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.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 4
.ce 0
.sp 1P
.ce 1000
\fBTESTING\ ARRANGEMENTS\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.327\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.1\ GENERAL\ ARRANGEMENTS\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.327''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.327	%'
.ce 0
.sp 1P
.PP
The guiding principles for the maintenance of automatic circuits as covered 
in Recommendations\ M.700 to\ M.734 are in general applicable to 
testing of System\ R1.
.sp 1P
.RT
.sp 2P
.LP
\fBRecommendation\ Q.328\fR 
.RT
.sp 2P
.ce 1000
\fB4.2\fR \ 
\fBROUTINE\ TESTING\ OF\ EQUIPMENT\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.328''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.328	%'
.ce 0
.sp 1P
.ce 1000
\fB(LOCAL\ MAINTENANCE)\fR 
.ce 0
.sp 1P
.PP
4.2.1
Test equipment for routine testing of individual items of
equipment such as circuit equipment, connecting circuits, registers, etc.,
should be provided in every international exchange. Routine tests should be
made in accordance with the practice followed in each country for the local
maintenance of switching equipment and may be made with suitable semi\(hyautomatic 
or automatic test equipment if available. 
.sp 1P
.RT
.PP
4.2.2
The testing equipment must conform to the following
principles:
.sp 9p
.RT
.LP
	\fIa)\fR 	an item of equipment must not be taken for test until it is  free;
.LP
	 \fIb)\fR an item of equipment taken for test will be marked engaged (busy) 
for the duration of the test. Before a circuit equipment 
is taken for test, the circuit will be withdrawn from service
at both international exchanges;
.LP
	 \fIc)\fR as an alternative to \fIb)\fR , a like item of equipment, known 
to be properly adjusted, may be switched in, and the item of equipment 
to be 
tested is switched out during the test.
.PP
4.2.3
Testing of the circuit and signalling equipment should include a check 
that the specifications of System\ R1 are met in regard to the 
following:
.sp 9p
.RT
.LP
	\fIa)\fR 	\fI2600\ Hz line signalling system:\fR \v'3p'
.LP
	\(em
	signal frequency;
.LP
	\(em
	transmitted signal levels;
.LP
	\(em
	signal frequency leak;
.LP
	\(em
	receiving equipment operate and non\(hyoperate limits;
.LP
	\(em
	receiving\(hyend line split;
.LP
	\(em
	sending\(hyend line split;
.LP
	\(em
	sending duration of signals.
.LP
	\fIb)\fR 	\fIPCM line signalling equipment:\fR \v'3p'
.LP
	\(em
	receiving equipment operate and non\(hyoperate limits;
.LP
	\(em
	sending duration of signals.
.bp
.LP
	\fIc)\fR 	\fIRegister signalling system:\fR \v'3p'
.LP
	\(em
	signal frequencies;
.LP
	\(em
	transmitted signal levels;
.LP
	\(em
	signal frequency leak;
.LP
	\(em
	sending duration of signals;
.LP
	\(em
	receiving equipment operate and non\(hyoperate limits;
.LP
	\(em
	operation of the receiving equipment in response to a series of pulses;
.LP
	\(em
	error checking features.
\v'1P'
.LP
.sp 2P
.LP
\fBRecommendation\ Q.329\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.3\fR \ 
\fBMANUAL\ TESTING\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.329''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.329	%'
.ce 0
.sp 1P
.sp 2P
.LP
4.3.1
	\fIFunctional testing of signalling arrangements\fR 
.sp 1P
.RT
.PP
Functional tests from one end of the circuit to the other can be made by 
verification of satisfactory signal transmission by initiating a test call 
to: 
.RT
.LP
	\fIa)\fR 	technical personnel at the distant\(hyend international
exchange; or
.LP
	\fIb)\fR 	a test call signal testing and answering device, if such
equipment is available at the distant\(hyend international exchange.
.LP
.sp 2P
.LP
4.3.2
	\fITest calls\fR 
.sp 1P
.RT
.PP
1)
Steps in the verification of satisfactory transmission of
signals, involved in the completion of test calls (manual method):
.sp 9p
.RT
.LP
	\fIa)\fR 	place a call to the technical personnel at the distant
international exchange;
.LP
	\fIb)\fR 	on completion of the connection the audible ringing tone
should be heard and the answer signal should be received
when the call is answered at the distant end;
.LP
	\fIc)\fR 	request distant end to initiate a hang\(hyup (clear\(hyback)
signal, followed by a re\(hyanswer signal;
.LP
	\fId)\fR 	a hang\(hyup (clear\(hyback) signal should be received and
recognized when the distant end hangs up and a second answer
signal should be received and recognized when the distant end
re\(hyanswers the call;
.LP
	\fIe)\fR 	initiate a ring\(hyforward (forward\(hytransfer) signal which
should be recognized at the distant end;
.LP
	\fIf\fR \fI)\fR 	terminate the call and observe that the circuit
restores to the idle condition.
.PP
2)
If incoming signalling testing devices are available at the
distant international exchange, the signal verification tests should be made
using this equipment to the extent that the applicable features indicated
in\ 1)\ above are available.
\v'1P'
.sp 9p
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.330\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.4\fR \ 
\fBAUTOMATIC\ TRANSMISSION\ AND\ SIGNALLING\ TESTING\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.330''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.330	%'
.ce 0
.sp 1P
.PP
Considering that automatic transmission and signalling testing of
international circuits is extremely desirable, Administrations using or
intending to use System\ R1 are encouraged to provide for this type of 
testing. Existing automatic testing equipment presently in use in world 
numbering 
Zone\ 1, may be used. When the automatic transmission measuring and signalling 
testing equipment (ATME)\ No.\ 2 becomes available, it may be used as an 
alternative by agreement of the Administrations concerned.
.bp
.sp 1P
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.331\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB4.5\ TEST\ EQUIPMENT\ FOR\ CHECKING\ EQUIPMENT\ AND\ SIGNALS\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.331''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.331	%'
.ce 0
.sp 1P
.sp 2P
.LP
4.5.1
	\fIGeneral\fR 
.sp 1P
.RT
.PP
For local checks of correct equipment operation and for readjusting the 
equipment, international exchanges should have test equipment available 
which includes:
.RT
.LP
	\fIa)\fR 	line and register signal generators;
.LP
	\fIb)\fR 	signal\(hymeasuring apparatus.
.sp 1P
.LP
4.5.2
	\fISignal generators\fR 
.sp 9p
.RT
.PP
The signal generators should be able to simulate all line and
register signals. The generators may be part of test equipment which cycles 
the equipment to be tested through actual signalling sequences, in a manner 
.PP
which enables rapid complete testing to determine whether the equipment 
meets system specifications. 
.RT
.sp 1P
.LP
1)
	\fILine signal generator characteristics as follows:\fR \v'3p'
.sp 9p
.RT
.LP
	\fIa)\fR 	signal frequency should be within \(+- | \ Hz of the nominal
signal frequency and shall not vary during the time required for testing;
.LP
	 \fIb)\fR signal levels should be variable between the limits given in 
the specification and be able to be set within \(+- | .2\ dB; 
.LP
	 \fIc)\fR signal durations should be long enough so that the signals can 
be recognized. See Recommendation\ Q.313, \(sc\ 2.3.3. 
.sp 1P
.LP
2)
	\fIRegister signal generator characteristics as follows:\fR \v'3p'
.sp 9p
.RT
.LP
	\fIa)\fR 	signal frequencies should be within \(+- | .5% of the nominal
signal frequency or frequencies and shall not vary during the time required 
for testing; 
.LP
	 \fIb)\fR signal levels should be variable between the limits given in 
the specification and be able to be set within \(+- | .2\ dB; 
.LP
	\fIc)\fR 	signal durations and intervals between signals shall be
within the limits given in the specification in Recommendation\ Q.322, 
\(sc\ 3.3.4, for normal operate values and in Recommendation\ Q.323, \(sc\ 
3.4.1\ \fId)\fR , for test operate values. 
.sp 1P
.LP
4.5.3
	\fISignal\(hymeasuring equipment\fR 
.sp 9p
.RT
.PP
Equipment capable of measuring signal frequencies, signal levels,
signal durations and other significant signal time intervals may be part 
of the test equipment referred to in \(sc\ 4.5.2, or separate instruments. 
.RT
.sp 1P
.LP
1)
	\fILine signal measuring equipment characteristics as follows:\fR \v'3p'
.sp 9p
.RT
.LP
	\fIa)\fR 	signal frequency between the extreme limits given in the
specification should be measured with an accuracy of\ \(+- | \ Hz;
.LP
	 \fIb)\fR level of the signal frequency measured over the range given 
in the specification should be measured with an accuracy of\ \(+- | .2\ 
dB; 
.LP
	\fIc)\fR 	signal durations, and other significant time intervals as
given in the specification should be measured with an accuracy of\ \(+- | \ ms
or\ \(+- | % of the nominal duration, whichever yields the higher value.
.LP
.sp 1P
.LP
2)
	\fIRegister signal measuring equipment characteristics as\fR 
\fIfollows:\fR \v'3p'
.sp 9p
.RT
.LP
	 \fIa)\fR signal frequency or frequencies between the extreme limits given 
in the specification, should be measured with an accuracy 
of\ \(+- | \ Hz;
.LP
	 \fIb)\fR level of the signal frequency or frequencies over the range 
given in the specification should be measured with an accuracy of\ \(+- | .2\ 
dB; 
.LP
	\fIc)\fR 	signal duration and intervals between signals as given in
the specification should be measured with an accuracy of\ \(+- | \ ms.
.PP
3)
In regard to measuring time intervals a recorder having a minimum of two 
input channels may be useful. The recorder characteristic should 
conform with the accuracy requirements quoted in\ 1) and\ 2) above and 
be easily connected to the circuit under test. The recorder input characteristic 
should be such as to have a negligible effect on circuit 
performance.
.bp
.sp 9p
.RT
.LP
.ce 1000
\s10\fBANNEX\ A\ TO\ THE\ SPECIFICATIONS\fR 
.RT
.ce 0
.ce 1000
\fBOF\ SIGNALLING\ SYSTEM\ R1\fR 
.ce 0
.sp 1P
.ce 1000
\fBSIGNAL\ SEQUENCES\fR \v'1P'
.EF '%	Fascicle\ VI.4\ \(em\ System\ R1''
.OF '''Fascicle\ VI.4\ \(em\ System\ R1	%'
.ce 0
.sp 1P
.LP
.rs
.sp 45P
.ad r
\fBTableau [A\(hy1], p.5\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBTableau [1\(hyA\(hy1], p.6\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE:\ \fR PAGE 26 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'12P'
\s12PART\ II
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBRecommendation\ Q.332\fR \v'2P'
.EF '%	 \ \ \ ^''
.OF ''' \ \ \ ^	%'
.ce 0
.sp 1P
.ce 1000
\fBINTERWORKING\ OF\ SIGNALLING\ SYSTEM\ R1\fR 
.ce 0
.sp 1P
.ce 1000
\fBWITH\ OTHER\ STANDARDIZED\ SYSTEMS\fR 
.ce 0
.sp 1P
.LP
.rs
.sp 29P
.LP
.bp
.LP
\fBMONTAGE:\fR PAGE 28 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 2P
.LP
\fBRecommendation\ Q.332\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB5.\ \fR \fBINTERWORKING\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.332''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.332	%'
.ce 0
.sp 1P
.sp 2P
.LP
5.1
	\fIGeneral\fR 
.sp 1P
.RT
.PP
System R1 is capable of interworking with any of the CCITT
standardized signalling systems.
.PP
Specifications on interworking of System\ R1 with other CCITT signalling 
systems are not yet available. 
.PP
Typical information is found in Recommendation\ Q.180 of
Fascicle\ VI.2.
.RT
.LP
.rs
.sp 38P
.LP
.bp
.LP
\fBMONTAGE:\fR PAGE 30 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'12P'
\s12PART\ III
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBRecommendations\ Q.400\ to\ Q.490\fR \v'2P'
.EF '%	 \ \ \ ^''
.OF ''' \ \ \ ^	%'
.ce 0
.sp 1P
.ce 1000
\fBSPECIFICATIONS\ OF\ SIGNALLING\ SYSTEM\ R2\fR 
.ce 0
.sp 1P
.LP
.rs
.sp 30P
.LP
.bp
.LP
\fBMONTAGE:\fR PAGE 32 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'6P'
\s10\fBSIGNALLING\ SYSTEM\ R\ 2 
.RT
.ce 0
.sp 1P
.ce 1000
\fBINTRODUCTION\fR 
.EF '%	Fascicle\ VI.4\ \(em\ System\ R2''
.OF '''Fascicle\ VI.4\ \(em\ System\ R2	%'
.ce 0
.sp 1P
.LP
\fIGeneral\fR 
.sp 1P
.RT
.PP
Signalling System R2 is used as an international signalling system within 
international regions (world numbering zones). Moreover, System\ R2 can 
be used for integrated international/national signalling if it is employed, 
in conformity with the present specifications, as a signalling system in 
the 
national networks of the region concerned. Suitable for both automatic and
semi\(hyautomatic working it offers a high reliability in transmission of the
information necessary for setting up a call. It allows for rapid call set\(hyup
and provides sufficient signals in both directions to permit the transmission 
of numerical and other information relating to the called and calling 
subscribers' lines and to increase routing facilities.
.PP
System R2 is specified for one\(hyway operation on analogue and digital 
transmission systems and for both\(hyway operation on digital transmission 
systems. Distinction is made between line signalling (supervisory signals) 
and interregister signalling (call set\(hyup control signals). Versions 
of line 
signalling are specified for use on 4\(hywire carrier or PCM circuits.
Nevertheless, the interregister signalling specified can also be used on 
2\(hywire circuits. System\ R2 is suitable for use on satellite links and 
3\ kHz spaced 
carrier circuits. It is not designed for use on transmission systems with
speech interpolation but it may be used on digital transmission systems with
speech interpolation as long as transparency for pulsed interregister signals 
is guaranteed. 
.PP
The interregister signalling is a compelled multifrequency code
system. This offers the possibility of end\(hyto\(hyend signalling and to take
advantage of modern switching systems by providing a sufficient number of
signals in both directions.
.PP
System R2 is capable of normal interworking with other CCITT
signalling systems.
.RT
.LP
.sp 1P
.LP
\fILine signalling\fR 
.sp 9p
.RT
.PP
The following versions of line signalling are
specified:
.RT
.LP
	\(em
	line signalling for carrier systems called the analogue
version;
.LP
	\(em
	line signalling for PCM systems called the digital
version.
.PP
Since multifrequency signalling permits exchange of a large amount of information 
between registers, the quantity of information that has to be 
transmitted in the form of line signals is small. The versions of line
signalling for System\ R2 have been designed accordingly. The analogue line
signalling version standardized originally for use on international circuits 
is also suitable for national working. An analogue (in\(hyband) line signalling 
version is only described for the specific use on 3\ kHz spaced carrier 
circuits of international submarine cables. 
.PP
The \fIanalogue version\fR  | s link\(hyby\(hylink using an out\(hyband, 
low\(hylevel continuous tone\(hyon\(hyidle signalling method. Signal transfer 
simply involves the transition from one signalling condition to the other, 
except for the clearing sequence which is based on additional timing criteria. 
It is necessary to have a device for protection against the effect of interruption 
in the signalling 
channel since interruption of the signalling frequency simulates a false
seizure or answer signal (interruption control). The signalling frequency is
transmitted at a low level which avoids overloading of the transmission 
system when the frequency is sent continuously in both directions on all 
circuits in the idle state. 
.bp
.PP
The \fIdigital version\fR  | s link\(hyby\(hylink using two signalling 
channels in each direction of transmission per speech circuit. The signalling 
channels are two of the four provided for channel associated signalling 
in a 2048\ kbit/s primary multiplex (see Recommendation\ G.732). Protection 
against the effects of faulty transmission is provided. 
.PP
The analogue version and the digital version of the line signalling
can be converted to each other by a transmultiplexer or other conversion
equipment. Such equipment forms a conversion point between analogue (FDM)
transmission on one hand and digital (PCM) transmission on the other hand. 
The System\ R2 line signalling, however, must be treated separately because 
for both transmission systems different line signalling versions are specified. 
Although both versions are described in some detail, a description of the 
actual 
conversion is given in Recommendation\ Q.430. Although these versions do not
include a forward\(hytransfer signal, forward\(hytransfer signalling may be
introduced for international working by bilateral agreement.
.RT
.sp 1P
.LP
\fIInterregister signalling\fR 
.sp 9p
.RT
.PP
The interregister signalling is performed end\(hyto\(hyend using a
2\(hyout\(hyof\(hy6 in\(hyband multifrequency code with forward and backward 
compelled 
signalling. The signalling frequencies do not therefore overlap with the 
line signalling frequency and differ according to the direction of transmission 
with a view to possible use of the multifrequency part of the system on 
2\(hywire 
circuits.
.PP
System R2 is designed to use six signalling frequencies (1380, 1500, 1620, 
1740, 1860 and 1980\ Hz) in the forward direction and six signalling 
frequencies (1140, 1020, 900, 780, 660 and 540\ Hz) in the backward direction. 
Nevertheless for national application less signalling frequencies may be 
used. 
.PP
End\(hyto\(hyend signalling
is a method for signalling between
registers over two or more links in tandem without signal regeneration in
intermediate exchanges (see Figure\ 1).
.RT
.LP
.rs
.sp 15P
.ad r
\fBFigure 1, p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
With this signalling method, in general only the address
information needed for routing the call through an intermediate (transit)
exchange is transferred from the outgoing register to the incoming register. 
In the 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. Such
end\(hyto\(hyend signalling is advantageous as it reduces the interregister
signalling equipment needed and minimizes the holding time of registers in
transit exchanges.
.PP
System R2 has been designed to allow end\(hyto\(hyend interregister
multifrequency signalling over several links in tandem. However, in
circumstances where transmission conditions do not comply with the requirements 
specified for System\ R2 and might consequently jeopardize the exchange 
of the interregister signals, or in case of using System\ R2 via a satellite 
link, the overall multi\(hylink connection is divided into sections, each 
with its 
individidual interregister signalling (signals being then relayed and
regenerated by a register at the point where the division is made).
.bp
.PP
In the case of satellite working, the register at the incoming end
of the satellite link must act as an outgoing\ R2 register (see also
Recommendation\ Q.7).
.PP
Generally transmission conditions in a national network comply with
the requirements specified for System\ R2 and as such allow end\(hyto\(hyend
signalling over complete connections between local exchanges.
.PP
In the case of international System R2 working transmission conditions 
impose division into at least two signalling sections, when both the outgoing 
and incoming countries use System\ R2 in the national network. The division 
must be made in an exchange in the outgoing country. The relaying or regenerating 
register situated at the point where the division is made is called \fIthe\fR 
\fIoutgoing international R2 register\fR . In the case when System\ R2 
is not used in the outgoing country the outgoing international\ R2 register 
receives 
address information via a national signalling system and it controls the 
call set\(hyup over the outgoing System\ R2 signalling section. 
.PP
\fIThe\fR 
\fIoutgoing R2 register\fR  | s generally defined as a
register 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. 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. 
.PP
When an \fIR2 register in a transit exchange\fR  | s working according 
to the definition above it is also called an \fIoutgoing\ R2 register\fR 
. \fIThe\fR 
\fIoutgoing international R2 register\fR is the special case of the outgoing R2
register when the outgoing signalling section comprises at least one
international link.
.PP
\fIThe\fR 
\fIincoming R2 register\fR  | s defined as a register
situated at the incoming end of a link on which System\ R2 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 incoming\ R2
register independently of the exchange type.
.PP
The following operational features are provided by using all the
15\ forward and 15\ backward combinations of the multifrequency
code:
.RT
.LP
	\(em
	capability of transferring address information for automatic,
semi\(hyautomatic and maintenance calls;
.LP
	\(em
	indicators in order to identify transit and maintenance
(test) calls;
.LP
	\(em
	language digits or discriminating digit(s) for international  calls;
.LP
	\(em
	 transfer of the next digit or repetition of the last but one, the last 
but two, or the last but three digit on request by the 
register at the incoming end;
.LP
	\(em
	forward and backward signals for control of echo
suppressors;
.LP
	\(em
	 information concerning the nature and the origin of the call (calling 
party's category) can be transferred to the register 
at the incoming end, i.e. whether national or international,
whether from an operator or from a subscriber, whether from
data\(hytransmission, maintenance or other equipment,\ etc.;
.LP
	\(em
	information concerning the nature of the circuit can be
requested by the register at the incoming end, i.e. whether
a satellite link is already included or not;
.LP
	\(em
	information on congestion, unallocated number and on the
condition of the called subscriber's line can be transferred
to the outgoing register, i.e. whether free, busy or out of
service,\ etc.;
.LP
	\(em
	a restricted number of signals left to the discretion of
Administrations for allocation of national meanings.
.bp
.PP
The interregister signalling specified for System R2 can also be used together 
with any non\(hystandardized line\(hysignalling system. The resulting combination 
is not considered to be System\ R2. 
.PP
System R2 gives potential for a short post\(hydialling delay using
\fIoverlap operation\fR with dialling and end\(hyto\(hyend signalling. The
outgoing\ R2 register starts 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 practice 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\fR register signalling i.e.\ the
transmission of all the address information as a whole in one sequence 
starting only after complete reception of the address information. 
.PP
Unused signalling capacity provides potential for development and
allows for future requirements yet undefined. This spare capacity may be 
used for increasing the number of signals and signalling procedures e.g.\ 
for new 
services to be offered to subscribers.
.RT
.LP
.rs
.sp 38P
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 1
.ce 0
.sp 1P
.ce 1000
\fBDEFINITIONS\ AND\ FUNCTIONS\ OF\ SIGNALS\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.400\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB1.1\ \ \fR \fBFORWARD\ LINE\ SIGNALS\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.400''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.400	%'
.ce 0
.sp 1P
.sp 2P
.LP
1.1.1
	\fBseizing signal\fR 
.sp 1P
.RT
.PP
A signal sent at the beginning of the call to initiate transition of the 
circuit at the incoming end from the idle state to seized state. At 
the incoming exchange it causes the association of equipment capable of
receiving register signals.
.RT
.LP
.sp 1P
.LP
1.1.2
	\fBclear\(hyforward signal\fR 
.sp 9p
.RT
.PP
A signal sent to terminate the call or call attempt and to release in the 
incoming exchange and beyond it all switching units held on the call. 
.PP
The signal is sent when:
.RT
.LP
	\fIa)\fR 	in semi\(hyautomatic working the operator of the outgoing
international exchange takes the plug out or performs an
equivalent operation;
.LP
	\fIb)\fR 	in automatic working, the calling subscriber clears or
performs an equivalent operation.
.PP
This signal is also sent by the outgoing international exchange
upon receiving a backward register signal requesting the outgoing international 
R2 register to clear the connection, or in the case of forced release of 
the 
connection as mentioned in Recommendation\ Q.118. This signal may also 
be sent as the result of abnormal release of the outgoing international\ 
R2 
register.
.sp 1P
.LP
1.1.3
	\fBforward\(hytransfer signal\fR 
.FS
This signal is not provided in
either the analogue or digital version of System R2 line signalling.
Information about possible arrangements for such a signal and signalling
procedures involved are contained in Annex\ A to the present
Specifications.
.FE
.sp 9p
.RT
.PP
A signal sent on semi\(hyautomatic calls when the outgoing
international exchange operator wants the help of an operator at the incoming 
international exchange. The signal will usually bring an assistance operator 
(see Recommendation\ Q.101) into the circuit. If the call is completed via an
incoming or delay operator at the incoming international exchange, the 
signal indicates that recall of this operator is wanted. 
.RT
.sp 1P
.ce 1000
\fB1.2\fR \ \ 
\fBBACKWARD\ LINE\ SIGNALS\fR 
.ce 0
.sp 1P
.sp 2P
.LP
1.2.1
	\fBseizing\(hyacknowledgement signal\fR 
.FS
This signal is only used in  the digital version of System\ R2 line signalling.
.FE
.sp 1P
.RT
.PP
A signal sent to the outgoing exchange to indicate the transition of the 
equipment at the incoming end from the idle state to seized state. 
Recognition of the seizing acknowledgement signal at the outgoing end causes
the state of the circuit to change from seized to seizure acknowledged.
.bp
.RT
.sp 1P
.LP
1.2.2
	\fBanswer signal\fR 
.sp 9p
.RT
.PP
A signal sent to the outgoing international exchange to indicate
that the called party has answered the call (see Recommendation\ Q.27). In
semi\(hyautomatic working this signal has a supervisory function.
.PP
In automatic working this signal is used:
.RT
.LP
	\(em
	 to start metering the charge to the calling subscriber, unless the register 
signal indicating no charge has been sent 
previously;
.LP
	\(em
	to start measurement of the call duration for international
accounting purposes.
.LP
.sp 1P
.LP
1.2.3
	\fBclear\(hyback signal\fR 
.sp 9p
.RT
.PP
A signal sent to the outgoing international exchange to indicate
that the called party has cleared. In semi\(hyautomatic working, this signal 
has a supervisory function. In automatic working, arrangements must be 
made in 
accordance with Recommendation\ Q.118, and the Notes of Recommendation\ Q.120,
\(sc\ 1.8 also apply.
.RT
.sp 1P
.LP
1.2.4
	\fBrelease\(hyguard signal\fR 
.sp 9p
.RT
.PP
A signal sent to the outgoing exchange in response to a
clear\(hyforward signal to indicate that the latter has been fully effective in
returning the switching units at the incoming end of the circuit to idle
condition. An international circuit is protected against subsequent seizure 
as long as the release operations initiated by the clear\(hyforward signal 
have not been completed at the incoming end. 
.RT
.sp 1P
.LP
1.2.5
	\fBblocking signal\fR 
.sp 9p
.RT
.PP
A signal sent on an idle circuit to the outgoing exchange to cause engaged 
conditions (blocking) to be applied to this circuit, guarding it 
against subsequent seizure.
.RT
.LP
.sp 1P
.ce 1000
\fB1.3\fR \ 
\fBFORWARD\ REGISTER\ SIGNALS\fR 
.ce 0
.sp 1P
.sp 2P
.LP
1.3.1
	\fBaddress signal\fR 
.sp 1P
.RT
.PP
A signal containing one element of information (digit\ 1, 2, . |  | , 9 
or 0, code\ 11, code\ 12 or code\ 13) about the called or calling party's 
number or the end of pulsing indication (code\ 15). 
.PP
For each call a series of address signals is sent (see
Recommendations\ Q.101 and Q.107).
.RT
.sp 1P
.LP
1.3.2
	\fBcountry\(hycode and echo\(hysuppressor indicators\fR 
.sp 9p
.RT
.PP
Signals indicating:
.RT
.LP
	\(em
	whether or not the country\(hycode is included in the address
information (international transit or terminal call);
.LP
	\(em
	whether or not an outgoing half\(hyecho suppressor should be
inserted in the first international exchange reached;
.LP
	\(em
	whether or not an incoming half\(hyecho suppressor should be
inserted (an outgoing half\(hyecho suppressor having already been
inserted in the connection).
.sp 1P
.LP
1.3.3
	\fBlanguage or discriminating digit\fR 
.sp 9p
.RT
.PP
A numerical signal occupying a predetermined position in the
sequence of address signals indicating:
.RT
.LP
	\(em
	 in semi\(hyautomatic working, the service language to be used in the 
incoming international exchange by the incoming, delay and 
assistance operators when they come in the circuit
(language digit);
.LP
	\(em
	the automatic working or any other special characteristic of
the call (discriminating digit).
.LP
.sp 1P
.LP
1.3.4
	\fBtest call indicator\fR 
.sp 9p
.RT
.PP
A signal occupying the position of the language digit when the call is 
originating from test equipment. 
.RT
.sp 1P
.LP
1.3.5
	\fBnature of circuit indicators\fR 
.sp 9p
.RT
.PP
Signals only sent on request by certain backward signals and using a second 
meaning of some signals, to indicate whether a satellite link is 
already included in the connection or not.
.bp
.RT
.sp 1P
.LP
1.3.6
	\fBend\(hyof\(hypulsing signal\fR 
.sp 9p
.RT
.PP
An address signal sent indicating (in semi\(hyautomatic service) that no 
other address signal will follow or (in\ automatic service) that the 
transmission of the code identifying the origin of the call is completed.
.RT
.sp 1P
.LP
1.3.7
	\fBcalling party's category signals\fR 
.sp 9p
.RT
.PP
A special group of signals providing, in addition to the information contained 
in the language or discrimination digit, supplementary information 
concerning the nature of the call (i.e. whether national or international) 
and its origin. 
.PP
Typical categories are:
.RT
.LP
	\(em
	operator capable of sending the forward\(hytransfer signal;
.LP
	\(em
	ordinary subscriber or operator with no forward\(hytransfer
facility;
.LP
	\(em
	subscriber with priority;
.LP
	\(em
	data transmission call;
.LP
	\(em
	maintenance call.
.sp 1P
.LP
1.3.8
	\fISignals for use on the national network\fR 
.sp 9p
.RT
.PP
Some of the Group\ II forward signals (see Recommendation\ Q.441,
\(sc\ 4.2.3.2) have been allocated for national use. When the outgoing
international\ R2 register receives them, it must react as specified in
Recommendation\ Q.480.
.RT
.sp 1P
.ce 1000
\fB1.4\fR \ 
\fBBACKWARD\ REGISTER\ SIGNALS\fR 
.ce 0
.sp 1P
.sp 2P
.LP
1.4.1
	\fISignals requesting transmission of address signals\fR 
.sp 1P
.RT
.PP
Five backward signals without particular names are provided; four of them 
are interpreted with reference to the latest address signal 
sent:
.RT
.LP
	\(em
	signal requesting the transmission of the address signal
following the latest address signal sent;
.LP
	\(em
	signal requesting repetition of the address signal preceding
the latest address signal sent (last but one);
.LP
	\(em
	signal requesting the repetition of the last but two address
signals sent;
.LP
	\(em
	signal requesting the repetition of the last but three address  signals sent;
.LP
	\(em
	signal requesting the transmission or repetition of the
language or discrimination digit.
.LP
.sp 1P
.LP
1.4.2
	\fISignal requesting information about the circuit\fR 
.sp 9p
.RT
.PP
A backward signal is provided to request the nature of the
circuit.
.RT
.sp 1P
.LP
1.4.3
	\fISignals requesting information about the call or\fR 
\fIcalling party\fR 
.sp 9p
.RT
.PP
Three backward signals without particular names are provided for this purpose:
.RT
.LP
	\(em
	signal inquiring the calling party's category;
.LP
	\(em
	signal requesting the repetition of the country\(hycode
indicator;
.LP
	\(em
	 signal inquiring whether or not incoming half\(hyecho suppressor should 
be inserted. 
.LP
.sp 1P
.LP
1.4.4
	\fICongestion signals\fR 
.sp 9p
.RT
.PP
Two congestion signals are provided:
.RT
.LP
	\(em
	a signal indicating international congestion, i.e. that the
call set\(hyup attempt has failed owing to congestion of the group of
international circuits, or congestion in the international
switching equipment, or to time\(hyout or abnormal release of an
incoming\ R2 register in an international transit exchange;
.LP
	\(em
	a signal indicating national congestion, i.e. that the call
set\(hyup attempt has failed owing to congestion in the national
network (excluding a busy called subscriber's line) or to
time\(hyout or abnormal release of an incoming\ R2 register in
a terminal international exchange or a national exchange.
.bp
.LP
.sp 1P
.LP
1.4.5
	\fBaddress\(hycomplete signals\fR 
.sp 9p
.RT
.PP
Signals indicating that it is no longer necessary to send another
address signal, and
.RT
.LP
	\(em
	either cause immediate passage to the speech position to
enable the calling subscriber to hear a tone or a recorded
announcement of the national incoming network;
.LP
	\(em
	or announce the transmission of a signal indicating the
condition of the called subscriber's line.
.sp 1P
.LP
1.4.6
	\fISignals indicating the condition of the called\fR \fIsubscriber's line\fR 
.sp 9p
.RT
.PP
Six signals sent in the backward direction are provided to give
information about the called subscriber's line and to indicate the end of
interregister signalling. These signals are:
.RT
.LP
	\(em
	\fBsend special information tone\fR 
.LP
	 a signal sent in the backward direction indicating 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);
.LP
	\(em
	\fBsubscriber line busy\fR 
.LP
	a signal indicating that the line or lines connecting the
called subscriber to the exchange are busy;
.LP
	\(em
	\fBunallocated number\fR 
.LP
	a signal indicating that the number received is not in use
(e.g.\ an unused country code or an unused trunk code or
subscriber number that has not been allocated);
.LP
	\(em
	\fBsubscriber line free, charge\fR 
.LP
	a signal indicating that the called subscriber's line is free
and that the call is to be charged on answer;
.LP
	\(em
	\fBsubscriber line free, no charge\fR 
.LP
	a signal indicating that the called subscriber's line is free
and that the call is not to be charged on answer. This signal
is used only for calls to special destinations;
.LP
	\(em
	\fBsubscriber line out of order\fR 
.LP
	a signal indicating that the subscriber's line is out\(hyof\(hyservice
or faulty.
.sp 1P
.LP
1.4.7
	\fISignals for use in the national network\fR 
.sp 9p
.RT
.PP
Some of the backward signals have been allocated for national use.
Since not all incoming registers can know the origin of the connection and
since end\(hyto\(hyend signalling is used, it may happen that the above\(hymentioned 
signals are sent to the outgoing international\ R2 register. When this 
register receives them it must react as indicated in Recommendations\ Q.474 
and\ Q.480.
.RT
.LP
.rs
.sp 18P
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 2
.ce 0
.sp 1P
.ce 1000
\fBLINE\ SIGNALLING,\ ANALOGUE\ VERSION\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.411\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB2.1\ \ LINE\ SIGNALLING\ CODE\fR 
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.411''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.411	%'
.ce 0
.sp 1P
.sp 2P
.LP
2.1.1
	\fIGeneral\fR 
.sp 1P
.RT
.PP
The System R2 line signalling, analogue version, is intended for
use on carrier circuits. The line signals are transmitted link\(hyby\(hylink. 
The 
code for the transmission of line signals is based on the 
\fItone\(hyon\(hyidle\fR signalling method
. It is required that the circuits on which the system is
.PP
employed are equipped in each direction of transmission with a signalling
channel outside the speech frequency band. When the circuit is in the idle
state, a low\(hylevel signalling tone is sent continuously in both directions 
over the signalling channels. The tone is removed in the forward direction 
at the 
moment of seizure and in the backward direction when the called subscriber
answers.
.PP
The connection is released when the signalling tone is restored in the 
forward direction; release causes the tone to be restored in the backward 
direction. If the called party is the first to clear, the signalling tone is
restored in the backward direction first. It is then restored in the forward
direction either when the caller clears or when a certain interval has 
elapsed after recognition of the signalling tone in the backward direction. 
This 
signalling method, requiring only simple equipment, provides rapid signal
recognition and retransmission. The signal transfer speed provided by
continuous type signalling compensates for the need of signal repetition
inherent in link\(hyby\(hylink transmission.
.PP
The signalling system is specified for one\(hyway operation of 4\(hywire
carrier circuits.
.RT
.sp 1P
.LP
2.1.2
	\fILine conditions\fR 
.sp 9p
.RT
.PP
Tone\(hyon or tone\(hyoff denotes a certain line signalling condition.
The line thus has two possible conditions in each direction, i.e.\ a total of
four line signalling conditions. Taking into account the time sequence, the
circuit may resume one of the six characteristic states shown in
Table\ 1/Q.411.
.RT
.LP
.rs
.sp 14P
.ad r
\fBTABLE [1/Q.411] p.\fR 
.ad b
.RT
.LP
.bp
.PP
The transition from one signalling condition to another
corresponds to the transfer of a line signal according to the definitions in
\(sc\ 1. To change from the release state to the idle state additional
criteria (timing) are necessary to ensure a defined sequence corresponding 
to the transfer of the release\(hyguard signal (see \(sc\ 2.2.2.6\ below). 
.LP
.sp 2P
.LP
\fBRecommendation\ Q.412\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB2.2\ \ CLAUSES\ FOR\ EXCHANGE\ LINE\ SIGNALLING\ EQUIPMENT\fR 
.FS
Although the signalling condition (tone\(hyon or tone\(hyoff)
physically only appears in transmission equipment, it is used in this
section as a reference criterion to specify functions of exchange
equipment.
.FE
.EF '%	Fascicle\ VI.4\ \(em\ Rec.\ Q.412''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.412	%'
.ce 0
.sp 1P
.sp 2P
.LP
2.2.1
	\fIRecognition time for transition of signalling condition\fR 
.sp 1P
.RT
.PP
The recognition time \fIt\fR\d\fIr\fR\ufor a changed condition (transition 
from tone\(hyon to tone\(hyoff or vice versa) is 40\ \(+-\ 10\ ms | 
.FS
Originally this value
was (20\ \(+-\ 7)\ ms. Since there will be no problem in the interworking 
between 
equipment having the original recognition time \fIt\fR\d\fIr\fR\u\ =\ (20\ 
\(+-\ 7)\ ms, and 
equipment having the new recognition time \fIt\fR\d\fIr\fR\u\ =\ (40\ \(+-\ 
10)\ ms, existing 
equipment need not necessarily be changed to the value 
.PP
\fIt\fR\d\fIr\fR\u\ =\ (40\ \(+-\ 10)\ ms.
.FE
. The recognition time is defined as the minimum
duration that the presence or absence of a direct current signal must have 
at the output of the signal receiver in order to be recognized as a valid 
signalling condition by the exchange equipment. Thus the specified value 
does not include the response time \fIt\fR\d\fIr\fR\\d\fIs\fR\uof signalling 
receivers (see 
Recommendation\ Q.415). However, it is determined on the assumption that 
there is interruption control (see Recommendation\ Q.416). 
.RT
.sp 2P
.LP
2.2.2
	\fIStates and procedures under normal conditions\fR 
.sp 1P
.RT
.sp 1P
.LP
2.2.2.1
	\fISeizure\fR 
.sp 9p
.RT
.PP
The outgoing end removes the tone in the forward direction. If
seizure is immediately followed by release, removal of the tone must be
maintained for at least 100\ ms to make sure that it is recognized at the
incoming end.
.RT
.LP
.sp 1P
.LP
2.2.2.2
	\fIAnswering\fR 
.sp 9p
.RT
.PP
The incoming end removes the tone in the backward direction. When another 
link of the connection using tone\(hyon\(hyidle continuous signalling 
precedes the outgoing exchange, the tone\(hyoff condition must be established 
on this link immediately after it is recognized in this exchange. When 
another 
signalling system is used on the preceding link, the rules for interworking 
are applicable. 
.RT
.sp 1P
.LP
2.2.2.3
	\fIClear\(hyback\fR 
.sp 9p
.RT
.PP
The incoming end restores the tone in the backward direction. When another 
link of the connection using tone\(hyon\(hyidle continuous signalling 
precedes the outgoing exchange the \fItone\(hyon\fR condition must be established 
on this link immediately after it is recognized in this exchange. When 
another 
signalling system is used on the preceding link, the rules for interworking 
are applicable. The provisions set forth in \(sc\ 2.2.2.6 below must also 
be taken into consideration. 
.RT
.LP
.sp 1P
.LP
2.2.2.4
	\fIClear\(hyforward procedure\fR 
.sp 9p
.RT
.PP
The outgoing end restores the tone in the forward direction
(see \(sc\ 2.2.2.1 above). The forward connection is released and the release\(hyguard 
sequence begins as soon as the changed signalling condition is recognized 
at 
the incoming end. In the outgoing exchange the circuit remains blocked until
the release\(hyguard sequence is terminated (see \(sc\ 2.2.2.6 below).
.bp
.RT
.sp 1P
.LP
2.2.2.5
	\fIBlocking and Unblocking procedure\fR 
.sp 9p
.RT
.PP
At the outgoing exchange the circuit stays blocked so long as the tone 
remains off in the backward direction. 
.PP
Restoration of the tone in the backward direction \(em\ accompanied by
the presence of the tone in the forward direction\ \(em restores the circuit to
the idle state. The circuit may then be seized for a new call.
.RT
.sp 1P
.LP
2.2.2.6
	\fIRelease and release\(hyguard sequence\fR 
.sp 9p
.RT
.LP
.PP
Release\(hyguard must be ensured whatever the state of the circuit
at the moment the clear\(hyforward signal is sent\ \(em seized prior to answer,
answered or cleared by the called party. It may also happen that answering
or clearing by the called party occurs when release has already begun at the
outgoing exchange. The cases are described below and shown in the
Figures\ 2/Q.412 to\ 4/Q.412. The exact timing is shown in
Figure\ 5/Q.412.
\v'3p'
.RT
.LP
	a)
	\fIRelease prior to answered state\fR 
.PP
The clear\(hyforward signal is sent from the outgoing end by
restoring the tone in the forward direction (see\ Figure\ 2/Q.412). Recognition 
of this tone has the following consequences at the incoming end: 
.RT
.LP
	i)
	the tone in the backward direction is removed;
.LP
	ii)
	the release of the switching units is initiated;
.LP
	iii)
	the release\(hyguard sequence starts.
.PP
When release operations at the incoming end are complete, but not before 
an interval\ \fIT\fR\d2\uhas elapsed after the removal, the 
tone is again restored at the incoming end in the backward direction.
.LP
.rs
.sp 21P
.ad r
\fBFIGURE 2/Q.412 p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
When \fIT\fR\d1\uhas elapsed the outgoing end must recognize that the tone\(hyoff 
condition in the backward direction is established. After this 
recognition the restoring of the tone in the backward direction returns the
circuit to the idle state and completes the release\(hyguard sequence.
.bp
.PP
At the incoming end the sending of an answer signal can only be
prevented after the clear\(hyforward signal has been recognized. To avoid any
false operation should answer coincide with release, transition from \fItone\(hyon\fR 
to \fItone\(hyoff\fR in the backward direction must not be interpreted, 
at the 
outgoing end, as part of the release\(hyguard sequence during an
interval\ \fIT\fR\d1\u. The interval\ \fIT\fR\d1\ustarts with the sending 
of the 
tone in the forward direction. It is long enough to make quite sure that the
clear\(hyforward signal is recognized and the \fItone\(hyoff\fR condition 
established at the incoming end. 
.PP
For the calculation of the intervals\ \fIT\fR\d1\uand\ \fIT\fR\d2\usee
\(sc\ 2.2.2.7\ below.
\v'3p'
.RT
.LP
	b)
	\fIRelease in answered state\fR 
.PP
In this case, the release operations differ only from a)\ above in so far 
as\ i) does not apply. At the incoming end, however, sending of a 
clear\(hyback signal can only be prevented after the clear\(hyforward signal 
has been recognized. Should there be a clear\(hyback signal the specified 
interval\ \fIT\fR\d1\uenables any resultant difficulties to be obviated 
(see 
Figure\ 3/Q.412).
.RT
.LP
.rs
.sp 21P
.ad r
\fBFigure 3/Q.412 p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
	c)
	\fIRelease in clear\(hyback state\fR 
.PP
The release operations are identical to those described in
a)\ above. Should there be a second answer signal, the specified
interval\ \fIT\fR\d1\uenables any resultant difficulties to be obviated (see
Figure\ 4/Q.412).
.RT
.LP
.sp 1P
.LP
2.2.2.7
	 \fICalculation of the intervals\fR T\d1\u\fIand\fR T\d2\u\fIspecified 
for\fR \fIrelease and release\(hyguard operations\fR 
.sp 9p
.RT
.PP
Figure\ 5/Q.412 shows the factors involved in calculating the
intervals\ \fIT\fR\d1\uand\ \fIT\fR\d2\u.
.PP
At the outgoing end when the interval \fIT\fR\d1\uhas elapsed
(Figure\ 5/Q.412, point\ D) the tone\(hyoff condition in the backward direction 
can be expected and recognized with certainty in all cases mentioned in 
\(sc\ 2.2.2.6 above. 
.PP
Similarly, the interval \fIT\fR\d2\upreceding the restoring of the tone 
in the backward direction may be applied in all cases. To avoid false operation 
in the event of coinciding forward and backward signals or an irregular 
sequence of signals, the time interval\ \fIT\fR\d2\umust also be observed 
with the release 
operation [see \(sc\ 2.2.2.6\ b)\ above].
.bp
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 4/Q.412, p.11\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 29P
.ad r
\fBFigure\ 5/Q.412, p.12\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The minimum value of \fIT\fR\d1\uis the sum of the maximum values of the 
times required for the various operations which take place between 
application of the tone in the forward direction and recognition of the 
absence of tone in the backward direction. 
.PP
\fIT\fR\d2\udelays release of the circuit. It must therefore be as short 
as possible. However, it must be long enough to ensure recognition of the 
tone\(hyoff condition in the backward direction at the outgoing end when 
\fIT\fR\d1\uis at its maximum, even when this condition begins as early 
as 
possible.
\v'3p'
.RT
.LP
	\fIa)\fR 	\fIExclusive terrestrial circuits\fR 
.PP
The calculation is based on a maximum one\(hyway transmission delay of 
30\ ms for a circuit. Thus, for circuits on high\(hyvelocity transmission 
systems via terrestrial lines (including submarine cables) the maximum 
operating range of the specified line signalling system is 4800\ km 
.FS
See Recommendation
G.114, Fascicle III.1.
.FE
.
.PP
Values used for the calculation of \fIT\fR\d1\uand \fIT\fR\d2\u:
\v'6p'
.RT
.LP
	0\ <\ \fIt\fR\d\fIp\fR\u\ <\ 30\ ms
.LP
0\ <\ \fIt\fR\d\fIo\fR\u\ <\ 30\ ms (see \(sc\ 2.3.2.4)
.LP
30\ ms\ <\ \fIt\fR\d\fIr\fR\u\ <\ 50\ ms
.LP
0\ <\ \fIt\fR\d\fIi\fR\u\ <\ 20\ ms
.LP
.sp 1
.PP
Calculation of intervals \fIT\fR\d1\uand \fIT\fR\d2\u:
\v'6p'
.LP
	\fIT\fR \d1\u > 
AC
	\fIT\fR \d1\u > 2
(\fIt
\dp\u\fR +
\fIt
\do\u\fR )
max. + \fIt
\dr\u\fR max. + \fIt
\di\u\fR max.
.LP
\fIT\fR \d1\u > (2 \(mu 60 + 50 + 20) ms
.LP
\fIT\fR \d1\u > 190 ms
.LP
.sp 1
.PP
Allowing a safety margin of 10\ ms and a tolerance of \(+- | 0%, the
specified value of \fIT\fR\d1\uis (250\ \(+-\ 50)\ ms.
\v'6p'
.LP
	\fIT\fR \d2\u > 
BF
	\fIT\fR \d2\u > \fIT\fR \d1\u
max. +
\fIt
\dr\u\fR max. + \fIt
\di\u\fR max. \(em 2
(\fIt
\dp\u\fR + \fIt
\do\u\fR )
min. \(em  \fIt
\dr\u\fR min. \(em \fIt
\di\u\fR min.
.LP
\fIT\fR \d2\u > (300 + 50 + 20 \(em 0 \(em 30 \(em 0) ms
.LP
\fIT\fR \d2\u > 340 ms
.LP
.sp 1
.PP
Allowing a safety margin of 20\ ms and a tolerance of \(+- | 0%, the
specified value of \fIT\fR\d2\uis (450\ \(+-\ 90)\ ms.
\v'3p'
.LP
	\fIb)\fR 	\fICircuits including a satellite link\fR 
.PP
The calculation is based on the assumption that the complete
connection includes two terrestrial sections with a maximum one\(hyway
transmission delay of 15\ ms each and a satellite section with a one\(hyway
transmission delay of (270\ \(+-\ 20)\ ms.
.PP
Values used for the calculation of \fIT\fR\d1\uand \fIT\fR\d2\u:
\v'6p'
.RT
.LP
	250\ <\ \fIt\fR\d\fIp\fR\u\ <\ 320\ ms
.LP
\ \ 0\ <\ \fIt\fR\d\fIo\fR\u\ <\ \ 30\ ms (see \(sc\ 2.3.2.4)
.LP
\ 30\ <\ \fIt\fR\d\fIr\fR\u\ <\ \ 50\ ms
.LP
\ \ 0\ <\ \fIt\fR\d\fIi\fR\u\ <\ \ 20\ ms
.PP
.sp 1
Calculation of intervals \fIT\fR\d1\uand \fIT\fR\d2\u:
\v'6p'
.LP
	\fIT\fR \d1\u > 
AC
	\fIT\fR \d1\u > 2
(\fIt
\dp\u\fR +
\fIt
\do\u\fR )
max. + \fIt
\dr\u\fR max. + \fIt
\di\u\fR max.
.LP
\fIT\fR \d1\u > (2 \(mu 350 + 50 + 20) ms
.LP
\fIT\fR \d1\u > 770 ms
.LP
.sp 1
.PP
Allowing a safety margin of 30\ ms and a tolerance of \(+- | 0%, the
specified value of \fIT\fR\d1\uis (1000\ \(+-\ 200)\ ms.
.LP
.sp 1
.bp
.LP
	\fIT\fR \d2\u > 
BF
	\fIT\fR \d2\u > \fIT\fR \d1\u
max. +  \fIt
\dr\u\fR max. + \fIt
\di\u\fR max. \(em 2
(\fIt
\dp\u\fR + \fIt
\do\u\fR )
min. \(em  \fIt
\dr\u\fR min. \(em \fIt
\di\u\fR min.
.LP
\fIT\fR \d2\u > (1200 + 50 + 20 \(em 2 \(mu 250 \(em 30 \(em 0) ms
.LP
\fIT\fR \d2\u > 740 ms
.PP
.sp 1
Allowing a safety margin of 60\ ms and a tolerance of \(+- | 0%, the
specified value of \fIT\fR\d2\uis 
(1000\ \(+-\ 200)\ ms.
\v'3p'
.LP
	 \fIc)\fR \fITerrestrial circuits and circuits including a satellite\fR 
\fIlink\fR 
.PP
The situation in which equipment can serve terrestrial circuits as well 
as circuits including a satellite link is not to be preferred because for 
the case of terrestrial circuits the release sequence is unduly prolonged. 
The calculation is based on the same assumption as in \fIb)\fR \ above, 
but with a 
minimum for (\fIt\fR\d\fIp\fR\u\ +\ \fIt\fR\d\fIo\fR\u)\ =\ 0. This does 
not affect the value 
of \fIT\fR\d1\u, so also in this situation \fIT\fR\d1\u\ =\ 1000\ \(+-\ 
200\ ms. 
.PP
Values used for the calculation of \fIT\fR\d2\u:
\v'6p'
.RT
.LP
	\ 0\ <\ \fIt\fR\d\fIp\fR\u\ <\ 320\ ms
.LP
\ 0\ <\ \fIt\fR\d\fIo\fR\u\ <\ \ 30\ ms (see \(sc 2.3.2.4)
.LP
30\ <\ \fIt\fR\d\fIr\fR\u\ <\ \ 50\ ms
.LP
\ 0\ <\ \fIt\fR\d\fIi\fR\u\ <\ \ 20\ ms
.LP
.sp 1
.PP
Calculation of interval \fIT\fR\d2\u:
\v'6p'
.LP
	\fIT\fR \d2\u > 
BF
	\fIT\fR \d2\u > \fIT\fR \d1\u
max. +
\fIt
\dr\u\fR max. + \fIt
\di\u\fR max. \(em 2
(\fIt
\dp\u\fR + \fIt
\do\u\fR )
min. \(em  \fIt
\dr\u\fR  |
min. \(em \fIt
\di\u\fR min.
.LP
\fIT\fR \d2\u > (1200 + 50 + 20 \(em 0 \(em 30 \(em 0) ms
.LP
\fIT\fR \d2\u > 1240 ms
.PP
.sp 1
Allowing a safety margin of 40\ ms and a tolerance of \(+- | 0%, the
specified value of \fIT\fR\d2\uis (1600\ \(+-\ 320)\ ms.
.LP
.sp 1P
.LP
2.2.3
	\fIAbnormal conditions\fR 
.sp 9p
.RT
.PP
The situations described below are those in which interruption
control of signalling channels (see\ Recommendation\ Q.416) does not function 
and which occur only during interruptions of individual channels or in 
the event of a fault in a line\(hysignalling equipment. In addition, the 
situations described in \(sc\(sc\ 2.2.3.3 and\ 2.2.3.4 below may also result 
from operation of interruption control at the incoming end of the circuit. 
In that case the circuit 
automatically returns to normal at the command of interruption control.
.RT
.PP
2.2.3.1
If an exchange recognizes tone\(hyoff condition in the backward
direction (premature answer) before the outgoing R2\ register has received a
signal\ A\(hy6 or a Group\ B\(hysignal, the connection must be released. 
Congestion 
information is then sent backwards or a repeat attempt is made to set up the
call.
.LP
.PP
2.2.3.2
In the case of non\(hyreception of the answer signal, of delay in
clearing by the calling subscriber in automatic working, or of non\(hyreception 
of the clear\(hyforward signal by the incoming exchange after the clear\(hyback 
signal has been sent, the provisions of Recommendation\ Q.118 apply. 
.PP
2.2.3.3
If, in the cases given in \(sc\ 2.2.2.6\ a) or\ c)\ above, the tone in
the backward direction is not removed, the circuit will remain blocked, 
since it cannot return to the idle state of its own accord. The action 
to be taken in such cases is described in \(sc\ 6.6. 
.PP
2.2.3.4
If after sending of the clear\(hyforward signal the signalling tone in 
the backward direction is not restored, the circuit stays blocked, as 
described in section \(sc\ 2.2.2.5 above. The same occurs when, in the 
idle state, the signalling tone in the backward direction is interrupted 
by a fault. 
.PP
2.2.3.5
When the signalling tone in the forward direction of an idle
circuit is interrupted owing to a fault, the incoming end recognizes seizure
and connects multifrequency signalling equipment, but no interregister
signalling follows.
.LP
	\fIa)\fR 	When the interruption is greater than the incoming\ R2
register time\(hyout (see Recommendation\ Q.476) the register will
release and the circuit must be brought into blocked state by
removal of the signalling tone in the backward direction. As
soon as the fault is cleared and the tone in the forward
direction consequently restored, the circuit returns to the idle
state in accordance with \(sc\ 2.2.2.6\ b) above.
.LP
	\fIb)\fR 	When the interruption is shorter than the time\(hyout,
restoration of the signalling tone in the forward direction will
return the circuit to the idle state in accordance with \(sc\ 2.2.2.6\ a)
above.
.bp
.sp 1P
.LP
2.2.4
	\fIAlarms for technical staff\fR 
.sp 9p
.RT
.PP
According to Recommendation\ Q.117, an alarm should in general be
given to technical staff as soon as an abnormal condition is recognized as
probably due to a fault.
.PP
It is recommended that a delayed action alarm should be operated at
the outgoing end for the conditions described in \(sc\(sc\ 2.2.2.5, 2.2.3.3
and\ 2.2.3.4 above, i.e.\ when the circuit does not revert to the idle state
after sending of the clear\(hyforward signal or receipt of the blocking signal.
.PP
Arrangements for the operation of the alarm will be made by each
Administration.
.PP
At both the outgoing and the incoming end, when interruption control (see 
Recommendation\ Q.416) functions, alarm condition must first be established 
for the transmission equipments. However, in this case a delayed\(hyaction 
alarm may also be given to the technical staff of the exchange. 
.RT
.LP
.rs
.sp 40P
.LP
\fBMONTAGE:\ \fR REC.\ Q.414 A LA FIN DE CETTE PAGE
.sp 1P
.RT
.LP
.bp