InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/6_4_05.tro

Text File | 1991-12-13 | 112.6 KB | 3,960 lines

.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\"                 Not Copyright ( c) 1991
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P

.rs
\v | 5i'
.sp 1P
.ce 1000
\v'3P'
SECTION\ 6
.ce 0
.sp 1P
.ce 1000
\fBTESTING\ AND\ MAINTENANCE\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ Q.490\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTESTING\ AND\ MAINTENANCE\fR
.EF '%    Fascicle\ VI.4\ \(em\ Rec.\ Q.490''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.490    %'
.ce 0
.sp 1P
.LP
6.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
In international working the guiding principles and testing
arrangements for maintenance as defined in Recommendations\ M.700 to\ M.728
and\ Q.134 also apply to Signalling System\ R2. The organization of routine
maintenance, tests and measurements of signalling and switching should
comply with Recommendations\ M.716, M.718, M.719, M.728 and\ M.732.
.PP
The analogue line signalling of System R2 differs from other CCITT
signalling systems in two significant respects:
.RT
.LP
    \(em
    line signals are sent over out\(hyband
signalling channels;
.LP
    \(em
    an \*Qinterruption control\*U protects the
line signalling from the consequences of interruptions of
the transmission path.
.LP
.PP
These two features of System R2 require special attention from a maintenance
point of view.
.sp 1P
.LP
6.2
    \fIAutomatic procedures for transmission measurements and\fR
\fIsignalling tests\fR
.sp 9p
.RT
.PP
Circuits operated with System\ R2 require elaborate transmission
measurements and signalling tests and also rapid and simple testing of
transmission and signalling. Both needs are preferably met by means of
automatic devices.
.PP
The specification for ATME\(hy2 as adopted by CCITT makes it applicable
to the testing of international circuits using System\ R2. The necessary
information for its use on such circuits is contained in
Recommendation\ O.22.
.PP
A description of a simplified programme for rapid testing of
signalling and checking the transmission quality of a circuit is given in
\(sc\ 6.3. Generally speaking, the arrangements for automatic testing consist
of
outgoing test equipment connected at the outgoing end of the circuit and
incoming test equipment connected at the incoming end.
.RT
.LP
.sp 1P
.LP
6.3
    \fIAutomatic test procedures for test equipments\fR
.sp 9p
.RT
.PP
Automatic test procedures provides a means for rapid testing of
signalling and also checking the transmission quality of circuits operated
with Signalling System\ R2.
.RT
.sp 1P
.LP
6.3.1
    \fINumbering of access to test equipment\fR
.sp 9p
.RT
.PP
In international working, to set up a call to maintenance equipment via
circuits operated with System\ R2, the following multifrequency signals
must be sent:
.RT
.LP
    \(em
    I\(hy13 (replacing the language digit, in
accordance with Recommendation\ Q.133),
.LP
    \(em
    I\(hy13,
.LP
    \(em
    two digits \*QXY\*U which will be associated
with the type of test equipment and the procedure for
testing to be employed (see Recommendation Q.107, Table\ 7),
.LP
    \(em
    I\(hy15 (if requested by the incoming equipment).
.bp
.LP
.PP
Provision is made for repetition of signal\ I\(hy13 to avoid
complications in the incoming\ R2 register in the country of destination. The
second signal\ I\(hy13 is stored in the place where the first digit of
the routing information is normally recorded. In this way, access to the
test equipment
requires no analysis, for routing purpose, of the signal which takes the
place of the language digit.
.PP
When calls are set up to the test equipment, it is desirable to avoid repetition
of the request for the access code or for any other digit. This is because
the calls may come from equipment which is not normally designed to
interpret signals\ A\(hy2, A\(hy7 or\ A\(hy8.
.PP
The address complete signal to be sent on calls to test equipment must
be one of the following:
.RT
.LP
    \(em
    A\(hy6 or A\(hy3 followed by B\(hy6 when incoming test equipment is
free,
.LP
    \(em
    A\(hy4 or A\(hy3 followed by B\(hy3 or B\(hy4 when incoming test
equipment is busy.
.PP
Precautions should be taken that signal\ A\(hy6 is only sent when it is
sure that the incoming test equipment is available for that call. When
receiving signal\ A\(hy3, the outgoing test equipment sends signal\ II\(hy7 in
response.
.PP
\fINote\fR \ \(em\ In national working, or in international working where the
language digit is omitted by bilateral agreement, the following multifrequency
signals must be sent:
.RT
.LP
    \(em
    I\(hy13.
.LP
    \(em
    Two digits \*QXY\*U.
.LP
    \(em
    I\(hy15 (if necessary).
.sp 1P
.LP
6.3.2
    \fITest sequence for simplified test\fR
.sp 9p
.RT
.PP
The test sequence is as follows:
.RT
.LP
    a)
    seizing of the automatic incoming test equipment;
.LP
    b)
    transition to answer state;
.LP
    c)
    sending backward of a composite identification signal
1020\ +\ 1140\ Hz; this signal will be acknow
ledged\ in\ a\ compelled
manner by the signal mentioned under\ d);
.LP
    d)
    recognition of a composite acknowledgement signal
1380\ +\ 1980\ Hz, sent in the forward direction;
.LP
    e)
    on the disappearance of the acknowledgement signal the
incoming test equipment passes to the clear\(hyback state;
.LP
    f
)
     on recognition of the clear\(hyback signal, the outgoing equipment will
send in a normal manner the clear\(hyforward signal
which will clear the connection and release incoming test
equipment. After release of the incoming line circuit the
release\(hyguard signal will be sent in the normal way.
.PP
Detection of failure is made by timing out at the outgoing
equipment.
.PP
The frequencies mentioned under\ c) and\ d) are those for System\ R2
interregister signalling; transmission and reception of these frequencies in
the incoming test equipment must be in accordance with Section\ 4.
.PP
Attenuation pads may be inserted in the send and receive paths of the outgoing
test equipment to shift the receive level at the input of the
multifrequency receivers of the outgoing and incoming test equipment toward
the lower operational limit. This makes it possible to diagnose abnormal
loss on
the circuit under test from defective multifrequency signal exchange between
outgoing and incoming test equipment. For testing international System\ R2
circuits, the additional attenuation produced by the pads should be
10\ \(+-\ 1\ dB.
.RT
.LP
.sp 1P
.LP
6.3.3
    \fIGood/no good transmission test equipment\fR
.sp 9p
.RT
.PP
In addition to the tests described in \(sc\(sc\ 6.3.1 and\ 6.3.2 a good/no
good transmission test may be provided as a simple means for fast error
localization. Such a test is described in Recommendation\ Q.137 for System
No.\ 4 (i.e.\ and the frequency of the test signal, the tolerances and
the deviation
from the nominal value, the test signal generators and receivers would
all be the same) but the sending level being \(em10\ dBm.
.PP
It is to be noted that loop transmission measurements of the kind
specified in Recommendation\ Q.136 cannot be made on System\ R2
circuits.
.RT
.sp 1P
.LP
6.4
     \fITesting of analogue line signalling equipment under abnormal\fR \fIconditions\fR
.sp 9p
.RT
.LP
.PP
The specification of the analogue line signalling equipment
contains clauses concerning operation under abnormal conditions, including
the action to be taken in case of interruption control alarm. The testing
equipment described in \(sc\ 6.2 is not applicable to such conditions and
therefore the
functioning of the analogue line signalling equipment under abnormal conditions
should be tested internally at each end of a circuit either manually or
automatically with special equipment.
.bp
.PP
The detailed programme for this testing will be specified by each
Administration.
.PP
The design and construction of the line signalling equipment should be
such as to permit both operational and limit testing in normal and abnormal
conditions.
.RT
.sp 1P
.LP
6.5
    \fIAlarms for the technical staff\fR
.sp 9p
.RT
.PP
Certain abnormal conditions in the signalling equipment should
cause alarms to be set off for the technical staff (see also
Recommendation\ Q.117). The relevant requirements are found in Section\
2 (line signalling equipment) and in Section\ 5 (time\(hyout in multifrequency
registers).
.PP
As indicated in \(sc\ 2.2.3, a fault occurring during release of a circuit
.PP
may result in an abnormal blocking condition. In this case there is a \*Qtone\(hyon\*U
condition in both signalling directions, yet the circuit is not in the
idle
condition since the release\(hyguard signal has not been received. If no
special action is taken, a temporary fault may therefore result in the
circuit's being out of service until it is manually restored by the maintenance
staff, after
receipt of an alarm (see \(sc\ 2.2.4).
.PP
It may accordingly be desirable to arrange for automatic restoration of
abnormally blocked circuits. For Administrations wishing to introduce this
function, the recommended arrangement is described below.
.RT
.LP
.sp 1P
.LP
6.6
     \fIRecommended method for automatic restoration of an abnormally\fR \fIblocked
circuit\fR
.sp 9p
.RT
.PP
When an outgoing link is abnormally blocked, periodic sending on
the outgoing link of the seizing signal, followed shortly afterwards by the
clear\(hyforward signal, is initiated.
.PP
Clearance of the fault which caused the abnormal blocked condition
will initiate a release\(hyguard signal at the incoming end whereupon the
outgoing end restores the link to the idle condition.
.PP
The intervals, at which the periodic sequence described above is
repeated, should be between 30\ seconds and 2\ minutes.
.PP
The first operation of the automatic device should be performed as
soon as possible, but not before 2\(hy3\ seconds have elapsed, after recognition
of the abnormally blocked condition at T1 (see \(sc\ 2.2).
.PP
After a period of three to six minutes a delayed alarm should be
given in accordance with Recommendation\ Q.412, \(sc\ 2.2.4.
.PP
In the event of a backward tone\(hyoff condition being detected, other
than in response to a periodic clear\(hyforward signal, the periodic sequence
is suspended until the backward tone is again recognized whereupon the
periodic
sending sequence is restarted.
.PP
If interruption control at the outgoing end occurs during the
abnormally blocked condition, the periodic sending sequence is suspended
until the interruption control reverts to normal, whereupon the periodic
sending
sequence is restarted.
.RT
.sp 1P
.LP
6.7
    \fIInstructions for the maintenance of channels and circuits using\fR
\fISystem R2 line signalling system at 3825\ Hz\fR
.sp 9p
.RT
.PP
The analogue line signalling equipment specified in Section\ 2 is
closely associated with the channel translating equipment and its operation
may be a function of the group and supergroup translating and through\(hyconnection
equipments. Maintenance of the circuits and groups which support them is
governed by the principles and Recommendations of Volume\ IV. However, the
introduction of out\(hyband signalling calls for a few complements to these
Recommendations, as described below.
.RT
.LP
.sp 1P
.LP
6.7.1
     \fIBringing into service of group, supergroup, mastergroup or\fR \fIsupermastergroup
links\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    \fI\(sc\(sc 2.1 and 7.6 of Recommendation\ M.460\fR
.PP
It should be noted that group and supergroup pilots placed at
140\ Hz from a virtual carrier frequency are incompatible with signalling at
3825\ Hz. Hence, the pilot on 84.140\ kHz should not be applied to groups in
which channel\ 6 is to be operated with this out\(hyband signalling. Similarly,
the pilot on 411.860\ kHz should not be applied to supergroups in which
channel\ 1 of the group in the group\ 3 position is to be operated with
signalling at
3825\ Hz.
.bp
.PP
If the channels of a group are to be operated with System\ R2, each
extremity of the group should be equipped, at the receiving end, with a
device to give protection against faulty signalling conditions which may
result from an interruption in the transmission channels (interruption
control). This
equipment, which is based on pilot level detection; must comply with the
conditions specified in \(sc\ 2.4.3 of Recommendation\ Q.416.
.PP
\fINote\fR \ \(em\ If the channels of a supergroup which are operated with
System\ R2 have the same extremities as the supergroup, a device based on
monitoring of the supergroup pilot can be used instead of one based on
monitoring of the group pilot. It will have to meet the same
specifications.
\v'3p'
.RT
.LP
    b)
    \fI\(sc 7.2 of Recommendation\ M.460\fR
.PP
The group\(hytranslating and through\(hyconnection equipments are
specified with a passband extending from 60.600\ kHz to 107.700\ kHz. If it is
wished to use channels\ 12 with signalling at 3825\ Hz, it is necessary
to ensure when the group is set up, that the corresponding frequency (60.175\
kHz) is
transmitted satisfactorily from end to end of the group link.
.PP
Provisionally, in view of the operating margin of the receiving part of
the signalling equipment, it is desirable to check that attenuation at
this frequency does not exceed the attenuation at the group pilot frequency
by more than 3\ dB.
.PP
A similar precaution should be taken on setting up group links when
signalling is to be used at 3825\ Hz on channel\ 12 of the group transmitted
in position\ 5 on the supergroup.
.RT
.sp 2P
.LP
6.7.2
     \fISetting\(hyup and lining\(hyup the channels of an international\fR
\fIgroup\fR
.sp 1P
.RT
.sp 1P
.LP
6.7.2.1
    \fISetting up the out\(hyband signalling channel for the\fR
\fISystem\ R2\fR
.sp 9p
.RT
.LP
.PP
Testing of the sending equipment:
.RT
.LP
    \(em
     The sending level of the signalling frequency corresponding to 3825\
Hz if the carrier is taken as the frequency of origin
must be lined up at \(em20\ \(+-\ 1\ dBm0. When this frequency is not to
be sent, its leak transmitted to line should not exceed \(em45\ dBm0.
.PP
Testing of the receiving equipment:
.LP
    \(em
    The signalling receiver must operate in the conditions
described in \(sc\(sc\ 2.3.2.1 and\ 2.3.2.2. It must not function
when a signal, of which the characteristics (level and frequency)
are such that the representative point is below the graph in
Figure\ 8/Q.415, is applied to the same point.
.LP
    This test may be replaced by the following one to check the
protection against unwanted signals (impulsive noise):
.LP
    \(em
     The sending part of the group terminal equipment is connected to its
receiving part by a closed\(hycircuit loop at the group
distribution frame, this loop introducing a slight gain (e.g.\ 3\ dB)
.LP
if possible. The standardized click generator (see Figure\ 7/Q.414) is
applied to each speech channel successively at the point where
this channel is connected to the switching equipment, and a check
is made to ensure that no wrong signals are retransmitted at the
receiving end to the switching equipment by the channel signalling
equipment concerned or by those of the other channels in the group.
