Blocked a f\ =\ 1,\ b f\ =\ 0 Abnormal, see Note 1 Abnormal, see Note 1 Idle Blocked
.TE
.LP
\fINote\ 1\fR
\ \(em\ In these abnormal conditions the outgoing end must prevent
a new seizure of the circuit. A delayed alarm should also be given
(see \(sc\ 3.2.6).
.LP
\fINote\ 2\fR
\ \(em\ Non\(hyrecognition of the seizing acknowledgement signal 100\ ms\(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 seizing 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 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 timeout period has
elapsed, the clear\(hyforward signal must be sent.
.LP
\fINote\ 4\fR
\ \(em\ In the case of recognition of b
b\ =\ 0 whilst in the answered
or clear\(hyback 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.
.nr PS 9
.RT
.ad r
\fBTableau [3/Q.422] + Remarques, p.7\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 7P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.2.4.2
\fIIncoming end\fR
.sp 9p
.RT
.ce
\fBH.T. [4/Q.422]\fR
.ce
TABLE\ 4/Q.422
.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
Blocked a b\ =\ 1,\ b b\ =\ 1 Abnormal seized see Note 5 Fault see Note 6 Blocked Fault see Note 6
.TE
.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 time\(hyout 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,
Section\ 4.3.3. If the answer signal is recognized during the time\(hyout 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 clear\(hyback signal
is recognized, at which stage the connection beyond the faulty circuit is
immediately released.
.LP
\fINote\ 4\fR
\ \(em\ Under these conditions the succeeding link must be
released immediately.
.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.
.nr PS 9
.RT
.ad r
\fBTableau [4/Q.422] + Remarques, p.8\fR
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 7P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.sp 2P
.LP
3.2.5
\fIAbnormal conditions\fR
.sp 1P
.RT
.sp 1P
.LP
3.2.5.1
\fISpecial release arrangements\fR \v'3p'
.sp 9p
.RT
.LP
a)
If an exchange where an outgoing R2 register is situated
recognizes a\db\u\ =\ 0, b\db\u\ =\ 1 (premature answer) before an
address\(hycomplete signal A\(hy6 or a Group\ B signal is received, the
connection must be released. Congestion information is then sent
backward or a repeat attempt is made to set up the call.
.LP
b)
In the cases of non\(hyreceipt of the answer signal, of delay in clearing
by the calling subscriber in automatic working and
of non\(hyreceipt of the clear\(hyforward signal by the incoming
exchange after the clear\(hyback signal has been sent, the
provisions of Recommendation Q.118 apply.
.sp 1P
.LP
3.2.5.2
\fISafeguard against failures\fR
.sp 9p
.RT
.PP
The PCM equipment and the exchange line signalling equipment should be
designed in such a way that at least those faults which are most likely
to occur in this equipment or in the interconnecting cables, result in
blocking of the circuit at the outgoing end and in the ultimate clearing
of the connection beyond the incoming switching equipment. This can be
achieved, as far as
possible, by ensuring that a\ =\ 1, b\ =\ 1 is sent on line upon:
.RT
.LP
\(em
removal of PCM or switching equipment by maintenance
personnel;
.LP
\(em
occurrences of abnormal conditions (e.g.\ open wire, low
voltage) in switching equipment.
.LP
.sp 1P
.LP
3.2.6
\fIAlarms for technical staff\fR
.sp 9p
.RT
.PP
According to Recommendation Q.117, an alarm must in principle be
given to the technical staff upon recognition of abnormal conditions.
.PP
Arrangements for these alarms are to be specified by the
Administrations.
.PP
It is recommended that a delayed alarm be given at the outgoing end
for the procedure described under \(sc\ 3.2.3.7 above (blocking) and for the
following reasons:
.RT
.LP
\(em
when the abnormal conditions covered by Note\ 1 to
Table\ 3/Q.422 are applicable;
.LP
\(em
when the seizing acknowledgement signal is not recognized
within the time specified in Note\ 2 to Table\ 3/Q.422 after
sending the seizing signal;
.LP
\(em
when, after recognition of the seizing acknowledgement signal and prior
to recognition of the answer signal, b\db\u\ =\ 0 is
received for 1\(hy2 seconds;
.LP
\(em
when the abnormal conditions covered by Note\ 4 to
Table\ 3/Q.422 are applicable.
.PP
It is also recommended that a delayed alarm be given under PCM
failure conditions specified in Recommendations\ G.732 and G.734.
.sp 1P
.LP
3.2.7
\fIBoth\(hyway working\fR
.sp 9p
.RT
.PP
System R2 is specified for one\(hyway working, but in principle the
line signalling code detailed in Recommendation\ Q.421 is also suitable
for use on both\(hyway circuits. Where Administrations have undertaken,
by bilateral
agreement, to use both\(hyway working, the clauses and additional specifications
for exchange signalling equipment detailed in \(sc\(sc\ 3.2.7.1 and 3.2.7.2
below,
must be observed.
.RT
.LP
.sp 1P
.LP
3.2.7.1
\fIProcedures under normal conditions\fR \v'3p'
.sp 9p
.RT
.LP
a)
\fIDouble seizure\fR
.LP
Double seizure is assumed if the outgoing equipment is in a seized state
and the signalling code a\db\u\ =\ 0, b\db\u\ =\ 0 is recognized instead
of
a\db\u\ =\ 1, b\db\u\ =\ 1 (seizure acknowledgement). In such a situation the
connection must be released at both ends and congestion information sent
to the calling subscriber or a repeat attempt must be made. On recognition
of double seizure the line signalling equipment at both ends must maintain
the seized
state for a minimum of 100\ ms after which the clear\(hyforward signal
a\df\u\ =\ 1, b\df\u\ =\ 0 must be sent.
.bp
.LP
100 ms after sending the clear\(hyforward signal and on recognition of
a\db\u\ =\ 1, b\db\u\ =\ 0 each end may assume the idle state.
.LP
The clear\(hyforward state a\df\u\ =\ 1, b\df\u\ =\ 0 must be maintained
for at least 100\ ms to ensure that it is recognized at the other end.
.LP
In the sense of preventive action it is recommended
that an opposite order of circuit selection be used by each
exchange of a both\(hyway circuit group to minimize double
seizure.
\v'3p'
.LP
b)
\fIRequirements for circuit release\fR
.LP
When a both\(hyway circuit is released, the end which acted as
the incoming end must maintain the signalling code
a\db\u\ =\ 1, b\db\u\ =\ 0 for at least 100\ ms to ensure that
the signal is recognized at the other end after which the
circuit becomes idle.
\v'3p'
.LP
c)
\fIBlocking and unblocking procedure\fR
.LP
When a both\(hyway circuit is blocked manually in its idle
state at one end (e.g.\ end B) the blocking signal must be
sent to the other end (A). The circuit must then be kept blocked
locally (at end A) against all calls in the A to B traffic
direction as long as the blocked state persists in the B to A
direction.
.LP
In order to avoid permanent blocking, end A should maintain the
signalling code a\ =\ 1, b\ =\ 0 in the direction A to B.
.PP
When the blocked state is removed, end B must send the
clear\(hyforward signal and must maintain that state for at least 100\
ms, before assuming the idle state.
.sp 1P
.LP
3.2.7.2
\fISpecial arrangement\fR
.sp 9p
.RT
.PP
The physical realization of signalling equipment terminating a
bothway circuit may allow that part of the equipment concerned with outgoing
calls to be removed without preventing the remaining equipment from being
used for incoming calls. In this case it is only necessary to block the
circuit
locally against outgoing calls and a blocking signal need not be sent to the
other end.
\v'2P'
.RT
.LP
.sp 2P
.LP
\fBRecommendation\ Q.424\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB3.3\ \fR \fBPROTECTION AGAINST THE EFFECTS OF FAULTY TRANSMISSION\fR
.EF '% Fascicle\ VI.4\ \(em\ Rec.\ Q.424''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.424 %'
.ce 0
.sp 1P
.PP
Faulty transmission conditions in PCM systems can lead to
degradation of the speech channels and erroneous signalling. In the case of
primary PCM multiplex equipment operating at 2048\ kbit/s failures due
to loss of frame or multi\(hyframe alignment and/or failure of any other
important
function results in both PCM terminals going into alarm condition in accordance
with Recommendations\ G.732 and\ G.734.
.sp 1P
.RT
.PP
Thus both PCM terminals apply the state corresponding to state\ 1 on the
PCM line on each \*Qreceive\*U signalling channel at the interfaces with
the switching equipment, as indicated in Table\ 4 of Recommendation\ G.732.
In this way, the incoming switching equipment receives the equivalent of
a\df\u\ =\ 1,
.PP
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.
.PP
These characteristics are taken into account in the present
specifications (see\ \(sc\ 3.2.4) so that:
.RT
.LP
\(em
at the outgoing end (see Table 3/Q.422) a PCM fault results in a blocked
state, seizure acknowledged state or clear\(hyback state. This means that
all circuits in the idle state of a faulty PCM multiplex will be blocked
against seizure and that seized circuits will go to or remain in the seizure
acknowledged or clear\(hyback state;
.LP
\(em
at the incoming end (see Table 4/Q.422) a PCM
fault can be identified and appropriate actions can be taken.
.bp
.PP
When the signalling equipment is a part of a digital exchange, it may receive
alarm indications in a form other than both signalling bits in
state one. The failure may be detected by the signalling equipment or an
indication be received from the PCM terminal according to
Recommendation\ G.734.
.PP
When the signalling equipment recognizes a failure it must:
.RT
.LP
\(em
block the detection of signalling transitions
to avoid recognition of erroneous signalling codes caused by the
failure. This action must be taken as soon as possible and at
least within 3\ ms as specified in Recommendation\ G.734 for a PCM
terminal,
.LP
\(em
react as specified in Tables 3/Q.422 and 4/Q.422 when a
signalling code a\ =\ 1, b\ =\ 1 is detected at the input of
signalling equipment situated at the analogue access of
a PCM terminal equipment complying with Recommendation\ G.732.
\v'2P'
.LP
.sp 2P
.LP
\fBRecommendation\ Q.430\fR
.RT
.sp 2P
.ce 1000
\fB3.5\ \fR \fBCONVERSION BETWEEN ANALOGUE AND DIGITAL VERSIONS\fR
.EF '% Fascicle\ VI.4\ \(em\ Rec.\ Q.430''
.OF '''Fascicle\ VI.4\ \(em\ Rec.\ Q.430 %'
.ce 0
.sp 1P
.ce 1000
\fBOF SYSTEM R2 LINE SIGNALLING\fR
.ce 0
.sp 1P
.PP
This Recommendation is applicable to a conversion equipment
placed on the circuit between two switching exchanges each using one of
the two versions specified for System\ R2 line signalling. Owing to this
particular use, all the specifications for the two versions of the line
signalling may not be fully observed. Nevertheless, the diagrams which
follow are based on the
principles of CCITT Recommendations\ Q.411, Q.412 and Q.416 for the analogue
version and on Recommendations\ Q.421, Q.422 and Q.424, for the digital
version. The only time conditions taken into account in this Recommendation
are those
set out in the aforementioned Recommendations. The operation of the
.sp 1P
.RT
.LP
interruption control device is also, wherever possible, that specified in
Recommendation\ Q.416. As stated in that Recommendation, the receiver is
blocked immediately whenever pilot tone off is detected: since this is
a routine
operation, it has not been represented explicitly in the diagrams.
.PP
The conversion diagrams have been divided into four parts:
.LP
\(em
for conversion between the analogue version at the incoming end and the
digital version at the outgoing end, into:
.LP
\(em
incoming analogue,
.LP
\(em
outgoing digital;
.LP
\(em
for conversion between the digital version at the incoming
end and the analogue version at the outgoing end, into:
.LP
\(em
incoming digital,
.LP
\(em
outgoing analogue.
.PP
It should be noted, however, that this Recommendation can be
simplified with respect to alarm processing when the conversion equipment is
connected directly at the input or output of a switching exchange; the
processes necessary for this application are shown on the diagrams with
thickened lines.
.LP
.sp 2P
.LP
\fB1\fR \fBDrawing conventions\fR \v'3p'
.sp 1P
.RT
.LP
\(em
tone
.LP
tf
=\ 1 tone on forward
.sp 2P
.LP
tf
=\ 0 tone off forward
.RT
.sp 2P
.LP
tb
=\ 1 tone on backward
.RT
.sp 2P
.LP
tb
=\ 0 tone off backward
.RT
.sp 2P
.LP
When recognized
.sp 2P
.LP
p
=\ 1 pilot tone on
.RT
.sp 2P
.IP
p
=\ 0 pilot tone off
.sp 1P
.RT
.LP
\(em
signalling bits
.PP
The conventions are those of Recommendation\ Q.421.
.bp
.sp 2P
.LP
\fB2\fR \fBConversion incoming analogue version to outgoing digital version\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIIncoming analogue\fR
.sp 9p
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure CCITT\(hy55980, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
List of timers:
.LP
T2:
Recommendation Q.412 (\(sc\ 2.2.2.7)
.LP
T3:\ 2\ to\ 3\ mn
Recommendation Q.118 (\(sc\ 4.3.3)
.PP
In sheets 2 and 4 the diagram for group pilot supervision is given.
.PP
In sheets 3 and 5 the diagram for supergroup pilot supervision is given.
.PP
Sheet 1 is for group and supergroup pilot supervision.
.RT
.LP
.rs
.sp 28P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE CCITT\(hy60881 (feuillet 1), p.10\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE CCITT\(hy60891 (feuillet 2), p.11\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE T1115760\(hy88 (feuillet 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE CCITT\(hy60901 (feuillet 4), p.12\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFIGURE T1115770\(hy88 (feuillet 5), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2
\fIOutgoing digital\fR
.sp 9p
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure CCITT\(hy55990, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
List of timers:
.LP
T6:\ Recommendation Q.422 (\(sc\ 3.2.4.1, Note 2 to Table 3)
.LP
.rs
.sp 30P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fR \fBFigure CCITT\(hy60911 (Sheet 1 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fR \fBFigure CCITT\(hy60920 (Sheet 2 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60930 (Sheet 3 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
\fB3\fR \fBConversion incoming digital version to outgoing analogue version\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIIncoming digital\fR
.sp 9p
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure CCITT\(hy56000, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
List of timers:
.LP
T3:\ 2 to 3 mn Recommendation Q.118 (\(sc\ 4.3.3)
.LP
.rs
.sp 30P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60940 (Sheet 1 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60950 (Sheet 2 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60960 (Sheet 3 of 3), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
3.2
\fIOutgoing analogue\fR
.sp 9p
.RT
.LP
.rs
.sp 11P
.ad r
\fBFigure CCITT\(hy50610, p.\fR
.sp 1P
.RT
.ad b
.RT
.PP
List of timers:
.LP
T1:
Recommendation Q.412 (\(sc\ 2.2.2.7)
.LP
T5:\ 100 ms
Recommendation Q.412 (\(sc\ 2.2.2.1)
.PP
Automatic restoration of an abnormally blocked circuit
Recommendation\ Q.490 (\(sc\ 6.6)
.LP
n:
number of attempts made
.LP
T4:
30 s to 2\ mn
.LP
T7:
2 to 3\ s
.LP
.rs
.sp 27P
.ad r
\fBBlanc\fR
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60971 (Sheet 1 of 5), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure CCITT\(hy60981 (Sheet 2 of 5), p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fR \fBFigure CCITT\(hy60991 (Sheet 3 of 5), p.\fR