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InfoMagic Standards 1994 January
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1988
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.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\" Not Copyright ( c) 1991
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.\" Assumes tbl, eqn, MS macros, and lots of luck.
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.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'12P'
\s12PART\ I
\v'4P'
.RT
.ce 0
.sp 1P
.ce 1000
\fBSeries O Recommendations\fR \v'2P'
.EF '% \ \ \ ^''
.OF ''' \ \ \ ^ %'
.ce 0
.sp 1P
.ce 1000
\fBSPECIFICATIONS\ FOR\ MEASURING\ EQUIPMENT\fR
.ce 0
.sp 1P
.LP
.rs
.sp 32P
.ad r
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.EF '% \ \ \ ^''
.OF ''' \ \ \ ^ %'
.ad b
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.LP
.bp
.LP
\fBMONTAGE:\fR \ PAGE 2 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 1
.ce 0
.sp 1P
.ce 1000
\fBGENERAL\fR
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ O.1\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSCOPE\ AND\ APPLICATION\ OF\ SERIES\ O\ RECOMMENDATIONS\fR
.EF '% Fascicle\ IV.4\ \(em\ Rec.\ O.1''
.OF '''Fascicle\ IV.4\ \(em\ Rec.\ O.1 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBScope of Series O Recommendations\fR
.sp 1P
.RT
.PP
The CCITT establishes various Recommendations covering:
.RT
.LP
a)
essential specifications for telecommunications equipments,
and
.LP
b)
operational matters, e.g. procedures for bringing circuits
into service and routing checks of performance.
.PP
The type of tests for checking compliance with these two
categories of Recommendations are essentially different, and this often
leads to a different choice of test equipment.
.PP
Category a) tests will normally be more comprehensive. Their purpose (often
based upon measurements of sample or prototype equipments) is to certify
compliance with design objectives and they may therefore be a prerequisite
to equipment being accepted for installation in an Administration's network.
Such tests are unlikely to be employed routinely and in general CCITT does
not
produce Recommendations for test equipment intended specifically for this
purpose.
.PP
Category b) tests, however, are used systematically and repetitively and
their widespread application may necessitate additional considerations,
in particular the need for:
.RT
.LP
1)
conformity of results when tests may be performed using test
equipment supplied by more than one manufacturer, and
.LP
2)
a common measurement technique to ensure compatibility when
a test requires test equipment at both ends of an international
circuit.
.PP
It is primarily for these circumstances that CCITT issues the
Series O\ Recommendations.
.PP
The above remarks apply quality to analogue and digital
techniques.
.RT
.sp 2P
.LP
\fB2\fR \fBApplication of measuring equipment for use on digital transmission
systems\fR
.sp 1P
.RT
.PP
This section is presented as an aid to selecting and applying
specifications in the Series O\ Recommendations concerning test and measuring
equipment for use on primary PCM and data multiplexers and digital transmission
systems.
.PP
Applications are divided into two categories:
.RT
.LP
a)
measurements and indications on primary PCM
multiplexers;
.LP
b)
measurements and indications on digital transmission
systems
including digital line systems, digital circuits and
digital multiplexers.
.bp
.PP
Figures 1/O.1 and 2/O.1 illustrate the range of test and
measurement capabilities applicable to primary PCM multiplexers, in the send
and receive directions, respectively.
.PP
Tables 1/O.1 and 2/O.1 illustrate the range of test and measurement
capabilities applicable to digital transmission systems.
.PP
The figures indicate the relevant Series O Recommendations to be
applied for each test and measurement parameter, and also show the connection
interface for the test instrument.
.PP
\fIExample\fR :
.PP
To measure quantising distortion on a primary PCM multiplexer:
.PP
Figure 1/O.1 shows that instruments conforming to
Recommendations\ O.131 and\ O.132 can be employed, connected to the audio
input interface of the send encoder.
.PP
Figure 2/O.1 shows that similar instruments are connected to the audio
output interface of the receive decoder to complete the measurement path.
.RT
.LP
.rs
.sp 40P
.ad r
\fBFigure 1/O.1, p. 1\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 30P
.ad r
\fBFigure 2/O.1, p. 2\fR
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T1.1]\fR
.ce
TABLE\ 1/O.1
.ce
\fBList of tests and measurements applicable to digital
.ce
\fBtransmission systems in the send direction\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | lw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
System hierarchical level First order Second order Third order Fourth order
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Bit rate . . 64 kbit/s . 1544 2048 kbit/s . 6312 8448 kbit/s {
32 | 64
34 | 68
44 | 36
kbit/s
} . . 139.264 Mbit/s
_
.T&
cw(54p) | cw(174p) .
Parameter Recommendation
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Error performance O.152 O.151 O.151 O.151 O.151
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Timing jitter O.171 O.171 O.171 O.171 O.171
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 1/O.1 [T1.1], p. 3\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.ce
\fBH.T. [T2.1]\fR
.ce
TABLE\ 2/O.1
.ce
\fBList of tests and measurements applicable to digital
.ce
\fBtransmission systems in the receive direction\fR
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(54p) | lw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
System hierarchical level First order Second order Third order Fourth order
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Bit rate . . 64 kbit/s . 1544 2048 kbit/s . 6312 8448 kbit/s {
32 | 64
34 | 68
44 | 36
kbit/s
} . . 139.264 Mbit/s
_
.T&
cw(54p) | cw(174p) .
Parameter Recommendation
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Error performance O.152 O.151 O.151 O.151 O.151
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Code violations O.161 O.161
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
{
Frame alignment
Signal monitor
} O.162 (2 Mbit/s)
_
.T&
lw(54p) | cw(30p) | cw(36p) | cw(36p) | cw(36p) | cw(36p) .
Timing jitter O.171 O.171 O.171 O.171 O.171
_
.TE
.nr PS 9
.RT
.ad r
\fBTableau 2/O.1 [T2.1], p. 4\fR
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB3\fR \fBApplication of measuring equipment for use on analogue transmission
systems\fR
.sp 1P
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fICharacteristics of 60\(hychannel transmultiplexing\fR
\fIequipments\fR , Vol.\ III, Rec.\ G.793.
.LP
[2]
CCITT Recommendation \fICharacteristics of 24\(hychannel transmultiplexing\fR
\fIequipments\fR , Vol.\ III, Rec.\ G.794.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ O.3\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBCLIMATIC\ CONDITIONS\ AND\ RELEVANT\ TESTS\ FOR\ MEASURING\ EQUIPMENT\fR
.EF '% Fascicle\ IV.4\ \(em\ Rec.\ O.3''
.OF '''Fascicle\ IV.4\ \(em\ Rec.\ O.3 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
The Recommendations of the Series O specify measuring equipment for a wide
range of applications. Reliable test equipment is an important
prerequisite when maintaining telecommunication equipment and telecommunication
networks. The reliability of measuring equipment can be affected by the
environmental conditions to which the equipment is exposed to during its use.
.PP
This Recommendation gives a range of climatic conditions for the
operation of measuring equipment specified in the Series O\ Recommendations.
In addition, climatic conditions for transportation and storage of measuring
equipment are defined.
.bp
.PP
In order to be able to prove that the requirements of this
Recommendation are fulfilled, test conditions simulating the various
environmental parameters are specified.
.PP
Where possible, this Recommendation is based on standards produced by other
bodies such as the international electrotechnical commission
(IEC)\ [1]; (CEPT)\ [2].
.RT
.sp 2P
.LP
\fB2\fR \fBClimatic conditions for the operation of measuring equipment\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fIOperation in indoor rooms\fR
.sp 9p
.RT
.PP
Considering that measuring equipment will be used in most of the
cases in weather\(hyprotected locations, the normal operating conditions
specified in Figure\ 1/O.3 define the range of climatic conditions under
which the
equipment specifications shall be met. These conditions may be found in
normal working areas, offices, telecommunication centres or storage rooms
for
sensitive products,\ etc.
.PP
The normal operating conditions are maintained by heating, cooling
and, where necessary, by forced ventilation. Humidity may normally not be
controlled.
.PP
Figure 1/O.3 implies that the measuring equipment is usually operated at
a temperature of approximately 25\(de | at a relative humidity of 45%.
.PP
The dotted field in the centre of the climatogram of Figure\ 1/O.3
specifies the climatic conditions which will be experienced during 90%
of the time.
.PP
The exceptional operating conditions shown in Figure 1/O.3 may exist, e.g.\
following failure of the climate controlling system. Under these
conditions the measuring equipment shall still operate without irreversible
faults. However, the measurement may be less accurate.
.PP
In some instances the measuring equipment may be exposed to solar
radiation and to heat radiation from other sources (e.g.\ from room heating).
Direct solar radiation should be avoided and the temperature in the vicinity
of the equipment shall not exceed the limits of Figure\ 1/O.3
.PP
The equipment may also be exposed to movements of the surrounding air due
to draughts in buildings (e.g.\ through open windows). It shall not be
subjected to condensation or precipitation.
.RT
.LP
.rs
.sp 25P
.ad r
\fBFigure 1/O.3, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.2
\fIOperation of measuring equipment in other environments\fR
.sp 9p
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fB3\fR \fBTransportation and storage\fR
.sp 1P
.RT
.PP
During transportation and storage the measuring equipment shall
tolerate temperatures between \(em40 | (deC and +70 | (deC without irreversible
failure. For relative humidities higher than 45% and temperatures higher
than 25 | (deC the limits of the climatogram of Figure\ 1/O.3 shall not
be exceeded for any
humidity/temperature combination. In this case the (uninterrupted) exposure
time is limited to 2\ months.
.PP
\fINote\ 1\fR \ \(em\ It is assumed that the measuring equipment is packed
in its usual shipping container and that the ambient conditions mentioned
above are
those outside the package.
.PP
\fINote\ 2\fR \ \(em\ This requirement is provisional and requires further
study.
.RT
.sp 2P
.LP
\fB4\fR \fBTest conditions\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fITesting conditions for indoor climates\fR
.sp 9p
.RT
.PP
It is assumed that the measuring equipment meets the requirements of \(sc\
2.1 if it tolerates the basic environmental testing procedures in
accordance with IEC Publication 68\(hy2\(hy3\ [3].
.PP
During these testing procedures, the mesuring equipment shall be
placed in the testing chamber for 4\ days. After a recovery time of 2\
hours the test specimen shall properly function and the specified error
limits shall not be exceeded.
.PP
\fINote\fR \ \(em\ This requirement is provisional and requires further
study.
.RT
.sp 1P
.LP
4.2
\fITesting conditions for other environments\fR
.sp 9p
.RT
.PP
Under study.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
IEC Publication 731\(hy3 \fIClassification of Groups of Environmental\fR
\fIParameters and their Severities\fR .
.LP
IEC\(hyPublication 721\(hy3\(hy3 \fIStationary Use at Weather\(hyProtected\fR
\fILocations\fR .
.LP
[2]
CEPT Recommendation T/TRw, Part B\(hy3 \fIEnvironmental Conditions and\fR
\fIEnvironmental Tests for Telecommunications Equipment\fR . (October\ 1987).
.LP
[3]
IEC\(hyPublication 68\(hy2\(hy3 \fIBasic Environmental Testing Procedures.\fR
\fIPart\ 2: Test Ca: Damp heat, steady state\fR .
.sp 2P
.LP
\fBRecommendation\ O.6\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fB1020\ Hz\ REFERENCE\ TEST\ FREQUENCY\fR
.EF '% Fascicle\ IV.4\ \(em\ Rec.\ O.6''
.OF '''Fascicle\ IV.4\ \(em\ Rec.\ O.6 %'
.ce 0
.sp 1P
.ce 1000
\fI(Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBIntroduction\fR
.sp 1P
.RT
.PP
The intent of this Recommendation is to specify a single nominal
reference frequeny of 1020\ Hz in order to provide guidance to manufacturers
and Administrations in the design and operation of new equipment and systems.
This Recommendation is not intended to have an effect on existing equipment
or
systems except where modifications are required to allow for interworking.
For instance, an older analogue exchange would need to be provided with
new
reference frequency capability if circuits were provided between it and
digital exchanges.
.RT
.sp 2P
.LP
\fB2\fR \fBTest frequencies on circuits routed over PCM systems\fR
.sp 1P
.RT
.PP
The selection of a suitable test frequency is a major consideration when
testing circuits routed over PCM systems. An error in level measurement
can arise on circuits routed over PCM systems if the test frequency is a
sub\(hymultiple of the PCM sampling rate. This error can be nearly as great as
\(+- | .15\ dB at 800\ Hz and \(+- | .20\ dB at 1000\ Hz with a sampling
rate of 8000\ Hz
employing 8\(hybit coding. In addition, errors in other parameters, such
as total distortion, may be even more significant.
.bp
.PP
Therefore, it is recommended that the use of a reference test
frequency that is a sub\(hymultiple of the PCM sampling rate should be avoided.
Studies within CCITT reveal that some Administrations have employed nominal
reference test frequencies offset from 800\ Hz or 1000\ Hz by varying amount
but within the ranges 804\(hy860\ Hz or 1004\(hy1020\ Hz. These studies
have confirmed that where interworking is not required, no significant
problems in maintenance have been encountered by Administrations and existing
test procedures and equipment may continue to be used.
.PP
In the case of interworking and for new equipment and systems, the
Administrations expressed a strong preference for the selection of a reference
test frequency of 1020\ Hz.
.RT
.sp 2P
.LP
\fB3\fR \fBConsiderations for new measuring equipment specifications\fR
.sp 1P
.RT
.PP
The following should be considered for new measuring equipment
specifications in the Series O\ Recommendations:
.RT
.LP
i)
A reference test frequency of 1020 Hz is recommended for
test frequency generating circuits or instruments that provide
reference test frequencies. The specified frequency tolerance
should be +2 to \(em7\ Hz
.FS
The negative tolerance of 7 Hz is
intended to allow the use of digitally generated test signals
that are generated by a sufficiently high number of samples to
achieve the measurement accuracy specified in certain Series
O\ Recommendations (e.g.\ Recommendation\ O.133).
.FE
.
.LP
ii)
The nominal level of the reference test frequency when used
on in\(hyservice equipment should not be greater that \(em10\ dBm0
\(+- | .1\ dB.
.LP
iii)
Measuring circuits or instruments which utilize the
reference test frequencies should provide, if possible, for
measurements of any frequencies within the nominal range of
1000\ to 1025\ Hz.
.PP
By agreement between the Administrations concerned, in the absence of the
required sending or measuring apparatus, the use of a measuring
frequency in the range of 800\ to 860\ Hz is admissible. Other considerations
about the deployment and use of reference test frequencies are given in
Recommendation\ M.20\ [1].
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fIMaintenance philosophy for analogue, digital
and\fR \fImixed networks\fR , Volume\ IV, Recommendation\ M.20.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ O.9\fR
.RT
.sp 2P
.ce 1000
\fBMEASURING\ ARRANGEMENTS\ TO\ ASSESS\fR
.EF '% Fascicle\ IV.4\ \(em\ Rec.\ O.9''
.OF '''Fascicle\ IV.4\ \(em\ Rec.\ O.9 %'
.ce 0
.sp 1P
.ce 1000
\fBTHE\ DEGREE\ OF\ UNBALANCE\ ABOUT\ EARTH\fR
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1972; amended at Malaga\(hyTorremolinos, 1984, and at Melbourne,\fR
\fI1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.PP
This Recommendation describes arrangements for measuring the
following parameters:
.RT
.LP
\(em
longitudinal conversion loss;
.LP
\(em
transverse conversion loss;
.LP
\(em
longitudinal conversion transfer loss;
.LP
\(em
transverse conversion transfer loss;
.LP
\(em
input longitudinal interference loss;
.LP
\(em
common\(hymode rejection;
.LP
\(em
output signal balance.
.PP
In practice, the above parameters are the seven most significant
unbalance parameters
. Limits for these parameters, special
considerations for test terminations and the measurement frequencies to
be used are given in the relevant Recommendation for the item under test.
.bp
.PP
This Recommendation is in agreement with the principles, the
nomenclature and the definitions, addressed in Recommendation\ G.117\ [1],
which considers the transmission aspects of unbalance about earth. References
are
made in the following sections, to the appropriate paragraphs/figures of
Recommendation\ G.117\ [1].
.PP
In \(sc 3, guidance is given regarding the construction of a test bridge
along with values of the required components.
.RT
.sp 2P
.LP
\fB2\fR \fBMeasuring arrangements\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
\fILongitudinal conversion loss (LCL)\fR
.sp 9p
.RT
.PP
The LCL of a one\(hy or two\(hyport network is a measure (a ratio
expressed in dB) of the degree of unwanted transverse signal produced at the
terminals of the network due to the presence of a longitudinal signal on the
connecting leads. It is measured as shown in Figure\ 1/O.9. This technique is
applicable to either the input or output terminals, e.g.,\ transpose terminals\
a and\ b with\ d and\ e respectively. (See \(sc\ 4.1.3 of
Recommendation\ G.117\ [1].)
.RT
.LP
.rs
.sp 20P
.ad r
\fBFigure 1/O.9, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.2
\fITransverse conversion loss (TCL)\fR
.sp 9p
.RT
.PP
The TCL of a one\(hy or two\(hyport network is a measure (a ratio
expressed in\ dB) of the degree of unwanted longitudinal signal produced
at the input (or output) of a network due to the presence of a transverse
signal at
the same port. TCL is measured as shown in Figure\ 2/O.9 (see \(sc\ 4.1.2 of
Recommendation\ G.117\ [1]).
.RT
.sp 1P
.LP
2.3
\fB\fILongitudinal conversion transfer loss (LCTL)\fR
.sp 9p
.RT
.PP
The LCTL is a measure (a ratio expressed in dB) of an unwanted
transverse signal produced at the output of a two\(hyport network due to the
presence of a longitudinal signal on the connecting leads of the input
port. It is measured as shown in Figure\ 3/O.9 (see \(sc\ 4.2.3 of
Recommendation\ G.117\ [1]).
.PP
If the item under test exhibits gain or loss between ports a/b and
d/e, this must be taken into account when specifying LCTL. In addition
to the general requirements of \(sc\ 3, the measurement range of the test
equipment must also take into account the gain or loss of the item under
test. In addition, if the item under test performs a signal conversion
(e.g.,\ in FDM or TDM
multiplexers) then the signal measured at \fIV\fR\d\fIT\fR\\d2\umay not
be at the same frequency as that of the energizing signal designated \fIV\fR\d\fIL\fR\\d1\u.
The signal at \fIV\fR\d\fIT\fR\\d2\umay even appear in coded form as a
digital
signal. Further study is required to define these signals and their
relationships.
.bp
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 2/O.9 and Note, p.
.sp 1P
.RT
.ad b
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 3/O.9 and note, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.4
\fITransverse conversion transfer loss (TCTL)\fR
.sp 9p
.RT
.PP
Transverse conversion transfer loss is a measure (a ratio expressed in\
dB) of an unwanted longitudinal signal produced at the output of a two\(hyport
circuit due to the presence of a transverse signal at the input port. It
is
measured as shown in Figure\ 4/O.9. If a signal conversion is performed
by the item under test (e.g.,\ in FDM or TDM multiplexers) then the signal
measured at \fIV\fR\d\fIL\fR\\d2\umay not be at the same frequency as that
of the energizing
signal designated \fIV\fR\d\fIT\fR\\d1\u. The energizing signal may even be
applied in coded form as a digital signal. Further study is required to
define these signals and their relationships (see \(sc\ 4.2.2 of
Recommendation\ G.117\ [1]).
.RT
.LP
.rs
.sp 27P
.ad r
\fBFigure 4/O.9, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.5
\fIInput longitudinal interference loss (ILIL)\fR
.sp 9p
.RT
.PP
The measurement of this parameter is applicable to receiving
devices (e.g.,\ amplifiers, level meters,\ etc.). ILIL is a measure (a ratio
expressed in\ dB) of the sensitivity of a receiving device to longitudinal
disturbances. It is measured as shown in Figure\ 5a/O.9 and\ 5b/O.9. In
principle, it is similar to the longitudinal conversion loss (LCL)
measurement. However, since the measurement is performed internally (using
a built\(hyin indicating device) or at the output of the item under test, not
only the impedance balance at port a/b, but also the effect of common\(hymode
rejection is measured. (See \(sc\ 4.4.1 of Recommendation\ G.117\ [1].)
.PP
Measurements in accordance with Figure 5b/O.9 are also applicable to devices
which perform a signal conversion (e.g.\ VF/CF side of channel
translating equipment, A/D side of PCM multiplex equipment,\ etc. See \(sc\ 2,
item\ f of Recommendation\ G.117\ [1]). In this case the measurement at the
.PP
output of the device under test requires an appropriate analyzer, namely a
selective level meter for measurements at channel translators or a digital
analyzer (see Recommendation\ O.133) for measurements at PCM\(hymultiplexers.
In
the equation
in Figure\ 5b/O.9 it is assumed that\ \fIV\fR\d0\uis measured at a 0\(hydBr
point. The quantity\ \fIX\fR\d1\uis the relative level at port a/b.
.bp
.RT
.LP
.rs
.sp 47P
.ad r
\fBFigure 5/O.9, p.\fR
.sp 1P
.RT
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 1P
.LP
2.6
\fICommon\(hymode rejection (CMR)\fR
.sp 9p
.RT
.PP
Common\(hymode rejection is another measurement (a ratio expressed
in\ dB) that is appropriate for receiving devices and is measured as shown in
Figure\ 6/O.9. Note that in this arrangement the input terminals are
short\(hycircuited and then energized (see \(sc\ 5.1 of
Recommendation\ G.117\ [1]).
.RT
.LP
.rs
.sp 20P
.ad r
\fBFigure 6/O.9, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.7
\fIOutput signal balance (OSB)\fR
.sp 9p
.RT
.PP
This measurement (a ratio expressed in dB) is applicable to signal outputs.
OSB is a measure of unwanted longitudinal signals at the output of
a device. It is measured as shown in Figure\ 7/O.9 (see \(sc\ 4.3.1 of
Recommendation\ G.117\ [1]).
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 7/O.9, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
The signal source \fIG\fR shown in Figure\ 7/O.9 can be internal or
external to the device under test. OSB measurements are also applicable to
devices which perform a signal conversion (e.g.\ CF/VF side of channel
translating equipment. D/A side of PCM multiplex equipment, etc. See \(sc\ 2,
item\ f of Recommendation\ G.117\ [1]). In this case an appropriate external
signal source, namely a signal generator for measurements at channel
translators or a digital signal generator (see Recommendation\ O.133) for
measurements at PCM\(hymultiplexers is required.
.sp 2P
.LP
\fB3\fR \fBRequirements for the measuring arrangements\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
\fIInherent balance\fR
.sp 9p
.RT
.PP
The measuring arrangements shown in Figures\ 1/O.9 through 7/O.9
include two independent impedances and a centre\(hytapped inductor arranged as
indicated to yield the equivalence of two matched impedances of the
value\ \fIZ\fR /2. The coil should be iron\(hycored with an accurate centre\(hytapped
connection, both the tightly coupled half windings being as symmetrical as
possible. The circuits shown in Figure\ 8/O.9 are electrically equivalent and
any one can be used to perform the measurements described in this
Recommendation. It should be noted that in the case of option\ \fIc)\fR of
Figure\ 8/O.9, the connection of point\ c to earth must be made via an
impedance which is virtually zero. For very low frequencies, the
arrangements\ \fIa)\fR and\ \fIb)\fR of Figure\ 8/O.9 may be unsuitable
and it may be
more convenient to use arrangement\ \fIc)\fR of Figure\ 8/O.9, with a small
(e.g.,\ 1\ ohm) resistor being inserted in the longitudinal arm, so that a
measure of longitudinal current can be obtained to derive the equivalent
voltage across\ \fIZ\fR /4.
.PP
The inherent balance of any measuring arrangements must be determined and
found to be sufficiently good before a measurement is made. This may be
done by replacing the equipment being tested with a second test bridge. The
inherent longitudinal conversion loss of the measuring arrangements should
be 20\ dB greater than the limit set for the item under test. This balance
should also be obtained when the connections at\ a and\ b are reversed.
This permits
an accuracy in the order of \(+-\ 1\ dB. An example of a practical test
bridge is
given in Recommendation\ G.117, Figure\ 21/G.117\ [1].
.RT
.LP
.rs
.sp 20P
.ad r
\fBFigure 8/O.9, p.\fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
3.2
\fIImpedances Z\fI\d\fIL\fR\\d\fIL\fR\\d\fI2\fR\u
[garbled text] \fIZ\fR\d1\uand \fIZ\fR\d2\uare the impedances connected in parallel to
the input and/or output port respectively of the item under test. \fIZ\fR\d1\uand
\fIZ\fR\d2\uare generally within \(+-\ 25% of the nominal impedance of
the
port to which they are connected. If measurements are made via high\(hyimpedance
input ports, an additional impedance \fIZ\fR\d1\ushould be connected between
points\ a and\ b. The longitudinal impedances \fIZ\fR\d\fIL\fR\\d1\uand
\fIZ\fR\d\fIL\fR\\d2\uare nominally equal to \fIZ\fR\d1\u/4 or \fIZ\fR\d2\u/4
respectively. Different
values, however, may be used. This may be necessary to more properly simulate
operating conditions of the item under test. In such cases the value of
\fIZ\fR\d\fIL\fR\\d1\uand/or \fIZ\fR\d\fIL\fR\\d2\ushall be specified by
the Recommendation convering the item under test.
.bp
.RT
.sp 1P
.LP
3.3
\fIMeasuring and generating the test signals\fR
.sp 9p
.RT
.PP
The voltages \fIV\fR\d\fIL\fR\uand \fIV\fR\d\fIT\fR\uare measured with
high\(hyimpedance voltmeters, and in such a way that the balance is not
disturbed. The actual
values of the internal impedance and e.m.f. of the generator\ G are irrelevant
if \fIV\fR\d\fIL\fR\\d1\uis measured. The design of the item under test
may impose a
limit on the permissible magnitude of the longitudinal excitation.
.PP
When the equipment being tested as shown in Figure\ 1/O.9 is a signal generating
device, \fIV\fR\d\fIT\fR\\d1\umust be measured selectively if it is
required to measure the longitudinal conversion loss while the signal generator
is active. Selective measurements are also preferable when high losses
are to be measured.
.RT
.sp 1P
.LP
3.4
\fIOther considerations\fR
.sp 9p
.RT
.PP
It may be necessary in some measurements to make provisions for
supplying a d.c.\ line holding current or a d.c.\ line current termination. In
these cases the Recommendation covering the requirements for the item under
test shall also specify the requirements for such d.c.\ line current
treatment.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fITransmission aspects of unbalance about earth\fR
Vol.\ III, Rec.\ G.117.
.LP
[2]
CCITT Recommendation \fITransmission characteristics of an international\fR
\fIanalogue exchange\fR Vol.\ VI, Rec.\ Q.45.
.LP
.rs
.sp 31P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 2
.ce 0
.sp 1P
.ce 1000
\fBMAINTENANCE\ ACCESS\fR \v'1P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ O.11\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMAINTENANCE\ ACCESS\ LINES\fR
.EF '% Fascicle\ IV.4\ \(em\ Rec.\ O.11''
.OF '''Fascicle\ IV.4\ \(em\ Rec.\ O.11 %'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1972; amended at Malaga\(hyTorremolinos, 1984,\fR \fIand at
Melbourne, 1988)\fR
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR \fBGeneral\fR
.sp 1P
.RT
.sp 1P
.LP
1.1
\fIIntroduction\fR
.sp 9p
.RT
.PP
In order to more effectively carry out manual and automatic
maintenance of international circuits in an automatic telephone network, the
following international maintenance access lines are recommended:
.RT
.LP
a)
a balanced quiet termination which initially returns a
\(em10\ dBm0 test tone;
.LP
b)
a maintenance test position or console access line with
multiple access codes for both voice communications and/or circuit testing;
.LP
c)
a test line to terminate the echo suppressor testing system (ESTS) (see
Recommendation\ O.25) responder;
.LP
d)
a loopback test line (analogue or digital);
.LP
e)
a test line to terminate the echo canceller test responder.
.LP
f
)
a test line to terminate the signalling system
functional testing and transmission measuring responder (type\ a) for use
with ATME\ No.\ 2 (Recommendation\ O.22);
.LP
g)
a test line which returns a busy flash signal for use with ATME\ No.\
2 (also referred to as type\ c responding equipment, see
Recommendation\ O.22).
.PP
These test lines should be provided as modular units to that each Administration
may choose the number of each type it wishes to install at a
given centre.
.PP
The test lines listed in a) to e) above will not provide reliable test
results for a circuit which is routed through a circuit multiplication
system (CMS) employing interpolation techniques [this includes the case
where a
circuit is routed over time division multiple access/digital speech
interpolation (TDMA/DSI) satellite channels] and therefore should not be
used in this instance unless a permanent trunk\(hychannel association in
both
directions of transmission can be made for the duration of the test sequence.
The reason for this is that without such a trunk\(hychannel association,
circuit continuity may not be maintained within the CMS in the absence
of a signal and during very low signal level conditions.
.bp
.RT
.sp 1P
.LP
1.2
\fIQuiet termination test line\fR
.sp 9p
.RT
.PP
The quiet termination test line is a dialable test line that
initially returns a nominal 1020\ Hz
.FS
For further information about the
choice of the test reference frequency refer to Recommendation\ O.6.
.FE
\(em10\ dBm0 tone for 13 to 15\ seconds. After the initial tone period,
the test
line should present a balanced 600\(hyohm termination to simulate the nominal
exchange impedance. This quiet termination should remain connected until the
calling party disconnects. This dialable test line is intended to allow
one\(hyman manual 1\(hyway loss, 1\(hyway noise (or noise with tone) measurements
and impulsive noise checks on any circuit from the distant switching centre.
.RT
.sp 1P
.LP
1.3
\fITest and/or communications access line\fR
.sp 9p
.RT
.PP
The test and/or communications access line is a dialable access
line intended to be located at the circuit maintenance test position or test
console location associated with the international switching centres. These
access lines are expected to be used for voice communications between the
circuit maintenance personnel at the appropriate maintenance elements and
as a test access point to make a variety of manual transmission tests.
These access lines are potential facilities as a fault report point (circuit)
or fault
report point (network) and/or testing point (transmission).
.PP
Separate access codes will be allocated for each of the access line
types described below. This is to ensure that if an Administration wishes to
separate the various maintenance functions (i.e.\ transmission testing,
switching testing and fault reports) it can do so. These allocations should
not, however, stop those Administrations that wish to combine one or more of
the functions, using a single access code.
.RT
.sp 1P
.LP
1.3.1
\fITransmission access test lines\fR
.sp 9p
.RT
.PP
The transmission access test line is a dialable test line intended to be
located at the circuit maintenance test position or test console location
associated with the international switching centres. These test lines are
expected to be used as a test access point to make a variety of manual
transmission tests. They may also be used for voice communication purposes
associated with the circuit testing.
.PP
The proposed dialling plan for these test lines enables a particular test
position or console to be selected when the distant switching centre is
equipped for this type of dialling access. If the normal test position
number (access code) is busy, it is expected that the call should route
to an idle
test position number via a hunting group. Generally, the allocation of
access codes should allow the digits\ 21 (see \(sc\ 2.4.2) to cause the
incoming test line call to route to the test position or maintenance console
normally assigned to the particular circuit group over which the incoming
call originated. Then the use of digits\ 22 to\ 29 (non CCITT\ No.\ 6 signalling)
would allow the
maintenance personnel to make a test line call to a specific test position
or maintenance console at the distant location. This will allow both flexibility
in assigning the test positions and consoles, and may also relieve the
need for all test positions or consoles to be equipped with the same test
equipment.
.RT
.sp 1P
.LP
1.3.2
\fIOther test and/or communication lines\fR
.sp 9p
.RT
.PP
A requirement exists for the provision of lines for manual
switching and signalling tests and for the provision of facilities for
a fault report point (circuit) or a fault report point (network). Codes
will be
allocated to these lines when the requirements are fully defined.
.RT
.sp 1P
.LP
1.4
\fIEcho suppressor test line\fR
.sp 9p
.RT
.PP
The echo suppressor test line is a dialable 4\(hywire test line
intended to terminate the echo suppressor testing system (ESTS) (see
Recommendation\ O.25) responder on an international switching centre. This
test line will allow the maintenance personnel at the distant switching
centre using the ESTS director equipment to make one\(hyman semi\(hyautomatic
echo suppressor
tests on the circuits between the two centres.
.bp
.RT
.sp 2P
.LP
1.5
\fILoopback test line\fR
.sp 1P
.RT
.sp 1P
.LP
1.5.1
\fIAnalogue loopback test line\fR
.sp 9p
.RT
.PP
The loopback test line is a dialable 4\(hywire test line that
initially returns a nominal 1020\ Hz \(em10\ dBm0 tone for 13 to 15\ seconds.
After the initial tone period, the test line should present a balanced
600\ ohm
termination to the \*QRETURN\*U direction for the next 13 to 15\ seconds.
The \*QGO\*U direction should also be terminated in a 600\(hyohm balanced
termination during
both these first two intervals.
.PP
After the second interval, the 600\(hyohm terminations should be
disconnected. Finally, the \*QGO\*U and the \*QRETURN\*U directions should
be connected (looped around) in the test responder at the correct level
until released by
the calling station.
.PP
The intent of this test facility is to provide a one\(hyman manual means
of performing fast transmission tests (level and noise) in both directions.
It will also allow seizure and rapid testing by an automatic device at
the calling station.
.RT
.sp 1P
.LP
1.5.2
\fIDigital loopback test line\fR
.sp 9p
.RT
.PP
The digital loopback test line provides a dialable 4\(hywire test line
capability intended both for use in measuring the error performance of
international digital circuits and as a quick method of verifying the
continuity of wholly digital, non\(hyPCM encoded and mixed analogue/digital
circuits. It consists of circuitry that accepts and loops back on a digital
basis the signal from a circuit. The test signal may be any arbitrary digital
test pattern or analogue test signal.
.PP
Once the tester has accessed the test line at a remote location, the tester
may transmit the desired analogue test signals or digital test patterns.
The tester may examine the returning signal for the received power (or
continuity) of the analogue test signals or the error performance (or
continuity) of the digital test patterns.
.PP
The proposed dialling plan for this test line enables a particular
line to be selected when the distant switching centre is equipped for this
type of dialling access. If the normal test line number (access code) is
busy, it is expected that the call should route to a busy indication.
.RT
.sp 1P
.LP
1.6
\fIEcho canceller test line\fR
.sp 9p
.RT
.PP
The echo canceller test line is a dialable 4\(hywire test line
intended to terminate the echo canceller test responder.
.PP
This test facility will allow maintenance personnel at the originating
switching centre to make tests of the echo canceller(s) on the circuit
under
test. Whether the test will be made on both echo cancellers or just the echo
canceller at the responder end of the circuit under test will depend on the
type of directing equipment being used.
.RT
.sp 1P
.LP
1.7
\fIATME No. 2 test lines\fR
.sp 9p
.RT
.PP
The ATME No. 2 test lines are dialable 4\(hywire test lines intended to
terminate the ATME\ No.\ 2 responders (see Recommendation\ O.22). The
responding equipment is available in two forms:
.RT
.LP
a)
a signalling system functional testing and transmission
measuring device (type\ \fIa\fR );
.LP
b)
a signalling system function testing device
(type \fIb)\fR .
.PP
The ATME No. 2 equipment, consisting of directing equipment at the outgoing
end and responding equipment at the incoming end, is intended to make automatic
transmission measurements and signalling system functional tests on all
categories of international circuits terminating in exchange with 4\(hywire
switching.
.sp 1P
.LP
1.8
\fIBusy flash signal test line\fR
.sp 9p
.RT
.PP
The busy flash test line is a dialable 4\(hywire test line intended
for use with the ATME\ No.\ 2 directing equipment (see Recommendation\
O.22). This test line, which is also referred to as type\ \fIc\fR responding
equipment in
Recommendation\ O.22, is required in cases when the signalling system used on
.PP
the circuits to be tested provides a busy flash signal. This test line
functionality may be provided within the exchange equipment or by separate
responding equipment.
.bp
.RT
.sp 2P
.LP
\fB2\fR \fBMethod of access\fR
.sp 1P
.RT
.PP
2.1
In general, access arrangements should conform to the
Recommendation\ M.565\ [1].
.sp 9p
.RT
.PP
2.2
Access to the test lines at the incoming international exchange
will be gained via the normal exchange switching equipment on a 4\(hywire
basis on all incoming and both\(hyway circuits.
.PP
2.3
The wiring loss build\(hyout arrangements for the test lines should conform
to the Recommendation\ M.565.
.sp 2P
.LP
2.4
\fIAddress information\fR
.sp 1P
.RT
.sp 1P
.LP
2.4.1
\fIAddress information sequence\fR
.sp 9p
.RT
.PP
The following address information will be used to gain access to
the maintenance access lines at the incoming international exchange:
.RT
.LP
i)
\fICCITT Signalling System No. 4\fR
.LP
a)
terminal seizing signal,
.LP
b)
code 13,
.LP
c)
code 12,
.LP
d)
digit 0,
.LP
e)
two digits associated with the particular
international test line type to be accessed (see \(sc\ 2.4.2 below),
.LP
f)
code 15.
.LP
ii)
\fICCITT Signalling System No. 5\fR
.LP
a)
KP1,
.LP
b)
digit 7 (non\(hyallocated language digit),
.LP
c)
code 12,
.LP
d)
digit 0,
.LP
e)
two digits associated with the particular
international test line type to be accessed (see \(sc\ 2.4.2 below),
.LP
f)
ST.
.LP
iii)
\fICCITT Signalling System No. 6\fR
.LP
The initial address message format for access to testing
devices is given in Recommendations\ Q.258\ [2] and Q.259\ [3]. The X\ digit
allocation should be as follows:
.LP
a)
1 (ATME No. 2 responding equipment type \fIa\fR for
signalling tests and transmission measurements),
.LP
b)
2 (ATME No. 2 responding equipment type \fIb\fR for
signalling tests only),
.LP
c)
3 (quiet termination test line),
.LP
d)
4 (echo suppressor test line),
.LP
e)
5 (loopback test line),
.LP
f)
6, 7 and 8 (transmission access test line). (See
Note),
.LP
g)
9 (echo canceller test line),
.LP
h)
10 (digital loopback test line).
.LP
\fINote\fR \ \(em\ The allocation of the X digit is under the responsibility
of Study Group\ XI. In Signalling System No. 6, the bits of the access
codes
(bit pattern) sent on the line need not be identical with the actual access
code number used by the maintenance staff. As Signalling System\ No.\ 6 will
mainly be used together with SPC exchanges, it will be possible to translate
any access code into an appropriate bit pattern.
.LP
iv)
\fICCITT Signalling System No. 7\fR
.LP
The initial address message format for access to testing
devices is given in Recommendation\ Q.722\ [4]. The two digits associated with
the particular international test line to be accessed are given in \(sc\ 2.4.2.
.LP
v)
\fICCITT Signalling System R1\fR
.LP
a)
KP,
.LP
b)
digits to be agreed upon between the Administrations concerned,
.LP
c)
ST.
.bp
.LP
vi)
\fICCITT Signalling System R2\fR
.LP
a)
test call indicator,
.LP
b)
code I\(hy13,
.LP
c)
two digits associated with the particular
international test line type to be accessed (see \(sc\ 2.4.2 below),
.LP
d)
code I\(hy15 (on request).
.sp 1P
.LP
2.4.2
\fITest line codes for CCITT Signalling Systems No. 4, 5, 7\fR
\fIand R2\fR \v'3p'
.sp 9p
.RT
.LP
i)
ATME No. 2 responding equipment type a
\ \ | 1
.LP
ii)
ATME No. 2 responding equipment type b
\ \ | 2
.LP
iii)
Busy flash signal
\ \ | 3
.LP
iv)
quiet termination
\ \ | 4
.LP
v)
echo suppressor
\ \ | 5
.LP
vi)
analogue loopback
\ \ | 6
.LP
vii)
digital loopback
\ \ | 8
.LP
viii)
multiple address capability for transmission access
test line
\ 21\(hy29
.LP
ix)
echo canceller test line
\ \ | 7
.sp 2P
.LP
\fB3\fR \fBSpecifications for the test line apparatus\fR
.sp 1P
.RT
.PP
The following specifications apply to all test line types unless
otherwise noted and apply over the range of climatic conditions specified in
Recommendation\ O.3.
.RT
.sp 1P
.LP
3.1
\fITone source characteristics (quiet termination and loopback\fR
\fItest lines)\fR \v'3p'
.sp 9p
.RT
.LP
a)
The nominal tone source frequency should fall within 1004 to 1020 Hz.
The tone source frequency including tone source stability and aging
should remain within 1002 to 1025\ Hz.
.LP
b)
Purity of output: ratio of total output to unwanted signal at least 50\ dB.
.LP
c)
Long\(hyterm level stability: \(+- | .03 dB.
.sp 1P
.LP
3.2
\fITransmitted level and timing intervals (quiet termination\fR
\fIand loopback test lines)\fR \v'3p'
.sp 9p
.RT
.LP
a)
The test tone level to be transmitted should be \(em10 dBm0
\(+- | .1\ dB.
.LP
b)
Tone interval for quiet termination test line: 14 s \(+-\ 1.0 s. Tone
and quiet termination intervals for the loopback test line: 14\ s
\(+- | .0\ s.
.sp 1P
.LP
3.3
\fIImpedance\fR \v'3p'
.sp 9p
.RT
.LP
a)
600 ohms, balanced.
.LP
b)
For all cases, longitudinal conversion loss (see
Figure\ 1/O.9): at least 46\ dB between 300 and 3400 | z increasing below
300\ Hz to at least 60\ dB at 50\ Hz.
.sp 1P
.LP
3.4
\fIReturn loss\fR
.sp 9p
.RT
.PP
At least 46 dB at 1020 Hz, and at least 30 dB between 300 and
3400\ Hz.
.RT
.sp 1P
.LP
3.5
\fIFrequency response\fR \v'3p'
.sp 9p
.RT
.LP
a)
\(+- | dB from 300 to 3000 Hz (quiet termination, echo
suppressor, echo canceller and loopback test lines).
.LP
b)
\(+- | .5 dB from 300 to 3000 Hz (transmission access test
line).
.bp
.sp 1P
.LP
3.6
\fILoopback test line level adjustment\fR
.sp 9p
.RT
.PP
The loopback test line equipment shall provide the proper buildout (loss
or gain) in the loopback measurement path to adjust its level to within
\(+- | .1\ dB of the required nominal value. The required nominal value
should be
determined using Recommendation\ M.560\ [5] and the reference level points at
which the loopback test line is employed.
.RT
.sp 1P
.LP
3.7
\fIDigital loopback test\fR
.sp 9p
.RT
.PP
The digital loopback test line provides a dialable, 4\(hywire test
line capability; this type of test line accepts and loops back received
octets from a digital circuit. The octets when looped back, are retransmitted
so that the positions of the bits within the octet are preserved; that
is, the most
significant bit of the retransmitted octet corresponds to the most significant
bit of the received octet, and so forth.
.PP
The loopbacks may be integrated into the switching network of the
digital switching machine, or may be provided in a stand\(hyalone mode,
having an external 4\(hywire 64\ kbit/s appearance on the switching machine,
similar to
existing test lines.
.RT
.sp 2P
.LP
\fB4\fR \fBSignalling system test line test sequence\fR
.sp 1P
.RT
.sp 1P
.LP
4.1
\fICircuit seizure\fR
.sp 9p
.RT
.PP
When an outgoing circuit is to be seized and connected at the
distant end to one of the international test lines, the appropriate address
information is transmitted in accordance with the specification for the
signalling system in use (see \(sc\ 2.4).
.RT
.sp 1P
.LP
4.2
\fITest line answer\fR
.sp 9p
.RT
.PP
When access is gained to the test line equipment, the answer signal (answer,
no charge if Signalling System\ No.\ 6) will be transmitted. If the test
line is occupied, a busy indication should be returned to the originating
end in accordance with the normal signalling for the circuit and for the
address
concerned.
.RT
.sp 1P
.LP
4.3
\fITest line not equipped\fR
.sp 9p
.RT
.PP
When a test line call is received at a switching centre not
equipped to handle that type of test call, the called switching centre
should respond with the standard \*Qunallocated number\*U signal where
available for the signalling system employed.
.RT
.sp 2P
.LP
\fBReferences\fR
.sp 1P
.RT
.LP
[1]
CCITT Recommendation \fIAccess points for international telephone\fR
\fIcircuits\fR , Vol.\ IV, Rec.\ M.565.
.LP
[2]
CCITT Recommendation \fITelephone signals\fR , Vol. VI, Rec. Q.258.
.LP
[3]
CCITT Recommendation \fISignalling\(hysystem\(hycontrol signals\fR ,
Vol.\ VI. Rec.\ Q.259.
.LP
[4]
CCITT Recommendation \fIGeneral function of telephone messages\fR
\fIand signals\fR , Vol.\ VI, Rec.\ Q.722.
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[5]
CCITT Recommendation \fIInternational telephone circuits \(em principles,\fR
\fIdefinitions and relative transmission levels\fR , Vol.\ IV, Rec.\ M.560.
.LP
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Blanc
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