.sp 1P
.LP
6.7.2.2
    \fIClosed\(hycircuit loop tests: response time\fR
.sp 9p
.RT
.PP
When the transmission\(hyreception loop of the terminal equipment is effected
at the group distribution frame or at an equivalent point, a check is made
to ensure that less than 30\ ms elapse between the moment when the change
of condition is applied to the transmitter associated with each channel
and the moment when it appears at the output of the corresponding
receiver.
.RT
.sp 1P
.LP
6.7.2.3
    \fIEnd\(hyto\(hyend tests\fR
.sp 9p
.RT
.PP
When the terminal channel\(hytranslating equipments are normally
connected to the extremities of the link, an end\(hyto\(hyend operating test is
carried out. The level of the line\(hysignalling frequencies transmitted and
.PP
received for each channel are likewise measured, to provide a reference,
at the group terminal distribution frames or at equivalent points.
.bp
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Signalling System R2 Specifications)
.sp 9p
.RT
.ce 0
.ce 1000
(see Recommendations Q.400 and Q.441)
.sp 9p
.RT
.ce 0
.ce 1000
\fBProvision of a forward\(hytransfer signalling facility\fR
.sp 1P
.RT
.ce 0
.LP
A.1
    \fIGeneral\fR
.sp 1P
.RT
.PP
The System\ R2 does not provide a forward\(hytransfer line signal.
However for certain relations it may be decided by bilateral or multilateral
agreement to introduce the forward\(hytransfer signalling facility into
System\ R2.
.PP
One possible procedure that has been adopted for use within Europe, is
to use the PYY in\(hyband signal of System\ No.\ 4. This solution is only
economical in regions where the facility is needed for a small proportion of
the calls.
.PP
For international working the method as described below may be
followed.
.PP
\fINote\fR \ \(em\ The method given in this Annex may also be adopted in
national networks where the forward\(hytransfer facility is considered
necessary for trunk offering and recalling operators. However, care must
be taken to see that the transmission limits applying to the forward\(hytransfer
signal specified are
observed.
.RT
.sp 1P
.LP
A.2
     \fIMethod recommended for introducing the forward\(hytransfer signalling\fR
\fIfacility into System\ R2\fR
.sp 9p
.RT
.PP
Forward\(hytransfer signalling will be provided by means of special
equipment which uses in\(hyband signalling and which is switched only on
to those connections which may require this facility. The amount of special
equipment necessary can, accordingly, be reduced to a minimum and adapted,
in a flexible manner, to actual needs. The in\(hyband signal constituting
the
forward\(hytransfer signal is sent end\(hyto\(hyend between the outgoing
and incoming
international exchanges. When the special equipment receives the
.PP
forward\(hytransfer signal, it performs the necessary operations at the
incoming exchange.
.RT
.sp 1P
.LP
A.2.1
    \fIAccess to the special equipment in an incoming international\fR
\fIexchange\fR
.sp 9p
.RT
.PP
In an incoming international exchange access to the special equipment for
forward\(hytransfer signalling can be determined by the use of the following
indicators:
.RT
.LP
    1)
     Special marking of incoming routes on which forward\(hytransfer signalling
is used.
.LP
    2)
    Language digit indicating semi\(hyautomatic traffic.
.LP
    3)
    Calls for code\ 11 or code\ 12 operator.
.LP
    4)
    Special interregister signalling sequence in which the
incoming exchange sends signal\ A\(hy5, \fIsend calling party's category\fR
. If
the forward\(hytransfer signalling facility is required the
outgoing R2\ register will respond to this by sending the
signal\ II\(hy10. This signal indicates an operator\(hyinitiated call
on which special equipment for forward\(hytransfer signalling is
needed.
.PP
The use of these indicators will depend on the amount of traffic for which
forward\(hytransfer signalling is employed. In some cases one or two
of the indicators will be utilized. In others, combinations of all will be
used to reduce to a minimum the amount of special equipment required.
.sp 1P
.LP
A.2.2
    \fIIn\(hyband forward\(hytransfer signalling\fR
.sp 9p
.RT
.PP
In System\ R2 the in\(hyband forward\(hytransfer signal is the same as
that used in System\ No.\ 4. For the definition of this signal see
Recommendation\ Q.120, \(sc\ 1.12. The signal is the signal PYY defined in
Recommendation\ Q.121, \(sc\ 2.3. The forward\(hytransfer signal is sent
in accordance with Recommendations\ Q.122 and\ Q.124.
.PP
The signal receiver and the splitting arrangements to be incorporated in
the special equipment at the incoming international exchange are in accordance
with Recommendations\ Q.123 and\ Q.124.
.PP
Provided it creates no difficulty for incoming national network
signalling, no splitting need be effected at the receiving end and the
caller will then hear the entire signal\ PYY.
.bp
.RT
.LP
\fBMONTAGE:\ \fR PAGE 144 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'12P'
\s12PART\ IV
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBSUPPLEMENTS\ TO\ THE\ SERIES\ Q\ RECOMMENDATIONS\fR
.EF '%     \ \ \ ^''
.OF ''' \ \ \ ^    %'
.ce 0
.sp 1P
.ce 1000
\fBCONCERNING\ SIGNALLING\ SYSTEMS\ R1\ AND\ R2\fR
.ce 0
.sp 1P
.LP
.rs
.sp 30P
.LP
.bp
.LP
\fBMONTAGE:\fR PAGE 146 = PAGE BLANCHE
.sp 1P
.RT
.LP
\fI\fR .bp
.sp 2P
.LP
\fBSupplement\ No.\ 1\fR
.RT
.sp 2P
.ce 1000
\fBLINE\ SIGNALLING\ FOR\ DC\ LINES\ WITH\ SYSTEM\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 1''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 1    %'
.ce 0
.sp 1P
.ce 1000
\fBR2\ INTERREGISTER\ SIGNALLING\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
In the following specification a line signalling system is defined for
2\(hywire, DC\(hylines with or without metering facility during speech.
.PP
The signalling polarity is provided by the incoming exchange and a
loop is provided in the outgoing exchange, so that in case of cable fracture
the outgoing exchange is informed automatically that the line(s) concerned
is(are) no longer available.
.PP
The line signal repertoire is based on the presence of System\ R2
interregister signalling.
.PP
Apart from the metering pulses, the line signalling is continuous,
which means that a certain state of a connection is characterized by a
.PP
special signalling condition which is maintained as long as the indicated
condition continues to exist.
.PP
The following states are provided:
.RT
.LP
    Forward direction:
.LP
    1)\ idle
.LP
    2)\ seized
.LP
    3)\ clear\(hyforward
.LP
    Backward direction:
.LP
    1)\ available
.LP
    2)\ seized before answer
.LP
only without metering
.FE
only with metering
.FE
    3)\ answered
.LP
    4)\ metering
.LP
    5)\ clear\(hyback
.LP
    6)\ forced release
.LP
    7)\ not available (blocking)
.LP
.sp 2P
.LP
\fB2\fR     \fBPrinciples of the signalling and speech circuit\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fISignalling circuit\fR
.sp 9p
.RT
.PP
An example of a signalling circuit is shown in Figure\ 1. Feeding
of the loop occurs at the incoming exchange; the direction of the current
can be reversed by contacts\ X and the feeding current can be switched off by
contacts\ Tu. Contacts\ Bl are also used to switch off the feeding current and
consequently, to block the circuit. This can only take place if the line
circuit in the outgoing exchange is detected as being in the open or high
resistance state.
.PP
When the contacts are in the position shown in the figure, normal
loop current flows and when the contacts\ X are switched over reversed loop
current flows.
.PP
In the outgoing exchange the state can be changed, by means of
contact\ W, from the high resistance condition with the current\(hydirection
sensitive detector\ H switched in, to a state with two low resistance
current\(hydirection sensitive detectors\ L and\ R.
.PP
In addition to contact\ W a contact\ K is provided to open the loop; the
open loop state is used to expedite the recognition of clear\(hyforward.
.RT
.LP
.sp 1
.bp
.PP
In the line circuit in the incoming exchange a filter is needed to provide
sufficient attenuation in the audible components arising in case of
polarity reversing. This is necessary, in particular, when metering pulses
are sent during conversation.
.PP
In the line circuit in the outgoing exchange a filter may be needed to
provide sufficient attenuation in the audible components arising when
detectors\ L and\ R are operated and/or released. This filter, if required at
all, can normally be much simpler than the one used in the incoming
exchange.
.RT
.sp 1P
.LP
2.2
    \fISpeech circuit\fR
.sp 9p
.RT
.PP
An example of a speech circuit is also shown in Figure\ 1. A circuit equipped
with the loop signalling system concerned has to be electrically
separated, from the preceding or following parts of the connection.
This prevents interference by longitudinal voltages in other parts
of the connection.
.PP
The detectors shall be of high impedance for speech.
.RT
.LP
.rs
.sp 20P
.ad r
\fBFigure 1 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR     \fBMeaning of the signalling states\fR
.sp 1P
.RT
.PP
In the Tables 1, 2 and\ 3 the meaning of the various signalling
states are shown.
.PP
Outgoing exchange:
.RT
.LP
    \(em
    high resistance\ =\ idle
.LP
    \(em
    low resistance\ =\ seized
.LP
    \(em
    open\ =\ clear\(hyforward.
.PP
Incoming exchange (\fIwithout\fR  | etering):
.LP
    \(em
    normal loop polarity\ =\ available, seized or clear\(hyback
.LP
    \(em
    reversed loop polarity\ =\ unavailable or answer
.LP
    \(em
    no voltage\ =\ unavailable (blocking).
.PP
Incoming exchange (\fIwith\fR  | etering):
.LP
    \(em
    normal loop polarity\ =\ available or seized
.LP
    \(em
    reversed loop polarity\ =\ unavailable or metering pulse
.LP
    \(em
    no voltage\ =\ unavailable (blocking) or forced release.
.LP
.sp 2P
.LP
\fB4\fR     \fBDiscrimination between the various signalling states\fR
.sp 1P
.RT
.PP
It is not necessary to be able to discriminate between each state of one
end and all states of the other end. However, the capabilities shown in
Tables\ 1, 2 and\ 3 should be provided.
.bp
.RT
.LP
.rs
.sp 10P
.ad r
\fBTable 1 p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 10P
.ad r
\fBTable 2 p.30\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 8P
.ad r
\fBTable 3 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB5\fR     \fBOperation\fR (see Figures\ 2a\(hy2f
)
.sp 1P
.RT
.PP
5.1
In the idle state the line circuit in the outgoing exchange
continuously checks whether or not the line is blocked by the high resistance
detector\ H. This detector operates when the line is intact and the normal
loop polarity is present in the incoming exchange indicating the state
\*Qavailable\*U.
.sp 9p
.RT
.PP
Detector\ V in the incoming exchange is marginal and does not
operate in this state.
.PP
5.2
If the circuit in the outgoing exchange is seized for a call the
.sp 9p
.RT
.LP
exchange switches in the low resistance state and the low resistance
detector\ L operates.
.PP
In the line circuit in the incoming exchange the detector\ V
operates and the incoming equipment assumes the seized state.
.sp 1P
.LP
5.3
    \fIThe B\(hysubscriber answers\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    \fIWithout metering\fR
.LP
     When the B\(hysubscriber answers this is indicated by the line circuit
in the incoming exchange by reversing the loop feeding
polarity to reversed loop polarity. In the circuit in the
outgoing exchange the low resistance detector\ R operates and\ L
releases.
.bp
.LP
    b)
    \fIWith metering\fR
.LP
    When the B\(hysubscriber answers this is indicated by the
incoming exchange (except in the case of a call that is free of
charge) by sending a metering pulse. The incoming exchange sends a
metering pulse by reversing the loop feeding polarity to reversed
loop polarity during the metering pulse.
.LP
    In the line circuit in the outgoing exchange the low
resistance detector\ R operates and\ L releases.
.PP
5.4
The equipment must allow the following rules to be applied with
respect to the sending of metering pulses.
.sp 9p
.RT
.LP
    \(em
     A metering pulse must be completed by the incoming exchange before sending
forced release.
.LP
    \(em
    After sending a metering pulse there is no minimum period
with normal loop polarity before forced release is sent.
.LP
    \(em
     During the receipt of a metering pulse the outgoing exchange is allowed
to start sending clear\(hyforward.
.LP
.sp 1P
.LP
5.5
    \fIBackward release\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    \fIWithout metering\fR
.LP
     The incoming exchange can inform the outgoing exchange that the B\(hysubscriber
has cleared by sending clear\(hyback. This signal
consists in reversing the loop feeding polarity to normal loop
polarity. In the line circuit of the outgoing exchange the low
resistance detector\ L operates and\ R releases.
.LP
    The incoming exchange remains in this state (clear\(hyback)
until the outgoing exchange sends clear\(hyforward or the
B\(hysubscriber reanswers.
\v'3p'
.LP
    b)
    \fIWith metering\fR
.LP
     The incoming exchange can inform the outgoing exchange that the connection
can be released by sending forced release. This
signal, which consists in switching off the loop feeding
potential, must persist for a minimum time\ T3. After
receiving forced release the line circuit of the outgoing
exchange must transmit clear\(hyforward within a time\ T4 which
is less than time\ T3.
.LP
    Time T3 finishes when the line circuit in the incoming
exchange is again available; normal loop polarity is then sent.
.LP
    The above mentioned cleard\(hyforward in the line circuit in
the outgoing exchange is followed (just as in the case of the
release without forced release described in \(sc\ 5.6 by the idle
state).
.PP
5.6
In order to release the circuit the outgoing exchange opens the
loop (clear\(hyforward) during a time\ T1, before switching in the high
ohmic detector.
.sp 9p
.RT
.PP
The incoming exchange must switch to one of the unavailable
states within a time\ T2 which is less than\ T1, unless the
circuit in this exchange is available before the time\ T2 has elapsed.
.PP
5.7
The incoming exchange can signal in two ways that it is not
available for a new call, namely by reversing the loop or by switching
off the feeding potentials.
.sp 9p
.RT
.PP
In so far as the unavailability of the line circuit in the
incoming exchange forms part of normal operation, this state should be
indicated by reversed loop polarity.
.PP
Unavailability of the line circuit in the incoming exchange for
other reasons should be indicated by switching off the feeding
potentials.
.RT
.LP
.PP
5.8
If during the seized state of the line circuit in the outgoing
exchange, the circuit is interrupted by disturbances or by the feeding
potential being switched off, the outgoing exchange has to react to it
in the same way as it does to clear\(hyback (without metering) or forced
release (with
metering), possibly followed by blocking.
.sp 9p
.RT
.PP
5.9
At the incoming exchange during the unavailable state and for
a subsequent period of 100\ ms during the available state, operation of
detector\ V should be ineffective.
.bp
.sp 9p
.RT
.LP
.rs
.sp 47P
.ad r
\fBFIGURES 2 a)/b) p.5\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURES 2 c)/d) p.6\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE 2 e) p.7\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE 2 f) p.8\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB6\fR     \fBTime requirements\fR
.sp 1P
.RT
.sp 1P
.LP
6.1
    \fIRecognition times\fR \v'3p'
.sp 9p
.RT
.LP
    a)
     When the outgoing exchanges is in the idle state but blocked the recognition
time of the unblocking condition (normal loop
polarity) must be 100\(hy300\ ms.
.LP
    b)
     In order to make a clear distinction between the reversal of the polarity
and no voltage the recognition time of forced
release must be 60\(hy180\ ms.
.LP
    c)
    The recognition time of all remaining conditions must be
10\(hy40\ ms.
.LP
.sp 1P
.LP
6.2
    \fIRelease times\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    The time T2 depends on the recognition time of
detector\ V and the reaction time of the incoming exchange which can be
assumed\ \(=\ 30\ ms; consequently the time\ T2 is defined 10\(hy70\ ms.
.LP
    b)
    \fIWithout metering\fR
.LP
     The worst case when releasing a circuit occurs if the B\(hysubscriber
releases just after the A\(hysubscriber releases, causing
clear\(hyback to be sent before the recognition time of clear\(hyforward
has elapsed. In order to safeguard the operation in that particular
situation the time\ T1 is defined 300\(hy600\ ms.
.LP
    c)
    \fIWith metering\fR
.LP
    The worst case when releasing a circuit occurs if within the
recognition time of clear\(hyforward a metering pulse starts and that within
the length of this pulse clear\(hyforward cannot be recognized. In order
to safeguard the operation in that particular situation the time\ T1 is
defined 500\(hy1000\ ms.
.LP
     The time T3 depends on the discharge time of the involved circuit and
the time\ T4. For the discharge time, a time\ \(=\ 80\ ms can be assumed.
The
time\ T4 depends on the recognition time of forced release [see \(sc\ 6.1 | )]
and
the reaction time of the outgoing exchange which can be assumed\ \(=\ 30\ ms;
consequently the time\ T4 is defined 60\(hy210\ ms. Addition of these times
leads to a time\ T3\ \(>="\ 300\ ms.
.sp 1P
.LP
6.3
    \fISending times\fR
.sp 9p
.RT
.PP
The length of the metering pulse to be sent shall be
120\(hy180\ ms.
.RT
.sp 2P
.LP
\fB7\fR     \fBMiscellaneous\fR
.sp 1P
.RT
.PP
This supplement does not describe values for the impedance of the detectors
and the cable and does not indicate operate/nonoperate limits for
the detectors, because these parameter are rather dependent on the capabilities
of the related network. Therefore these requirements must be provided by
each Administration.
.RT
.sp 2P
.LP
\fBSupplement\ No.\ 2\fR
.RT
.sp 2P
.ce 1000
\fBBOTH\(hyWAY\ WORKING\ OF\ THE\ ANALOGUE\ LINE\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 2''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 2    %'
.ce 0
.sp 1P
.ce 1000
\fBSIGNALLING\ VERSION\ OF\ SIGNALLING\ SYSTEM\ R2\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBBoth\(hyway working\fR
.sp 1P
.RT
.PP
In principle the Signalling System\ R2 is specified for one\(hyway
working. The following additional clauses therefore apply only to cases
where Administrations have undertaken by bilateral agreement to use both\(hyway
working.
.PP
Equipment which must be equally usable in both\(hyway and in one\(hyway
operation should be so designed that it can be easily adapted to the
requirements of either mode of operation.
.PP
A peculiarity of both\(hyway working with the system under consideration
is that a blocking signal cannot be distinguished from a seizing signal
at
either end of a circuit, since the transition of the signalling condition
corresponding to these signals is the same, namely from \fItone\(hyon\fR to
\fItone\(hyoff\fR .
.bp
.PP
When a both\(hyway circuit is seized simultaneously at both ends, the
signalling tone is disconnected in both directions of transmission; this
is the criterion for detecting the double\(hyseizure situation.
.PP
The special arrangements required for both\(hyway working relate to the
two cases mentioned above. For all other signalling phases the specifications
for one\(hyway working remain valid without modification.
.RT
.LP
.sp 2P
.LP
1.1
    \fINormal conditions\fR
.sp 1P
.RT
.sp 1P
.LP
1.1.1
    \fIDouble\(hyseizure\fR
.sp 9p
.RT
.PP
When the signalling equipment at one end of a both\(hyway circuit
seizes that circuit by disconnecting the signalling tone, it must verify
that cessation of the signalling tone in the opposite direction does not
occur
within 250\ \(+-\ 50\ ms of the disconnection of the signalling tone in
the forward direction. If the signalling equipment detects the removal
of the signalling
tone within that interval then a double\(hyseizure situation is recognized.
Each end must return to the idle state after sending the clear\(hyforward
signal
and recognizing \fItone\(hyon\fR condition on the signalling channel.
.PP
However, each end must, even if immediately seized for an outgoing
call, maintain \fItone\(hyon\fR condition for at least 100\ ms on the outgoing
signalling channel to ensure that the end of the double seizure situation is
recognized at the other end.
.PP
Although a double seizure has been recognized, the \fItone\(hyoff\fR
 | ondition in the backward direction is passed on backwards. This will be
regarded as an erroneous answer signal and lead to the release of the
connection in accordance with \(sc\ 2.2.3 in the Specifications. However, as
.PP
specified in \(sc\ 1.2.1 below the clear\(hyforward signal (\fItone\(hyon\fR
 | ondition) must not be sent until the \fItone\(hyoff\fR condition has
been maintained for at least
1250\ \(+-\ 250\ ms. Each end after sending of the clear\(hyforward signal
returns to
the idle condition when the time interval 250\ \(+-\ 50\ ms (see \(sc\
2.2.2.6 in the
Specifications) has elapsed, and the sending of the \fItone\(hyon\fR condition
from
the other end has been recognized.
.PP
In the sense of preventive action it is recommended that an opposite order
of circuit selection is used by each exchange of a both\(hyway circuit
group to minimize double seizure.
.RT
.LP
.sp 1P
.LP
1.1.2
    \fIMinimum duration of idle state after release\(hyguard\fR
.sp 9p
.RT
.PP
When a both\(hyway circuit is released, the end which acted as the
incoming end must, even if immediately seized for a call in the opposite
traffic direction, maintain the \fItone\(hyon\fR condition for at least
100\ ms to
ensure that the release\(hyguard sequence is recognized at the other end.
.RT
.sp 1P
.LP
1.1.3
    \fIBlocking\fR
.sp 9p
.RT
.PP
When a both\(hyway circuit is blocked manually in its idle state at
one end (A), the blocking signal, must be transmitted to the other end (B),
where it will nevertheless be interpreted as a seizing signal. This will
mean that an incoming R2\ register is seized, but is not receiving any
interregister signal. After the lapse of this register's time\(hyout delay
the circuit must be kept blocked locally (at end\ B) against all calls
in the B\(hyA\ direction so long as the \fItone\(hyoff\fR condition persists
in A\(hyB direction.
.PP
To avoid certain difficulties (see \(sc\(sc 1.2.1 and 1.2.2 below) and in
contrast to \(sc\ 2.2.3.5 in the Specifications the \fItone\(hyoff\fR condition
is not
applied in the opposite direction\ (B\(hyA) to the blocking direction\
(A\(hyB).
.PP
When the blocking is removed at end A the signalling tone is again
transmitted in direction\ A\(hyB and the B\(hyend interprets the onset of the
signalling tone as a clear\(hyforward signal, thereby initiating the release\(hyguard
sequence in the B\(hyA\ direction.
.RT
.sp 1P
.LP
1.2
    \fIAbnormal conditions\fR
.sp 9p
.RT
.PP
The cases described below relate to interruption of the individual signalling
channels or to faults in the individual line\(hysignalling equipment. Interruption
control does not function in these cases.
.bp
.PP
In any circuit the interruption of one or both signalling channels can
bring about signalling sequences different from those described in \(sc\
2.2.3 in the Specifications for one\(hyway working.
.RT
.PP
1.2.1
When an interruption of the signalling channel in one of the
two directions brings about a signalling state corresponding to blocking,
the release\(hyguard sequence will be initiated the moment the interruption
ends
(see \(sc\ 1.1.3).
.sp 9p
.RT
.PP
The release\(hyguard sequence implies that the signalling tone in
the backward direction be disconnected for an interval 450\ \(+-\ 90\ ms.
In both\(hyway working this \fItone\(hyoff\fR condition must not be interpreted
as seizing. To avoid a repetition of the exchange of release\(hyguard sequences
certain precautions
must be taken.
.PP
The following additional requirements should then be met:
.RT
.LP
    \(em
    when the \fItone\(hyoff\fR  | ondition has lasted for an interval of
less than 750\ \(+-\ 150\ ms the return to \fItone\(hyon\fR condition must
not initiate a release\(hyguard sequence;
.LP
    \(em
    once the signalling condition corresponding to seizing has
been established, it must be maintained for at least 1250\ \(+-\ 250\ ms
(this is a deviation to the requirement in \(sc\ 2.2.2.1 in the
Specifications).
.PP
When the interruption of one of the signalling channels has
brought about blocking of the circuit at one end (B), as described above,
that circuit can be seized at the other end\ (A). The end\ A will not have
received
the blocking signal from end\ B (see \(sc\ 1.1.3) because that would cause
permanent blocking of the circuit, which would then no longer be able to
restore itself to normal functioning. Should a seizing now occur, this
will lead to loss of a call; but subsequently, since the clear\(hyforward
signal cannot be transmitted, the circuit will remain blocked at end\ A.
The whole further signalling sequence for reverting the circuit under consideration
to idle follows the specification for one\(hyway circuits.
.LP
.PP
1.2.2
An interruption of both signalling channels on any circuit will be interpreted
by the equipment at each end of the line as seizing and the
equipments will be blocked after the lapse of the time\(hyout delay of the
incoming R2\ registers.
.sp 9p
.RT
.PP
If, after an interruption, only one signalling channel is
restored, the equipment at the incoming end in relation to that signalling
channel will interpret the \fItone\(hyon\fR condition as a clear\(hyforward
signal and
therefore bring into operation the release\(hyguard sequence. The terminal
equipment at that end will revert to the idle state, while the terminal
equipment at the other end remains blocked. This is the situation envisaged
in \(sc\ 1.2.1 above.
.PP
When both signalling channels are simultaneously restored, the
terminal equipment at both ends will interpret the onset of the signalling
tone as a clear\(hyforward signal and this will bring the release\(hyguard
sequence into operation. The result will be that the terminal equipment
at both ends will
again recognize the \fItone\(hyoff\fR condition for a brief interval.
.PP
The following additional clause must be observed, to avoid permanent blocking
of the circuit in this condition:
.RT
.LP
    \(em
    When, after blocking, the line\(hysignalling equipment at one
end\ (A) of a both\(hyway circuit has recognized the clear\(hyforward
signal, it must complete the release\(hyguard sequence and restore
the signalling tone after 450\ \(+-\ 90\ ms in the direction\ A\(hyB,
even if the tone in direction\ B\(hyA is interrupted. If such
interruption (in direction\ B\(hyA) lasts for less than 750\ \(+-\ 150\ ms,
the circuit returns to the idle state when the signalling tone is
restored in both directions. If the interruption is longer than
750\ \(+-\ 150\ ms, restoration of the signalling tone in
direction\ B\(hyA will initiate a new release\(hyguard sequence in
direction\ A\(hyB (see \(sc\ 1.2.1 above).
.PP
1.2.3
If an abnormal condition according to \(sc\ 2.2.3.3 in the
Specifications occurs at one end of a both\(hyway circuit, this end is
blocked for outgoing traffic. Such blocking should, however, not prevent
the circuit being used in the other traffic direction.
.sp 9p
.RT
.LP
.sp 2P
.LP
\fB2\fR     \fBSpecial conditions regarding the interruption control for\fR
\fBboth\(hyway working\fR
.sp 1P
.RT
.PP
2.1
As soon as an operating condition has been established on a
both\(hyway circuit and the outgoing and incoming ends of the circuit have been
determined with certainty, the interruption control specifications for
one\(hyway working become equally applicable to both\(hyway circuits.
.bp
.sp 9p
.RT
.PP
2.2
When a both\(hyway circuit is in the idle state, transition to
alarm of the interruption control of one direction of transmission must
bring about operations to ensure that the signalling condition existing
at that
moment on the signalling channel of the opposite direction is maintained
\(em\ in contrast to specification\ 2.4.2.1 | ) | ) in the Specifications
for one\(hyway
.LP
working. This precaution obviates a permanent blocking of a both\(hyway circuit
when interruption of the signalling channels occurs simultaneously in both
directions. It does not ensure immediate blocking of the circuit; this
will not occur until the circuit has been seized by the next call.
.PP
2.3
In all operating conditions intermediate between the \fIidle\fR
 | tate and the condition at the moment when the direction of seizure of the
both\(hyway circuit is determined (see above), the line\(hysignalling equipment
at
both ends will be locked by interruption control in the condition in which
it was before interruption control passed to alarm.
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 3\fR
.RT
.sp 2P
.ce 1000
\fBUSE\ OF\ THE\ ANALOGUE\ LINE\ SIGNALLING\ VERSION\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 3''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 3    %'
.ce 0
.sp 1P
.ce 1000
\fBON\ 2048\ kbit/s\ PCM\ TRANSMISSION\ SYSTEMS\fR
.ce 0
.sp 1P
.ce 1000
(refer to Recommendation G.732)
.sp 9p
.RT
.ce 0
.sp 1P
.PP
This solution is restricted for use within national networks or internationally
subject to bilateral agreements because it requires some
conventions which otherwise would have to be agreed upon in\ CCITT. However,
cost aspects may be a more decisive factor than the required conventions.
.sp 1P
.RT
.PP
The analogue version of the line signalling is used on both the
analogue and the digital transmission systems.
.PP
Two examples of the use of the analogue line signalling on digital
transmission systems are shown in Figure\ 1.
.PP
Apart from the interruption control handling, the transmultiplexer or other
conversion equipment is transparent to the line signalling.
.PP
The out\(hyslot signalling is carried in time slot 16 of 2048 kbit/s
systems (refer to Recommendation\ G.732, Table\ 3). Bit\ \fIa\fR of time
slot\ 16 is
used to transmit the line signalling state of the corresponding analogue
channel. Bit\ \fIb\fR is used to indicate that the analogue transmission
system is in the alarm condition with the following convention. For all
the digital
circuits connected to the circuits of this analogue group bit\ \fIb\fR
\ =\ 1 means
alarm condition on the analogue group.
.RT
.PP
\fB1\fR
In order to ensure the correct working of the line signalling under fault
conditions when employing T\ MUX some time requirements must be
fulfilled.
.sp 1P
.RT
.sp 1P
.LP
1.1
    \fIThe fault occurs on a PCM multiplex\fR  | see Figure 2)
.sp 9p
.RT
.PP
If the fault occurs on PCM multiplex No. 1, the transmission of
the alarm indication will take place in the following time conditions:
.LP
    \(em
    the fault occurs at \fIT\fR ;
.LP
    \(em
    the fault is detected by the transmultiplexer at
\fIT\fR \ +\ \fIt\fR\d1\u;
.LP
    \(em
    the transmultiplexer stops sending the pilot on GP\d1\u,
GP\d2\u\fR and GP\d3\uat \fIT\fR \ +\ \fIt\fR\d1\u\fR \ +\ \fIt\fR\d2\u;
.LP
    \(em
     the alarm indication is detected at the analogue distant end at \fIT\fR
\ +\ \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ +\ \fIt\fR\d3\u\ +\ \fIt\fR\d\fIp\fR\u,
.LP
where:
.LP
    \(em
    \fIt\fR\d1\uis the time needed for recognition of the faulty
transmission on a PCM 2048\ kbit/s multiplex;
.LP
    \(em
     \fIt\fR\d2\uis a processing time needed by the transmultiplexer after
detection of alarm on the PCM\ multiplex;
.LP
    \(em
     \fIt\fR\d3\uis the response time for the pilot receiver when the pilot
level falls: it is the time \fIt\fR \(da specified in
Recommendation\ Q.416 (\fIt\fR \(da\ <\ \fIt\fR\d\fIr\fR\\d\fIs\fR\u | dm\\di\\dn\u\
+\ 13\ ms), applicable
only for the recognition time \fIt\fR \ =\ 20\ \(+-\ 7\ ms;
.LP
    \(em
    \fIt\fR\d\fIp\fR\uis the propagation delay on the analogue
section.
.bp
.LP
.rs
.sp 26P
.ad r
\fBFIGURE 1 p.9\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 9P
.ad r
\fBFigure 2, p.10\fR
.ad b
.RT
.PP
In the same situation, if the transmission fault disturbs
signalling information, erroneous signals will be transmitted in the following
time conditions:
.LP
    \(em
    the fault occurs at \fIT\fR ;
.LP
    \(em
    the erroneous signalling condition appears at the input of
the analogue channel at \fIT\fR \ +\ \fIt\fR\d4\u;
.LP
    \(em
    the erroneous signalling condition appears at the input of
the distant signalling equipment at \fIT\fR \ +\ \fIt\fR\d4\u\ +\ \fIt\fR\d5\u\
+\ \fIt\fR\d\fIp\fR\u,
.LP
where:
.LP
    \(em
    \fIt\fR\d4\uis the time needed for transferring a line signal
from digital access to analogue access;
.LP
    \(em
     \fIt\fR\d5\uis the response time of the line signals receiver at the
distant analogue end (\fIt\fR\d\fIr\fR\\d\fIs\fR\uin Signalling System\
R2 Specifications);
.LP
    \(em
    \fIt\fR\d\fIp\fR\uis the propagation delay on the analogue section.
.bp
.PP
If \fIt\fR\d\fIr\fR\uis the recognition time of line signals specified in
Recommendation\ Q.412, correct working can be ensured if:
.LP
     \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ +\ \fIt\fR\d3\u\ +\ \fIt\fR\d\fIp\fR\u\
\(=\ \fIt\fR\d4\u\ +\ \fIt\fR\d5\u\ +
\fIt\fR\d\fIp\fR\u\ +\ \fIt\fR\d\fIr\fR\u
.LP
or
.LP
     \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ +\ \fIt\fR\d3\u\ \(=\ \fIt\fR\d4\u\ +\
\fIt\fR\d5\u\ +\ \fIt\fR\d\fIr\fR\u
.LP
or
.LP
     \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ +\ \fIt\fR \(da\ \(=\ \fIt\fR\d4\u\ +\
\fIt\fR\d\fIr\fR\\d\fIs\fR\u\ +\ \fIt\fR\d\fIr\fR\u.
.LP
.PP
Recommendation Q.416 specifies that
\fIt\fR \(da\ \(=\ \fIt\fR \s6\fIrs\fR  | in.
.PS 10
\ +\ \fIt\fR \s6\fIr\fR  | in.
.PS 10
(where
\fIt\fR \s6\fIr\fR  | in.
.PS 10
\ =\ 13\ ms). Thus, if \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\(=\ \fIt\fR\d4\u,
correct working of line signalling can be ensured.
.RT
.PP
This inequality indicates simply that the time needed for
detection of a faulty transmission on a PCM multiplex plus the time needed
for stopping pilot sending when the alarm is detected must be less than
the
transfer time of a line signal across the transmultiplexer. This time
requirement can be fulfilled, if necessary, by introducing in the
transmultiplexer a small delay in line signals transmission.
.RT
.sp 1P
.LP
1.2
    \fIThe fault occurs on an analogue group\fR
.sp 9p
.RT
.PP
If, for example, the fault occurs on the analogue group GP\d1\u, the transmission
of the alarm indication will take place in accordance with the
following time conditions:
.RT
.LP
    \(em
    the fault occurs at \fIT\fR ;
.LP
    \(em
    the fault is detected by the transmultiplexer at
\fIT\fR \ +\ \fIt\fR\d1\u;
.LP
    \(em
    bit \fIb\fR is set to 1 on the digital channels concerned
at \fIT\fR \ +\ \fIt\fR\d1\u\ +\ \fIt\fR\d2\u;
.LP
    \(em
    the alarm indication appears at the distant digital end at
\fIT\fR \ +\ \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ +\ \fIt\fR\d3\u\ +\ \fIt\fR\d\fIp\fR\u,
.LP
where:
.LP
    \(em
    \fIt\fR\d1\uis the time needed for detection of loss of pilot;
.LP
    \(em
     \fIt\fR\d2\uis the time needed for transferring alarm information to
the digital output;
.LP
    \(em
     \fIt\fR\d3\uis the response time of the signalling equipment of the digital
multiplex;
.LP
    \(em
    \fIt\fR\d\fIp\fR\uis propagation delay.
.PP
If the same fault disturbs signalling information, erroneous
signals will be transmitted in the following time conditions:
.LP
    \(em
    the fault occurs at \fIT\fR ;
.LP
    \(em
    the erroneous signalling condition is detected by the
transmultiplexer at \fIT\fR \ +\ \fIt\fR\d4\u;
.LP
    \(em
     bit\ \fIa\fR is changed at the sending end of the digital section by
the transmultiplexer at \fIT\fR \ +\ \fIt\fR\d4\u\ +\ \fIt\fR\d5\u;
.LP
    \(em
    the erroneous signalling condition appears at the input of
the distant signalling equipment at \fIT\fR \ +\ \fIt\fR\d4\u\
+\ \fIt\fR\d5\u\ +\ \fIt\fR\d6\u\ +\ \fIt\fR\d\fIp\fR\u,
.LP
where:
.LP
    \(em
     \fIt\fR\d4\uis the response time of the signalling tone receiver in the
transmultiplexer;
.LP
    \(em
    \fIt\fR\d5\uis the time needed for transferring a line signal
from
the output of the signalling tone receiver to the digital output
(change of bit\ \fIa\fR );
.LP
    \(em
     \fIt\fR\d6\uis the response time of the signalling equipment of the PCM
2048\ kbit/s multiplex (\fIt\fR\d3\u\ =\ \fIt\fR\d6\u).
.PP
Correct working of line signalling is ensured if:
.LP
     \fIt\d1\u\ +\ \fIt\d2\u\ +\ \fIt\d3\u\ +\ \fIt\fR\d\fIp\fR\u\ \(=\ \fIt\d4\u\
+
\fIt\d5\u\ +\ \fIt\fR\d6\u\ +\ \fIt\fR\d\fIp\fR\u\ +\ \fIt\fR\d\fIr\fR\u
.LP
or
.LP
     \fIt\fR\d1\u\ +\ \fIt\fR\d2\u\ \(=\ \fIt\fR\d4\u\ +\ \fIt\fR\d5\u\ +\
\fIt\fR\d\fIr\fR\u
.LP
and if \fIt\fR\d\fIr\fR\uhas its minimum value \fIt\d1\u\ +\ \fIt\d2\u\
\(=\ \fIt\d4\u\ +\
\fIt\d5\u\ +\ 13\ ms.
.PP
This inequality indicates that the time for detecting loss of
pilot plus the time needed for setting bit \fIb\fR to 1 after loss of pilot
detection by the transmultiplexer must be less than the response time of the
signalling tone receiver in the transmultiplexer plus the transfer time
of line signal plus\ 13\ ms.
.bp
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 4\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBIN\(hyBAND\ LINE\ SIGNALLING\ FOR\ 3\ kHz\ SPACED\ CHANNELS\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 4''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 4    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBLine signalling code\fR
.sp 1P
.RT
.sp 1P
.LP
1.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
For 3\ kHz spaced carrier circuits, an in\(hyband line signalling
system is necessary. For this purpose the line signalling of Signalling
System No.\ 4 (Recommendations\ Q.121, \(sc\(sc\ 2.1, 2.2, 2.3 and\ Q.122)
must be used.
.RT
.LP
.sp 1P
.LP
1.2
    \fILine signals\fR
.sp 9p
.RT
.PP
The following line signals of Signalling System No.\ 4 are necessary in
combination with Signalling System\ R2 interregister signalling.
.RT
.sp 1P
.LP
1.2.1
    \fIForward signals\fR
.sp 9p
.RT
.LP
    \(em
     Terminal seizing: in case of transit this is indicated by the interregister
signalling;
.LP
    \(em
     Forward\(hytransfer: although the forward\(hytransfer facility is not
provided in Signalling System\ R2, it can be used when
Recommendation\ Q.400, \(sc\ 1.1.3 is implemented;
.LP
    \(em
    Clear\(hyforward.
.sp 1P
.LP
1.2.2
    \fIBackward signals\fR
.sp 9p
.RT
.LP
    \(em
    Answer,
.LP
    \(em
    Clear\(hyback,
.LP
    \(em
    Release\(hyguard,
.LP
    \(em
    Blocking,
.LP
    \(em
    Unblocking: this signal is not separately defined in the
Specifications of Signalling System\ R2, but it is similar to
restoring the tone (see Recommendation\ Q.412,
\(sc\ 2.2.2.5).
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 5\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBLINE\ SIGNALLING\ (ANALOGUE\ VERSION)\ WITH\ METERING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 5''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 5    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
Signalling System\ R2 may be used as an integrated signalling system for
national and international traffic in a national network. Under certain
conditions it is desirable to have additional line signals available, and in
particular a metering signal in order to permit the charging of national
calls and international calls generated in the national network concerned.
.PP
This supplement to the specifications of Signalling System\ R2 deals
only with the clauses for exchange line signalling equipment which has been
changed in order to take care of the addition of new operating conditions
created by the additional metering signals and related only to the requirements
of a national network. The conditions of the interruption control have
been
adapted accordingly.
.PP
The transmission of the metering signal can be extended over a maximum
of three links between the subscriber exchange and the exchange where the
charging equipment has been installed.
.RT
.sp 2P
.LP
\fB2\fR     \fBLine conditions\fR
.sp 1P
.RT
.PP
Taking into account the time sequence, the circuit will have the
seven characteristic operating conditions shown in Table\ 1.
.bp
.RT
.LP
.rs
.sp 13P
.ad r
\fBTABLE 1 p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR     \fBClauses for exchange line signalling equipment\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIRecognition time for transition of signalling condition\fR
.sp 9p
.RT
.PP
The recognition time for a changed condition (transition from
tone\(hyon to tone\(hyoff or vice versa) is 40\ \(+-\ 10\ ms according
to the decisions
taken by Study Group\ XI of the CCITT. The definition of the recognition
time is indicated in Recommendation\ Q.412, \(sc\ 2.2.1.
.RT
.sp 2P
.LP
3.2
    \fINormal operating conditions\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
Except for the states, metering and forced release, the other
states (seizure, answered, release, blocking and release\(hyguard) follow the
same states as those indicated in Recommendation\ Q.412, \(sc\ 2.2.2. Instead
of the situation \*Qrelease in clear\(hyback state\*U a situation \*Qrelease in
forced release state\*U is possible.
.RT
.LP
.sp 1P
.LP
3.2.2
    \fIMetering\fR
.sp 9p
.RT
.PP
The metering signals are pulse\(hytype signals transmitted backwards during
the conversation on a link\(hyby\(hylink basis. They are the only signals
for which a repetition of the actual signal in a link\(hyby\(hylink basis
is necessary in order to avoid an inacceptable distortion of the metering
signals.
.PP
For the meter pulses the following limits have to be
respected:
.RT
.LP
    \(em
    sending:\ 120\(hy180\ ms;
.LP
    \(em
    recognition time between the
recognized transitions at the receiving side:\ 60\(hy90\ ms.
.PP
For the interval between metering signals, the following sending limit
has to be observed: minimum 300\ ms.
.PP
The time at the sending end between the answer signal and the start of
the first metering signal and between the end of the last metering signal
and the start of the forced release signal shall be more than 300\ ms.
.RT
.LP
.sp 1P
.LP
3.2.3
    \fIForced release\fR  | see Figures 1 and 2)
.sp 9p
.RT
.PP
When the called subscriber clears at the end of a call, the
exchange which controls the connection will receive the clear\(hyback signal
from the called subscriber's end. If the calling subscriber does not clear
within a period defined by the Administration concerned for national traffic,
and
according to Recommendation\ Q.118 for international traffic, the controlling
exchange stops metering, transmits forced release to the preceding exchange
and clears forward the succeeding part of the connection. In the preceding
exchange, the forced released signal will only be recognized after 300\ ms or
more in order to avoid confusion with a metering signal.
.bp
.PP
After recognition of the forced release signal in the originating
exchange, the tone\(hyon condition will be transmitted forwards and the part of
the connection to the controlling exchange will be released.
.PP
The release procedure is identical to the one specified for the
analogue version of the line signalling.
.PP
There is no forced release in case of no reception of the answer
signal in the controlling exchange following an address\(hycomplete signal.
After a period defined by the Administration concerned for national traffic,
and
according to Recommendation\ Q.118 for international traffic the controlling
exchange sends busy tone to the calling subscriber and sends clear\(hyforward
to release the succeeding part of the connection.
.RT
.LP
.rs
.sp 18P
.ad r
\fBFigure 1 p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 2 p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB4\fR     \fBMode of operation of interruption control\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
Generally speaking, it can be said that the mode of operation of
the interruption control complies with the specifications of Signalling
System\ R2, and in particular with Recommendation\ Q.416. However, it is
necessary to define the work of operation of the interruption control for
the following conditions:
.RT
.LP
    a)
    circuit in answered state (metering in the
backward direction);
.LP
    b)
    circuit in forced release state.
.sp 1P
.LP
4.2
    \fIMode of operation of interruption control at the incoming end\fR
\fI(transmission interrupted in the forward direction)\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    \fICircuit in answered state\fR
.LP
    Transition of interruption control to alarm brings about:
.LP
    i)
    locking of the sending unit in its position, i.e. in the
tone\(hyoff condition; if, at the moment of operation of interruption control
the tone\(hyon condition existed on the backward direction (metering signal),
it will be locked in the tone\(hyoff condition;
.LP
    ii)
    locking of the receiving unit in its position, i.e. in the
tone\(hyoff condition.
.LP
    The other conditions are also in agreement with the specifications
described in Recommendation\ Q.416, \(sc\ 2.4.2.1 | ).
\v'3p'
.LP
    b)
    \fICircuit in forced release state (transmission of\fR
\fIforced release signal in backward direction)\fR
.LP
    Transition of interruption control to alarm brings about:
.LP
    i)
    locking of the sending unit in its position, i.e. in the
tone\(hyon condition;
.LP
    ii)
     locking of the receiving unit in its position, i.e.\ in the tone\(hyoff
condition;
.LP
    iii)
    immediate release of the part of the connection beyond
faulty circuit (including the called subscriber's line).
.LP
    The conditions are similar to the specifications described in
Recommendation\ Q.416, \(sc\ 2.4.2.1 | ), \*Qclear\(hyback state\*U.
.LP
.sp 1P
.LP
4.3
     \fIMode of operation of the interruption control at the outgoing end\fR
\fI(transmission in the backward direction interrupted)\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    \fICircuit in answered state\fR
.LP
    In this case, transition of the interruption control to alarm
does not cause immediate action. A clear\(hyforward signal sent on
the part of the connection preceding the faulty circuit must be
repeated forward to ensure that, if the forward signalling channel
is left intact, the part beyond the faulty circuit is cleared.
.LP
    Once the interruption control reverts to normal, the
connection is maintainted provided the caller and the called
subscriber are still holding. On the other hand, by the time the
interruption control reverts to normal, the clear\(hyforward signal
may already have been sent and the situation will be the one
described under circuit seized but not in answered
state.
\v'3p'
.LP
    b)
    \fICircuit in forced release state (transmission\fR
\fIforced release signal in backward direction)\fR
.LP
    Transition of interruption control to alarm causes locking
of the receiving unit in its position, i.e.\ the tone\(hyon
condition. The procedures are similar to those in the position
\*Qclear\(hyback state\*U in the specifications of the analogue version
of the line signalling, Recommendation\ Q.416,
\(sc\ 2.4.2.2\ b).
.bp
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 6\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBLINE SIGNALLING (DIGITAL VERSION) WITH METERING\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 6''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 6    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
Signalling System R2 line signalling, digital version, is a line
signalling system for use over digital line transmission equipment conforming
to Recommendation\ G.732.
.PP
For many national applications it is desirable that the digital
version has additional line signals available to enable the charging of calls.
.PP
This supplement proposes possible solutions to provide for charging of
calls, namely the provision of a meter signal and a forced release signal.
.RT
.sp 2P
.LP
\fB2\fR     \fBSignal codes\fR
.sp 1P
.RT
.PP
The signalling codes are given in the Table\ 1 below.
.RT
.LP
.ce
\fBH.T. [A/T1]\fR
.ce
TABLE\ 1
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(96p) | cw(18p) sw(18p) sw(18p) sw(18p) , ^  | c s | c
^  | c | c | c | c.
State of the circuit    Signalling Code
    Forward    Backward    a f    b f    a b    b b
_
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Idle/released    1    0    or  1    or  0
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Seized    0    0    or  1    or  0
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Seizure acknowledged    0    0    or  1    or  1
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Answered/meter    0    0    or  0    or  1
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Meter/seizure acknowledged    0    0    or  1    or  1
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Clear\(hyforward    1    0    or  0    or  1
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
            or 1    or  1
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
            or 0    or  0
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Forced release    0    0    or  0    or  0
.T&
lw(96p) | cw(18p) | cw(18p) | cw(18p) | cw(18p) .
Blocked    1    0    or  1    or  1
_
.TE
.nr PS 9
.RT
.ad r
\fBTable [A/T1], p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR     \fBChoice of meter codes\fR
.sp 1P
.RT
.PP
Some line signalling systems indicate a meter pulse by a signal
identical to a \*Qpulsed clear\(hyback\*U, signal. In this circumstance
for ease of
signal conversion a\db\u\ =\ 1, b\db\u\ =\ 1, which normally indicates
clear\(hyback,
may be used to represent a meter pulse. Other signalling schemes however
use a \*Qpulsed answer\*U signal to indicate a meter pulse. In this circumstance
a\db\u\ =\ 0, b\db\u\ =\ 1 may be used to represent a meter pulse.
.RT
.sp 2P
.LP
\fB4\fR     \fBClauses for exchange line signalling equipment\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fINormal operating conditions\fR
.sp 9p
.RT
.PP
The following operating conditions apply in addition to those
described in Recommendation\ Q.422.
.RT
.PP
4.1.1
\fIMeter:\fR  | etering signals are pulse type signals transmitted backwards
during the conversation from the call charging point to the
subscriber's call meter in the originating exchange.
.bp
.sp 9p
.RT
.LP
.PP
In the case of \*Qpulsed clear\(hyback\*U meter pulses, a pulse is
indicated by a change from the answer (a\db\u\ =\ 0, b\db\u\ =\ 1) signal to an
a\db\u\ =\ 1, b\db\u\ =\ 1 signal and then a change back to a\db\u\ =\
0, b\db\u\ =\ 1. To avoid confusion between meter pulses and clear\(hyback
the use of clear\(hyback is
not allowed.
.PP
In the case of \*Qpulsed answer\*U meter pulses, a pulse is indicated by
a change of a\db\u\ =\ 1, b\db\u\ =\ 1 to a\db\u\ =\ 0, b\db\u\ =\ 1 and
back to a\db\u\ =\ 1, b\db\u\ =\ 1. The first pulse indicates answer, it
may also indicate a meter
pulse. A clear\(hyback signal is not provided.
.PP
Meter pulses must be longer than 30\ ms to ensure recognition at the
outgoing end.
.RT
.LP
.PP
4.1.2
\fIForced release:\fR  | rior to answer and after a period defined by the
Administration concerned for national traffic and according to
Recommendation\ Q.118 for international traffic, the charge controlling
exchange transmits the forced release signal to the preceding exchange and
clears forward the succeeding part of the connection. When the called
subscriber clears at the end of a call, the exchange which controls call
charging will receive the clear\(hyback signal from the called subscriber's
end. If the calling subscriber does not clear within a period defined for
national traffic by the Administration concerned and for international
traffic according to Recommendation\ Q.118, the charge controlling exchange
stops metering,
transmits the forced release signal to the preceding exchange and clears
forward the succeeding part of the connection. A forced release signal is
indicated by a change to a\db\u\ =\ 0, b\db\u\ =\ 0.
.sp 9p
.RT
.PP
On recognition of forced release in a preceding exchange the
connection is released, the forced release signal repeated to any other
preceding exchanges, and a clear forward signal sent on the link. The
succeeding exchange, on receipt of the clear forward, returns an idle signal
and returns the link to the idle state.
.PP
Figure 1 shows line signals for a sequence of meter pulses followed by
forced release in the case of \*Qpulsed clear\(hyback\*U meter pulses.
.RT
.sp 1P
.LP
4.2
    \fIActions appropriate to various signalling conditions\fR
.sp 9p
.RT
.PP
Tables\ 2 and\ 3 indicate the states appropriate to each signalling code
recognized and the actions to be taken at the outgoing and incoming ends
respectively.
.RT
.LP
.rs
.sp 27P
.ad r
\fBFigure 1, p.15\fR
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [A/T2]\fR
.ce
TABLE\ 2
.ce
\fBOutgoing end\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(36p) | cw(36p) sw(36p) sw(36p) sw(36p) , ^  | ^  | c | c | c | c.
 {
Normal state at the outgoing end
 }    Sent code    Received code
        a b\ =\ 0,\ b b\ =\ 0    a b\ =\ 0,\ b b\ =\ 1    a b\ =\ 1,\ b b\ =\ 0    a b\ =\ 1,\ b b\ =\ 1
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Idle/released    a f\ =\ 1,\ b f\ =\ 0    Abnormal,  see Note 1    Abnormal,  see Note 1    Idle    Blocked
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Seized    a f\ =\ 0,\ b f\ =\ 0    Abnormal,  see Note 2    Abnormal,  see Note 2    Seized,  see Note 2    Seizure acknowledged
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Seizure acknowledged    a f\ =\ 0,\ b f\ =\ 0    Forced release    Answered/ meter    Abnormal,  see Note 3    Seizure acknowledged
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
 {
Answered | ua\d\u)\d/meter | ub\d\u)\d
 }    a f\ =\ 0,\ b f\ =\ 0    Forced release    Answered/ meter    Abnormal,  see Note 4    Meter/seizure acknowledged
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
 {
Meter | ua\d\u)\d/seizure acknowledged | ub\d\u)\d
 }    a f\ =\ 0,\ b f\ =\ 0    Forced release    Answered/ meter    Abnormal,  see Note 4    Meter/seizure acknowledged
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Forced release    a f\ =\ 0,\ b f\ =\ 0    Forced release,  see Note\ 5    Abnormal,  see Note 5    Abnormal,  see Note 5    Abnormal,  see Note 5
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Clear\(hyforward    a f\ =\ 1,\ b f\ =\ 0    Clear\(hyforward    Clear\(hyforward    Released =  Idle    Clear\(hyforward
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Blocked    a f\ =\ 1,\ b f\ =\ 0    Abnormal,  see Note 1    Abnormal,  see Note 1    Idle    Blocked
.TE
.LP
\ua\d\u)\d\ Used for \*Qpulsed clear\(hyback\*U meter pulses.
.LP
\ub\d\u)\d\ Used for \*Qpulsed answer\*U meter pulses.
.LP
\fINote\ 1\fR
\ \(em\ In these conditions the outgoing end must prevent a new
seizure of the circuit. A delayed alarm should also be given.
.LP
\fINote\ 2\fR
\ \(em\ Non\(hyrecognition of the seizing acknowledgement signal
100\(hy200\ ms after sending the seizing signal on a terrestrial link or
1\(hy2\ seconds after sending the seizing signal on a satellite link results in
an alarm and either congestion information being sent backward or a repeat
attempt being made to set up the call. The outgoing end must prevent a new
seizure of the circuit. When the seizure acknowledgement signal is recognized after the time\(hyout period has elapsed, the clear\(hyforward signal must be sent.
.LP
\fINote\ 3\fR
\ \(em\ Receipt of a
b\ =\ 1,\ b
b\ =\ 0 by the outgoing switching
equipment for 1\(hy2\ seconds after recognition of the seizing acknowledgement
signal and prior to recognition of the answer signal, results in an alarm and either congestion information being sent backward or a repeat attempt being
made to set up the call. The outgoing end must prevent new seizures of the
circuit. When b
b reverts to 1 after the 1\(hy2\ seconds time\(hyout period has
elapsed, the clear\(hyforward signal must be sent.
.LP
\fINote\ 4\fR
\ \(em\ In the case of recognition of a
b\ =\ 1,\ b
b\ =\ 0 whilst in
the answered state, immediate action is not necessary.
On\ receipt of
clearing from the preceding link, the clear\(hyforward signal (a
f\ =\ 1,
b
f\ =\ 0) must not be sent until b
b is restored to 1.
A\ delayed alarm
should also be given.
.LP
\fINote\ 5\fR
\ \(em\ After forced release is recognized, the outgoing switching
equipment must be released and then the idle signal (a
f\ =\ 1,\ b
f\ =\ 0)
sent on the link. The outgoing end must prevent a new seizure on the circuit
until the link returns to the idle state upon reception of a
b\ =\ 1,
b
b\ =\ 0. The forced release signal must be sent on the preceding link
(if any).
.nr PS 9
.RT
.ad r
\fBTableau [A/T2], p.16\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 4P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [A/T3]\fR
.ce
TABLE\ 3
.ce
\fBIncoming end\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(36p) | cw(36p) sw(36p) sw(36p) sw(36p) , ^  | ^  | c | c | c | c.
 {
Normal state at the incoming end
 }    Sent code    Received code
        a f\ =\ 0,\ b f\ =\ 0    a f\ =\ 0,\ b f\ =\ 1    a f\ =\ 1,\ b f\ =\ 0    a f\ =\ 1,\ b f\ =\ 1
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Idle/released    a b\ =\ 1,\ b b\ =\ 0    Seized    Fault,  see Note 1    Idle    Fault,  see Note 1
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Seizure acknowledged    a b\ =\ 1,\ b b\ =\ 1    Seizure acknowledged    Fault,  see Note 2    Clear\(hyforward    Fault,  see Note 2
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
 {
Answered | ua\d\u)\d/meter | ub\d\u)\d
 }    a b\ =\ 0,\ b b\ =\ 1    Answered/ meter    Fault,  see Note 3    Clear\(hyforward    Fault,  see Note 3
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
 {
Meter | ua\d\u)\d/seizure acknowledged | ub\d\u)\d
 }    a b\ =\ 1,\ b b\ =\ 1    Meter/seizure acknowledged    Fault,  see Note 3    Clear\(hyforward    Fault,  see Note 3
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Forced release    a b\ =\ 0,\ b b\ =\ 0    Forced release    Fault,  see Note 8    Clear\(hyforward  see Note 4    Fault,  see Note 8
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Clear\(hyforward     {
a
b\ =\ 0,\ b
b\ =\ 1
or
a
b\ =\ 1,\ b
b\ =\ 1
 }    Abnormal seized  see Note 7    Fault,  see Note 7    Clear\(hyforward  see Note 7    Fault,  see Note 7
_
.T&
lw(48p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Blocked    a b\ =\ 1,\ b b\ =\ 1    Abnormal seized  see Note 5    Fault,  see Note 6    Blocked    Fault, see Note 6
.TE
.LP
\ua\d\u)\d\ Used for \*Qpulsed clear\(hyback\*U meter pulses.
.LP
\ub\d\u)\d\ Used for \*Qpulsed answer\*U meter pulses.
.LP
\fINote\ 1\fR
\ \(em\ When in the idle/released state b
f changes to 1,
b
b must be changed to\ 1.
.LP
\fINote\ 2\fR
\ \(em\ In these cases a timeout device is started which after a
certain interval clears the connection beyond the faulty circuit: this
timing arrangement may be the one specified in Recommendation\ Q.118,
\(sc\ 4.3.3. If the answer signal is recognized during the timeout delay, the
timer is stopped but the answer signal is not sent on the preceding link until recognition of a
f\ =\ 0,\ b
f\ =\ 0. If the clear\(hyback signal is recognized
while the fault persists, the connection beyond the faulty circuit must be
released immediately. Additionally, when the incoming register has not
started to send the last backward signal, the rapid release procedure
described in Note\ 5 may be used.
.LP
\fINote\ 3\fR
\ \(em\ In these cases no action is taken until the forced release
signal or the clear\(hyback signal (if the exchange is the call metering
control point) is recognized, at which stage the connection beyond the
faulty circuit is immediately released and the forced release signal
sent to the preceding exchange.
.LP
\fINote\ 4\fR
\ \(em\ After a
f = 1, b
f = 0 is recognized, the circuit is
returned to the idle state by sending a
b\ =\ 1,\ b
b\ =\ 0.
.LP
\fINote\ 5\fR
\ \(em\ In this case, immediate action is not necessary. However,
rapid release of the circuit should occur if the incoming end simulates
answer by sending a
b\ =\ 0,\ b
b\ =\ 1.
.LP
\fINote\ 6\fR
\ \(em\ Under these conditions no action is taken.
.LP
\fINote\ 7\fR
\ \(em\ After clear\(hyforward signal is recognized and until the code
a
b\ =\ 1,\ b
b\ =\ 0 is sent, all transitions in the forward direction
shall be ignored.
.LP
\fINote\ 8\fR
\ \(em\ The circuit is kept in the forced release state until
a
f\ =\ 1,\ b
f\ =\ 0 is recognized.
.nr PS 9
.RT
.ad r
\fBTableau [A/T3], p.17\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 7P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB5\fR     \fBProtection against the effects of faulty transmission\fR
.sp 1P
.RT
.sp 1P
.LP
5.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
When faulty transmission conditions in PCM systems are detected
both PCM terminals apply the state corresponding to state 1 on the PCM
line on each \*Qreceive\*U signalling channel at the interface with the
switching
equipment, as indicated in Table\ 4 of Recommendation\ G.732. In this way the
incoming switching equipment receives the equivalent a\df\u\ =\ 1, b\df\u\
=\ 1 on
the PCM line and the outgoing switching equipment receives the equivalent of
a\db\u\ =\ 1, b\db\u\ =\ 1.
.RT
.sp 1P
.LP
5.2
    \fIIncoming switching equipment\fR
.sp 9p
.RT
.PP
At the incoming end a PCM fault results in a\df\u\ =\ 1, b\df\u\ =\ 1:
so this fault can be identified and appropriate actions according to Table\ 3
can be taken.
.RT
.LP
.sp 1P
.LP
5.3
    \fIOutgoing switching equipment\fR
.sp 9p
.RT
.PP
At the outgoing end a PCM fault results in a\db\u\ =\ 1, b\db\u\ =\ 1.
.PP
Two cases are to be considered:
.RT
.LP
    a)
    Meter pulses are indicated by a\db\u\ =\ 0, b\db\u\ =\ 1
.LP
     A fault results, as it is stated in Table\ 2, in a blocked state or seizure
acknowledged state. This means that all circuits in the idle state of a
faulty PCM multiplex will be blocked and that seized circuits will go to
or
remain in the seizure acknowledged state.
.LP
    b)
    Meter pulses are indicated by a\db\u\ =\ 1, b\db\u\ =\ 1
.LP
     A PCM fault will result in the recognition of a meter pulse each time
a failure appears. To avoid this recognition, the outgoing switching
equipment must handle the service alarm information given by the PCM terminal
equipment in a separate way.
.LP
    When the outgoing switching equipment detects a service alarm
information it must block the detection of signalling
transitions to avoid recognition of erroneous signalling codes
caused by the failure.
.LP
    The reception of a clear\(hyforward signal on the preceding link or
the detection of the calling subscriber's release will cause,
after the end of the PCM failure, the sending of a clear\(hyforward
signal on the succeeding part of the connection.
.sp 2P
.LP
\fB6\fR     \fBBothway working\fR
.sp 1P
.RT
.PP
The additions described in this contribution do not affect the
suitability of the digital version for bothway use.
.RT
.LP
.sp 2P
.LP
\fBSupplement\ No.\ 7\fR
.RT
.sp 2P
.ce 1000
\fBSEMI\(hyCOMPELLED\ AND\ NON\(hyCOMPELLED\ MULTIFREQUENCY\ INTERREGISTER\fR
.EF '%    Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 7''
.OF '''Fascicle\ VI.4\ \(em\ Suppl.\ No.\ 7    %'
.ce 0
.ce 1000
\fBSIGNALLING\ FOR\ NATIONAL\ SATELLITE\ APPLICATIONS\ BASED\ ON\ SYSTEM\
R2\fR
.ce 0
.sp 1P
.ce 1000
\fBINTERREGISTER\ SIGNALLING\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
1.1
The Semi\(hyCompelled and Non\(hyCompelled Multifrequency
Signallings, herein specified and based on Signalling System\ R2
(Fully\(hyCompelled Signalling), make use of a pulse signal sending procedure
and are supposed to increase signalling speed on national satellite circuits.
Their application is restricted to those cases in which the consequences
of increased propagation times over Fully\(hyCompelled Signalling may bring
about insolvable
technical problems for the national network, may make impossible the retention
of the information capabilities and facilities provided by that signalling
or may make rather expensive the operation of circuits.
.sp 9p
.RT
.PP
This may occur in national networks which have a large number of satellite
circuits, e.g.\ when national satellites are used.
.bp
.PP
1.2
Parameters related to operation of national networks may be
affected by great increase in satellite propagation time, compared with the
terrestrial value, such as:
.sp 9p
.RT
.LP
    \(em
    increase in the holding times of the telecommunications
network;
.LP
    \(em
    increase post\(hydialling delay;
.LP
    \(em
     increased amount of equipment to handle the same traffic and consequently
larger space taken up by equipment;
.LP
    \(em
    the maximum capacity of exchanges is reached at lower traffic values.
.PP
The negative effect over those parameters implies a loss in
service quality and an increase in investments made in national networks.
.PP
Better performances may be obtained through the Semi\(hyCompelled
Multifrequency Signalling, which speeds up the process of interchange of
signals via satellite.
.RT
.LP
.PP
1.3
In some cases, the characteristics of national networks where the features
of the Signalling System R2 are fully used may require that the
process of interchange of signals via satellite must be still more accelerated
so that delays may be kept within certain limits, otherwise those
characteristics should be changed. Some of the said characteristics are the
following:
.sp 9p
.RT
.LP
    \(em
    time\(hyout requirements;
.LP
    \(em
    routing plan;
.LP
    \(em
    charging method;
.LP
    \(em
    sending of complete calling subscriber number (total
identification of calling subscriber);
.LP
    \(em
    information about called subscriber condition by means of
Group\ B signals, instead of simple Address\(hyComplete signal
(signal\ A\(hy6);
.LP
    \(em
    traffic restriction through analysis of calling subscriber
category in destination (Group\ II signal in acknowledgement to signal\
A\(hy3).
.LP
.PP
Relative to the above\(hymentioned cases, the choice falls on the
Non\(hyCompelled Multifrequency Signalling which allows a substantial increase
in speed as regards signal interchange.
.PP
1.4
Unlike the Fully\(hyCompelled Multifrequency Signalling, the
Semi\(hyCompelled and Non\(hyCompelled Signal
lings here described permit that,
within
certain particular limitations, the characteristics, facilities and mode of
operation (including network management) already existing in the national
networks which use Signalling System\ R2 may be maintained, making possible
the operation of satellite circuits with an information interchange rate
similar to that of Signalling System\ R2 which operates on the terrestrial
links.
.sp 9p
.RT
.sp 2P
.LP
\fB2\fR     \fBLine signalling\fR
.sp 1P
.RT
.PP
The line signalling to be used together with the Non\(hyCompelled
Interregister Signalling must include a Proceed\(hyto\(hySend signal.
.PP
All remaining signals may be used in the original form.
.PP
As for digital circuits, line signalling\(hydigital version of Signalling
System\ R2 may be fully used. The seizing acknowledgement signal in this
application is used as Proceed\(hyto\(hySend indication.
.PP
A pulsed line signalling which presents an excellent performance over terrestrial
or satellite links and can be used with Non\(hyCompelled Signallings is
specified in \(sc\ 4.
.RT
.sp 2P
.LP
\fB3\fR     \fBInterregister signalling\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The Semi\(hyCompelled and Non\(hyCompelled Multifrequency Signallings
here specified basically show the same characteristics and facilities existing
in the Fully\(hyCompelled Multifrequency Signalling used with Signalling
System\ R2, except, obviously, the way of sending and receiving MF signals.
.PP
This Supplement specifies only the characteristics and facilities
which differ from those foreseen in Specifications of Signalling System\
R2 and the meanings of some signals which are used in a different way from
that
system.
.bp
.RT
.LP
.sp 2P
.LP
3.2
    \fISemi\(hyCompelled Signalling\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
The Semi\(hyCompelled Signalling over satellite links can be usually used
in the end\(hyto\(hyend method, between the signalling equipment of the
origin of the call and the signalling equipment at the incoming end of
the satellite link, as recommended in Specifications of Signalling System\
R2 except when, for charging or management reasons, the signalling equipment
at the outgoing end of the satellite link is not released until the complete
setting\(hyup of the call.
.PP
The pulsed form of sending backward signals (Groups\ A and\ B) is the
only difference that such signalling presents in relation to Specifications
of Signalling System\ R2.
.RT
.sp 1P
.LP
3.2.2
    \fIPulse duration\fR
.sp 9p
.RT
.PP
As regards backward signals, pulse duration corresponds to
100\ \(+-\ 20\ ms.
.RT
.sp 1P
.LP
3.2.3
    \fIComposition of the Groups of Signals\ I and\ II (forward) and\ A\fR
\fIand\ B (backward) and Meaning of the Signals\fR
.sp 9p
.RT
.PP
The composition of the Groups of Signals and their respective
meanings are thoroughly identical with those foreseen in Signalling System\
R2, as well as combinations of frequencies which form the various signals.
.RT
.sp 1P
.LP
3.2.4
    \fIBuild\(hyup and Time Specifications of a Complete Forward\fR
\fISemi\(hyCompelled Signalling Cycle\fR
.sp 9p
.RT
.PP
Figure\ 1 shows in detail the build\(hyup and time sequence of a
semi\(hycompelled signalling cycle.
.PP
If the values of \fIT\fR \s6int |
.PS 10
and \fIT\fR \s6int |
.PS 10
lie within certain limits, they do not contribute to
the total duration of the semi\(hycompelled signalling cycle, as can be
seen from Figure\ 1. Then, the total duration \fIT\fR\dS\\dC\uof a complete
semi\(hycompelled signalling cycle is given by the formula:
\v'6p'
.RT
.LP
\fIT\fR \dSC
\u = \fIT\fR \dPF
\u + \fIT\fR \dPB
\u
+
@ left {  pile { { fIT\fR~dR~D~\u~+~\fIT\fR~\dO~A~\u } above { \fIT\fR~`~\dR~D~\u~+~\fIT\fR~`~\dO~A~\u } }  right } @
+ \fIT\fR \dint |
\u   + \fIT\fR \dS
1
D
\u +
\fIT\fR \dS
1
A
\u + \fIT\fR \dP\u
or
\v'9p'
.LP
.sp 1
.PP
The subscripts D and A apply respectively to the outgoing and the incoming
registers.
.PP
Considering the values established in Recommendation\ Q.457, \(sc\ 4.5.2
and assuming that:
\v'6p'
.RT
.sp 1P
.ce 1000
\fIT\fR \dS
1
D
\u +
\fIT\fR \dS
1
A
\u
= \fIT\fR \dS
1
\u + \fIT\fR \dS
2
\u and \fIT\fR \dP\u =
100 \(+- 20 ms,
.ce 0
.sp 1P
.LP
.sp 1
.LP
the probable extreme values of the semi\(hycompelled signalling cycle
\fIT\fR\dS\\dC\uwould be:
.sp 1P
.ce 1000
620 ms \(= \fIT\fR\dS\\dC\u\(= 840 ms
.ce 0
.sp 1P
.LP
3.2.5
    \fICall routing procedures\fR
.sp 9p
.RT
.PP
Whenever technically feasible, the overlap method may be used for call
routing.
.PP
The Semi\(hyCompelled Signalling is applied just like the Fully\(hyCompelled
Signalling (System R2), though there are minor restrictions towards its
use on satellite channels.
.RT
.sp 1P
.LP
3.2.6
    \fIOther characteristics of the Semi\(hyCompelled Signalling\fR
.sp 9p
.RT
.PP
As concerns other characteristics related with the signalling
(Multi\(hyfrequency Signalling Equipment, Time and Transmission
Requirements,\ etc.), Specifications of Signalling System\ R2 are
applicable.
.RT
.sp 2P
.LP
3.3
    \fINon\(hyCompelled Signalling\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
The Non\(hyCompelled Signalling over satellite links is used in the
link\(hyby\(hylink method between signalling equipment correspondent to
the outgoing and incoming ends of the satellite link.
.bp
.PP
The basic differences that such signalling shows in relation to
Specifications of Signalling System\ R2 are the way of sending signals
in both directions (those forward and backward signals are sent in the
form of pulses) and the non\(hyexistence of Group\ A of Signalling System\
R2.
.RT
.sp 1P
.LP
3.3.2
    \fIPulse duration and minimum pulse interval\fR
.sp 9p
.RT
.PP
Pulse duration corresponds to 100\ \(+-\ 20\ ms for both forward and
backward signals.
.PP
The minimum interval between two consecutive forward pulses is
100\ \(+-\ 20\ ms.
.RT
.sp 2P
.LP
3.3.3
     \fIComposition of the Groups of Signals (I, II and B) and Meaning\fR
\fIof the Signals\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.3.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The Non\(hyCompelled Signalling is composed of the Groups of Signals\ I
and\ II (forward signals) and\ B (backward signals) correspondent to the
same
Groups as those of Signalling System\ R2.
.PP
The Group\ A of backward signals of Signalling System\ R2 is unnecessary
by the following reasons:
.RT
.LP
    \(em
    The signalling equipment at the incoming end of the satellite
link operates as storage point for information coming from the
origin and operates without sending via satellite the signals
A\(hy1, A\(hy2, A\(hy3, A\(hy5, A\(hy7, A\(hy8, A\(hy11, A\(hy12, A\(hy13
and A\(hy14.
.LP
    \(em
     The meaning of signal A\(hy4 is transferred to Signal\ B\(hy9 (spare
for national use in the Fully\(hyCompelled Signalling System\ R2).
.LP
    \(em
     The use of signal A\(hy6 is not required. Signals of Group\ B can be
used. In case it is necessary to use the meaning of A\(hy6, it can
be allocated to Signal\ B\(hy10 (spare for national use in the
Fully\(hyCompelled Signalling System\ R2).
.LP
    \(em
    Signals A\(hy9 and A\(hy10 are spare for national use in the
Fully\(hyCompelled Signalling System\ R2.
.PP
The Groups of Signals I, II and B maintain the same structure
(including the same frequency combinations) as that used in the Fully\(hyCompelled
Signalling System\ R2, using the same signalling senders and receivers.
.PP
Some modifications, exclusions or inclusions in the meaning of some
signals in relation to the Fully\(hyCompelled Signalling System\ R2 allow the
Non\(hyCompelled Signalling the following facilities:
.RT
.LP
    \(em
    Sending of category and number of calling subscriber, through
positioning of Signals\ I\(hy12 and I\(hy15 respectively before and
after the sending of this complete information. Category
information can be transmitted only through that same procedure.
Such a method for sending the calling subscriber category and
number by means of Signals\ I\(hy12 and I\(hy15 is carried out in a
predetermined sequence between two successive digits of the
transmission of the called subscriber number.
.LP
.sp 1P
.LP
3.3.3.2
    \fIMeaning of the signals for national use\fR
.sp 9p
.RT
.PP
Only the signals which have shown some variation in relation to
their usual meanings in the Fully\(hyCompelled Signalling System\ R2 are
presented next.
.RT
.sp 1P
.LP
3.3.3.2.1
    \fIGroup I forward signals\fR \v'3p'
.sp 9p
.RT
.LP
I\(hy12
    It indicates that only the category or the category and the
number of the calling subscriber will follow.
.LP
I\(hy13
    a)
    Test call indicator.
.LP
    b)
    Access to test equipment (code\ 13).
.LP
    Both a) and b) have the same meanings as those of the
Fully\(hyCompelled Signalling System R2. The meaning \*QSatellite Link not
Included\*U was deleted.
.sp 1P
.LP
3.3.3.2.2
    \fIGroup B backward signals\fR \v'3p'
.sp 9p
.RT
.LP
B\(hy9
    Congestion in the national network (before changeover from
Group\ A signals to Group\ B signals in the Fully\(hyCompelled Signalling
System\ R2) or if time\(hyout in the signalling equipment at the destination
end of the satellite link has occurred.
.LP
B\(hy10
    Address\(hycomplete, charge, set\(hyup speech conditions (only if
destination equipment of the national network cannot send the usual
end\(hyof\(hyselection signals).
.bp
.sp 1P
.LP
3.3.4
    \fIConfigurations of the signalling network\fR
.sp 9p
.RT
.PP
The Non\(hyCompelled Signalling may be basically used:
.RT
.LP
    a)
    Between the Signalling Equipment of two Switching Exchanges
(Translation Points coincide with Switching Points).
.LP
    Signalling equipment of switching exchanges located at both ends
of the satellite links must be able to send and receive
Non\(hyCompelled Signalling, as illustrated in Figure\ 2.
.LP
    For that configuration, adequate functional changes are required
in the signalling equipment of those switching exchanges.
.LP
    b)
    Between Signalling Translation Equipment separated from the
Switching Exchanges (Translation Points do not coincide with
Switching Points).
.LP
    Signalling Translation Equipment is independent of signalling
equipment of switching exchanges. It may be installed near those
exchanges or in separate places, as illustrated in Figure\ 3.
.LP
    For that configuration, there is not any change in any equipment
of the national network, and the introduction of signalling
translators may be carried out just through the simple
interconnection with distribution frames.
.PP
\fINote\fR \ \(em\ A combined solution is also possible.
.sp 2P
.LP
3.3.5
    \fICall routing procedures\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.5.1
    \fIRelative to the starting point\fR
.sp 9p
.RT
.PP
There are no restrictions for applying the overlap method when
using the Non\(hyCompelled Signalling.
.PP
There are two main kinds of calls:
.RT
.LP
    a)
    Calls for subscribers from a national (or international)
numbering area different from that of the calling subscriber.
.LP
    The national (or international) prefix and code are to be
dialled.
.LP
    b)
     Calls for subscribers from the same numbering area as that of the calling
subscriber.
.LP
    The national (or international) prefix and code are not to
be dialled, but only the subscriber number.
.PP
In both cases a) and b), the starting point at the Signalling
Translation Point at the outgoing end of the satellite link occurs after
reception of the sufficient number of digits to route the call.
.PP
If configuration presented in \(sc\ 3.3.4\ b) (Signalling Translation
Equipment separated from the Switching Exchanges) is adopted, signals may be
sent forward as soon as they are received by the Signalling Translation
Equipment at the Signalling Translation Point.
.RT
.LP
.sp 1P
.LP
3.3.5.2
    \fIRelative to the sending sequence of Group I and II forward\fR
\fIsignals\fR
.sp 9p
.RT
.PP
The main cases concerning the sending sequence of non\(hycompelled
signals are the following:
.RT
.LP
    a)
    Calls with complete identification of the calling subscriber
number (i.e.\ for centralized toll ticketing).
.LP
    After reception of a sufficient number of digits of the
called
subscriber number to route the call, they may be sent \fIen bloc\fR .
Then, there is the sending of category and number of calling
subscriber, which are preceded and followed by signals\ I\(hy12 and
I\(hy15, respectively. Such signals can also be sent \fIen bloc\fR if
it does not contribute to delay routing procedures. After
reception of signal\ I\(hy15, the digits of the called subscriber
number continue to be sent so far as they are dialled and
available for sending (overlap method).
.LP
    A scheme corresponding to national calls is shown in Figure\ 4.
.LP
    b)
    Calls without complete identification of the calling
subscriber number.
.LP
    After reception of a sufficient number of digits of the called
subscriber number to route the call, they may be sent \fIen bloc\fR .
Then, there is the sending of the calling subscriber category,
which is preceded and followed by Signals\ I\(hy12 and I\(hy15,
respectively. Such signals can also be sent \fIen bloc\fR . After
reception of Signal\ I\(hy15, the digits of the called subscriber
number continue to be sent so far as they are dialled and
available for sending (overlap method).
.bp
.LP
    The scheme corresponding to that kind of call is identical with
that shown in Figure\ 4, however, without the signals
corresponding to the calling subscriber number (ID\ N\dj\u).
.LP
    \fINote\fR \ \(em\ As for international calls, the sending sequence
begins with the international prefix, which is followed by the
sufficient number of digits of the international number of the
called subscriber to route the call. The remaining sequence is
also similar to that used for national calls in Items\ a) and\ b)
above.
.PP
When configuration presented in \(sc\ 3.3.4\ b) (Signalling
Translation Equipment separated from the Switching Exchanges) is adopted,
signals may be sent forward as soon as they are received by the Signalling
Translation Equipment at the Signalling Translation Point, although the
relative position for sending the calling subscriber identification (between
two determined digits of called subscriber number) may be at any fixed point.
.PP
If the procedures for sending forward signals are defined for each
different type of call, a check towards reception of forward signals may be
made by the Signalling Equipment at the destination end of the satellite
link by simply counting the signals received. Signals\ I\(hy12 and I\(hy15
serve as
reference points.
.RT
.LP
.sp 1P
.LP
3.3.5.3
    \fIRelative to the sending of Group B backward signals\fR
.sp 9p
.RT
.PP
A Group B backward signal may be sent at any time during the period for
sending of Group\ I and\ II forward signals provided that there is a
condition which must require interruption of the call setting\(hyup process,
such as time\(hyout or congestion at any point of the national or international
network and non\(hyexistent national or international code or non\(hyexistent
exchange
prefix.
.RT
.sp 2P
.LP
3.3.6
    \fIOperational procedures of the system\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.6.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
The Non\(hyCompelled Signalling, based on the Signalling System\ R2, is
conceived for the purpose of making possible retention of the mode of
operation, facilities and other characteristics of a national network, which
uses the Signalling System\ R2, after introduction of telephone satellite
communications on a large scale. Modifications necessary for operation on
satellite links must be restricted only to equipment connected with the
involved links so as to avoid any undesirable effect on the remaining system.
.PP
The use of the Non\(hyCompelled Signalling requires modifications only
in the equipment connected with satellite links [\(sc\ 3.3.4\ a)]. Besides,
a
solution which will not interfere at all in the existing equipment may
be also adopted [\(sc\ 3.3.4\ b)].
.RT
.sp 1P
.LP
3.3.6.2
    \fIInterface procedures at the signalling translation points\fR
.sp 9p
.RT
.PP
Figure 5 shows the most general case concerning setting\(hyup of a
call via satellite by means of the Non\(hyCompelled Signalling in a national
network which operates with the Signalling System\ R2 and using configuration
of \(sc\ 3.3.4\ a).
.PP
The signalling equipment which precedes the Signalling Translation
Point at the outgoing end of the satellite link will operate with the
end\(hyto\(hyend method up to this point, at which the Fully\(hyCompelled
Signalling
will be converted into the Non\(hyCompelled Signalling.
.PP
The inverse conversion, that is, from the Non\(hyCompelled Signalling to
the Fully\(hyCompelled Signalling, will be performed at the Signalling
Translation Point at the incoming end of the satellite link, from which
signalling will become fully\(hyCompelled using the end\(hyto\(hyend method.
.PP
The procedures carried out towards call setting\(hyup by using the
Non\(hyCompelled Signalling are basically the following for national calls:
.PP
The Signalling Translation Point at the outgoing end of the satellite link
receives the sufficient number of digits to route the call
(ON\d1\u\ .\ .\ .\ N\di\u) and then starts (starting point) the procedures for
sending those digits forward in the form of pulses (it sends the Seizure
signal and receives the Proceed\(hyto\(hySend signal) and it sends digits
from 0 to N\di\u. The sending sequence continues through the sending of
Signal\ I\(hy12, which
determines the beginning of transmission of the category (CAT) and number
(ID\ N\dj\u) of the calling subscriber. Signal\ I\(hy15 follows after the
sending of the last digit of that subscriber number. Then, the sending
of the digits of
the called subscriber number (.\ .\ .\ N\dK\u\ .\ .\ .) succeeds up to
the last digit (N\dL\u).
.PP
The Signalling Translation Point at the outgoing end of the satellite link
starts call routing immediately after receiving the sufficient number of
digits, thus establishing a process of signalling with subsequent signalling
equipment in the end\(hyto\(hyend method up to reception
.bp
.PP
of Signal\ A\(hy3 and   an
End\(hyof\(hySelection signal (Group\ B Signal). At that moment, that last
signal is repeated backward in the form of pulse up to the Signalling Translation
Point at the outgoing end of the satellite link. The final signal interchange
is
carried out between that point and the preceding signalling equipment (A\(hy3,
CAT,\ B) and then the speech path is set up.
.PP
If there is no need to send the calling subscriber number, only the
category is sent forward and Signals\ I\(hy12 and I\(hy15 are maintainted
before and after the sending of that calling subscriber category, which
is used by the
Signalling Translation Point at the destination end in acknowledgement to
Signal\ A\(hy3 at the end of the call setting\(hyup procedure.
.PP
The signalling process may be interrupted at any time by a Group\ B
signal, as explained in \(sc\ 3.3.5.3.
.PP
\fINote\fR \ \(em\ As for international calls, procedures include receiving
of international prefix and international code, but they are similar to
those used for national calls.
.PP
If configuration presented in \(sc\ 3.3.4\ b) (Signalling Translation
Equipment separated from the Switching Exchanges) is adopted, signals in
both outgoing and incoming Signalling Translation Equipment at the Signalling
Translation Points may be sent forward as soon as they are received by
Signalling Translation Equipment.
.RT
.sp 1P
.LP
3.3.7
    \fIMultifrequency signalling equipment\fR
.sp 9p
.RT
.PP
Recommendations for Signalling System\ R2 other than for exclusive use
in Fully\(hyCompelled Signalling are applicable to Non\(hyCompelled Signalling.
Thus, the requirements related to transmission and to the sending and receiving
parts of the multifrequency equipment may be applied to that signalling.
The
same signal senders and receivers specified for Signalling System\ R2 may be
used.
.PP
The use of such signal senders and receivers avoids the development of
new equipment, and they will operate easily in relation to their sending
and
receiving characteristics, taking into consideration that they have been
dimensioned for end\(hyto\(hyend operation, but with Non\(hyCompelled Signalling
they
operate link\(hyby\(hylink.
.RT
.sp 2P
.LP
3.3.8
    \fITime requirements\fR
.sp 1P
.RT
.sp 1P
.LP
3.3.8.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
As Non\(hyCompelled Signalling is performed to operate between two
signalling points inserted in a multi\(hypoint signalling network using
Signalling System\ R2, time requirements should be compatible with the
specifications for this system.
.RT
.sp 1P
.LP
3.3.8.2
    \fITime\(hyout conditions\fR \v'3p'
.sp 9p
.RT
.LP
    a)
    In the signalling equipment at the outgoing end of the
satellite link, the time\(hyout delay between the Seizing signal and the
sending of the first forward interregister signal and between the sending
of each two subsequent forward interregister signals until the reception
of the Group\ B
signal should not be less than\ 24\ s.
.LP
    b)
    In the signalling equipment at the incoming end of the
satellite link, the time\(hyout delay between the sending of the Proceed\(hyto\(hySend
signal and the reception of the first forward interregister signal and
between the reception of each two subsequent forward interregister signals
until the
sending of the Group\ B signal should not be less than 24\ s.
.LP
.sp 2P
.LP
\fB4\fR     \fBPulsed line signalling\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
    \fIIntroduction\fR
.sp 9p
.RT
.PP
The line signalling herein presented and foreseen to be used in FDM carrier
circuits is a pulsed, high level, out\(hyof\(hyband signalling which operates
link\(hyby\(hylink. It may also be used on PCM systems (with channel\(hyassociated
signalling).
.RT
.sp 1P
.LP
4.2
    \fIDescription of the signals\fR \v'3p'
.sp 9p
.RT
.PP
4.2.1
\fISeizure Signal\fR \ \(em\ It is a signal which is sent forward, from
the outgoing junctor, in order to drive the associate incoming junctor
to the
seizure condition.
.PP
4.2.2
\fIProceed\(hyto\(hySend Signal\fR \ \(em\ It is a signal which is sent
backward, from the incoming junctor to the associate outgoing junctor,
in order to
indicate that a destination interregister signalling equipment has been
already seized and that interregister signalling may start.
.bp
.PP
4.2.3
\fIAnswer Signal\fR \ \(em\ It is a signal which is sent backward, from
the incoming junctor to the associate outgoing junctor, so as to indicate
that the called subscriber has answered.
.LP
.PP
4.2.4
\fIClear Back Signal\fR \ \(em\ It is a signal which is sent backward,
from the incoming junctor to the associate outgoing junctor, so as to indicate
that the called subscriber has hung up or that a similar operation has
occurred.
.PP
4.2.5
\fIClear Forward Signal\fR \ \(em\ It is a signal which is sent forward,
from the outgoing junctor to the associate incoming junctor, in order to
release the equipment involved in the connection.
.PP
4.2.6
\fIRelease Guard Signal\fR \ \(em\ It is a signal which is sent backward,
from the incoming junctor to the associate outgoing junctor, in response
to a Clear Forward signal, so as to indicate that the release of equipment
associated to the incoming junctor has occurred.
.PP
4.2.7
\fIForced Release Signal\fR \ \(em\ It is a signal which substitutes, after
time\(hyout, the Clear Back signal at a charging point. With reception
of Forced Release signal, the speech path is immediately opened.
.PP
4.2.8
\fIMultimetering Signal\fR \ \(em\ It is a signal which is sent backward,
from the incoming junctor to the associate outgoing junctor, according
to the cadence corresponding to the charging rate, as from the multimetering
charging point.
.LP
.PP
4.2.9
\fICall\(hyBack Signal\fR \ \(em\ It is a signal which is sent forward, from
the outgoing junctor to the associate incoming junctor, when an operator
wants to call back the called subscriber (or another operator) after he
has hung
up.
.PP
4.2.10
\fIBlocking Signal\fR \ \(em\ It is a signal which is sent backward, from
the incoming junctor to the associate outgoing junctor, by means of a manual
or automatic procedure, in order to indicate that the circuit or a group
of
circuits is blocked.
.PP
Taking into consideration the transmission level, the duration of the signal
and the conventional load in satellite circuits, its use must be
avoided when the number of telephone circuits is large in relation to the
total number of circuits of the route. In this case, when there is blocking,
the line signalling system itself already foresees procedures that can
prevent
successive losses of calls, as described in \(sc\ 4.6.1.
.sp 2P
.LP
4.3
    \fICharacteristics of the signals\fR
.sp 1P
.RT
.sp 1P
.LP
4.3.1
    \fIDuration of the signals\fR
.sp 9p
.RT
.PP
Line signals show the following durations:
.RT
.LP
.ce
\fBH.T. [B/T1]\fR
.ce
TABLE\ 1
.ce
\fBPulsed Line Signals\fR
.ce
\fBSending Times and Tolerances\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(36p) sw(36p) | cw(60p) , ^  | c | c | ^ .
Signal     {
Nominal duration (ms) | ua\d\u)\d
 }    Sending tolerances (ms)
    Forward    Backward
_
.T&
lw(60p) | cw(36p) | lw(36p) | cw(60p) .
Seizure    150        \(+-\ 30
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Proceed\(hyto\(hysend        150    \(+-\ 30
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Answer or re\(hyanswer        150    \(+-\ 30
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Multimetering        150    \(+-\ 30
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Call\(hyback    150        \(+-\ 30
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Clear\(hyforward    600        \(+-120
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Clear\(hyback        600    \(+-120
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Release guard        600    \(+-120
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Forced release        600    \(+-120
.T&
lw(60p) | cw(36p) | cw(36p) | cw(60p) .
Blocking        continuous     {
\(em
\ua\d\u)\d
Short signal:
150 ms
Long signal:
600 ms
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTable [B/T1], p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
4.3.2
    \fIRecognition times of the signals\fR
.sp 9p
.RT
.PP
Recognition times of the signals are presented in Table\ 2 and they take
into account time distortions introduced by transmission equipment and
tolerances of switching equipment which adopts the conventional
electromechanical technology.
.RT
.ce
\fBH.T. [B/T2]\fR
.ce
TABLE\ 2
.ce
\fBPulsed Line Signals\fR
.ce
\fBRecognition Times and Tolerances\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) .
Signal    Nominal recognition time (ms)    Receiving tolerances (ms)
_
.T&
lw(48p) | cw(48p) | cw(48p) .
Short    \ 80    \(+- 20
.T&
lw(48p) | cw(48p) | cw(48p) .
Long    375    \(+- 75
_
.TE
.nr PS 9
.RT
.ad r
\fBTable [B/T2], p.\fR
.ad b
.RT
.LP
    a)
    The recognition time of short signals ranges from 80\ \(+-\ 20\ ms to
375\ \(+-\ 75\ ms. Any received signal with duration between 100\ ms
and 300\ ms will be necessarily recognized as a short
signal.
.LP
    b)
    The recognition time of long signals corresponds to 375\ \(+-\ 75\ ms.
Any received signal with duration superior to 450\ ms will be
necessarily recognized as a long signal.
.LP
    c)
    The received signals with duration between 300\ ms and 450\ ms may
be recognized as long or short signals, depending on the
adjustment characteristics of the equipment.
.LP
    d)
    The receiver ignores interruptions up to 20\ ms.
.sp 1P
.LP
4.3.3
    \fIMinimum interval between signals\fR
.sp 9p
.RT
.PP
The minimum interval between two consecutive signals must be 240\ ms at
the transmission end. Distortion may reduce this interval at the receiving
end.
.RT
.sp 1P
.LP
4.3.4
    \fITransmission of signals\fR
.sp 9p
.RT
.PP
The transmission of signals between the switching equipment and the transmission
equipment and vice versa is made by sending a polarity which
corresponds to the battery voltage.
.RT
.sp 2P
.LP
4.4
    \fITransmission characteristics of the line signalling in FDM\fR
\fIequipment\fR
.sp 1P
.RT
.sp 1P
.LP
4.4.1
    \fISignal sender\fR
.sp 9p
.RT
.PP
The signalling frequency measured at the sending point has a value of 3825\
\(+-\ 4\ Hz.
.PP
The send level of the signalling frequency measured at the group
distribution frame or an equivalent point must be \(em5\ \(+-\ 1\ dBm0.
.RT
.sp 1P
.LP
4.4.2
    \fISignal receiver\fR
.sp 9p
.RT
.PP
The receiver must recognize as valid signals which lie between
3825\ \(+-\ 6\ Hz.
.PP
The receiving levels are determined in accordance with the relative
levels of the transmission plans adopted by each Administration.
.RT
.LP
.sp 1P
.LP
4.5
    \fIOperational procedure of the system\fR \v'3p'
.sp 9p
.RT
.PP
4.5.1
When the circuit is idle, there is no signal on the line. The
seizure of the outgoing junctor causes the forward sending of a short signal
(Seizure signal). This signal causes the seizure of the associate incoming
junctor and the seizure of equipment capable of receiving interregister
signals.
.PP
4.5.2
Immediately after the seizure of equipment for interregister
signalling interchange, the incoming junctor sends back a short signal
(Proceed\(hyto\(hySend signal).
.PP
4.5.3
When called subscriber answers, a short signal (Answer signal)
is sent back, thus causing the start of call charging.
.PP
4.5.4
When calling subscriber hangs up, a long signal (Clear Forward
signal) is sent forward, thus causing equipment release. After such release,
a Release Guard signal is sent back and the circuit comes back to idle
condition.
.bp
.LP
.PP
4.5.5
If the called subscriber hangs up first, a Clear Back signal
will be sent and then, after time\(hyout at a determined point of the network,
there will be the sending of a Clear Forward signal, thus completing the
process, as described in \(sc\ 4.5.4. If another Answer signal appears during
the time supervision period, timing will be interrupted and the equipment
involved will return to the speech condition. If the calling subscriber
hangs up during the time supervision period, the same procedure as that
described in \(sc\ 4.5.4 will occur.
.PP
After time\(hyout, the Clear Back signal is replaced by the Forced
Release signal between the charging point and the preceding exchange.
.PP
\fINote\fR \ \(em\ When there is coincidence of two signals, the forward
signal will always prevail.
.RT
.sp 2P
.LP
4.6
    \fIBehaviour of the system during interruption in transmission\fR
.sp 1P
.RT
.sp 1P
.LP
4.6.1
    \fIInterruption during the Seizure signal\fR
.sp 9p
.RT
.PP
The Seizure signal does not get to the incoming junctor and
therefore there is not its seizure. After time\(hyout, the outgoing junctor
sends the Clear Forward signal. As the incoming junctor has not been seized,
the
Release Guard signal will not be sent. So, time\(hyout in the outgoing junctor
occurs and then a maintenance alarm is activated and another Seizure signal
is sent, being followed by the Clear Forward signal. Such sequence is repeated
at intervals identical with those of the time supervision period of the
junctor. After the reset up of the transmission system and the next reception
in
sequence of the Seizure and Clear Forward signals, the incoming junctor
sends the Release Guard signal, thus releasing the outgoing junctor.
.RT
.sp 1P
.LP
4.6.2
    \fIInterruption during the Proceed\(hyto\(hySend signal\fR
.sp 9p
.RT
.PP
The Proceed\(hyto\(hySend signal does not get to the outgoing junctor and
therefore interregister signalling does not start. Two cases are
possible:
.RT
.LP
    a)
     After time\(hyout in the signalling equipment at the incoming end of
the link, the specific interregister backward signal is sent back. The
signalling equipment at the incoming end of the link releases and the outgoing
junctor sends forward the Clear Forward signal.
.LP
    b)
     After time\(hyout, the signalling equipment at the outgoing end of the
link releases and the outgoing junctor sends forward the Clear Forward
signal.
.sp 1P
.LP
4.6.3
    \fIInterruption during the Answer signal\fR
.sp 9p
.RT
.PP
The Answer signal does not get to the outgoing junctor and the call may
be completed even if charging has not started. After time\(hyout in the
origin, the Clear Forward signal is sent. The incoming junctor sends the
Release Guard signal, thus releasing the outgoing junctor.
.RT
.sp 1P
.LP
4.6.4
    \fIInterruption during the Clear Forward signal\fR
.sp 9p
.RT
.PP
The Clear Forward signal does not get to the incoming junctor and therefore
it cannot send the Release Guard signal. After time\(hyout, a
maintenance alarm is activated and the Seizure signal is sent, being followed
by the Clear Forward signal. Such sequence is repeated at intervals identical
with those of the time supervision period of the outgoing junctor until
the
Release Guard signal is received.
.PP
If there is a short interruption in the transmission system, thus
preventing reception of the Clear Forward signal at the incoming junctor
and in case the called subscriber will hang up during the time supervision
period of the outgoing junctor, the Clear Back signal will be taken as
a Release Guard
signal and therefore there will be the release in the origin. However, the
equipment which has not received the Clear Foward signal will remain set up
until it has been requested again and released by another call, which will
not be successful.
.RT
.sp 1P
.LP
4.6.5
    \fIInterruption during the Clear Back signal\fR
.sp 9p
.RT
.PP
The Clear Back signal does not get to the outgoing junctor and the release
of the equipment will be dependent on the calling subscriber
hang\(hyup.
.RT
.sp 1P
.LP
4.6.6
    \fIInterruption during the Release Guard signal\fR
.sp 9p
.RT
.PP
The Release Guard signal does not get to the outgoing junctor and, after
time\(hyout, the procedure used is the same as that established in
\(sc\ 4.6.4.
.RT
.LP
.sp 1P
.LP
4.6.7
    \fIInterruption during the Forced Release signal\fR
.sp 9p
.RT
.PP
The Forced Release signal does not get to the outgoing junctor and the
release of the equipment will be dependent on the calling subscriber
hang\(hyup.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 1, p.20\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 24P
.ad r
\fBFigure 2, p.21\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 3, p.22\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 4, p.23\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 5, p.24\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp