be limited to 3\ seconds
in view of the load on the carrier systems in the case of international
calls.
.PP
The following conditions must be observed in transmitting pulsed interregister
signals
(see Figure\ 14/Q.442):
.LP
    \(em
     the minimum delay between the end of transmission of the last signal
of the compelled cycle and the start of transmission of
the pulse signal must be 100\ ms;
.LP
    \(em
    the pulse duration must be 150\ \(+-\ 50\ ms.
.PP
Reception of a pulse signal must cause interruption of any forward signal
in course of transmission at the outgoing\ R2 register. It is sometimes
impossible, however, to prevent a forward signal from being sent by the
outgoing\ R2 register at the very moment when one of the backward signals\
A\(hy3, A\(hy4, A\(hy6 or A\(hy15 is sent in pulse form by the register
at the incoming end.
.PP
To reduce the operating difficulties which may result, the incoming\ R2
register must be so designed that no forward multifrequency combination
can be recognized during and after the transmission of signals\ A\(hy4,
A\(hy6 or A\(hy15 in
pulse form or during 300\ \(+-\ 100\ ms from the start of transmission of the
address\(hycomplete signal\ A\(hy3 in pulse form (900\ \(+-\ 180\ ms when
signal\ A\(hy3 is
transmitted over a satellite link) (see Figures\ 14/Q.442 and 15/Q.442).
When the end of a pulse signal\ A\(hy3 has been recognized in the outgoing\ R2
register, a Group\ II signal must be sent forward. The incoming\ R2 register
will acknowledge this signal by a Group\ B signal.
.bp
.PP
On recognizing signal\ A\(hy4, A\(hy6 or A\(hy15 no forward signal is sent
by the outgoing\ R2 register. The end of these backward signals must cause
the
dismissal of the outgoing and incoming\ R2 registers in accordance with
Recommendation\ Q.475.
.PP
The conditions under which pulse transmission of the backward
signals\ A\(hy3, A\(hy4, A\(hy6 or A\(hy15 apply are specified in Section\ 5.
\v'6p'
.RT
.LP
.rs
.sp 27P
.ad r
\fBFigure\ 14/Q.442, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.ce 1000
\fB4.4\ MULTIFREQUENCY\ SIGNALLING\ EQUIPMENT\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.450\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.4.1\ GENERAL\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.450''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.450    %'
.ce 0
.sp 1P
.PP
Since System\ R2 can provide, in international working, end\(hyto\(hyend
signalling from the outgoing international R2\ register to an incoming
R2\ register at the called subscriber's local exchange (see
Recommendation\ Q.440), the specifications for multifrequency signalling
equipment take account of transmission conditions in both the international
.sp 1P
.RT
.LP
and national networks. The incoming national network may include both 4\(hywire
and 2\(hywire links.
.PP
However, it is assumed in the following specifications for
multifrequency signalling equipment for outgoing international R2\ registers
and incoming R2\ registers in international exchanges including the incoming
international exchange that the registers are directly connected by four
wires to the virtual switching points of the links. The registers thus
contain a
multifrequency signalling equipment with a transmitting part and a receiving
part, each separately connected to the GO and RETURN path of the 4\(hywire
circuit respectively
(see\ Figure\ 16/Q.451).
.bp
.PP
When the outgoing international R2\ register is situated in a national
exchange preceding the outgoing international exchange, or when the incoming
R2\ register is situated in a national exchange following the incoming
international exchange, special conditions apply (see Recommendation\ Q.457).
.PP
The upper and lower limits specified for the sending level and for the
national extension attenuation leave a degree of freedom, thus simplifying
the problem of interworking among different networks. The outgoing international
R2\ register relays the interregister signals by the method described in
Recommendation\ Q.478. The present specification ensures that the system
has an adequate range.
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.451\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.4.2\ DEFINITIONS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.451''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.451    %'
.ce 0
.sp 1P
.LP
4.4.2.1
    \fIMultifrequency signalling equipment\fR
.sp 1P
.RT
.PP
During the exchange of multifrequency combinations the link or
multi\(hylink section is terminated at both ends by equipment allowing
multifrequency combinations to be sent and received under mutual, compelled
control, as indicated in Recommendation\ Q.440. Generally speaking, the
equipment involved in the signal transfer at each end of the multi\(hylink
section has the following functions:
.RT
.LP
    \(em
    reception of multifrequency combinations;
.LP
    \(em
    protection against disturbances (e.g.\ 2\(hyout\(hyof\(hy\fIn\fR \(hycheck,
0\(hyout\(hyof\(hy\fIn\fR \(hycheck, see Recommendation\ Q.458);
.LP
    \(em
    transfer of signals to and from the registers or equivalent   equipment;
.LP
    \(em
    sending of multifrequency combinations.
.PP
This equipment as a whole can be considered as a single functional unit,
henceforth called the multifrequency signalling equipment.
.PP
The functions of the multifrequency signalling equipment may be
distributed among a number of sub\(hyunits, according to the design principles
adopted in each particular case; these, within certain limits, are open to
choice.
.PP
For the purpose of the present specification, the multifrequency
signalling equipment is divided into a sending part and a receiving part.
.RT
.sp 1P
.LP
a)
    \fIFour\(hywire multifrequency signalling equipment\fR
.sp 9p
.RT
.PP
Multifrequency signalling equipment connected to the speech path by two
pairs of wires is called 4\(hywire multifrequency signalling equipment
(see
Figure\ 16/Q.451). In such cases, the speech path itself is generally 4\(hywire
too.
.PP
In Figure 16/Q.451, point\ B is the output of the sending part and
point\ C the input to the receiving part of the 4\(hywire multifrequency
signalling equipment. The latter includes the devices for protection against
disturbances and the equipment for transferring signals to the register
or equivalent
equipment.
.RT
.sp 1P
.LP
b)
    \fITwo\(hywire multifrequency signalling equipment\fR
.sp 9p
.RT
.PP
Because different frequencies are used for interregister signalling in
the two directions of transmission, a single pair of wires connecting the
speech path to the multifrequency signalling equipment can be used for
simultaneous sending and reception of multifrequency combinations.
.PP
Multifrequency signalling equipment connected to the speech path by a single
pair of wires is called 2\(hywire multifrequency signalling equipment (see
Figure\ 17/Q.451).
.PP
In Figure\ 17/Q.451, point\ A is the output of the sending part and, at
the same time, the input to the receiving part. The latter includes the
devices for protection against disturbances and for transferring signals
to the
register or equivalent equipment.
.RT
.LP
.sp 1P
.LP
4.4.2.2
    \fIOperate and release times of the receiving part of the\fR
\fIsignalling equipment\fR
.sp 9p
.RT
.PP
The speed and reliability of the compelled interregister signal
transfer is dependent on the operation and release times\ \fIT\fR\d0\u,
\fIT\fR\d\fIR\fR\u, \fIT\fR `\d0\uand\ \fIT\fR `\fI
\fI\d\fIR\fR\udefined below. These times include the minimum recognition
times referred to in
\(sc\ 4.4.5.3\ below.
.bp
.RT
.LP
.rs
.sp 15P
.ad r
\fBFIGURE\ 16/Q.451, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
a)
    \fIOperation time\fR
.sp 9p
.RT
.PP
If the two frequencies making up a multifrequency combination are
applied simultaneously to the input of the receiving part of the multifrequency
signalling equipment, the time interval between the application of both
frequencies and recognition of the multifrequency combination is called
operation time\ \fIT\fR\d0\u.
.PP
If one of the two frequencies making up a multifrequency combination is
applied to the input of the receiving part of the multifrequency signalling
equipment somewhat after the other frequency, the time interval between the
application of the second frequency and recognition of the multifrequency
combination is called operation time\ \fIT\fR `\d0\u.
.RT
.sp 1P
.LP
b)
    \fIRelease time\fR
.sp 9p
.RT
.PP
If the two frequencies making up a multifrequency combination are
simultaneously cut off from the input of the receiving part of the
multifrequency signalling equipment, the time interval between the cut\(hyoff
and recognition of the end of the multifrequency combination is called
release
time\ \fIT\fR\d\fIR\fR\u.
.PP
If one of the two frequencies making up a multifrequency combination is
cut off from the input of the receiving part of the multifrequency signalling
equipment somewhat after the other frequency, the time interval between
the cut\(hyoff of the second frequency and recognition of the end of the
multifrequency combination is called release
time\ \fIT\fR `\fI
\fI\d\fIR\fR\u.
.RT
.LP
.sp 2P
.LP
4.4.2.3
    \fIInternal operation time\fR
.sp 1P
.RT
.PP
a)
If the equipment at a switching centre has to analyse one or
more of the signals received and if it has to carry out routing and switching
operations before being able to determine which backward signal should
be sent, it can delay completion of the compelled signalling cycle. Such
delay depends on the function the centre has and on the design of the switching
equipment
used in it. The delay cannot therefore be specified.
.sp 9p
.RT
.PP
The time required by an incoming R2\ register to determine which
backward signal to send in reply to a forward signal is denoted as
\fIT\fR \s6\fIint\fR \ 1
.PS 10
. The duration of the cycle is increased by the whole of this time, which
must therefore be kept to a minimum. Its value
will be zero if the signal to be sent is already determined.
.RT
.PP
b)
An outgoing R2\ register sends a forward signal after
interpreting the backward signal it has received. The time required to
determine the appropriate signal is denoted
as\ \fIT\fR \s6\fIint\fR \ 2
.PS 10
.
.sp 9p
.RT
.LP
.PP
c)
At the end of a forward signal the incoming R2\ register may
have to perform certain functions in order to be ready to receive the next
signal. The time required for these functions is denoted
as\ \fIT\fR \s6\fIint\fR \ 3
.PS 10
.
.bp
.sp 9p
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.452\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.4.3\ REQUIREMENTS\ RELATING\ TO\ TRANSMISSION\ CONDITIONS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.452''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.452    %'
.ce 0
.sp 1P
.LP
4.4.3.1
    \fIImpedances\fR
.sp 1P
.RT
.PP
The impedance\ \fIZ\fR\d\fIA\fR\umeasured at the terminals\ A (see
Figure\ 17/Q.451) of a 2\(hywire multifrequency signalling equipment will
have a
nominal value equal to the nominal terminating impedance\ \fIZ\fR\d\fIT\fR\uof
the links at the exchange under consideration and will be balanced to earth.
In most
cases this value\ \fIZ\fR\d\fIT\fR\uwill be 600\ ohms non\(hyreactive.
The impedance\ \fIZ\fR\d\fIA\fR\uwill then satisfy the conditions:
\v'6p'
.RT
.ce 1000
20 log
@ left | { 00~+~\fIZ~\dA\u\fR } over { 00~\(em~\fIZ~\dA\u\fR }  right | @  \(>=" 10 dB
.ce 0
.ad r
(1)
\v'7p'
.ad b
.RT
.LP
.sp 1
in the 300\(hy3400\ Hz band, and
\v'6p'
.ce 1000
20 log
@ left | { 00~+~\fIZ~\dA\u\fR } over { 00~\(em~\fIZ~\dA\u\fR }  right | @  \(>=" 16 dB
.ce 0
.ad r
(2)
\v'7p'
.ad b
.RT
.LP
.sp 1
in the 520\(hy1160\ Hz and 1360\(hy2000\ Hz bands.
.PP
The impedances\ \fIZ\fR\d\fIB\fR\uand\ \fIZ\fR\d\fIC\fR\umeasured at the
terminals\ B
and\ C (see Figure\ 16/Q.451) of a 4\(hywire multifrequency signalling
equipment
will have a nominal value equal to the nominal terminating impedance\ \fIZ\fR\d\fIT\fR\uat
the exchange under consideration and will be balanced to earth. In most
cases this value\ \fIZ\fR\d\fIT\fR\uwill be 600\ ohms non\(hyreactive.
The impedances\ \fIZ\fR\d\fIB\fR\u
and\ \fIZ\fR\d\fIC\fR\uwill then satisfy condition\ (1) above in the 300\(hy3400\
Hz band and condition\ (2) above in the 520\(hy1160\ Hz or 1360\(hy2000\
Hz bands, according to the set of frequencies generated by the equipment
concerned.
.PP
All the above requirements must be met, whether signalling frequencies
are being transmitted or not.
.RT
.sp 1P
.LP
4.4.3.2
    \fIEchoes\fR
.sp 9p
.RT
.PP
The balance return loss presented to the international link by
different national networks varies considerably. Recommendation\ G.122
gives the desirable values based on transmission requirements and these
values could
hardly be improved on simply in order to facilitate signalling, especially
as the balance return loss would then have to be very high.
.PP
The multifrequency signalling equipment must therefore function with an
echo signal. Allowance is made for this in the test conditions (see
Recommendation\ Q.455).
.PP
In order to eliminate disturbing and unwanted double\(hyecho effects,
outgoing international R2\ registers must be provided with 4\(hywire signalling
equipment; the 4\(hywire loop will then remain open at the outgoing end of the
multi\(hylink section during signalling.
.PP
For the same reason, it is recommended that 4\(hywire signalling
equipment be provided whenever 4\(hywire switching equipment is used.
.RT
.sp 1P
.LP
4.4.3.3
    \fILocation and connection of mutifrequency signalling\fR
\fIequipment associated with outgoing international R2\ registers\fR
.sp 9p
.RT
.PP
The multifrequency signalling equipment of the outgoing
international R2\ registers is assumed to be directly connected to the
virtual switching point of the links in an international exchange. This
equipment may be situated in a national switching centre of the country
of origin on the
.PP
national network side of the outgoing international exchange provided that
the 4\(hywire extension links between this centre and the outgoing international
exchange have the same upper limit for the standard deviation of transmission
loss variations with time (1\ dB) as the international links.
.PP
Should the national extension links not have a nominal transmission
loss of 0.5\ dB between the national exchange and the virtual switching
point in the outgoing international exchange, there must be suitable compensation
of the power level of the multifrequency combinations.
.bp
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.454\fR
.RT
.sp 2P
.ce 1000
\fB4.4.4\ \fR \fBTHE\ SENDING\ PART\ OF\ THE\ MULTIFREQUENCY\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.454''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.454    %'
.ce 0
.sp 1P
.ce 1000
\fBSIGNALLING\ EQUIPMENT\fR
.ce 0
.sp 1P
.LP
4.4.4.1
    \fISignalling frequencies\fR
.sp 1P
.RT
.PP
The composition of the multifrequency combinations is specified in Recommendation\
Q.441.
.PP
The frequencies in the forward direction are:
.PP
\fIf\fR\d0\u\ =\ 1380, \fIf\fR\d1\u\ =\ 1500, \fIf\fR\d2\u\ =\ 1620, \fIf\fR\d3\u\
=\ 1740, \fI\fR
\fIf\fR\d4\u\ =\ 1860, \fIf\fR\d5\u\ =\ 1980\ Hz.
.PP
The frequencies in the backward direction are:
.PP
\fIf\fR\d0\u\ =\ 1140, \fIf\fR\d1\u\ =\ 1020, \fIf\fR\d2\u\ =\ 900, \fIf\fR\d3\u\
=\ 780,
\fIf\fR\d4\u\ =\ 660, \fIf\fR\d5\u\ =\ 540\ Hz.
.PP
The frequency variation at the sending point must not exceed \(+- | \ Hz
relative to the nominal value.
.RT
.sp 1P
.LP
4.4.4.2
    \fIAbsolute power level transmitted\fR \v'3p'
.sp 9p
.RT
.PP
a)
Four\(hywire multifrequency signalling equipment for outgoing
international\ R2 and incoming R2\ registers assumed to be directly connected
to the virtual switching point in an international exchange:
.LP
    i)
    The absolute power level of each non\(hymodulated signalling
frequency transmitted by the sending part of the multifrequency
signalling equipment in the international exchange concerned
will have a nominal value of \(em8\ dBm0 with a
tolerance \(+- | \ dB. At an analogue input of the exchange, this corresponds
to \(em11.5\ dBm\ \(+-\ 1\ dB.
.LP
    ii)
    The difference in level between the two signalling
frequencies making up a multifrequency combination must be
less than\ 1\ dB.
.PP
The tolerances specified apply to the sending point itself,
i.e.\ terminal\ B in Figure\ 16/Q.451.
.LP
.PP
b)
Four\(hywire multifrequency signalling equipment for outgoing
international\ R2 registers situated in a national exchange further down
in the network of the country of origin:
.sp 9p
.RT
.LP
    i)
    The sending\(hylevel conditions mentioned above under\ a) are
applicable in such national exchanges, provided that the national
4\(hywire extension links between the national exchange and the
outgoing international exchange have the same nominal
transmission loss (0.5\ dB) and the same upper limit of
standard deviation of transmission loss variations with time
(1\ dB) as the international links.
.LP
    ii)
     If these national links do not have a nominal transmission loss of 0.5\
dB, the level of interregister frequencies must
be compensated as required.
.PP
c) \fR Multifrequency signalling equipment for incoming R2\ registers in
national exchanges:
.sp 9p
.RT
.LP
.PP
The nominal absolute power level\ \fIN\fR  | f a single signalling
frequency transmitted by the sending part of the multifrequency signalling
equipment (2\(hywire or 4\(hywire) in any national exchange must be chosen
within the limits:
\v'6p'
.ad r
    \fIN\fR \(>=" \fIA
\db\u\fR + 0,5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 31 dBm
(1)
.ad b
.RT
.LP
    .sp 1
and
\v'6p'
.ad r
    \fIN\fR \(= \fIA
\db\u\fR \(em 11.5 dBm
(2)
.ad b
.RT
.LP
    .sp 1
or
\v'6p'
.ad r
    \fIN\fR \(= \fIA
\db\u\fR + 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 9 dBm
(3)
.ad b
.RT
.LP
    .sp 1
.LP
whichever of (2) or (3) yields the lower value.
.PP
In order to avoid marginal operation, it is recommended that
levels higher than the minimum levels given by formula\ (1) be specified.
.bp
.PP
In these formulae:
.RT
.LP
    \(em
     \fIm\fR \ =\ the number of 4\(hywire links switched in tandem between
the outgoing international R2\ register and the incoming international
exchange. The number\ \fIm\fR thus includes the national 4\(hywire extension
links in the country of origin (see Recommendation\ Q.457) and the international
links. In
formula\ (1) \fIm\fR \ should always be given the maximum value\ 4. In
formula\ (3),
\fIm\fR \ should be given all its values, from minimum to maximum, and
the lowest
value so obtained or derived from formula\ (2) is to be taken as the upper
limit of\ \fIN\fR .
.LP
    \(em
     \fIk\fR \ =\ the number of national 4\(hywire extension links switched
in tandem between the incoming international terminal exchange
and the national exchange. The maximum value of\ \fIk\fR will be\ 4.
.LP
    \(em
    \fIA\fR\d\fIb\fR\u\ =\ the nominal transmission loss at 800\ Hz in the
backward direction between the output terminals of the sending part of the
multifrequency signalling equipment of the incoming R2\ register in the
exchange under consideration and the \fIsend\fR side of the virtual switching
point of the backward speech path in the incoming international exchange.
.PP
Formulae\ (1), (2) and\ (3) were derived as shown in Annex\ A to
Section\ 4.
.PP
The variation in level relative to the nominal value\ \fIN\fR  | hosen
for a given exchange must not exceed\ \(+- | \ dB.
.PP
However, the difference in level between the two signalling
frequencies making up a multifrequency combination must not exceed\ 1\ dB.
.RT
.sp 1P
.LP
4.4.4.3
    \fISignalling frequency leak level\fR
.sp 9p
.RT
.PP
The total power level of the leak current transmitted to line must  be:
.RT
.LP
    a)
    at least 50\ dB below the nominal level of one signalling
frequency when no multifrequency combination is being sent;
.LP
    b)
     at least 30\ dB below the level of either of the signalling frequencies
when a multifrequency combination is being sent. Furthermore, any single
leak current must be at least 34\ dB below the level of either of the
signalling frequencies when a multifrequency combination is being sent.
.sp 1P
.LP
4.4.4.4
    \fIHarmonic distortion and intermodulation\fR
.sp 9p
.RT
.PP
The total power level of all frequencies due to harmonic distortion and
intermodulation within the frequency band 300\(hy3400\ Hz must be at least
37\ dB below the level of one signalling frequency.
.RT
.sp 1P
.LP
4.4.4.5
    \fITime tolerance for multifrequency combinations\fR
.sp 9p
.RT
.PP
The time interval between the start of sending of each of the two frequencies
constituting a multifrequency combination must not exceed\ 1\ ms.
.PP
The time interval between the cessation of sending of each of the two frequencies
must not exceed\ 1\ ms.
\v'2P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.455\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.4.5\ \fR \fBTHE\ RECEIVING\ PART\ OF\ THE\ MULTIFREQUENCY\ EQUIPMENT\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.455''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.455    %'
.ce 0
.sp 1P
.LP
4.4.5.1
    \fISensitivity range\fR
.sp 1P
.RT
.PP
The power levels given below relate to the nominal impedance of the receiving
part of the multifrequency signalling equipment.
.PP
The receiving part of the multifrequency signalling equipment shall
have a sensitivity range of\ \(em31.5\ dBm0 to\ \(em5\ dBm0
.FS
For equipments already
in service the sensitivity range is \(em35\ dBm to\ \(em5\ dBm.
.FE
.
.bp
.RT
.sp 1P
.LP
4.4.5.2
    \fIOperate and release time requirements\fR
.sp 9p
.RT
.PP
The operating and release times of the receiving part of the
multifrequency signalling equipment depend on the design and, for a given
design, on:
.RT
.LP
    \(em
     the time difference between the instants of reception of each of the
two frequencies making up a multifrequency combination;
.LP
    \(em
    the level of each of the two frequencies;
.LP
    \(em
    the difference in level between the two frequencies;
.LP
    \(em
    the level, spectrum and instant of onset of the noise.
.PP
The factors vary with transmission conditions. With certain types of switching
equipment it may prove advisable to embody devices to counteract low\(hyfrequency
disturbances in the multifrequency signalling equipment.
.PP
Time requirements have been specified for two types of
\fImultifrequency test combinations\fR , A\ and\ B, applied to the input of the
receiving part of the multifrequency signalling equipment in the presence of
disturbing signals as specified below.
.PP
When test combinations and disturbing frequencies as specified
under\ a) to\ c) below are applied to the terminals\ A (see Figure\ 17/Q.451)
of
2\(hywire multifrequency signalling equipment or to the terminals\ C (see
Figure\ 16/Q.451) of 4\(hywire multifrequency signalling equipment, the
following time requirements must be met:
.RT
.LP
    \(em
    for type\ A test combinations:
\v'6p'
.sp 1P
.ce 1000
\fIT\fR \d0\u + \fIT
\dR\u\fR \(= 70 ms
.ce 0
.sp 1P
.LP
.sp 1
    \(em
    for type\ B test combinations:
\v'6p'
.sp 1P
.ce 1000
\fIT\fR \d0\u + \fIT
\dR\u\fR \(= 80 ms
.ce 0
.sp 1P
.LP
.sp 1
    \(em
    for test combinations of types\ A and\ B:
\v'6p'
.sp 1P
.ce 1000
(\fIT\fR `
\d0\u + \fIT\fR `
\fI
\dR\u\fR ) \(= (\fIT\fR \d0\u +
\fIT
\dR\u\fR ) + 5 ms
.ce 0
.sp 1P
.LP
.sp 1
.PP
For definitions of \fIT\fR\d0\u, \fIT\fR `\d0\u,
\fIT\fR\d\fIR\fR\u,
and \fIT\fR `
\fI
\dR\u\fR see Recommendation\ Q.451.
.PP
For the third requirement, the only cases to be considered are those in
which the frequency first appearing is also the first to disappear
(transmission delay effect). The \fIT\fR `
\d0\u and
\fIT\fR `
\fI
\dR\u\fR time requirements are specified to ensure proper
functioning of the multifrequency signalling equipment when the received
multifrequency combination is affected by group delay distortion, for example.
The appropriate procedure for this test depends on the design of the equipment
to be tested; in many cases it will be convenient to assume that a delay
of one second or more for the second frequency constitutes the most unfavourable
case.
.PP
When a multifrequency combination has caused the receiving part of the
multifrequency signalling equipment to operate, the latter cannot release
if
the signal frequencies are interrupted for not more than\ 7\ ms. A method of
improving the system reliability in case of interrupted signals is described
in Annex\ B of Section\ 4.
.RT
.sp 1P
.LP
a)
    \fIMultifrequency test combinations type\ A\fR
.sp 9p
.RT
.LP
    \(em
    The multifrequency test combination consists of any
2\(hyout\(hyof\(hy\fIn\fR combination of the \fIn\fR signalling frequencies;
.LP
    \(em
     each frequency differs from the nominal frequency by not more than\ \(+- | \
Hz;
.LP
    \(em
    the absolute power level of each of the two frequencies of
the multifrequency combination lies between\ \(em5\ dBm and\ \(em20\ dBm;
.LP
    \(em
    the difference in level between the two frequencies is not
greater than\ 3\ dB.
.bp
.sp 1P
.LP
b)
    \fIMultifrequency test combinations type\ B\fR
.sp 9p
.RT
.LP
    \(em
    The multifrequency test combination consists of any
2\(hyout\(hyof\(hy\fIn\fR combination of the \fIn\fR \ signalling frequencies;
.LP
    \(em
     each frequency differs from the nominal frequency by not more than\ \(+- | 0\
Hz;
.LP
    \(em
    the absolute power level of each of the two frequencies of
the multifrequency combination lies between \(em5\ dBm and \(em35\ dBm;
.LP
    \(em
    the difference in level between the two frequencies is not
greater than\ 5\ dB for adjacent frequencies and\ 7\ dB for
non\(hyadjacent frequencies.
.sp 1P
.LP
c)
    \fIDisturbing frequencies\fR
.sp 9p
.RT
.PP
The disturbing frequencies to be applied are:
.RT
.LP
    \(em
     in all cases one or more of the \fIn\fR  | requencies for which the receiving
part under test is designed, with a total power
level of \(em55\ dBm or less, when no multifrequency test
combination is being applied;
.LP
    \(em
    when a multifrequency test combination is applied, one or
more of the (\fIn\fR \ \(em\ 2) remaining frequencies with a total power
level 20\ dB
below the highest test combination frequency level during application of the
test combination;
.LP
    \(em
    for testing the receiving part of 4\(hywire multifrequency
signalling equipment in an outgoing international R2\ register:
.LP
     any multifrequency combination consisting of two frequencies out of the
forward group of frequencies, each of these two frequencies having a
level of 13.5\ dB above the lowest test\(hycombination frequency level in the
backward direction; an upper limit of \(em12.5\ dBm is nevertheless specified
for the level of the disturbing signal.
.LP
     System\ R2 interregister signalling may be used in the country of origin
on the national links preceding the out\(hygoing international\ R2 register.
In that case, the receiving part of 4\(hywire multifrequency signalling
equipment connected to the forward speech path of the national 4\(hywire
links may have to function in the presence of frequencies used in the backward
direction. No
general specification can be given for the level of these disturbing
frequencies; it is recommended that Administrations formulate their own
specifications.
.LP
    \(em
    for testing the receiving part of 2\(hywire multifrequency
signalling equipment:
.LP
    any multifrequency combination at the highest level used in
operational signalling (measured at point\ A, Figure\ 17/Q.451)
by the sending part of the 2\(hywire multifrequency signalling
equipment concerned.
.sp 1P
.LP
4.4.5.3
    \fINon\(hyoperate and non\(hyrecognition requirements\fR
.sp 9p
.RT
.PP
The receiving part of the multifrequency signalling equipment must remain
in the \fInon\(hyoperate\fR state when the following disturbances, singly
or
together, are the only signals that are applied to the terminals\ A or\ C (see
Figures\ 17/Q.451 and\ 16/Q.451):
.RT
.LP
    \(em
     any single pure sine wave or any combination of two pure sine waves,
each with a power level of\ \(em38.5\ dBm0 within the 300\(hy3400\ Hz
band;
.FS
For equipments already in service, the non\(hyoperation level is
\(em42\ dBm.
.FE
.LP
    \(em
     any single pure sine wave or any combination of two pure sine waves,
each with a power level of \(em42\ dBm within the 300\(hy3400 Hz band;
.LP
    \(em
    any combination of two pure sine waves, each with a power
level of\ \(em5\ dBm within the 1300\(hy3400\ Hz band for the set of frequency
receivers used in the backward direction; and within the 330\(hy1150\ Hz
and 2130\(hy3400\ Hz
bands for the set of frequency receivers used in the forward direction.
.LP
.PP
Furthermore, when signalling tones have activated the receiving
part of the multifrequency signalling equipment, this must assume the
\fInon\(hyoperate\fR state when the signalling tones are removed in the
presence of
these same disturbances, singly or together, at the above\(hymentioned
terminals.
.PP
The receiving part of the multifrequency signalling equipment must not
recognize a combination consisting of two signalling frequencies out of
the set of frequencies normally used in the transmission direction considered,
each
having a level not exceeding \(em5\ dBm and a duration of less than 7\ ms.
.PP
The receiving part of the multifrequency signalling equipment must not
recognize a combination consisting of two signalling frequencies used in
the
transmission direction considered, having a difference in level of 20\ dB or
more.
.bp
.RT
.LP
.sp 1P
.LP
4.4.5.4
    \fIInfluence of transient disturbances\fR  | see also
Recommendation\ Q.458)
.sp 9p
.RT
.PP
The recognition of faulty signals due to short\(hylived transient
conditions can largely be avoided if a multifrequency combination is recognized
only after a specified minimum time, during which two, and only two, of
the
individual receivers are active and if the absence of multifrequency
combinations is recognized only after a minimum time, during which all
individual receivers are at rest. These times are included in the operating
and release times\ \fIT\fR\d0\uand \fIT\fR\d\fIR\fR\u.
.PP
Typical transient disturbances, such as clicks, change of polarity,
etc., generated by the switching equipment, must not change signals transferred
from the receiving part of the signalling equipment to the register.
.PP
It is recommended that Administrations formulate their own
specification for a test method according to the type of disturbances
encountered in their switching equipment.
\v'6p'
.RT
.LP
.ce 1000
\fB4.5\ RANGE,\ SPEED\ AND\ RELIABILITY\fR
.ce 0
.sp 1P
.ce 1000
\fBOF\ INTERREGISTER\ SIGNALLING\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.457\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.5.1\ \fR \fBRANGE\ OF\ INTERREGISTER\ SIGNALLING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.457''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.457    %'
.ce 0
.sp 1P
.LP
4.5.1.1
    \fINumber of international links\fR
.sp 1P
.RT
.PP
The number of international links switched in tandem for
establishing an international connection using System\ R2 must not exceed\
4 (see Recommendation\ Q.440).
.PP
Assumptions for the transmission loss in 4\(hywire international
links:
.RT
.LP
    i)
    nominal transmission loss at 800\ Hz:\ 0.5\ dB
(Recommendation\ G.101, \(sc\ 5);
.LP
    ii)
    standard deviation of transmission loss variations with
time must not exceed 1\ dB [Recommendation\ G.151, \(sc\ 3, a)];
.LP
    iii)
     the difference between the mean value and the nominal is assumed to be
0 [as in Recommendations\ G.122, \(sc\ 1.2),
and G.131, \(sc\ 1].
.sp 2P
.LP
4.5.1.2
    \fINumber of national links\fR
.sp 1P
.RT
.sp 1P
.LP
a)
    \fIOutgoing international\ R2 register and number of national 4\(hywire\fR
\fIextension links in the country of origin\fR
.sp 9p
.RT
.PP
The outgoing international\ R2 register is always provided with
4\(hywire multifrequency signalling equipment and the 4\(hywire loop will
be open
during interregister signalling.
.PP
The outgoing international\ R2 register must be placed in an exchange from
where the incoming international exchange in the country of destination
is reached by not more than four 4\(hywire links switched in tandem (see
Recommendation\ Q.440).
.PP
It is understood that the national 4\(hywire links in the country of
origin shall have the same standard deviation of transmission loss variations
with time (1\ dB) as the international links and that, if these national
links do not have the same nominal transmission loss as the international
links
.PP
(0.5\ dB), appropriate compensation of the multifrequency combination levels
will be made in both directions of transmission.
.RT
.sp 1P
.LP
b)
    \fINumber (k) of national 4\(hywire extension links in the country\fR
\fIof destination\fR
.sp 9p
.RT
.PP
Not more than four national 4\(hywire extension links may be used.
.PP
Forward transmission loss in the country of destination:
.RT
.LP
    i)
     The standard deviation of transmission loss variations with time in the
national 4\(hywire extension links in the country of
destination must not exceed 1\ dB.
.bp
.LP
    ii)
    The nominal transmission loss at 800\ Hz in the forward
direction (\fIA\fR\d\fIf\fR\u) between the virtual switching point in
the incoming international exchange and any incoming\ R2 register
in the country of destination must not exceed:
.LP
    11.4\ dB for a country using 3\ national 4\(hywire
extension links at the most
.LP
    or
.LP
    11.0\ dB for a country using 4\ national 4\(hywire
extension links at the most,
.LP
    and must never be less than:
\v'6p'
.sp 1P
.ce 1000
\fIA\fR \fI
\df\fR min.\fI
\u\fR = \(em2.5 \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) ~+ (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  dB.
.ce 0
.sp 1P
.PP
.sp 1
The values for the minimum forward transmission loss
\fIA\fR \fI
\df\fR min.\fI
\u\fR resulting from this formula are shown
in Table\ 10/Q.457 (for
the definitions of \fIm\fR and \fIk\fR see Recommendation\ Q.454). In practice
the
forward transmission loss must not fall below these values.
.PP
The formula has been determined as shown in Annex\ C to Section\ 4.
.PP
When System\ R2 end\(hyto\(hyend signalling is applied in a national network,
the 4\(hywire links involved may not conform to the characteristics specified
by the CCITT for international circuits. Also, national transmission plans
may be based on principles different from those of the international transmission
plan. Consequently, the range over which end\(hyto\(hyend signalling is
possible must be established using calculations, e.g. as shown in Annex\
C to Section\ 4 (see also \(sc\(sc\ 4.5.1.3 and 4.5.1.4\ below).
.RT
.LP
.rs
.sp 16P
.ad r
\fBTable 10/Q.457, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
4.5.1.3
    \fITotal attenuation distortion\fR
.sp 9p
.RT
.PP
It has been assumed that at all frequencies within the 530\(hy1990\ Hz
band the overall attenuation distortion relative to 800\ Hz between the
outgoing international\ R2 register and any incoming\ R2 register will
not exceed\ \(+- | \ dB. Attention is drawn to the fact that on some national
connections these
assumptions might not be fulfilled.
.PP
As type\ B test signals (see Recommendation\ Q.455) allow for a 5\ dB
difference in level between two adjacent signalling frequencies, and a 7\ dB
difference between two non\(hyadjacent signalling frequencies, a 4\ dB
attenuation distortion of the multi\(hylink section can be allowed for
two adjacent
frequencies and a 6\ dB distortion for two non\(hyadjacent frequencies,
provided
that the level of the weakest signalling frequency is not lower than \(em35\
dBm at the terminals of the receiving part of the multifrequency signalling
equipment.
.PP
The values 4\ dB and 6\ dB were obtained by allowing for a 1\ dB difference
in sending level.
.bp
.RT
.LP
.sp 1P
.LP
4.5.1.4
    \fIIntermodulation\fR
.sp 9p
.RT
.PP
A multifrequency signalling system in conformity with the above
specifications will allow satisfactory working over a multi\(hylink section
introducing intermodulation products from two signalling frequencies and
falling within the 520\(hy1160\ Hz and 1360\(hy2000\ Hz bands, the level
of each of
such products being at least 24\ dB below the highest signal frequency
level.
.RT
.sp 1P
.LP
4.5.2
    \fIBuild\(hyup and time specification of a complete forward\fR
\fIcompelled signalling cycle\fR
.sp 9p
.RT
.PP
Figure\ 18/Q.457 shows in detail the build\(hyup and time sequence of a
compelled signalling cycle.
.RT
.LP
.rs
.sp 33P
.ad r
\fBFigure 18/Q.457 p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
In this figure:
.LP
     \fIT\fR\d\fIP\fR\\d\fIF\fR\udenotes the transmission delay of the slower
of the two frequencies of a forward multifrequency combination;
.LP
     \fIT\fR\d\fIP\fR\\d\fIB\fR\udenotes the transmission delay of the slower
of the two frequencies of a backward multifrequency combination;
.LP
    \fIT\fR\d0\uand \fIT\fR `\d0\u\fR denote the operating times as
defined in Recommendation\ Q.451;
.LP
    \fIT\fR\d\fIR\fR\uand \fIT\fR `
\fI\fI\d\fIR\fR\udenote the release times as
defined in Recommendation\ Q.451;
.LP
    \fIT\fR \s6\fIint\fR \ 1
.PS 10
, \fIT\fR \s6\fIint\fR \ 2
.PS 10
and \fIT\fR \s6\fIint\fR \ 3
.PS 10
denote the internal operation times as
defined in Recommendation\ Q.451.
.bp
.RT
.PP
If the values of \fIT\fR \s6\fIint\fR \ 2
.PS 10
and
\fIT\fR \s6\fIint\fR \ 3
.PS 10
lie within certain limits, they do not contribute to the total duration
of the compelled signalling cycle, as can be seen from
Figure\ 18/Q.457.
.RT
.LP
     \fIT\fR\d\fIS\fR\\d1\uand \fIT\fR\d\fIS\fR\\d2\udenote respectively the
time required for starting and stopping the sending of a
multifrequency combination (switching\(hyon or
switching\(hyoff times, exclusive of logic operations).
.PP
It thus appears that the total duration \fIT\fR of a complete
compelled signalling cycle is given by the formula:
\v'6p'
.ce 1000
\fIT\fR = 2 (\fIT
\dPF
\u\fR + \fIT
\dPB
\u\fR ) +
@ left {  pile { { \fIT\fR~0~+~\fIT~\dR\u\fR )\fI~\dD\u\fR~+~ (\fIT\fR~\d0\u~+~\fIT~\dR\u\fR )\fI~\dA\u\fR } above { (\fIT\fR~`~\d0\u~+~\fIT\fR~`~\fI~\dR\u\fR )\fI~\dD\u\fR~~+ (\fIT\fR~`~\d0\u~+~\fIT\fR~`~\fI~\dR\u\fR )\fI~\dA\u\fR } }  right } @
+ \fIT
\dint\fR 1\fI
\u\fR + (\fIT
\dS\fR 1\fI
\u\fR +
\fIT
\dS\fR 2\fI
\u\fR )\fI
\dD
\u\fR + (\fIT
\dS\fR 1\fI
\u\fR +
\fIT
\dS\fR 2\fI
\u\fR )\fI
\dA
\u\fR
.ce 0
.LP
or
\v'9p'
.LP
.sp 1
.PP
The subscripts \fID\fR and \fIA\fR apply respectively to the outgoing and
the incoming registers.
.PP
\fIT\fR\d\fIP\fR\\d\fIF\fR\uand \fIT\fR\d\fIP\fR\\d\fIB\fR\udepend on the
propagation characteristics of the forward and backward speech paths respectively
and therefore cannot be specified.
.PP
A value of 10\ ms for \fIT\fR\d\fIP\fR\\d\fIF\fR\uand \fIT\fR\d\fIP\fR\\d\fIB\fR\ucan
be considered
as typical, e.g. for average terrestrial regional connections and 320\ ms for
circuits including a satellite link.
.PP
The maximum value of \fIT\fR\d0\u\ +\ \fIT\fR\d\fIR\fR\uhas been fixed
at 70\ ms. A
value of 35\ ms could be taken in a certain number of cases as representing
the minimum duration of \fIT\fR\d0\u\ +\ \fIT\fR\d\fIR\fR\u.
.PP
\fIT\fR \s6\fIint\fR \ 1
.PS 10
, \fIT\fR \s6\fIint\fR \ 2
.PS 10
and \fIT\fR \s6\fIint\fR \ 3
.PS 10
are dependent on the type of exchange and
therefore cannot be specified; but their contribution to the total duration
of the compelled signalling cycle must be kept as small as possible.
.RT
.PP
If the influence of \fIT\fR \s6\fIint\fR \ 1
.PS 10
,
\fIT\fR \s6\fIint\fR \ 2
.PS 10
and \fIT\fR \s6\fIint\fR \ 3
.PS 10
is ignored, and if the extreme values of \fIT\fR\d0\u\ +\ \fIT\fR\d\fIR\fR\uand
for
\fIT\fR\d\fIS\fR\\d1\u\ +\ \fIT\fR\d\fIS\fR\\d2\uare assumed to be identical
for the
outgoing and the incoming register, the extreme values of
\fIT\fR\d\fIS\fR\\d1\u\ +\ \fIT\fR\d\fIS\fR\\d2\ubeing taken as
5\ ms\ \(=\ \fIT\fR\d\fIS\fR\\d1\u\ +\ \fIT\fR\d2\u\ \(=\ 10\ ms and if
the value of 10\ ms indicated above as typical is adopted for \fIT\fR\d\fIP\fR\\d\fIF\fR\uand
\fIT\fR\d\fIP\fR\\d\fIB\fR\u,
the probable extreme values of the compelled signalling cycle\ \fIT\fR would
be:
.RT
.EF '%    ''
.OF '''    %'
.PP
for terrestrial connections:\ 120\ ms\ \(=\ \fIT\fR \ \(=\ 200\ ms.
.PP
for circuits including a satellite link:\ 1080\ ms\ \(=\ \fIT\fR \ \(=\
1440\ ms.
.PP
The signalling rates would be between approximately 8 and 5\ signalling
cycles per second for terrestrial circuits. These values are not absolute
limits; the signalling cycle could, for example, be longer on a complex
connection or in the presence of noise or other conditions approaching
those of type\ B test combinations (see Recommendation\ Q.455).
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.458\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.5.3\ \fR \fBRELIABILITY\ OF\ INTERREGISTER\ SIGNALLING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.458''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.458    %'
.ce 0
.sp 1P
.LP
4.5.3.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
In signal transmission, reliability and speed are to some extent
conflict requirements: the slower the signalling, the more reliable it is
likely to be. System\ R2 combines the two essential requirements of speed and
reliability, since it is a compelled system, adapting its signalling speed
to the working conditions with minimum loss of reliability.
.PP
System\ R2 is protected against the acceptance of faulty information
(multifrequency combinations consisting either of one frequency only or
of more than two frequencies) by means of the \fI2\(hyout\(hyof\(hyn\fR
method of checking the
number of frequencies received.
.PP
This protection is inoperative in the case of disturbances (noise,
clicks, etc.) activating two, and only two, of the single frequency receivers;
nor does it prevent the release of all the receivers (thus wrongly indicating
the end of a multifrequency combination) in the event of an interruption
caused by disturbances during transmission of a multifrequency combination.
.PP
Disturbances causing the operation of two single frequency receivers or
the release of all the receivers are due mainly to short\(hylived, transient
conditions. The recognition of faulty information due to such conditions can
therefore largely be avoided by so designing the receiving part of the
multifrequency signalling equipment that a multifrequency combination will
be recognized only after a specified minimum time. During this time two,
and only two, of the individual receivers are
.bp
.PP
active and the absence of
multifrequency
combinations will be recognized only after a specified minimum time, during
which all individual receivers are at rest. The degree of protection against
faults due to the above\(hymentioned conditions is dependent on these times,
which are included in the operating and release times defined for the receiving
part of the multifrequency signalling equipment in Recommendation\ Q.451.
.RT
.LP
.sp 1P
.LP
4.5.3.2
    \fIError rate for compelled working\fR
.sp 9p
.RT
.PP
The test of the multifrequency signalling equipment as a whole
consists in continuous, compelled transmission of multifrequency
combinations.
.PP
It must be ensured that all possible combinations of the forward and backward
multifrequency combinations have equal probability of occurrence
during the test period.
.PP
The error rate is observed at the receiving part at both ends of the link
and is defined, for each end, as the number of errors divided by the
number of combinations sent by the corresponding sending parts at each
end of the link.
.PP
It is for each Administration to define the sources of permanent and impulsive
noise to be applied to the interface between the sending and
receiving parts in the light of its experience and local conditions.
.PP
The compelled working may be tested, on the one hand, by using test
combinations of Type\ A (see Recommendation\ Q.455) in the presence of
noise at a power level of \(em40\ dBm and a uniform power distribution
in the 300\(hy3400\ Hz band (filtered white noise) and, on the other hand,
by using Type\ B test
combinations in the presence of noise at a power level of \(em45\ dBm and
a uniform power distribution in the 300\(hy3400\ Hz band.
.PP
The error rates in these conditions will be:
.RT
.LP
    \(em
    for Type\ A test combinations and noise at
\(em40\ dBm:\ \(=\ 10\uD\dlF261\u5\d;
.LP
    \(em
    for Type\ B test combinations and noise at
\(em45\ dBm:\ \(=\ 10\uD\dlF261\u4\d.
.LP
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Section 4)
.sp 9p
.RT
.ce 0
.ce 1000
(see Recommendation Q.454)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDevelopment of formulae for the power level of signalling\fR \fBfrequencies\fR
.sp 1P
.RT
.ce 0
.PP
The formulae\ (1), (2), and\ (3) of Recommendation\ Q.454
describing the nominal absolute power level\ \fIN\fR of a transmitted single
signalling frequency were derived as follows:
.sp 1P
.RT
.LP
.PP
1.
The nominal transmission loss in the backward direction
between the incoming R2\ register and the outgoing international R2\ register
is given by (see Recommendation\ Q.457):
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\fIA\fR\d\fIb\fR\u\ +\ 0.5\ \fIm\fR \ dB.
.ce 0
.sp 1P
.PP
.sp 1
2.
On the assumption that the contribution of the national 2\(hywire links
to transmission loss variations with time is negligible and with
allowance for the standard deviation of transmission loss variations with
time of the international and national 4\(hywire circuits and in the exchanges
(see
CCITT Recommendation\ Q.45: \(*s\ =\ 0.2\ dB), the total transmission loss
variation for a 1% probability of it being exceeded is given by:
\v'6p'
.sp 9p
.RT
.LP
.sp 1P
.ce 1000
\(+- 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) (0.2) \u2\d } @  dB.
.ce 0
.sp 1P
.PP
.sp 1
3.
Given a total attenuation distortion of \(+- | \ dB relative to
800\ Hz (see Recommendation\ Q.457) and a tolerance of \(+- | \ dB on the
nominal
power level\ \fIN\fR , the lower and upper limits of the level received in the
outgoing international R2\ register will be:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\fIN\fR \(em \fIA
\db\u\fR \(em 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 3 \(em 1 dBm
.ce 0
.sp 1P
.LP
.sp 1
and
\v'6p'
.sp 1P
.ce 1000
\fIN\fR \(em \fIA
\db\u\fR \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  + 3 + 1 dBm.
.ce 0
.sp 1P
.LP
.sp 1
respectively.
.LP
.bp
.PP
4.
The receiving part of the multifrequency signalling equipment has a sensitivity
range between
.sp 9p
.RT
.sp 1P
.ce 1000
\(em35\ dBm and \(em5\ dBm (see Recommendation\ Q.455).
.ce 0
.sp 1P
.PP
The minimum value of\ \fIN\fR  | s thus given by:
\v'6p'
.sp 1P
.ce 1000
\fIN\fR \(em \fIA
\db\u\fR \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 4 = \(em 35 dBm
.ce 0
.sp 1P
.LP
.sp 1
hence
\v'6p'
.ce 1000
\fIN\fR \(>=" \fIA
\db\u\fR + 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~~+~1) 0.04 } @  \(em 31 dBm
.ce 0
.ad r
(1)
.ad b
.RT
.LP
.sp 1
.PP
The maximum value of \fIN\fR  | s given by:
\v'6p'
.sp 1P
.ce 1000
\fIN\fR \(em \fIA
\db\u\fR \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  + 4 = \(em 5 dBm
.ce 0
.sp 1P
.LP
.sp 1
hence
\v'6p'
.ce 1000
\fIN\fR \(= \fIA
\db\u\fR + 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~~+~1) 0.04 } @  \(em 9 dBm
.ce 0
.ad r
(3)
.ad b
.RT
.LP
.sp 1
.PP
5.
The nominal level of the backward signals at the virtual
switching point of the incoming international exchange must not be higher
than\ \(em11.5\ dBm; thus
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\fIN\fR \(em \fIA
\db\u\fR \(= \(em 11.5 dBm
.ce 0
.sp 1P
.LP
.sp 1
hence
\v'6p'
.ce 1000
\fIN\fR \(= \fIA
\db\u\fR \(= \(em 11.5 dBm.
.ce 0
.ad r
(2)
.ad b
.RT
.LP
.sp 1
.ce 1000
ANNEX\ B
.ce 0
.ce 1000
(to Section 4)
.sp 9p
.RT
.ce 0
.ce 1000
(see Recommendation Q.455)
.sp 9p
.RT
.ce 0
.ce 1000
\fBPossible method of improving protection from interruptions\fR
.sp 1P
.RT
.ce 0
.PP
If the receivers are locked through an internal function of the registers
until the times\ \fIQ\fR and\ \fIS\fR (see Figure\ B\(hy1) the intervals
during
which there is a risk that interruptions may cause their release are reduced
by\ \fIPQ\fR and\ \fIRS\fR respectively.
.sp 1P
.RT
.PP
This method can be used on both terrestrial and satellite
circuits.
.PP
To ensure that the duration of the compelled signalling cycle is not prolonged
on terrestrial circuits (short transmission delay). \fIPQ\fR and \fIRS\fR
must be calculated with:
.RT
.LP
.sp 1P
.ce 1000
\fIT\fR\d\fIP\fR\\d\fIF\fR\u= \fIT\fR\d\fIP\fR\\d\fIB\fR\u\( = 0 ms: \fIPQ\fR
\(= \fIT\fR\d\fIi\fR\\d\fIn\fR\\d\fIt\fR\\d1\u\fR +
\fIT\fR\d\fIS\fR\\d1\u\fR + \fIT\fR\d0\u+ \fIT\fR\d\fIS\fR\\d2\u
.sp 9p
.RT
.ce 0
.sp 1P
.LP
and
.sp 1P
.ce 1000
\fIRS\fR \(= \fIT\fR\d\fIS\fR\\d2\u\fR + \fIT\fR\d\fIR\fR\u+ \fIT\fR\d\fIS\fR\\d2\u
.sp 9p
.RT
.ce 0
.sp 1P
.PP
To ensure that the duration of the compelled signalling cycle is not prolonged
on satellite circuits (long transmission delay) \fIPQ\fR and \fIRS\fR must
be calculated with:
.sp 9p
.RT
.sp 1P
.ce 1000
\fIT\fR\d\fIP\fR\\d\fIF\fR\u+ \fIT\fR\d\fIP\fR\\d\fIB\fR\u\( = 250 ms:
\fIPQ\fR \(= 500 ms + \fIT\fR\d\fIi\fR\\d\fIn\fR\\d\fIt\fR\\d1\u\fR + \fIT\fR\d\fIS\fR\\d1\u+
\fIT\fR\d0\u+ \fIT\fR\d\fIS\fR\\d2\u
.sp 9p
.RT
.ce 0
.sp 1P
.LP
and
.sp 1P
.LP
\fIRS\fR \(= 500 ms + \fIT\fR\d\fIS\fR\\d2\u+ \fIT\fR\d\fIR\fR\u+ \fIT\fR\d\fIS\fR\\d2\u.bp
.sp 9p
.RT
.sp 1P
.ce 1000
.ce 0
.sp 1P
.LP
.rs
.sp 31P
.ad r
\fBFigure B\(hy1/Q.455, p.\fR
.sp 1P
.RT
.ad b
.RT
.ce 1000
ANNEX\ C
.ce 0
.ce 1000
(to Section 4)
.sp 9p
.RT
.ce 0
.ce 1000
(see Recommendation Q.457)
.sp 9p
.RT
.ce 0
.ce 1000
\fBDevelopment of a formula for the admissible forward\fR
.sp 1P
.RT
.ce 0
.ce 1000
\fBtransmission loss in a country of destination\fR
.ce 0
.PP
The formula used in Recommendation\ Q.457 for the calculation of the minimum
forward transmission loss\ \fIA
\df\fR \ min.\fI
\u\fR a country of destination was determined as follows:
.sp 1P
.RT
.PP
1.
According to Recommendation\ Q.454 the lowest and highest sending levels
will be, respectively,
.sp 9p
.RT
.sp 1P
.ce 1000
\(em11.5\ \(em\ 1\ =\ \(em12.5\ dBm
.ce 0
.sp 1P
.LP
and
.LP
\(em11.5\ +\ 1\ =\ \(em10.5\ dBm.
.bp
.sp 1P
.ce 1000
.ce 0
.sp 1P
.PP
2.
Let\ \fIA\fR\d\fIf\fR\ube the nominal transmission loss at 800\ Hz in the
forward direction, between the virtual switching point in the incoming
international exchange and the incoming R2\ register concerned.
.sp 9p
.RT
.PP
The total nominal transmission loss between the outgoing
international R2\ register and the incoming R2\ register will then be:
\v'6p'
.sp 1P
.ce 1000
\fIA\fR \fI
\df
\u\fR + 0.5 \fIm\fR dB.
.ce 0
.sp 1P
.PP
.sp 1
3.
On the assumption that the contribution of the national 2\(hywire links
to transmission loss variations with time is negligible, and that the
standard deviation of transmission loss variation in the exchange is 0.2\ dB
(see Recommendation\ Q.45), the total transmission loss variation, calculated
for a 1% probability of it being exceeded will be:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\(+- 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.2~\u2\d } @  dB.
.ce 0
.sp 1P
.LP
.sp 1
.PP
4.
With allowance for a total attenuation distortion of \(+- | \ dB
relative to 800\ Hz (see Recommendation\ Q.457) the lower and upper limits
of the level of each frequency at the input of the incoming R2\ register
will be
respectively:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\(em12.5 \(em \fIA\fR \fI
\df
\u\fR \(em 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 3 dBm
.ce 0
.sp 1P
.LP
.sp 1
and
\v'6p'
.sp 1P
.ce 1000
\(em10.5 \(em \fIA\fR \fI
\df
\u\fR \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  + 3 dBm.
.ce 0
.sp 1P
.LP
.sp 1
.PP
5.
The receiving part of the multifrequency signalling equipment
has a sensitivity range of \(em35\ dBm to \(em5\ dBm.
.sp 9p
.RT
.LP
.PP
6.
The maximum value of \fIA\fR\d\fIf\fR\uis thus given by:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\(em12.5 \(em \fIA\fR \fI
\df\fR max.\fI
\u\fR \(em 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  \(em 3 = \(em 35 dBm
.ce 0
.sp 1P
.LP
.sp 1
hence
\v'6p'
.sp 1P
.ce 1000
\fIA\fR \fI
\df\fR max.\fI
\u\fR = 19.5 \(em 0.5 \fIm\fR \(em 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  dB.
.ce 0
.sp 1P
.LP
.sp 1
.PP
7.
The minimum value for\ \fIA\fR\d\fIf\fR\uis given by:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\(em10.5 \(em \fIA\fR \fI
\df\fR min.\fI
\u\fR \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  + 3 = \(em 5 dB
.ce 0
.sp 1P
.LP
.sp 1
hence
\v'6p'
.sp 1P
.ce 1000
\fIA\fR \fI
\df\fR min.\fI
\u\fR = \(em2.5 \(em 0.5 \fIm\fR + 2.3
@ sqrt { (\fIm\fR~+~\fIk\fR ) + (\fIm\fR~+~\fIk\fR~+~1) 0.04 } @  dB.
.ce 0
.sp 1P
.LP
.sp 1
.PP
According to Recommendation\ Q.457, the maximum number of 4\(hywire
links with \fIinternational\fR characteristics is\ \fIm\fR \ =\ 4.
.PP
The maximum number of national 4\(hywire extension links is\ \fIk\fR \ =\ 4.
.RT
.LP
.rs
.sp 5P
.LP
.bp
.LP
\fBMONTAGE:\ \fR PAGE 114 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 5
.ce 0
.sp 1P
.ce 1000
\fBSIGNALLING\ PROCEDURES\fR
.ce 0
.sp 1P
.PP
A major characteristic of System\ R2 is the inherent
flexibility in the interregister signalling procedures which allow efficient
signal information transfer, adapted to the particular requirements relating
to different call types, traffic conditions and switching equipments. This
flexibility is primarily achieved by the principle that the interregister
signalling sequence is controlled by the incoming\ R2 register by means of
backward signals.
.sp 1P
.RT
.PP
In this context the function of an outgoing\ R2 register is
basically to respond with the forward signal requested by the incoming\ R2
register. At the incoming\ R2 register the determination of the backward
signal to be sent, thus controlling the signalling sequence, is closely
related to the analysis necessary to determine the routing and handling
of the call.
.PP
In this Section the signalling procedures are specified. Although
System\ R2 in principle allows a high degree of freedom in the combination of
these procedures within the signalling sequence for call set\(hyup, the
procedures to be used for normal international calls connected via terrestrial
links are described below. These procedures may vary when a satellite link
is employed in a connection because the register at the incoming end of
a satellite link also acts as an outgoing R2\ register (see Recommendation\
Q.440, \(sc\ 4.1.1). For
national application of System\ R2 the signalling sequences to be applied
have to be defined in accordance with the limitations of the present specifications
by the Administration concerned.
\v'2P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.460\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.1\fR \ \
\fBNORMAL\ CALL\ SET\(hyUP\ PROCEDURES\ FOR\ INTERNATIONAL\ WORKING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.460''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.460    %'
.ce 0
.sp 1P
.LP
5.1.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
During call set\(hyup an outgoing international\ R2 register is
connected to an international link. This register signals to at least one
incoming\ R2 register situated in an international exchange and possibly,
depending upon the routing, to as many as 4\ successive incoming\ R2 registers
in international exchanges and 4\ successive incoming\ R2 registers situated
in
national exchanges in the destination country where System\ R2 is employed.
.PP
The duration of the normal call set\(hyup procedure can vary because
different phases of the signalling sequence between the outgoing
international\ R2 register and successive incoming\ R2 registers may be
repeated.
.bp
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.462\fR
.RT
.sp 2P
.ce 1000
\fB5.1.2\fR \ \
\fBSIGNALLING\ BETWEEN\ THE\ OUTGOING\ INTERNATIONAL\ R2\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.462''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.462    %'
.ce 0
.sp 1P
.ce 1000
\fBREGISTER\ AND\ AN\ INCOMING\ R2\ REGISTER\ IN\ AN\ INTERNATIONAL\ EXCHANGE\fR
.ce 0
.sp 1P
.PP
The address signals from an operator or a subscriber must be stored in
an outgoing international\ R2 register. When a sufficient number of
digits is available an outgoing link is selected and a seizing (line) signal
is sent. When the seizing signal is recognized an incoming\ R2 register
is
associated with the link.
.sp 1P
.RT
.PP
Immediately the outgoing link is seized the outgoing
international\ R2 register sends the first interregister signal.
.LP
.sp 1P
.LP
5.1.2.1
    \fISignalling to an international transit exchange\fR
.sp 9p
.RT
.PP
When the outgoing link is to an international exchange from which a transit
routing is required to the destination country, the first interregister
signal sent is a country code indicator. This is one of signals\ I\(hy11,
I\(hy12,
I\(hy14 depending upon the requirement for echo suppressors (see
Recommendation\ Q.479).
.PP
On recognition of a country code indicator the incoming\ R2 register
determines that the call is to be internationally transit switched. The
incoming\ R2 register sends signal\ A\(hy1 when it requests the first digit
of the country code. The outgoing international\ R2 register sends this
address digit (a signal\ I\(hy1 to I\(hy10). The incoming\ R2 register
may send signal\ A\(hy1 to request the next digit.
.PP
The incoming\ R2 register examines the address digit(s) and if a further
digit (or digits) is required for routing, signal\ A\(hy1 is sent to request
the
next digit.
.PP
When sufficient digits are stored at the incoming exchange to permit the
call to be routed to the next exchange, the backward signal is determined
by
the nature of the signalling system employed on the outgoing link.
.RT
.PP
a)
If the outgoing link employs System\ R2, one of two backward
signals is sent immediately the outgoing link is seized:
.sp 9p
.RT
.LP
    i)
    If the outgoing link is to another international transit
exchange from which a transit routing is required to the destination country,
signal\ A\(hy11 is sent to request repetition of the country code indicator.
.LP
    On recognition of signal\ A\(hy11 the outgoing international\ R2
register sends a country code indicator as the first signal to be received
by the incoming\ R2 register in the next international transit exchange.
This is
one of signals\ I\(hy12 or I\(hy14. If signal\ I\(hy11 was sent initially,
signal\ I\(hy14 is sent subsequently.
.LP
    On recognition of a country code indicator the incoming\ R2
register determines that the call is to be internationally transit switched.
The signalling procedure which follows is identical to that described above.
.LP
    ii)
    If the outgoing link is to an incoming international
exchange in the destination country, signal\ A\(hy12 is sent to
.LP
request a language or discriminating digit.
.PP
In both these cases after the backward signal is sent and the
compelled signalling sequence is complete, the transit exchange releases the
incoming\ R2 register and through\(hyconnects the speech\(hypath between
the outgoing exchange and the next exchange.
.PP
b)
If the outgoing link employs a signalling system other than
System\ R2, then the acting incoming\ R2 register is the last incoming\ R2
register. The exchange seizes an outgoing international link to a further
international transit exchange or an incoming international exchange in the
destination country. Signalling continues between the outgoing international\
R2 register and the last incoming\ R2 register and interworking takes place
with
the other signalling system.
.sp 9p
.RT
.PP
If congestion is encountered signal\ A\(hy15 is sent, if necessary in
pulse form. After the compelled signalling sequence is complete or after the
end of the pulse signal the transit exchange dismisses the register.
.bp
.PP
On recognition of signal\ A\(hy15 the outgoing exchange may initiate a
repeat attempt, a re\(hyrouting or cause the return of congestion information
to the calling subscriber. In all cases the outgoing (multi\(hy)link section
is
released.
.RT
.sp 1P
.LP
5.1.2.2
    \fISignalling to an incoming international exchange\fR
\fIin the destination country\fR
.sp 9p
.RT
.PP
When the outgoing international link is a direct link to an incoming international
exchange in the destination country the first interregister
signal sent is a language or discriminating digit.
.PP
Alternately, if the outgoing multi\(hylink section is routed via one, two
or three international transit exchanges then on recognition of signal\
A\(hy12 the outgoing international\ R2 register sends a language or discriminating
digit as the first signal to be received by the incoming\ R2 register in
the terminal
international exchange in the destination country.
.PP
The first signal\ A\(hy12 received from an international transit exchange
by the outgoing international\ R2 register informs it that an international
link
terminating at an incoming international exchange has been added to the
(multi\(hy)link section.
.PP
In both cases, on recognition of a language or discriminating digit (a
signal\ I\(hy1 to I\(hy10), the incoming\ R2 register determines that the
call is to
be routed to the national network, and selects the next backward
signal:
.RT
.LP
    i)
    The incoming\ R2 register may send signal\ A\(hy14 to request
information about the requirement for echo suppression.
.LP
    \(em
     If an incoming half\(hyecho suppressor is required the outgoing international\
R2 register sends signal\ I\(hy14.
.LP
    In response to signal\ I\(hy14 the incoming\ R2 register sends
signal\ A\(hy1 to request the first digit of the national (significant)
number. In response to signal\ A\(hy1 the outgoing international R2\ register
sends the first digit of the national (significant) number.
.LP
    \(em
    If no echo suppressor is required the outgoing
international\ R2 register sends the first digit of the national (significant)
number.
.LP
    ii)
    Alternatively, if it is known that no echo suppressor is
required to be inserted the incoming\ R2 register may send signal\ A\(hy1
to request the first digit of the national (significant) number. In response
to signal\ A\(hy1 the outgoing international\ R2 register sends the first
digit of the national
(significant) number.
.PP
The incoming\ R2 register examines the first digit of the national
(significant) number and if a further digit (or digits) is required for
routing, signal\ A\(hy1 is sent to request the next digit.
.PP
When sufficient digits are stored at the incoming exchange to permit the
call to be routed to the next exchange the backward signal (if any) is
determined by the nature of the signalling system employed on the outgoing
link and the national routing principles.
.RT
.PP
a)
If the outgoing national link employs System\ R2 and
international/national end\(hyto\(hyend signalling is used, a backward
signal may be sent after the outgoing link is seized to request the address
digit required as the first signal to be received by the incoming\ R2 register
in the following
national exchange.
.sp 9p
.RT
.LP
.PP
The appropriate signal is one of signals\ A\(hy1, A\(hy2, A\(hy7, A\(hy8
or A\(hy12. These signals may be sent after any digit, and can be repeated
provided they do not conflict with the logic procedure.
.PP
However, if the address digit \fIon\(hyline\fR  | s the digit required as the
first signal to be received by the incoming\ R2 register in the next exchange,
it is possible for the transit exchange to release the incoming\ R2 register
and through\(hyconnect the speech\(hypath after the outgoing link is seized
without
sending a backward signal.
.PP
Otherwise, after the appropriate backward signal is sent and the
compelled signalling sequence is complete the transit exchange releases the
register and through\(hyconnects the speech path.
.RT
.PP
b)
If the outgoing national link employs System\ R2 but end\(hyto\(hyend
international/national signalling cannot be used, the register in the incoming
international exchange relays the multifrequency signals: it acts as an
outgoing\ R2 register. It requests the remainder of the address digits by
repetitive use of signal\ A\(hy1. The digits received by the outgoing\
R2 register are retransmitted over the outgoing national link at the request
of the
incoming\ R2 register in the following national exchange(s) (see
Recommendation\ Q.478).
.bp
.sp 9p
.RT
.LP
.PP
c)
If the outgoing link employs a signalling system other than
System\ R2 then the acting incoming\ R2 register is the last incoming\ R2
register. The exchange seizes a national link. Signalling continues between
the outgoing international\ R2 register and the last incoming\ R2 register
and
interworking takes place with the other signalling system.
.sp 9p
.RT
.PP
If congestion is encountered, congestion signal\ A\(hy4 or A\(hy15 is
transmitted (if necessary in pulse form) and the incoming\ R2 register is
dismissed.
.PP
On recognition of the congestion signal\ A\(hy4 the outgoing exchange
releases the outgoing link or connection and causes the return of congestion
information to the calling subscriber.
.PP
On recognition of the congestion signal\ A\(hy15 the outgoing exchange
may initiate a repeat attempt, re\(hyrouting or cause the return of congestion
information to the calling subscriber. In all cases the outgoing link or
connection is released.
.PP
It is desirable to use the congestion signal\ A\(hy15 solely in the case
of incoming international terminal traffic when repeat attempt or re\(hyrouting
may be expected to be successful.
.RT
.sp 2P
.LP
\fBRecommendation\ Q.463\fR
.RT
.sp 2P
.ce 1000
\fB5.1.3\fR \
\fBSIGNALLING\ BETWEEN\ THE\ OUTGOING\ INTERNATIONAL\fR  |
\fBR2\ REGISTER\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.463''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.463    %'
.ce 0
.ce 1000
\fBAND\ AN\ INCOMING\ R2\ REGISTER\ IN\ A\fR  | \fR \fBNATIONAL\ EXCHANGE\
IN\ THE\fR
.ce 0
.sp 1P
.ce 1000
\fBDESTINATION\ COUNTRY\fR
.ce 0
.sp 1P
.LP
5.1.3.1
    \fISignalling to a national transit exchange\fR
.sp 1P
.RT
.PP
The outgoing international\ R2 register sends the requested address
digit as the first signal to be received by the incoming\ R2 register in the
national transit exchange in the destination country.
.PP
The incoming\ R2 register examines the digit and if a further digit (or
digits) is required for routing, signal\ A\(hy1 is sent to request the
next digit.
.PP
When sufficient digits are stored at the incoming exchange to permit the
call to be routed to the next exchange the backward signal (if any) is
determined by the nature of the signalling system employed on the outgoing
link and the national routing principles.
.RT
.PP
a)
If the outgoing national link employs System\ R2 a backward signal
may be sent after the outgoing link is seized to request the address digit
required as the first signal to be received by the incoming\ R2 register
in the next exchange. The signalling procedure which occurs is similar
to that
described in \(sc\ 5.1.2.2\ a)\ above.
.sp 9p
.RT
.PP
b)
If the outgoing link employs System\ R2 but end\(hyto\(hyend
international/national signalling cannot be used, the register in the national
exchange relays the interregister signals: it acts as an outgoing R2 register.
The digits received by this outgoing\ R2 register are retransmitted over
the
outgoing link at the request of the incoming\ R2 register in the following
exchange(s) (see Recommendation\ Q.478).
.sp 9p
.RT
.LP
.PP
c)
If the outgoing link employs a signalling system other than
System\ R2 then the acting incoming\ R2 register is the last incoming\ R2
register. The exchange seizes an outgoing national link to the next national
exchange. Signalling continues between the outgoing international\ R2 register
and the last incoming\ R2 register and interworking takes place with the
other signalling system.
.sp 9p
.RT
.PP
If congestion is encountered signal\ A\(hy4 is sent (if necessary in
pulse form) and the incoming\ R2 register is released.
.PP
On recognition of congestion signal\ A\(hy4 the outgoing exchange releases
the outgoing multi\(hylink section and causes the return of congestion
information to the calling subscriber.
.RT
.sp 1P
.LP
5.1.3.2
    \fISignalling to a national exchange to which the called\fR
\fIsubscriber is connected\fR
.sp 9p
.RT
.PP
When the outgoing multi\(hylink section is routed to the national
exchange to which the called subscriber is connected the acting incoming\ R2
.PP
register is the last incoming\ R2 register: the outgoing international\ R2
register sends the requested address digit as the first signal to be received
by the last incoming\ R2 register and signalling continues as described
below.
.bp
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.464\fR
.RT
.sp 2P
.ce 1000
\fB5.1.4\fR \
\fBSIGNALLING\ BETWEEN\ THE\ OUTGOING\ INTERNATIONAL\ R2\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.464''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.464    %'
.ce 0
.sp 1P
.ce 1000
\fBREGISTER\ AND\ THE\ LAST\ INCOMING\ R2\ REGISTER\fR
.ce 0
.sp 1P
.LP
5.1.4.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
The usual System\ R2 signalling procedure is to request in succession the
remainder of the address digits stored in the outgoing international\ R2
register by the repetitive use of signal\ A\(hy1 until it is determined at the
incoming end that the complete address information has been received by the
incoming exchange or that the call cannot be routed.
.PP
System\ R2 enables transmission of information concerning a large number
of different conditions of called subscriber's line or reasons why call
set\(hyup has failed. But this can only be sent if the switching systems
and other
signalling systems employed on the remaining links of the connection offer
the possibility of differentiating several line conditions. Group\ B\(hysignals
are
provided for this purpose.
.PP
Transition from Group\ A to Group\ B meanings is indicated by means of
address\(hycomplete signal\ A\(hy3. However, if the incoming exchange is
unable to
send any signals concerning the condition of the called subscriber's line
it is unnecessary to send signal\ A\(hy3 followed by a Group\ B signal.
In such cases the address\(hycomplete signal\ A\(hy6, provided for the
purpose is used.
.PP
If congestion is encountered after transmission of the address\(hycomplete
signal\ A\(hy3 the congestion signal\ B\(hy4 is sent in place of signal\
A\(hy4 or
A\(hy15.
.RT
.sp 1P
.LP
5.1.4.2
    \fIWhen the last incoming\ R2 register is able to transmit\fR
\fIthe condition of the called subscriber's line\fR
.sp 9p
.RT
.LP
.PP
When the condition of the called subscriber's line can be determined the
incoming\ R2 register can send signals conveying this information after
receipt of the address digits.
.PP
As soon as the last address digit is received the last incoming\ R2
register sends the address\(hycomplete signal\ A\(hy3 to announce changeover
to the
transmission of Group\ B signals. In response the outgoing international\ R2
register sends the appropriate calling party's category signal (II\(hy7
to II\(hy10). The last incoming\ R2 register acknowledges this with the
relevant Group\ B
signal indicating the condition of the called subscriber's line.
.PP
Immediately the compelled signalling sequence is complete the
incoming\ R2 register is released and depending upon the Group\ B signal
sent the speech\(hypath may be through\(hyconnected.
.PP
When the condition of the called subscriber's line is determined by an
electrical signal to the last incoming\ R2 register and if the called
subscriber's line is free the address\(hycomplete signal\ A\(hy6 can be
sent instead of signal\ A\(hy3, possibly in pulse form. This will be the
last interregister
signal. After signal\ A\(hy6 is sent the incoming\ R2 register is released,
the
.PP
speech\(hypath is through\(hyconnected and ringing tone returned to the calling
subscriber. Outgoing international\ R2 registers must be able to interpret
all Group\ B signals.
.PP
On recognition of the last backward signal the outgoing exchange
releases the outgoing international\ R2 register and either through\(hyconnects
the speech\(hypath or releases the outgoing connection and causes the return
of an
appropriate tone or special announcement or both alternately to the calling
subscriber.
.RT
.sp 1P
.LP
5.1.4.3
    \fIWhen the last incoming\ R2 register is not able to transmit\fR
\fIthe condition of the called subscriber's line\fR
.sp 9p
.RT
.PP
In this case the last incoming\ R2 register sends the address\(hycomplete
signal\ A\(hy6, possibly in pulse form, as the last interregister signal.
After
this is sent, the last incoming\ R2 register is released and the speech\(hypath
is through\(hyconnected.
.PP
When the last incoming\ R2 register is in the exchange to which the
called subscriber is connected, an appropriate tone is returned to the
calling subscriber from this exchange.
.PP
On recognition of address\(hycomplete signal\ A\(hy6, the outgoing exchange
releases the outgoing international\ R2 register and through\(hyconnects the
speech\(hypath. The calling subscriber will then hear ringing tone, busy tone,
special information tone or a recorded announcement alternately with special
information tone sent by the incoming equipment.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ Q.465\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.1.5\ PARTICULAR\ CASES\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.465''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.465    %'
.ce 0
.sp 1P
.LP
5.1.5.1
    \fIUnallocated number\fR
.sp 1P
.RT
.PP
When, after the reception of any digit, the incoming\ R2 register
determines that the address information corresponds to an unallocated number,
the address\(hycomplete signal\ A\(hy3 is sent immediately without requesting
all the address digits. In response the outgoing international\ R2 register
sends the
appropriate Group\ II signal. This is then acknowledged by signal\ B\(hy5
\fIunallocated number\fR .
.RT
.LP
.sp 1P
.LP
5.1.5.2
    \fICongestion in the national network\fR
.sp 9p
.RT
.PP
If congestion is encountered in the national network the
incoming\ R2 register sends congestion signal\ A\(hy4, possibly in pulse form.
However, if address\(hycomplete signal\ A\(hy3 has already been sent, congestion
signal\ B\(hy4 is sent in acknowledgement of the Group\ II signal which
commences
the last compelled signalling sequence.
.RT
.sp 1P
.LP
5.1.5.3
    \fIOperator calls\fR
.sp 9p
.RT
.PP
The procedures described in Recommendations\ Q.462\(hyQ.464 are also
valid for a semi\(hyautomatic call. However, in this case the address information
is always terminated by the end\(hyof\(hypulsing signal\ I\(hy15.
.PP
For code\ 11 or code\ 12 calls only a limited number of backward signals
can be employed as the last interregister signal (e.g. signal\ A\(hy4,
A\(hy6
or\ B\(hy6).
.RT
.LP
.sp 1P
.LP
5.1.5.4
    \fIRequest of calling party's category\fR
.sp 9p
.RT
.PP
At any time calling party's category information may be requested by the
incoming\ R2 register interrupting the normal transmission of address
information. The incoming\ R2 register sends signal\ A\(hy5 in
acknow
ledgement\ of\ a
Group\ I signal and the outgoing international\ R2 register sends the appropriate
Group\ II signal (a signal\ II\(hy7 to II\(hy10) in reply. If this Group\
II signal is acknowledged by a signal different from address\(hycomplete
signal\ A\(hy3 or
signal\ A\(hy5 the next forward signal sent will be one of the Group\ I.
\v'2P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.466\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.1.6\fR \ \
\fBSUPERVISION\ AND\ RELEASE\ OF\ THE\ CALL\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.466''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.466    %'
.ce 0
.sp 1P
.PP
An answer signal is sent when the called subscriber's off\(hyhook condition
is detected. Each transit exchange in the connection, relays this
line signal. At the outgoing international exchange, receipt of the answer
signal normally causes call charging to take place and metering for
international accounting purposes to start.
.sp 1P
.RT
.PP
When the called subscriber's on\(hyhook condition is detected a
clear\(hyback signal is sent and relayed by each transit exchange.
.PP
When the calling subscriber's on\(hyhook condition is detected a
clear\(hyforward signal is relayed by the outgoing international exchange
over the outgoing international link. On receipt of the clear\(hyforward
signal on an
incoming link, release operations are initiated and the clear\(hyforward
signal is repeated forward on the outgoing link.
.PP
Immediately release operations at an exchange are complete (although the
outgoing circuit may still be held) a release\(hyguard sequence is initiated
on the incoming link. After recognition of the end of the release\(hyguard
sequence at the outgoing exchange the link reverts to the idle state.
.PP
Supervision of a call must be in accordance with
Recommendation\ Q.118.
.bp
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.468\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.2\ \ ROUTING\ AND\ NUMBERING\ FOR\ INTERNATIONAL\ WORKING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.468''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.468    %'
.ce 0
.sp 1P
.ce 1000
(See Recommendations Q.107 and Q.107 | fIbis\fR , Fascicle VI.1.)
\v'6p'
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fB5.3\fR \
\fBTERMINATION\ OF\ INTERREGISTER\ SIGNALLING\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.470\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.3.1\ AT\ AN\ INCOMING\ R2\ REGISTER\ SITUATED\ IN\ A\ TRANSIT\ EXCHANGE\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.470''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.470    %'
.ce 0
.sp 1P
.LP
5.3.1.1
    \fISuccessful routing\fR
.sp 1P
.RT
.PP
Normally, interregister signalling is terminated in one of the
following ways:
.RT
.LP
    \fIa)\fR     The last forward interregister signal received by the
incoming\ R2 register at the transit exchange is not acknowledged from that
register. After an outgoing link to the next exchange is seized, the register
is dismissed and the speech\(hypath is through\(hyconnected. The forward
signal
remains on\(hyline and is the first signal received by the next incoming\ R2
register. Provision must be made for the switching operations to be completed
so as to ensure that the signal will remain on\(hyline and be received
by the
succeeding register.
.LP
    \fIb)\fR     The last forward interregister signal received by the
incoming\ R2 register at the transit exchange is acknowledged by a backward
signal (A\(hy1, A\(hy2, A\(hy7, A\(hy8, A\(hy11 or A\(hy12) requesting
transmission of a clearly specified signal as the first to be received
by the next incoming\ R2 register. When the compelled signalling sequence
is complete the register is dismissed
and the speech\(hypath is through\(hyconnected.
.LP
    Because it is not possible to send signals\ A\(hy2, A\(hy7, A\(hy8,
A\(hy11 or A\(hy12 in pulse form, precautions are necessary to
.LP
avoid acknowledging the last address digit (on automatic calls) until
the signalling system employed on the outgoing link is known. If signal\
A\(hy1 is sent in acknowledgement of the last address digit and if the
outgoing link
employs System\ R2 it may not then be possible to send one of these signals
and therefore end\(hyto\(hyend signalling to the next exchange is no longer
feasible (see also Recommendation\ Q.474).
.LP
     In international working signals\ A\(hy2, A\(hy7 and A\(hy8 may be used
to acknowledge receipt of any forward signal.
.LP
    Signal\ A\(hy11 must be used to request a country code indicator.
.LP
    Signal\ A\(hy12 must generally be used to request the language or
discriminating digit. However, in the case where an incoming\ R2 register is
equipped with only 5\ backward signalling frequencies only one of the
signals\ A\(hy2, A\(hy7 or A\(hy8 can be used for this purpose. Attention
is drawn to the fact that in this case the language or discriminating digit
may not be sent by all outgoing international\ R2 registers.
.PP
Although it is not normally necessary to request a repeat of a
digit\ \fIn\fR because it remains on the line until acknowledged (but see
.PP
Recommendation\ Q.476) such repetition may prove necessary after an interruption
of digit transmission (e.g. to request information concerning the calling
party's category) or if the completion of switching operations referred
to in method \fIa)\fR \ above, cannot be guaranteed with a time compatible
with the
time\(hyout of the outgoing (international)\ R2 register (see
Recommendation\ Q.476). The procedure is then as follows:
.PP
Signal\ A\(hy2 is sent, eliciting the digit\ \fIn\fR \(hy1; this is immediately
acknowledged by signal\ A\(hy1 to elicit the required digit\ \fIn\fR .
When the digit\ \fIn\fR in question is the first digit in the store of
the outgoing\ R2 register this
procedure is not applicable.
.PP
\fI\fR At an international transit exchange method\ \fIb)\fR above, must
be used and only one of the signals\ A\(hy11 or A\(hy12 applies.
.bp
.PP
When the outgoing link connects to a further international transit
exchange signal\ A\(hy11 must be used to request a country code indicator. On
recognition of signal\ A\(hy11 the outgoing international\ R2 register
must send a country code indicator (signal\ I\(hy12 or I\(hy14, see Recommendation\
Q.479) as the first forward signal to be received by the next incoming\
R2 register.
.PP
Signal\ I\(hy12 or I\(hy14 may be requested as many times as necessary by
sending signal\ A\(hy11.
.PP
When the outgoing link connects to an incoming international terminal
exchange signal\ A\(hy12 must be used to request the language or discriminating
digit. On recognition of signal\ A\(hy12 the outgoing international\ R2
register
must send the language or discriminating digit (a signal\ I\(hy1 to I\(hy10)
as the
first forward signal to be received by the next incoming\ R2 register.
.PP
On recognition of signal\ A\(hy12 (sent from an international transit
exchange) an outgoing international\ R2 register is informed that an
international link connected to an incoming international terminal exchange
has been added to the (multi\(hy)link section and that call set\(hyup is now in
progress in the national destination network. This is of importance when
signal\ A\(hy9 or A\(hy10 are, in the originating country, amongst those
used to
set\(hyup international calls.
.RT
.sp 1P
.LP
5.3.1.2
    \fICongestion\fR
.sp 9p
.RT
.PP
If it is impossible to set\(hyup the desired connection in the transit
exchange the incoming\ R2 register terminates interregister signalling
by
transmission of the congestion signal\ A\(hy4 or A\(hy15. The backward
signal may
serve as acknowledgement of the last forward signal received by the incoming\
R2 register at the transit exchange or is sent in pulse form.
.PP
The two congestion signals\ A\(hy4 and A\(hy15 are provided to enable an
outgoing international\ R2 register to determine whether congestion is
occurring in the international network or in that of the destination country
so that
provision for repeat attempt or re\(hyrouting can be made in the former
case:
.RT
.LP
    \(em
    Signal\ A\(hy15 is sent from an international exchange.
.LP
    \(em
     Signal\ A\(hy4 is sent from a national exchange or possibly from a terminal
international exchange. [See also \(sc\ 5.1.2.2\ c).]
.LP
.PP
Because receipt of congestion signal\ A\(hy15 by an outgoing
international\ R2 register may initiate repeat attempt or re\(hyrouting it is
possible to transmit congestion signal\ A\(hy4 from international exchanges
where repeat attempt or re\(hyrouting may be expected useless.
.LP
.sp 2P
.LP
\fBRecommendation\ Q.471\fR
.RT
.sp 2P
.ce 1000
\fB5.3.2\ \ AT\ THE\ LAST\ INCOMING\ R2\ REGISTER\ SITUATED\ IN\ THE\ EXCHANGE\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.471''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.471    %'
.ce 0
.sp 1P
.ce 1000
\fBTO\ WHICH\ THE\ CALLED\ SUBSCRIBER\ IS\ CONNECTED\fR
.ce 0
.sp 1P
.LP
5.3.2.1
    \fISuccessful routing\fR
.sp 1P
.RT
.PP
When a call has been completely set up by means of System\ R2
interregister signalling, the incoming\ R2 register terminates interregister
signalling immediately on receipt of the entire number.
.PP
The following criteria are used to determine whether the number
received by the incoming\ R2 register is complete:
.RT
.LP
    \fIa)\fR     analysis\ \(em\ to determine the last digit;
.LP
    \fIb)\fR     electrical conditions given by the switching equipment
succeeding the incoming\ R2 register;
.LP
    \fIc)\fR     receipt of the end\(hyof\(hypulsing signal (I\(hy15);
.LP
     \fId)\fR the assumption, after a specified time has elapsed, that no
further digits will be sent (see Recommendation\ Q.476).
.PP
When criterion \fIa)\fR (analysis) is applied:
.LP
    \(em
    if the incoming\ R2 register is equipped to send Group\ B
signals to provide information about the condition of the called
subscriber's line the address\(hycomplete signal\ A\(hy3 is
transmitted on receipt of the last digit. As soon as it is known
whether the connection with the subscriber's line can be
established, only the appropriate Group\ B signal needs to be
sent. The use of the Group\ B signals is detailed in
Recommendation\ Q.474;
.LP
    \(em
    if the incoming\ R2 register is not equipped to receive
information about the condition of the called subscriber's line, the
address\(hycomplete signal\ A\(hy6 is sent immediately after
.LP
reception of the last digit and no Group\ B signal will be
transmitted.
.bp
.PP
In both cases the time interval between the end of a signal\ A\(hy6 or
a Group\ B signal and the start of the subsequent answer signal must not
be less than 75\ ms.
.PP
When criterion \fIb)\fR (electrical conditions) is applied:
.PP
It is recommended that, to avoid delay in sending the answer signal, no
Group\ B signal should be sent when the called subscriber's line is free,
and that the setting\(hyup of speech conditions be ensured by sending address\(hycomplete
signal\ A\(hy6 immediately the electrical conditions are recognized. The
time
interval between the end of signal\ A\(hy6 and the start of transmission of the
subsequent answer signal must be not less than 75\ ms (see also
Recommendations\ Q.412 and Q.475).
.PP
Criterion \fIc)\fR (end\(hyof\(hypulsing) can be applied only if the incoming\
R2 register is equipped to receive the 6\ forward signalling frequencies
(see also Recommendation\ Q.473). When signal\ I\(hy15 is received and
recognized the last
incoming\ R2 register can perform in the way described under
criterion\ \fIa)\fR .
.PP
When criterion \fId)\fR (time\(hyout) is applied:
.PP
Address\(hycomplete signal\ A\(hy6 must be sent in pulse form as soon as the
specified time has elapsed. The time between the end of signal\ A\(hy6 and the
start of transmission of the subsequent answer signal must be, as indicated
above for criterion \fIb)\fR , not less than 75\ ms (see also Recommendations\
Q.412 and Q.472).
.PP
It may happen, however, that the called subscriber answers before the
specified time has elapsed. In such exceptional circumstances the pulse
signal\ A\(hy6 must be sent immediately the answer signal is recognized.
In this
case the time between the end of signal\ A\(hy6 and the start of the transmission
of the subsequent answer signal must be 75\ ms or more but less than 150\
ms. The calling subscriber will not hear the ringing tone.
.PP
This disadvantage can be avoided by not using a received digit to set up
the call until after the following digit has been received or until a certain
time has elapsed. This procedure, however, may give rise to difficulties
if the time\(hyout devices provided in the switching equipment succeeding
the incoming\ R2 register are set for too short a delay [see also Recommendation\
Q.120,
\(sc\ 1.5.5.2\ b) iv)].
.RT
.sp 1P
.LP
5.3.2.2
    \fICongestion\fR
.sp 9p
.RT
.PP
An incoming\ R2 register should terminate interregister signalling
immediately any conditions preventing complete setting\(hyup of a call
have been recognized.
.PP
If congestion is encountered congestion signal\ A\(hy4 is sent, possibly
in pulse form. However if address\(hycomplete signal\ A\(hy3 has already
been sent then congestion signal\ B\(hy4 is sent in acknowledgement of
the Group\ II signal
which commences the last compelled signalling sequence.
\v'1P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.472\fR
.RT
.sp 2P
.ce 1000
\fB5.3.3\ AT\ THE\ LAST\ INCOMING\ R2\ REGISTER\ SITUATED\ IN\ A\ TRANSIT\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.472''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.472    %'
.ce 0
.sp 1P
.ce 1000
\fBEXCHANGE\fR
.ce 0
.sp 1P
.LP
5.3.3.1
    \fISuccessful routing\fR
.sp 1P
.RT
.PP
Interregister signalling to such a register can be terminated after all
the address digits are received. In order to determine that the number
is complete the same criteria as described in Recommendation\ Q.471 are
used.
.PP
When criterion \fIa)\fR (analysis) is applied:
.RT
.LP
    1)
    if the signalling system employed on the outgoing link
enables the condition of the called subscriber's line to be sent backwards
within an acceptable period compared to the time\(hyout of the outgoing
international\ R2 register, the last incoming R2\
register can react in
accordance with one of the following methods:
.LP
    i)
    address\(hycomplete signal\ A\(hy3 is sent in acknowledgement of
the last address digit followed by the relevant Group\ B signal depending
upon the condition of the called subscriber's line;
.bp
.LP
    ii)
     signal\ A\(hy1 is sent in acknowledgement of the last address digit,
and signal\ I\(hy15 if received, to deliberately suspend compelled
signalling and later,
.LP
    \(em
     when the condition of the called subscriber's line is known, address\(hycomplete
signal\ A\(hy3 is sent in pulse form followed by the relevant
Group\ B signal. This makes it possible to avoid maintaining on\(hyline the
Group\ II signal sent after reception of signal\ A\(hy3,
.LP
    \(em
     when the called subscriber's line is free, it is preferable to send the
address\(hycomplete signal\ A\(hy6 in pulse form,
.LP
    2)
     if the signalling system employed on the outgoing link does not enable
the condition of the called subscriber's line to be transmitted
backwards or if such information is only available at the last incoming\ R2
register after a delay incompatible with the time\(hyout of the outgoing
international\ R2 register, then address\(hycomplete signal\ A\(hy6 is sent in
acknowledgement of the last address digit.
.LP
.PP
When criterion \fIb)\fR (electrical conditions) is applied:
.PP
Only signal\ A\(hy1 can be used to acknowledge each address digit. Upon
receipt of an electrical signal on the outgoing link, the last incoming\ R2
register acts in one of the following ways:
.RT
.LP
    \(em
     if the condition of the called subscriber's line is not known or is known
to be \fIfree\fR , address\(hycomplete signal\ A\(hy6 is sent in pulse
form;
.LP
    \(em
     if the condition of the called subscriber's line is known to be other
than \fIfree\fR , address\(hycomplete signal\ A\(hy3 is sent in pulse
form, followed by the relevant Group\ B signal.
.PP
Criterion \fIc)\fR (end\(hyof\(hypulsing) is only applicable if the last
incoming\ R2 register can receive 6\ forward signalling frequencies (see also
Recommendation\ Q.473). In this case, when end\(hyof\(hypulsing signal\
I\(hy15 is
received and recognized, the last incoming\ R2 register can perform in
the way described under criterion \fIa)\fR .
.PP
When criterion \fId)\fR (time\(hyout) is applied:
.PP
Address\(hycomplete signal\ A\(hy6 is sent in pulse form after the specified
time has elapsed (see Recommendation\ Q.476).
.RT
.sp 1P
.LP
5.3.3.2
    \fICongestion\fR
.sp 9p
.RT
.PP
If congestion is encountered, the procedure described in
Recommendation\ Q.470 is followed. However, if address\(hycomplete signal\
A\(hy3
has already been sent then congestion signal\ B\(hy4 is sent in acknowledgement
of the Group\ II signal which commences the last compelled signalling
cycle.
\v'3P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.473\fR
.RT
.sp 2P
.ce 1000
\fB5.3.4\fR \
\fBUSE\ OF\ END\(hyOF\(hyPULSING\ SIGNAL\ I\(hy15\ IN\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.473''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.473    %'
.ce 0
.sp 1P
.ce 1000
\fBINTERNATIONAL\ WORKING\fR
.ce 0
.sp 1P
.PP
In international working, the end\(hyof\(hypulsing signal\ I\(hy15 is used in
accordance with Recommendation\ Q.468. Signal\ I\(hy15 (end\(hyof\(hypulsing)
is sent
immediately after the last digit.
.sp 1P
.RT
.PP
In national working, signal\ I\(hy15 may be used too.
.PP
In semi\(hyautomatic operation, calls to operators' positions are always
terminated by transmission of signal\ I\(hy15. This signal can only be
interpreted if the incoming\ R2 register is equipped for reception of 6\
forward frequencies. However, when an incoming\ R2 register is equipped
for reception of only
.PP
5\ forward signalling frequencies no provision can be made for recognition of
signal\ I\(hy15. Such an incoming\ R2 register will then act as though
signal\ I\(hy15 had not been sent. Consequently the next interregister
signal is only one of
the signals\ A\(hy3, A\(hy4 or A\(hy6 sent in pulse form.
.bp
.RT
.sp 1P
.LP
5.3.4.1
    \fIProcedures to be followed after receipt of end\(hyof\(hypulsing\fR
\fIsignal\ I\(hy15 by the last incoming\ R2 register (situated in a\fR
\fItransit exchange or in the exchange to which the called\fR \fIsubscriber
is connected)\fR
.sp 9p
.RT
.PP
Incoming\ R2 registers equipped for the reception of all 6\ forward
signalling frequencies can acknowledge receipt of the end\(hyof\(hypulsing
signal\ I\(hy15 by sending an appropriate backward signal to complete the
compelled signalling cycle. Interregister signalling is terminated according
to the procedures specified in Recommendations\ Q.471 or Q.472 when criterion
\fIa)\fR (analysis) is applied.
.PP
In particular, if the last incoming\ R2 register acknowledges signal\ I\(hy15
with signal\ A\(hy1 the outgoing international\ R2 register will not send
any signal and the incoming\ R2 register can only send one of signals\
A\(hy3, A\(hy4, A\(hy6 or A\(hy15 in pulse form.
.PP
Since there is no compulsion to equip incoming\ R2 registers in national
exchanges with receivers for all 6\ forward signalling frequencies, the
signal\ I\(hy15 sent by an outgoing international\ R2 register may not
be recognized by the incoming\ R2 register. In such cases other criteria
can be used to
determine whether the number received by the incoming\ R2 register is complete.
.PP
When the incoming\ R2 register determines that the number received is
complete using criteria other than \fIc)\fR (end\(hyof\(hypulsing) it may
be that the
last digit of the subscriber number is acknowledged by signal\ A\(hy3,
A\(hy4, A\(hy6 or A\(hy15. In this case interregister signalling is terminated
without request for the signal\ I\(hy15, in the normal way according to
the procedures specified in
Recommendations\ Q.471 or Q.472 (a compelled signalling cycle including
signal\ I\(hy15 is saved).
.RT
.sp 1P
.LP
5.3.4.2
    \fIProcedure to be followed after receipt of signal\ I\(hy15\fR
\fIby an incoming\ R2 register situated in a transit exchange\fR
.sp 9p
.RT
.LP
.PP
Signal\ A\(hy1, A\(hy2, A\(hy7, A\(hy8, A\(hy11 or A\(hy12 may be sent in
acknowledgement of signal\ I\(hy15 (end\(hyof\(hypulsing). However, at
a transit exchange precautions are necessary to avoid acknowledgement of
signal\ I\(hy15 before the
signalling system employed on the outgoing link has been identified. If
signal\ A\(hy1 is sent in acknowledgement of signal\ I\(hy15 and if the
outgoing link employs System\ R2, it is not then possible to send backward
signal\ A\(hy2, A\(hy7,
A\(hy8, A\(hy11 or A\(hy12 after the end of the compelled signalling cycle
because these signals cannot be sent in pulse form. Therefore end\(hyto\(hyend
signalling to the
next exchange is no longer possible.
\v'2P'
.RT
.sp 2P
.LP
\fBRecommendation\ Q.474\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.3.5\fR \
\fBUSE\ OF\ GROUP\ B\ SIGNALS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.474''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.474    %'
.ce 0
.sp 1P
.PP
Group\ B signals are used to transmit information about the
condition
of switching equipment in the incoming exchange or the called subscriber's
line, to the outgoing international\ R2 register, which can then take the
necessary action.
.sp 1P
.RT
.PP
The address\(hycomplete signal\ A\(hy3 is sent by an incoming\ R2 register
to announce changeover to sending Group\ B signals. In addition, signal\
A\(hy3
indicates that the incoming\ R2 register has received all the Group\ I forward
signals it requires from the outgoing international\ R2 register. On recognition
of signal\ A\(hy3 an outgoing\ R2 register sends a Group\ II signal. The
incoming\ R2 register may interpret the Group\ II signal giving information
about calling
.PP
party's category, in order to control the switching operations accordingly
(e.g.\ suppression of automatic ringing for operator initiated calls or to
prevent subscriber access to data transmission terminals). Finally, a Group\
II forward signal is acknowledged by any Group\ B backward signal.
.PP
In cases where outgoing\ R2 registers are able to interpret all Group\
B signals there is generally no need to provide equipment at the incoming
end
able to send, in addition to Group\ B signals, the tones and/or announcements
corresponding to those signals, except in the case of ringing tone.
.bp
.PP
In general, outgoing\ R2 registers must be equipped with devices
permitting, after reception of signal\ A\(hy3:
.RT
.LP
    \(em
    the exchange of an additional cycle of interregister signals
before the register is released;
.LP
    \(em
    changeover from Group\ A to Group\ B meanings of backward
signals.
.PP
Outgoing international\ R2 registers, however, must be able to
interpret all Group\ B signals.
.LP
.sp 1P
.LP
5.3.5.1
    \fIProcedures to be followed by an outgoing international\ R2\fR
\fIregister on receipt of Group\ B signals\fR
.sp 9p
.RT
.PP
Signal\ B\(hy1 is interpreted by an outgoing international\ R2 register
as signal\ B\(hy6: the register is released and the speech\(hypath is through\(hyconnected.
A subsequent answer signal initiates call charging.
.PP
Signal\ B\(hy2 send special information tone is sent by the incoming\ R2
register:
.RT
.LP
    \(em
    when the number of the called party has been changed,
.LP
    \(em
    when the three following conditions are fulfilled together:
.LP
    i)
    the called party's line condition does not fit with one
of the meanings of the present Group\ B signals,
.LP
    ii)
    it does not lead to setting up the speech path,
.LP
    iii)
    it is not incompatible with return of special
information tone to the calling party.
.PP
After recognizing signal\ B\(hy2, the outgoing international\ R2 register
clears forward and causes the transmission of only special information tone.
.PP
The subscriber's line busy signal\ B\(hy3 is sent by the incoming register
when the called subscriber's line is engaged. On recognition of this signal,
the outgoing register releases the connection and causes transmission of the
busy tone.
.PP
When the congestion condition is encountered following the changeover
from Group\ A signals to Group\ B signals, the congestion signal\ B\(hy4
shall be
transmitted on the conditions specified for congestion signal\ A\(hy4.
In all cases recognition of the signal causes release of the call and transmission
of
congestion information.
.PP
After recognizing unallocated number signal\ B\(hy5, the outgoing
international\ R2 register clears the call and causes transmission of special
information tone or a recorded announcement and special information tone,
alternately, to the calling party.
.PP
After recognizing signal\ B\(hy6, the outgoing international\ R2 register
sets up speech conditions so that a caller may hear the ringing tone. In
this case, a subsequent answer signal activates the call\(hycharging mechanism.
.PP
After recognizing signal\ B\(hy7 the outgoing international\ R2 register
sets up speech conditions, so that a caller may hear the ringing tone.
In this case, a subsequent answer signal does not activate the call\(hycharging
mechanism.
However, in an outgoing international\ R2 register signal\ B\(hy7 may be
interpreted as B\(hy6 if there is no international agreement on non\(hychargeable
calls.
.PP
After recognizing signal\ B\(hy8 subscriber's line out of order, the
outgoing international\ R2 register clears forward and causes the transmission
of a special information tone or recorded announcement and special information
tone alternately to the calling party.
.PP
Receipt of signal\ B\(hy9 or B\(hy10 by an outgoing international\ R2 register
causes release of the outgoing connection and return of special information
tone to the calling subscriber, i.e. these signals should be interpreted as
signal\ B\(hy2.
.PP
If an outgoing international\ R2 register receives one of signals\ B\(hy11
to B\(hy15 the call should be released and indication of this returned
to the calling subscriber or operator, i.e. this signal should be interpreted
as
signal\ B\(hy4.
.RT
.LP
.sp 1P
.LP
5.3.5.2
    \fISpecial procedures for national working\fR
.sp 9p
.RT
.PP
Outgoing\ R2 registers in national exchanges may not be able to
recognize and interpret Group\ B signals. In such networks it is essential
that the equipment at the incoming end must transmit not only the Group\
B signals
but also the corresponding tones and/or announcements, when the incoming\ R2
register does not know whether the outgoing\ R2 register is capable of
interpreting Group\ B signals.
.bp
.PP
In the case where the incoming\ R2 register is able to make only two or
three distinctions of conditions of the called subscriber's line the following
procedure may be adopted: When the only distinction that can be made is
between subscriber's line free and subscriber's line engaged,
.RT
.LP
    i)
    signal\ B\(hy3 is sent if the line is engaged;
.LP
    ii)
    otherwise signal\ B\(hy6, or signal\ A\(hy6 alone is sent
so the caller can hear the ringing tone sent by
the incoming equipment.
.LP
.PP
In the case where outgoing\ R2 registers in national exchanges are only
able to interpret a limited number of Group\ B signals or are indeed not
able to interpret any, it is essential that such equipment be able to respond
to signal\ A\(hy3 in the specific manner and at least to recognize the
next
backward signal (which is a Group\ B signal) as indicating the end of
interregister signalling.
.sp 1P
.LP
5.3.5.3
    \fIPossible application of signal\ B\(hy1 in national working\fR
.sp 9p
.RT
.PP
Signal\ B\(hy1, for example, may be used to indicate that the call must
remain under the control of the incoming equipment, insofar as this is
possible (e.g.\ for maintenance reasons, to trace malicious calls, etc.).
The incoming
exchange sets up speech conditions, so that the calling subscriber can
hear the ringing tone. At present such a use of signal\ B\(hy1 in international
working is not envisaged.
.bp
.RT
.sp 2P
.LP
\fBRecommendation\ Q.475\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.4\ NORMAL\ RELEASE\ OF\ OUTGOING\ AND\ INCOMING\ R2\ REGISTERS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.475''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.475    %'
.ce 0
.sp 1P
.PP
An outgoing international\ R2 register must be released once it has received
an appropriate backward interregister signal terminating the
interregister signalling, or on receipt of a clear\(hyforward (line) signal
from the preceding link.
.sp 1P
.RT
.PP
An incoming\ R2 register must be released once it has accomplished
the necessary switching control and terminated the interregister signalling
required, or on receipt of a clear\(hyforward (line) signal from the preceding
link.
.PP
The last recognized interregister signal preceding setting up of speech
conditions will normally be a backward signal: e.g.\ address\(hycomplete
signal\ A\(hy6, subscriber's line free signals\ B\(hy6 or B\(hy7.
.PP
The multifrequency combination receivers at the two ends must be
disconnected before the switching equipment passes to the speech condition;
this procedure eliminates any possibility of their operating or being held
under the influence of speech or line signals. The following conditions
regarding the duration of the various phases should be observed (see
Figure\ 20/Q.475):
.RT
.LP
     \fIa)\fR the multifrequency signalling equipment of the incoming\ R2
register must be disconnected within 30\ ms after recognition of the end
of
transmission of the last backward signal;
.LP
     \fIb)\fR the multifrequency signalling equipment of the outgoing\ R2
register must be disconnected within 30\ ms after recognition of the end
of the last backward signal;
.LP
     \fIc)\fR at the outgoing exchange speech conditions must be set up between
30 and 60\ ms after recognition of the end of the last backward signal.
However, at the exchange where the outgoing international\ R2 register
is
situated, the setting\(hyup of speech conditions depends upon the signalling
system employed on the preceding link;
.LP
     \fId)\fR at the incoming exchange at least 75\ ms must elapse between
the end of transmission of the last backward signal and the
setting up of speech conditions.
.LP
.rs
.sp 2P
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 20/Q.475 p.13\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.476\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.5\fR \
\fBABNORMAL\ RELEASE\ OF\ OUTGOING\ AND\ INCOMING\ R2\ REGISTERS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.476''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.476    %'
.ce 0
.sp 1P
.PP
To limit the holding time of R2\ registers, when interregister
signalling is interrupted either by a fault or by any other cause, all
R2\ registers must be equipped with devices for continuous supervision of the
time taken by the various phases of interregister signalling. The time\(hyout
delay of these devices must be as short as possible, but long enough not to
interrupt normal operation.
.sp 1P
.RT
.sp 1P
.LP
5.5.1
    \fITime\(hyout of outgoing international\ R2 register\fR
.sp 9p
.RT
.PP
In an outgoing international\ R2 register, the intervals during which a
forward multifrequency combination is transmitted and the intervals
.PP
during which no such combination is transmitted are supervised separately.
.RT
.sp 1P
.LP
5.5.1.1
    \fISupervision during sending of forward multifrequency\fR
\fIcombinations\fR
.sp 9p
.RT
.PP
The lower limit of the time\(hyout delay is a function of the time
required for the switching procedures in a transit exchange.
.PP
On this basis, the time\(hyout delay is specified as 15\ \(+-\ 3\ seconds.
.PP
The supervision device will start functioning at the beginning of the
transmission of a forward multifrequency combination and be reset with the
deactivation of the senders involved. It will start again at the beginning
of the transmission of the next forward multifrequency combination.
.RT
.sp 1P
.LP
5.5.1.2
     \fISupervision during intervals when no forward\fR \fImultifrequency
combination is being sent\fR
.sp 9p
.RT
.PP
The lower limit of the time\(hyout delay is a function of:
.RT
.LP
    a)
    the maximum permissible time interval between dialling of
two successive digits by the subscriber;
.LP
    b)
    the time\(hyout delay specified for incoming\ R2 registers
(see \(sc\ 5.5.2 below).
.LP
.PP
On this basis, the time\(hyout delay is specified to be longer than
24\ seconds (a longer delay and an upper limit may be specified by each
Administration).
.PP
If this specification is observed an incoming\ R2 register, which has
acknowledged the last received digit with the signal\ A\(hy1, is bound to be
released before the supervision device of the outgoing international\ R2
register initiates the alarm condition.
.RT
.sp 1P
.LP
5.5.1.3
    \fIProcedure to be followed if time\(hyout occurs\fR
.sp 9p
.RT
.PP
If time\(hyout occurs, the time supervision devices mentioned in
\(sc\(sc\ 5.5.1.1 and\ 5.5.1.2\ above will bring about operations producing:
.RT
.LP
    \(em
     return of an appropriate signal and/or audible tone to inform the calling
party,
.LP
    \(em
    release of the outgoing international\ R2 register and of the
connection as far as the latter is not necessary for the
above\(hymentioned operation.
.PP
Fault recording equipment may start functioning and/or a delayed
alarm may alert the technical staff.
.LP
.sp 1P
.LP
5.5.1.4
    \fITime\(hyout of outgoing\ R2 register\fR
.sp 9p
.RT
.PP
It is recommended that the same principles outlined in \(sc\(sc\ 5.5.1.1
to 5.5.1.3\ above be applied by analogy to outgoing\ R2 registers.
.RT
.sp 1P
.LP
5.5.2
    \fITime\(hyout of incoming\ R2 register\fR
.sp 9p
.RT
.PP
The time\(hyout device shall supervise the interval elapsing between seizure
of the register and recognition of the first forward multifrequency
combination as well as the interval elapsing between the recognition of two
successive multifrequency combinations in the forward direction.
.bp
.RT
.sp 1P
.LP
5.5.2.1
    \fITime\(hyout delay\fR
.sp 9p
.RT
.PP
The lower limit of the time\(hyout delay is a function of:
.RT
.LP
    a)
    the maximum permissible time interval between the
recognition of 2\ successive forward multifrequency combinations; this time
interval may in certain cases be influenced by the maximum
permissible time interval between dialling of 2\ successive
digits by the subscriber;
.LP
    b)
    the maximum time required for setting\(hyup the call under
conditions which slow down the interregister signalling.
.LP
.PP
In view of the desirability expressed in \(sc\ 5.5.1.2 above that the
incoming\ R2 register be released before expiry of the time\(hyout delay
specified for the outgoing international\ R2 register, an upper limit should
be fixed as well.
.PP
On this basis the time\(hyout delay should be specified within the range
of 8\(hy24\ seconds. A minimum delay of 15\ seconds corresponding to the
time\(hyout
delays in other CCITT standardized signalling systems is to be preferred.
.PP
For incoming\ R2 registers using the criterion \fId)\fR (time\(hyout) indicated
in Recommendation\ Q.471 to determine completion of the number, the time
referred to there as the \fIspecified time\fR may exceptionally be shorter than
8\ seconds, but never less than 4\ seconds.
.RT
.sp 1P
.LP
5.5.2.2
    \fIProcedure to be followed if time\(hyout occurs\fR
.sp 9p
.RT
.PP
If time\(hyout occurs, the time supervision device will bring about
operations producing:
.RT
.LP
    \(em
    sending of a congestion signal (A\(hy4 or A\(hy15) in pulse form;
.LP
    \(em
     release of the incoming\ R2 register and other equipment in the incoming
exchange;
.LP
    \(em
    on time\(hyout of the initial digit:
.LP
    i)
    line signalling, analogue version: establishment of the
blocked state on the incoming circuit until recognition of the clear\(hyforward
signal (see Recommendation\ Q.412, abnormal conditions);
.LP
    ii)
    line signalling, digital version: no further action
required.
.PP
Fault recording equipment may start functioning and/or a delayed
alarm may alert the technical staff.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ Q.478\fR
.RT
.sp 2P
.ce 1000
\fB5.6\fR \ \
\fBRELAY\ AND\ REGENERATION\ OF\ R2\ INTERREGISTER\ SIGNALS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.478''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.478    %'
.ce 0
.sp 1P
.ce 1000
\fBBY\ AN\ OUTGOING\ R2\ REGISTER\ IN\ A\ TRANSIT\ EXCHANGE\fR
.ce 0
.sp 1P
.PP
When the overall multi\(hylink connection is divided into
end\(hyto\(hyend signalling sections, regeneration of R2\ interregister
signals is
required by either an outgoing international\ R2 register or an outgoing\ R2
register (see Recommendation\ Q.440).
.sp 1P
.RT
.PP
There are three possible procedures for relaying interregister
signals by an outgoing\ R2 register:
.LP
     \fIa)\fR the outgoing\ R2 register acknowledges each signal received
over the incoming link by transmitting the appropriate backward
signal; this operation is independent of the operations entailed
in retransmitting on the outgoing link;
.LP
    \fIb)\fR     the forward address signal with rank \fIn\fR \ +\ 1 is
acknowledged on the incoming link as soon as the forward address signal with
rank \fIn\fR is acknowledged on the outgoing link;
.LP
    \fIc)\fR     as soon as a forward signal is received on the incoming
link, a signal is sent on the outgoing link; the acknowledgement
signal is sent on the incoming link only when such a signal
has been received on the outgoing link.
.bp
.PP
Methods\ \fIa)\fR and \fIb)\fR provide the most rapid transfer of
information and are therefore the preferable methods of relaying the
information necessary for setting up the call. It is essential, however,
that the outgoing\ R2 register be provided with adequate storage capacity
in the case of method\ \fIa)\fR .
.PP
Method\ \fIb)\fR can only be applied after method\ \fIa)\fR .
.PP
Method\ \fIc)\fR should be used for relaying information relating to the
procedures for the termination of interregister signalling.
.PP
The changeover from method\ \fIa)\fR or \fIb)\fR to method\ \fIc)\fR may
require
transmission of an address\(hycomplete signal\ A\(hy3 in pulse form as
indicated in
Recommendation\ Q.442 (see Figure\ 21/Q.478).
.PP
The procedure for disconnecting the multifrequency combination
receivers and setting\(hyup speech conditions for each link, incoming and
outgoing, is given in Recommendation\ Q.475.
.PP
When method\ \fIa)\fR or \fIb)\fR is used, the time\(hyouts of the R2\
registers
associated with the first signalling section may expire if the signalling on
the second signalling section is too slow. Relatively long time\(hyouts are
recommended (see Recommendation\ Q.476).
.PP
\fINote\fR \ \(em\ The use of signal A\(hy3 on circuits with very long
transmission delay, e.g.\ satellite circuits, for relaying such information
(method c) may
result in premature release in certain incoming local exchanges with very
short time guard. The problem may be avoided if the outgoing R2 register
immediately following the satellite link uses signal A\(hy5 to obtain the
calling party's
category information previously to the receipt of signal A\(hy3 from those
incoming local exchanges.
.RT
.LP
.rs
.sp 29P
.ad r
\fBFigure 21/Q.478 p.14\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.479\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.7\fR \ \
\fBECHO\(hySUPPRESSOR\ CONTROL\ \(em\ SIGNALLING\ REQUIREMENTS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.479''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.479    %'
.ce 0
.sp 1P
.LP
5.7.1
    \fIIntroduction\fR
.sp 1P
.RT
.PP
Recommendations Q.42 and Q.115 give fundamental requirements with which
the employment of echo suppressors must comply.
.PP
There are two methods of connecting echo suppressors to a circuit. One
method is by use of permanently connected echo suppressors and the other
is by the insertion of echo suppressors from a pool, when required.
.PP
In System R2 (see Recommendation\ Q.441) two forward signals (I\(hy12 and
I\(hy14) and one backward signal (A\(hy14) are provided to indicate whether
or not an incoming half\(hyecho suppressor (IHES) is required.
.PP
A third forward signal (I\(hy11) is also available for use by bilateral
agreement to indicate that an outgoing half\(hyecho suppressor (OHES) must
be
employed.
.PP
The following principles must be taken into account.
.RT
.sp 1P
.LP
5.7.2
    \fIPrinciples of echo\(hysuppressor control\fR \v'3p'
.sp 9p
.RT
.PP
5.7.2.1
The outgoing international exchange may be able to determine
the need for echo suppressors in the connection by analysing the received
country code.
.PP
5.7.2.2
In direct traffic between 2 countries the use of echo
suppressors generally takes place according to fixed rules. Echo\(hysuppressor
control signalling is not, therefore, necessary in these cases unless it is
applied for the sake of uniformity.
.LP
.PP
5.7.2.3
In international transit traffic the outgoing half\(hyecho
suppressor (OHES) will normally be employed at the outgoing international
exchange, and the incoming half\(hyecho suppressor (IHES) at the incoming
international exchange, unless other arrangements are agreed upon with the
Administration of the international transit exchange(s) (see \(sc\ 5.7.2.5
below).
.PP
However, in cases where an outgoing satellite link is selected by a transit
exchange without the knowledge of the outgoing international
exchange, the signal I\(hy12 may be sent over the satellite link. In such cases
half\(hyecho suppressors are required and will normally be permanently
fitted at each end of the satellite link.
.PP
5.7.2.4
An incoming international exchange, equipped for the connection of IHES,
must ask the outgoing international exchange whether or not an IHES
must be employed unless this is known from other criteria (e.g.\ line
classification). It will do this by sending the backward signal A\(hy14 as an
acknowledgement of the discriminating or language digit (Z\(hydigit).
.sp 9p
.RT
.LP
.PP
When a satellite link is used in the connection the exchange
situated at the incoming end of the satellite link responds to the A\(hy14
signal instead of the outgoing international exchange (see Recommendation\
Q.7).
.PP
5.7.2.5
It may be agreed upon bilaterally that in international transit traffic
the OHES (IHES) will not be employed in the outgoing (incoming)
international exchange, but in the international transit exchange, e.g.\
in the case where most of the traffic on the circuit group between the
outgoing
exchange and the transit exchange (between the transit exchange and the
incoming exchange) needs no echo\(hysuppressor.
.sp 9p
.RT
.LP
    a)
    When echo suppressors are needed and the OHES must be
employed at the international transit exchange the outgoing international
exchange sends the signal I\(hy11 as a country code indicator.
.LP
     If an international connection is routed via two or more transit exchanges,
signal I\(hy11 must not be sent beyond the first transit exchange.
Therefore the outgoing exchange, after having sent the signal\ I\(hy11
once, must send the signal I\(hy14 if the country code indicator is requested
again
(signal\ A\(hy11).
.LP
    b)
    When echo suppressors are needed and the IHES must be
employed at the international transit exchange this is known by the
international transit exchange. In this case the incoming international
exchange will not send signal A\(hy14.
.bp
.PP
5.7.2.6
When echo suppressors are employed they will remain disabled
until the answer signal is received. This condition is necessary in order to
permit compelled interregister signalling to (e.g.\ national) exchanges
further on in the connection.
.sp 9p
.RT
.PP
Alternatively, when the ability exists to detect that
interregister signalling has been completed, the echo\(hysuppressor may
be enabled at that time without awaiting the answer signal.
.sp 1P
.LP
5.7.3
    \fIExamples of echo\(hysuppressor control signalling\fR
.sp 9p
.RT
.PP
The following situations may arise:
.RT
.sp 1P
.LP
5.7.3.1
    \fIDirect interregister signalling between two countries\ A\fR
\fIand\ B.\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    No echo\(hysuppressor control signalling is applied.
.LP
     This may be for one of two reasons. Either the connection does not normally
require echo suppressors or echo suppressors are required and are
permanently connected to the circuit.
.LP
     The signalling procedure is indicated in Table\ 11/Q.479, column a. If
echo suppressors are necessary, the OHES is employed at A and the IHES
is employed at B.
.LP
    b)
    Echo\(hysuppressor control signalling is applied.
.LP
    There are two cases:
.LP
    i)
    No echo suppressors are required (see column\ b of
Table\ 11/Q.479).
.LP
    ii)
    Echo suppressors are required (see column c of
Table\ 11/Q.479). The OHES is employed at A and the IHES is employed at B.
.LP
.sp 1P
.LP
5.7.3.2
    \fITraffic between two countries A and D via two international\fR
\fItransit exchanges B and C\fR
.sp 9p
.RT
.PP
There are two cases:
\v'3p'
.RT
.PP
5.7.3.2.1
The connection is via terrestrial circuits only.
.LP
    a)
    No echo suppressors are required (see column a of
Table\ 12/Q.479).
.LP
    b)
    Echo suppressors are required (see columns\ b, c, d,\ e of
Table\ 12/Q.479).
.LP
    The following examples may be mentioned:
.LP
    \(em
    OHES in A:\ IHES in D (column b);
.LP
    \(em
    OHES in B:\ IHES in D (column c).
.PP
The country code indicator I\(hy11 is used by bilateral agreement and indicates
that B must employ the OHES. When the country code indicator is to be sent
to C, B asks A to do this by sending signal A\(hy11. A, now sends signal\
I\(hy14 instead of signal\ I\(hy11, because B has employed the OHES. The
signal\ A\(hy14, which is sent from D as an acknowledgement of the Z\(hydigit
will, of course, also be
answered by signal\ I\(hy14.
.LP
    \(em
    OHES in A: IHES in C (column\ d).
.PP
In accordance with \(sc\ 5.7.2.5\ b) above, C knows that D cannot
employ an IHES and C itself will therefore make the connection. D will
naturally not send signal\ A\(hy14.
.LP
    \(em
    OHES in B: IHES in C (column\ e).
.LP
.PP
5.7.3.2.2
The connection includes a satellite link.
.sp 9p
.RT
.PP
The following examples are given as typical situations that may
arise:
.LP
    a)
    The first link in the connection is via satellite.
.LP
    In Table 13/Q.479, P and Q both know that echo suppressors are
required.
.LP
    If Q has a permanently connected IHES then:
.LP
    \(em
    OHES in P; IHES in Q (column\ a).
.LP
    When R or S is able to employ an IHES then:
.LP
    \(em
    OHES in P; IHES in R (column\ c);
.LP
    \(em
    OHES in P; IHES in S (column\ b).
.LP
    b)
    A later link in the connection is via satellite.
.LP
    In Table 14/Q.479:
.LP
    When P knows that Q\(hyR is via satellite:
.LP
    \(em
    OHES in P; IHES in R or S (column b or d).
.LP
    When P does not know that Q\(hyR is via satellite:
.LP
    \(em
    OHES in Q; IHES in R or S (column\ a or\ c).
.bp
.LP
.rs
.sp 16P
.ad r
\fBTableau 11/Q.479 p.15\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 31P
.ad r
\fBTableau 12/Q.479 p.16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 23P
.ad r
\fBTableau 13/Q.479 (disposition \*`a l'italienne c\* | te\(hy\*`a\(hyc\* | te
avec
Tableau 14: page pleine), p.17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 24P
.ad r
\fBTableau 14/Q.479 (\*`a l'italienne avec tableau 13), p.18\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.480\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.8\ \ \fR \fBMISCELLANEOUS\ PROCEDURES\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.480''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.480    %'
.ce 0
.sp 1P
.LP
5.8.1
    \fINature of circuit procedure for international working\fR
.sp 1P
.RT
.PP
An incoming R2 register in an international transit exchange or in the
country of destination can elicit the nature of the circuit as soon
as at least one forward signal has been received from an outgoing register.
.PP
The incoming R2 register requests nature of circuit by sending the
backward signal\ A\(hy13. The outgoing R2 register, if capable, sends
the nature of the circuit indicator signal I\(hy13 or I\(hy14 in reply.
.PP
Signal\ A\(hy13 can be sent after any forward signal (Groups I and II)
and particularly after any address digit, but it can only be sent prior
to any
transmission of signal\ A\(hy3.
.PP
If the outgoing R2 register does not have the capability of providing the
nature of circuit, signal\ I\(hy12 (request not accepted) is sent in reply
to signal\ A\(hy13. The incoming R2 register will then ask for the following
address digit by sending signal\ A\(hy1, for example. If the outgoing R2
register receives signal\ A\(hy13 again it will send signal\ I\(hy12 again.
.PP
For existing equipment if the outgoing international R2 register does not
have the capability of providing the nature of the circuit, but is capable
of sending identification information as defined in the \fIYellow Book\fR
, the
procedure starts with the first digit of the country code.
.RT
.sp 1P
.LP
5.8.2
    \fIIdentification procedure for national working\fR
.sp 9p
.RT
.LP
.PP
System R2 makes provision for the signalling necessary to identify the
calling subscriber's line: for example, by repetition of signal\ A\(hy5
or by using one of signals\ A\(hy9 or A\(hy10. For the time being this
procedure is
restricted to national working only; outgoing international\ R2 registers
prevent its use over international links (see \(sc\ 5.8.4). The outgoing R2
register at the incoming end of an international satellite link must similarly
prevent its use via that link.
.RT
.sp 1P
.LP
5.8.3
    \fIProcessing of Group\ II signals reserved for national use\fR
.sp 9p
.RT
.PP
The Group II signals reserved for national use must be converted in the
outgoing international\ R2 register to Group\ II signals used for
international working.
.PP
The conversion must be carried out as follows:
.RT
.LP
    II\(hy1 must be converted to II\(hy7
.LP
    II\(hy2 must be converted to II\(hy7 or II\(hy9
.LP
    II\(hy3 must be converted to II\(hy7
.LP
    II\(hy4 must be converted to II\(hy7
.LP
    II\(hy5 must be converted to II\(hy7 or II\(hy10
.LP
    II\(hy6 must be converted to II\(hy8
.LP
    II\(hy11 to II\(hy15 must be converted to II\(hy7.
.PP
Since there are no Recommendations yet regarding handling of
priority calls in automatic international working, conversion of signal\
II\(hy2 to signal\ II\(hy9 must be the subject of bilateral agreement.
.PP
If an incoming R2 register is situated in a national exchange and
because signals\ II\(hy7 to II\(hy10 are not used for national working,
then analysis of Group\ II signals enables a distinction to be made between
nationally and
internationally originated calls.
.PP
If an incoming R2 register knows a call is of international origin and
if a Group\ II signal reserved for national use is received, signal\ A\(hy4
or B\(hy4 (congestion on the national network) should be sent in acknowledgement.
This
procedure cannot be applied if an incoming\ R2 register in the destination
country is employed for national and international working and is not able
to detect the origin of the call.
.bp
.RT
.sp 1P
.LP
5.8.4
     \fIProcedures to be followed by outgoing international R2 registers\fR
\fIon receipt of particular backward signals\fR
.sp 9p
.RT
.PP
An outgoing international R2 register must send the appropriate
calling party's category signal (II\(hy7 to II\(hy10) in reply to signals\
A\(hy3
and\ A\(hy5.
.PP
On recognition of one of the signals A\(hy9 or A\(hy10 an outgoing
international R2 register sends signal\ I\(hy12 (request not accepted)
in response. Therefore, national incoming R2\ registers using these signals
should be
equipped to receive signal\ I\(hy12.
.PP
The incoming national R2 register receiving I\(hy12 has to determine the
appropriate international standardized signal to be sent in response to
signal\ I\(hy12 and which substitutes for signals\ A\(hy9 or\ A\(hy10.
.PP
In reply to signal A\(hy14 an outgoing international R2 register
sends:
.RT
.LP
    \(em
    signal I\(hy14 when an incoming half\(hyecho supressor is
required;
.LP
    \(em
    the next address digit (a signal I\(hy1 to I\(hy10) when no
incoming half\(hyecho suppressor is required.
.PP
If an outgoing international R2 register receives a backward
signal requesting an impossibility in the logical procedure (e.g.\ receipt of
signal\ A\(hy8 after sending the country code indicator), the call shall be
released.
.LP
.rs
.sp 38P
.LP
.bp
.LP
\fBMONTAGE:\ \fR PAGE 138 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp