InfoMagic Standards 1993 July/Disc.iso/ccitt/1988/troff/4_1_12.tro

Text File | 1991-12-13 | 112.1 KB | 3,722 lines

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.rs
\v | 5i'
.LP
\fBMONTAGE: REC.722 EN\(hyT\* | TE DE CETTE PAGE\fR
.sp 2P
.LP
\v'15P'
\fBRecommendation\ M.723\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBCIRCUIT\ CONTROL\ STATION\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.723''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.723    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBDefinition of circuit control station\fR
.sp 1P
.RT
.PP
The circuit control station is the point within the general
maintenance organization for the international automatic and semi\(hyautomatic
telephone service that fulfils the control responsibilities for the automatic
circuits assigned to\ it.
.PP
The responsibilities, functions and criteria for appointing circuit
control stations given in \(sc\(sc\ 2 to\ 4 below apply to circuits provided
solely by analogue transmission and switching systems and those involving
a
mixture   of analogue and digital systems
.
.RT
.sp 2P
.LP
\fB2\fR     \fBResponsibilities\fR
.sp 1P
.RT
.PP
The circuit control station is responsible for ensuring that an
automatic circuit assigned to it is set up and maintained to the required
standards in both directions of transmission and that, if the circuit fails,
the outage time is kept to a minimum.
.RT
.sp 2P
.LP
\fB3\fR     \fBFunctions\fR
.sp 1P
.RT
.PP
3.1
Arranging for the setting\(hyup of the circuit, and of the
signalling and switching equipment associated directly with the circuit, and
the related adjustment.
.sp 9p
.RT
.PP
3.2
Controlling lining\(hyup measurements to within the recommended
limits.
.PP
3.3
Ensuring that routine maintenance measurements and tests are
carried out in accordance with the agreed schedule using the specified
methods and in such a way that interruptions to service are limited to the
shortest possible duration.
.PP
3.4
Requesting that the circuit sub\(hycontrol station take action as
required.
.PP
3.5
Arranging for the blocking of circuits as required.
.PP
3.6
Ensuring that fault location and clearing is carried out by the
responsible testing point and/or maintenance unit in a proper manner.
.PP
3.7
Initiating investigation of repeated circuit faults.
.PP
3.8
Controlling the withdrawal of circuits from service.
.PP
3.9
Controlling the return of circuits to service, after the fault
clearance.
.PP
3.10
Being continuously informed of the condition of the automatic
circuits under its control.
.bp
.PP
3.11
Keeping up to date records of the routing of the automatic
circuits under its control.
.PP
3.12
Knowing what are the possibilities of rerouting any faulty
circuits and making arrangements for such reroutings where necessary.
.sp 2P
.LP
\fB4\fR     \fBAppointment of circuit control stations\fR
.sp 1P
.RT
.PP
A circuit control station is appointed for each international
circuit used for the automatic and semi\(hy
automatic telephone service. When
the circuit is operated unidirectionally the circuit control station is
.PP
generally at the outgoing end. When the circuit is operated both\(hyway, the
circuit control station can be at either end by common agreement between the
technical services of the Administrations concerned. In making the choice,
special consideration will be given to:
.RT
.LP
    \(em
     whether the location to be nominated as the circuit control station is
permanently attended,
.LP
    \(em
    the amount of work at each terminal point,
.LP
    \(em
    the length of the circuit within the territory of each
terminal country.
\v'2P'
.sp 2P
.LP
\fBRecommendation\ M.724\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBCIRCUIT\ SUB\(hyCONTROL\ STATION\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.724''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.724    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBDefinition of circuit sub\(hycontrol station\fR
.sp 1P
.RT
.PP
The circuit sub\(hycontrol station is a point within the general
maintenance organization for the international automatic and semi\(hyautomatic
telephone service that assists the circuit control station and fulfils the
control responsibilities for a circuit section assigned to it.
.PP
The responsibilities, functions and criteria for appointing circuit
sub\(hycontrol stations given in \(sc\(sc\ 2 to\ 4 below apply to circuits
provided solely by analogue transmission and switching systems and those
involving a
mixture of analogue and digital systems
.
.RT
.sp 2P
.LP
\fB2\fR     \fBResponsibilities\fR
.sp 1P
.RT
.PP
It is the responsibility of the circuit sub\(hycontrol station to
inform the circuit control station about all noted events likely to affect
the circuit under their control. If the circuit sections are assigned to
the
circuit sub\(hycontrol for the purpose of controlling them, the circuit
sub\(hycontrol is responsible for these circuit sections in the same way as the
circuit control station is for the complete circuit.
.RT
.sp 2P
.LP
\fB3\fR     \fBFunctions\fR
.sp 1P
.RT
.PP
3.1
Performing the control functions for circuit sections,
especially national sections, as given for the circuit control
station.
.sp 9p
.RT
.PP
3.2
Cooperating with the circuit control station and other circuit
sub\(hycontrol stations in ensuring that routine maintenance fault location and
clearance are carried out by the responsible testing points and/or maintenance
units in a proper manner.
.PP
3.3
Arranging that all relevant details concerning the location and
subsequent clearance of faults are reported to the fault report point (circuit)
at the controlling end.
.bp
.sp 2P
.LP
\fB4\fR     \fBAppointment of circuit sub\(hycontrol stations\fR
.sp 1P
.RT
.PP
For each circuit used for the automatic and semi\(hyautomatic
telephone service a terminal circuit sub\(hycontrol station is appointed.
This is generally the end of the circuit remote from the circuit control
station. In
transit countries in which a circuit is brought to audio frequencies, an
intermediate circuit sub\(hycontrol station is appointed at a suitable
point for each direction of transmission. It is left to the Administration
concerned to choose:
.RT
.LP
    \(em
    where this point shall be,
.LP
    \(em
     whether the sub\(hycontrol functions for the two directions of transmission
are vested in one station or two stations,
.LP
    \(em
     whether, as may be desirable in the case of a large country, each direction
of transmission has more than one circuit sub\(hycontrol
station per transit country.
.PP
The technical service of the Administration concerned indicates
its choice to the technical service of the Administration responsible for
the control station.
.sp 2P
.LP
\fBRecommendation\ M.725\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBRESTORATION\ CONTROL\ POINT\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.725''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.725    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBDefinition of restoration control point (RCP)\fR
.sp 1P
.RT
.PP
The restoration control point (RCP) is an element within the
general maintenance organization for the international telecommunication
services. It initiates and coordinates service restoration activities in
case of failures or planned outages of transmission systems in accordance
with plans and \fIad hoc\fR arrangements agreed by the technical services
of the
Administrations concerned.
.PP
Since two or more RCPs are involved in agreed restoration plans, it is
practical to nominate one RCP as the Overall RCP which then initiates and
controls implementation of the plan. The additional responsibilities and
functions of an Overall RCP are given in \(sc\ 3 below.
.RT
.sp 2P
.LP
\fB2\fR     \fBResponsibilities and functions\fR
.sp 1P
.RT
.PP
The restoration control point (RCP) is responsible for the
following set of functions:
.RT
.PP
2.1
Initiating the implementation of a restoration plan and \fIad\fR \fIhoc\fR
arrangements with the other stations involved within its
Administration's boundaries.
.sp 9p
.RT
.PP
2.2
Monitoring the implementation of the restoration plan.
.PP
2.3
Coordinating the restoration activities of the repeater stations and other
stations involved within its Administration's boundaries.
.PP
2.4
Liaising with restoration control points of other Administrations as necessary
and agreeing the times of events with them.
.PP
2.5
Exchanging information with the network management
(
implementation and control point
) (see Recommendation\ E.413\ [1])
for coordination purposes as appropriate.
.PP
2.6
Monitoring and coordinating the return to normal service
conditions after the fault has been cleared or the planned work has been
finished.
.PP
2.7
Keeping, throughout the period during which the restoration and
the return to normal conditions is executed, an accurate log of events,
including any circuit, channel, group, supergroup, etc., or baseband patching
which takes place.
.PP
2.8
Requesting and receiving reports from other RCPs and disseminating this
information within its own Administration as required.
.PP
2.9
Reporting the events to the responsible authorities of
its Administration as desired and advising the system availability information
point about the progress of restoration.
.bp
.PP
2.10
Sending a final restoration report, after the return to normal,
containing all relevant data (including agreed times) for accounting purposes
to the responsible authorities within its Administration.
.PP
2.11
If no restoration plan exists or, for some reason, an existing
plan cannot be implemented, advising the responsible authorities in
its own Administration and suggesting suitable \fIad hoc\fR arrangements in the
light of the information available.
.sp 2P
.LP
\fB3\fR     \fBAdditional responsibilities of an overall RCP\fR
.sp 1P
.RT
.PP
The responsibilities of an overall RCP are much the same as an
ordinary RCP but with additional responsibilities as follows:
.RT
.PP
3.1
Initiating the implementation of a restoration plan with other  RCPs concerned.
.sp 9p
.RT
.PP
3.2
Requesting and receiving reports from other RCPs and disseminating this
information as necessary.
.PP
3.3
Coordinating and controlling all restoration activities including the return
to normal conditions.
.sp 2P
.LP
\fB4\fR     \fBFacilities\fR
.sp 1P
.RT
.PP
The restoration control point should be provided with the following facilities:
.RT
.PP
4.1
Appropriate communication facilities in order to assume its
responsibilities.
.sp 9p
.RT
.PP
4.2
Access to information appropriate to its functions and this
includes:
.LP
    a)
    status of relevant international transmission systems;
.LP
    b)
    current restoration plans;
.LP
    c)
    list of the sections of border\(hycrossing transmission traffic
routes;
.LP
    d)
    routing information for international group, supergroup, etc.,
links;
.LP
    e)
    inventory of spare transmission facilities, in its own and
neighbouring countries, lending themselves to restoration.
.sp 2P
.LP
    \fBReference\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIInternational network management \(hy Planning\fR , |
Vol.\ II, Rec.\ E.413.
.sp 2P
.LP
\fBRecommendation\ M.726\fR
.RT
.sp 2P
.ce 1000
\fBMAINTENANCE ORGANIZATION FOR THE WHOLLY DIGITAL INTERNATIONAL\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.726''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.726    %'
.ce 0
.sp 1P
.ce 1000
\fBAUTOMATIC AND SEMI\(hyAUTOMATIC TELEPHONE SERVICE\fR
.ce 0
.sp 1P
.PP
The recommended maintenance organization for a wholly digital international
telephone service is under study by Study Group\ IV. The detailed development
of such an organization cannot be undertaken until such time as
Administrations have gained sufficient experience of the operation and
maintenance of digital transmission and switching systems \(em these systems
being relatively few in number in the international network at present.
However,
based on present knowledge and experience, Study Group\ IV intends that the
maintenance organization for the fully digital international telephone
service be based on the following principles and concepts:
.sp 1P
.RT
.LP
    \(em
    That there be a gradual evolution of the current maintenance
organization (which is intended to cover the wholly analogue and
mixed analogue/digital situations) towards the organization
suitable for the wholly digital network. The rate of this
evolution will reflect the rate of introduction of digital
systems in the international and national networks.
.LP
    According to this principle, it is recognized that, in the
transition from a wholly analogue to a wholly digital network,
the maintenance organization of a particular international centre
may be responsible for wholly analogue, wholly digital and mixed
analogue/digital circuits since the three types may be
terminated at a single international centre.
.bp
.LP
    \(em
    That the \*Qelement\*U approach to defining a maintenance
organization, as currently used in Recommendations\ M.710
to\ M.725, be used to define future maintenance organizations.
.LP
    By the intended adoption of this concept it is recognized
that the maintenance element approach offers the means of
specifying a maintenance organization which can meet the needs of
all Administrations, irrespective of the number of international
circuits and international switching centres they operate.
.PP
In accordance with the current Study Group\ IV practice,
significant national trends in the area of maintenance organization (for
example, the trend towards increased centralization of maintenance) should
be reflected in the Series\ M Recommendations where appropriate.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ M.729\fR
.RT
.sp 2P
.ce 1000
\fBORGANIZATION\ OF\ THE\ MAINTENANCE\ OF\ INTERNATIONAL\ PUBLIC\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.729''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.729    %'
.ce 0
.sp 1P
.ce 1000
\fBSWITCHED\ TELEPHONE\ CIRCUITS\ USED\ FOR\ DATA\ TRANSMISSION\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
1.1
Data transmissions may be made over the public switched
telephone network in a manner similar to voice transmissions. Such data
calls, while expected in most cases to be satisfactory, cannot always be
assured
success in view of the variety of routing and transmission characteristics
that may be found in national extensions between international switching
centers and user stations.
.sp 9p
.RT
.PP
1.2
As the exact configuration of an international call is essentially impossible
to determine without an extensive and complicated tracing process, some
means must be specified to enable each Administration to investigate, as
it considers necessary, reports of data transmission difficulties.
.sp 2P
.LP
\fB2\fR     \fBFault investigations and maintenance\fR
.sp 1P
.RT
.PP
2.1
Each country agreeing to the transmission of data over the public switched
telephone network shall set up a
Data Coordinating Point
(DCP)
.FS
The term \*Qpoint\*U is used in the same sense as in the M.700\ series
of Recommendation\ \(em\ see particularly Recommen\(hy
dations\ M.710.
.FE
. This point:
.sp 9p
.RT
.LP
    \(em
    shall be the contact point between Administrations for
referring data transmission difficulties for investigation in
respective national networks;
.LP
    \(em
    shall be the point to undertake discussions and agree on a
course of action to be taken on public telephone network
circuits regarding data transmission difficulties. It should be
noted that agreement may be reached to take no actions regarding
the international circuits;
.LP
    \(em
    shall initiate any actions related to national network
extensions in accordance with its national practices and
procedures.
.PP
2.2
Fault investigations undertaken should be on the basis of the
transmission requirements of public telephone calls. Such investigations,
while possibly initiated by a DCP, will be carried out by the maintenance
organization (Recommendation\ M.710) according to standards defined by
Recommendation\ M.580,\ etc.
.LP
.sp 1
.bp
.PP
2.3
Transmission tests \fI(fault location or scheduled routine\fR
\fImeasurements)\fR between subscriber locations, that is, on an end\(hyto\(hyend
basis, are not expected to be made. Considering routing complexities and
the low
probability of duplicating an exact connection, such end\(hyto\(hyend tests
would not necessarily be meaningful and would be very difficult to coordinate.
However, if end\(hyto\(hyend tests are deemed to be essential by an Administration,
then such tests shall be implemented in accordance with agreements reached
by the
respective DCPs.
.PP
2.4
Routine maintenance measurements will be accomplished according
to agreements reached in conformity with Recommendation\ M.605.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ M.730\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMAINTENANCE\ METHODS\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.730''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.730    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
In order to meet the service demands of a progressive and rapidly expanding
international fully automatic telephone network with the best
possible quality of service, it is essential that all factors adversely
affecting the quality of service should be detected and service restored as
quickly as possible. In setting this objective it is recognized that perfect
performance is unattainable and that beyond a certain point, costs can rise
sharply out of proportion compared with service quality gain.
.PP
When choosing a suitable maintenance method or a combination of
methods one should consider:
.RT
.LP
    \(em
    the reliability of the plant to be maintained;
.LP
    \(em
    the availability of testing and supervisory facilities as
well as the availability and quality of manpower in the maintenance
organization;
.LP
    \(em
     the availability of facilities in the plant that indicate the existence
and frequency of disturbances;
.LP
    \(em
    the availability of arrangements for automatic remedial
action;
.LP
    \(em
    the availability of automatic means to process and analyse
operational data received from the plant;
.LP
    \(em
    the final objective i.e\ to ensure a satisfactory overall
service quality (subscriber\(hyto\(hysubscriber) in the international
connection, giving equal importance to the national and
international parts of the chain that constitute the connection.
.PP
It is recognized that a combination of maintenance methods may be  applied.
.sp 2P
.LP
\fB2\fR     \fBPreventive maintenance methods\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The introduction of
stored program control (SPC) exchanges
and digital transmission systems reduce the need for preventive maintenance.
SPC exchanges should in general be provided with functions which supervise
the signalling, switching and transmission processes. If a fault occurs
or if
pre\(hyset disturbance limits are reached, data which indicate the concerned
device(s) or circuit(s) should be printed out.
.PP
External supervision, testing and fault localization functions should be
avoided if internal functions in SPC exchanges or digital transmission
systems can provide the same facilities.
.RT
.sp 2P
.LP
2.2
    \fIFunctional tests\fR
.sp 1P
.RT
.PP
2.2.1
In carrying out functional tests, ordinary working conditions apply and
the equipment and circuits are taken as found.
.sp 9p
.RT
.PP
They are carried out on a systematic basis to discover faults that would
influence the quality of service. The response to each signal may be
tested by equipment provided for this purpose. Such tests may be applied
to any part of the signalling path.
.bp
.PP
2.2.2
Functional tests are carried out locally, or from either end of
an international circuit to the other.
.PP
2.2.3
The organization of the programme for carrying out functional
tests locally is left to the discretion of the Administration responsible
for the international exchange.
.PP
2.2.4
Overall functional tests on an international circuit are such that they
can be made from one end of the circuit without cooperation of technical
personnel at the other end of the circuit. These tests may utilize the
switching equipment at each end of the circuit, but such equipment is not
being tested directly, only the circuit.
.PP
The verification of satisfactory signalling operation may be done by using
various types of tests:
.LP
    \(em
    Certain types of tests not requiring any special equipment,
for example checking that a seizing signal is followed by the
return of a proceed\(hyto\(hysend signal and that a clear\(hyforward
signal is followed by the return of a release\(hyguard signal.
.LP
    \(em
    Other types combining several tests, using special equipment
at both ends. Any type which is in general use by Administrations
may be used if suitable and agreed between the Administrations
concerned
.FS
See the specification for the CCITT Automatic Transmission
Measuring and Signalling Testing Equipment ATME\ No.\ 2
(Recommendation\ O.22\ [1]).
.FE
.
.sp 2P
.LP
2.3
    \fICircuit limit tests\fR
.sp 1P
.RT
.PP
2.3.1
A circuit limit test is made to verify that the international circuit meets
specified operating margins. These tests enable the performance of the
whole international circuit to be checked. They will be made as required
but normally at the following times:
.sp 9p
.RT
.LP
    \(em
    before putting the circuit into service;
.LP
    \(em
     according to a systematic test programme which may be based on measurement
results or fault (trouble) statistics or quality of
service observations (see Recommendation\ M.605).
.PP
They may also be made if functional tests indicate a fault, in
order to locate such a fault.
.PP
Circuit limit tests may be made with respect either to
transmission or to signalling conditions.
.RT
.PP
2.3.2
The frequency of such tests will be determined by the
Administrations concerned and the test conditions to be applied will be in
conformity with CCITT Recommendations.
.PP
2.3.3
The test equipment, the specifications and methods of gaining
access to this equipment are described in the specifications of international
signalling, switching and transmission equipment.
.sp 2P
.LP
2.4
    \fILimit tests on the constituent parts of a circuit\fR
.sp 1P
.RT
.PP
2.4.1
These limit tests are made to verify that the constituent parts of a circuit
meet specified operating margins. They will be made as required
but normally at the following times:
.sp 9p
.RT
.LP
    \(em
    at installation;
.LP
    \(em
     if functional or limit tests on the circuit indicate a fault, if such
tests will help in fault location;
.LP
    \(em
    systematic test programmes which may be based on measurement
results or trouble statistics or quality of service
observations.
.PP
2.4.2
The frequency of such tests will be determined by the
Administrations concerned and the test conditions to be applied will be in
conformity with CCITT Recommendations.
.bp
.PP
2.4.3
Limit tests on constituent parts may indicate that the latter need to be
readjusted; in such a case, measurements are made on those constituent
parts and they are then readjusted in accordance with the relevant CCITT
Recommendations.
.PP
2.4.4
The test equipment, its specification and the provision of access points
will be determined by the Administration concerned taking into account
the relevant CCITT Recommendations.
.sp 2P
.LP
2.5
    \fIMaintenance measurements\fR
.sp 1P
.RT
.sp 1P
.LP
2.5.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
Maintenance measurements are made periodically on complete circuits (and
exceptionally, are indicated in Recommendation\ M.610 on their constituent
parts). Their object is to indicate whether the circuits and equipments
are
maintained to their specified values when first put into service and, if
not, to allow the necessary readjustment to be carried out.
.PP
Some maintenance measurements are made to check signalling; others are
made to check transmission. They are carried out by the respective technical
services responsible for signalling and transmission.
.RT
.sp 1P
.LP
2.5.2
    \fIMeasurements concerning signalling\fR
.sp 9p
.RT
.PP
The conditions for carrying out such measurements, the apparatus
used and the periodicity of operations are determined by the relevant
Series\ Q\ Recommendations. Interventions following such measurements are
determined by:
.RT
.LP
    a)
    CCITT Recommendations;
.LP
    b)
    equipment specifications when these are not given in detail  by the CCITT.
.PP
Information on the equipment and functions required are given in the Recommendations
listed in Table\ 1/M.730.
.ce
\fBH.T. [T1.730]\fR
.ce
TABLE\ 1/M.730
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(60p) | cw(60p) .
Signalling System    Recommendation
_
.T&
cw(60p) | cw(60p) .
No. 4    Q.138\ [2]
.T&
cw(60p) | cw(60p) .
No. 5    Q.164\ [3]
.T&
cw(60p) | cw(60p) .
No. 6    Q.295\ [4]
.T&
cw(60p) | cw(60p) .
R2    Q.490\ [5]
.T&
cw(60p) | cw(60p) .
No. 7    Q.707\ [6]
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 1/M.730 [T1.730], p.  \fR
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.5.3
    \fIMeasurements concerning transmission\fR
.sp 9p
.RT
.PP
These measurements include:
.RT
.LP
    \(em
     local measurements, for which the Administrations concerned decide the
conditions and periodicity;
.LP
    \(em
    circuit and line measurements for which the conditions are
generally defined in the Series\ M Recommendations.
.PP
These Series\ M Recommendations give, in particular, the
periodicity of the measurements and the conditions for readjustment of
transmission equipment. (See also Recommendation\ M.733.)
.PP
The CCITT has already specified certain transmission measuring
apparatus, and other apparatus specifications are being studied.
.bp
.RT
.sp 2P
.LP
\fB3\fR     \fBCorrective maintenance methods\fR
.sp 1P
.RT
.PP
These methods may apply to certain parts of the plant where it is possible
to locate and clear faults solely after they have affected the
service. Corrective maintenance, if exclusively practised in the entire
plant, can create unsatisfactory service conditions due to extreme variations
in
functional quality and can cause very irregular application of maintenance
effort.
.PP
The application of exclusively corrective maintenance methods would
presuppose such system design that even if breakdowns of single units or
parts of the plant occur, they should have a minor effect on the service
quality
offered to the subscribers.
.RT
.sp 2P
.LP
\fB4\fR     \fBControlled maintenance methods\fR
.sp 1P
.RT
.PP
Whereas it has been the practice to undertake programmes of
preventive maintenance procedures together with day\(hyto\(hyday corrective
maintenance procedures, recent equipment development has made it possible to
introduce new maintenance methods. Modern systems can provide immediate
information concerning the existence of irregularities and of abnormal
conditions. Although preventive maintenance gives a comparatively good
service, the number of defects caused by interference of preventive operations
may be
considerable.
.PP
A maintenance method utilizing the supervising facilities now
available may enable the maintenance organization to considerably reduce
preventive routines in the maintenance work. Preventive routine tests may
then be replaced by methods of continuous supervision of the function of the
plant and by means which check continuously the performance of the equipment
and give signals to the maintenance staff when the quality of service is
.PP
below a preset acceptance limit. Alternatively, when facilities for continuous
supervision are not available, a sampling technique could be introduced
to
determine the number of routine tests necessary to gain a reasonable assurance
that all equipments are in proper order.
.PP
Introduction of a system of maintenance control of this kind will
necessitate a certain degree of centralization of administrative and technical
means in the maintenance organization. Rapid and informative indication
of
the state and performance of the international and concerned parts of the
national network is required from the maintenance point of view at strategic
points in the network.
.PP
Various types of information on operational conditions in the plant
can be utilized for maintenance supervision purposes, such as:
.RT
.LP
    \(em
    traffic data;
.LP
    \(em
    accounting data;
.LP
    \(em
    maintenance data;
.LP
    \(em
    service performance data.
.PP
Such data may be analysed manually but could also be processed in computers,
allowing for a more extensive analysis, for instance, to compare
performance statistics with preset standards which are set for particular
.PP
routes, circuits, etc. Information held in the computer store may be extracted
on\(hyline and could be made directly available to those maintenance and
management centres where it is required.
.PP
Application of computer processing as described necessitates a high
degree of centralization, but also other factors support a centralized
maintenance organization such as the increasing use of network management
signals. The introduction of processor\(hycontrolled switching and digital
transmission systems is also expected to increase the possibilities to apply
remote controlled and centralized maintenance supervision methods in the
future.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fICCITT automatic transmission measuring and\fR
\fIsignalling testing equipment ATME\ No.\ 2\fR ,
Vol.\ IV, Rec.\ O.22.
.LP
[2]
    CCITT Recommendation \fIInstruments for checking equipment and\fR
\fImeasuring signals\fR , Vol.\ VI, Rec.\ Q.138.
.LP
[3]
    CCITT Recommendation \fITest equipment for checking equipment\fR
\fIand signals\fR , Vol.\ VI, Rec.\ Q.164.
.LP
[4]
    CCITT Recommendatiion \fITesting and maintenance\ \(em\ Overall tests of\fR
\fISignalling System No.\ 6\fR , | Vol.\ VI, Rec.\ Q.295.
.LP
[5]
    CCITT Recommendation \fITesting and maintenance\fR , Vol.\ VI, Rec.\ Q.490.
.LP
[6]
    CCITT Recommendation \fITesting and maintenance\fR , Vol.\ VI, Rec.\ Q.707.
.bp
.sp 2P
.LP
\fBRecommendation\ M.731\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSUBJECTIVE\ TESTING\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.731''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.731    %'
.ce 0
.sp 1P
.PP
\fB1\fR
The need for subjective testing of circuits depends to a great extent on
whether or not automatic or semi\(hyautomatic supervisory, testing and
fault localization equipment is already provided. For example, subjective
testing of circuits is not necessary on routes where ATME\ No.\ 2 (as described
in Recommendation\ O.22\ [1]) is available. Also, the supervisory and fault
localization functions built into
SPC exchanges
and digital
transmission systems reduce or even remove the need for subjective testing.
For those Administrations wishing to use subjective testing, the methods
described in \(sc\(sc\ 2\(hy4 below are recommended.
.sp 1P
.RT
.PP
\fB2\fR
Circuits used for the automatic and semi\(hyautomatic telephone
service may be tested subjectively to reveal gross faults, by systematic
test calls from circuit Terminal\ A to a telephone located at circuit Terminal\
B.
(See Figure\ 1/M.731.) Such test calling may be done independently of all
other tests or combined with functional signalling test calls as described
in the
\fISecond method\fR in Recommendations\ Q.139\ [2] and Q.163\ [3] for Signalling
Systems\ No.\ 4 and No.\ 5, respectively. Such test calls may be classed as
type\ 3 test calls as defined in Recommendation\ E.424\ [4]. They may be
applied on a periodic basis for systematically checking each trunk in a
group for
excessive echo, clipping, loss, noise, distortion and crosstalk. Any fault
suspected as a result of this subjective check should be investigated in the
normal manner. When type\ 3 test calls are used in this manner a test telephone
is assumed to exist at the distant international centre. The test telephone
is connected to a local exchange, if possible, not located at the same
point as
the international centre so as to permit a realistic appraisal of the
service quality. The test should be initiated at the outgoing terminal for
one\(hyway circuits and at both terminals sequentially on both\(hyway circuits.
Such test calls for checking service quality should be scheduled with the
distant international centre during light load periods.
.sp 9p
.RT
.PP
\fB3\fR
Another method of subjective testing, that may be
alternatively considered involves \fItype\ 1 test calls\fR as defined in
Recommendation\ E.424\ [4]. It permits systematic evaluation from Terminal\
A to a location at Terminal\ B which would not consist of a test telephone,
as shown
in Figure\ 1/M.731, but rather to a test location at Terminal\ B that is not
associated with a local exchange. Such an agreement might not be as effective
in detecting echo control problems (since the simulation of a normal connection
would be less realistic) but might be useful when the first technique suggested
above is impractical due to local conditions.
.sp 9p
.RT
.LP
.rs
.sp 17P
.ad r
\fBFigure 1/M.731, p.   \fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
\fB4\fR
In order to obtain the greatest value from subjective tests it might be
advantageous to apply them in association with the tests prescribed in
Recommendation\ M.610 and with \fIin\(hystation\fR tests such as those
for the
maintenance of echo suppressors.
.sp 9p
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation
\fIAutomatic transmission and signalling testing equipment ATME\ No.\ 2\fR ,
Vol.\ IV, Rec.\ O.22.
.LP
[2]
    CCITT Recommendation \fIManual testing\fR , Vol.\ VI, Rec.\ Q.139.
.LP
[3]
    CCITT Recommendation \fIManual testing\fR , Vol.\ VI, Rec.\ Q.163.
.LP
[4]
    CCITT Recommendation \fITest calls\fR , Vol. II, Rec.\ E.424.
\v'1P'
.sp 2P
.LP
\fBRecommendation\ M.732\fR
.RT
.sp 2P
.ce 1000
\fBSIGNALLING\ AND\ SWITCHING\ ROUTINE\ MAINTENANCE\ TESTS\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.732''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.732    %'
.ce 0
.sp 1P
.ce 1000
\fBAND\ MEASUREMENTS\fR
.ce 0
.sp 1P
.PP
The object of routine maintenance tests and measurements of
signalling and switching is to detect changes in the functioning of signalling
and switching which are likely to cause a reduction in the quality of service
provided. These changes are those which occur in relation to the values
indicated in the specifications for the signalling systems concerned (see
the pertinent Series\ Q Recommendations). In the various sections of the
Series\ Q Recommendations, limits are laid down within which:
.sp 1P
.RT
.LP
    \(em
    no action is necessary,
.LP
    \(em
    action is required by the maintenance service at either of
the terminal exchanges.
.PP
For
Signalling Systems
\ Nos.\ 4, 5, 6, 7 and R2, reference should be made to Recommendations\
Q.139\ [1], Q.163\ [2], Q.295\ [3], Q.707\ [4]
and Q.490\ [5] respectively which contain guidance on the methods to be
used for signalling and switching routine tests, together with the minimum
frequencies at which such tests should be carried out. On routes where
ATME\ No.\ 2
(Recommendation\ O.22\ [6]) is in use, many of the required tests and
measurements can be performed by that equipment. Supervision and fault
localization functions included in the exchange and/or in the transmission
system also reduce or remove the need for routine maintenance tests and
measurements.
.PP
Where staffing arrangements permit, manual and semi\(hyautomatic routine
maintenance of signalling and switching equipment should be done at times
when traffic is light. Any routines performed during normal working hours
must be
carried out with great care to ensure that the effect on live traffic is
minimized.
.PP
In
stored program control
(SPC) and digital exchanges many of the required checks for correct functioning
of signalling and switching
equipment are carried out automatically by supervisory functions within the
exchange, thus removing the need for the majority of manual and semi\(hyautomatic
routine tests. One of the characteristics of such supervisory functions
is that performance \*Qthresholds\*U have to be set which, if exceeded,
cause appropriate outputs to alert maintenance staff (for example, alarms,
printouts,\ etc.).
Maintenance staff should not only ensure that all relevant supervisory
functions are invoked, but must regularly review the thresholds set to
ensure that faults and problems will be detected before service is unacceptably
affected.
.PP
Where the outputs to maintenance staff from SPC and digital exchanges indicate
that a fault exists or is suspected, suitable action must be taken to localize
the problem. Before seeking cooperation from the distant maintenance centre,
maintenance staff shall ensure that the problem is not within their own
exchange. As examples, ATME\ No.\ 2 (Recommendation\ O.22\ [6]) the facilities
given in Recommendation\ O.11\ [7] and the internal self\(hydiagnostic routines
within the exchange should be used to this end.
.bp
.PP
In view of the variety of different types of international exchange
now in use and the differing facilities offered by these exchanges, it
is not possible to specify any particular periodicity for routine maintenance
tests on signalling and switching equipment. The most appropriate periodicity
must be
established by the Administration concerned based on such factors as:
.RT
.LP
    \(em
    the availability of staff;
.LP
    \(em
    the technology of the exchange (for example, crossbar,
Strowger, digital);
.LP
    \(em
    the incidence of faults and problems within the exchange;
.LP
    \(em
    the possible need for cooperation from distant maintenance
centres;
.LP
    \(em
    the periodicities recommended by the manufacturer of the
exchange or equipment involved;
.LP
    \(em
    the periodicities given in the Series Q Recommendations cited above.
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIManual testing\fR , Vol.\ VI, Rec.\ Q.139.
.LP
[2]
    CCITT Recommendation \fIManual testing\fR , Vol.\ VI, Rec.\ Q.163.
.LP
[3]
    CCITT Recommendation \fITesting and maintenance\ \(em\ Overall tests of\fR
\fISignalling System No.\ 6\fR , Vol.\ VI, Rec.\ Q.295.
.LP
[4]
    CCITT Recommendation \fITesting and maintenance\fR , Vol.\ VI, Rec.\ Q.707.
.LP
[5]
    CCITT Recommendation \fITesting and maintenance\fR , Vol.\ VI, Rec.\ Q.490.
.LP
[6]
    CCITT Recommendation \fICCITT automatic transmission measuring and\fR
\fIsignalling testing equipment ATME\ No.\ 2\fR ,
Vol.\ IV, Rec.\ O.22.
.LP
[7]
    CCITT Recommendation \fIMaintenance access lines\fR , | Vol.\ IV, Rec.\ O.11.
.sp 2P
.LP
\fBRecommendation\ M.733\fR
.RT
.sp 2P
.ce 1000
\fBTRANSMISSION\ ROUTINE\ MAINTENANCE\ MEASUREMENTS\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.733''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.733    %'
.ce 0
.sp 1P
.ce 1000
\fBON\ AUTOMATIC\ AND\ SEMI\(hyAUTOMATIC\ TELEPHONE\ CIRCUITS\fR
.ce 0
.sp 1P
.PP
The object of routine maintenance measurements is to detect
changes in transmission conditions before such changes cause a reduction
in the quality of service provided. These changes are those which occur
relative to
the values recorded for maintenance purposes for the circuits or link
concerned. In the various sections of the Series\ M Recommendations limits
are laid down within which:
.sp 1P
.RT
.LP
    \(em
    no readjustment is necessary,
.LP
    \(em
    readjustment may be made at the terminal stations,
.LP
    \(em
    readjustment must be made along the whole circuit or
link.
.PP
Routine maintenance measurements should be made according to an
agreed maintenance schedule (see Recommendation\ M.605). The periodicities
for the measurements are given in Tables\ 1/M.610 and\ 2/M.610. These are
to be considered as recommended values and may be increased or reduced
if special
circumstances require.
.PP
Routine maintenance measurements must normally be made at times of
light traffic, where staffing arrangements permit. If such measurements
have to be made on a large group of circuits, it may nevertheless be necessary
to do
the measurements on some of the circuits during the busy period, if the
operating services are not adversely affected thereby.
.PP
Circuits on a given route are generally measured in batches based on the
way in which the maintenance schedule has been arranged (see
Recommendation\ M.605). The advantages are:
.RT
.LP
    \(em
     once cooperation has been arranged for routine testing with a distant
station, time is saved if test cooperation can be
maintained for as long as necessary;
.LP
    \(em
    testing a large number of circuits on one route within a
fairly short period enables a more accurate overall notion of the route
to be obtained than could be gained from measurements on only a few circuits.
.PP
Routine maintenance measurements should be made on a complete
circuit and should include measurements of overall loss and levels at one
and several frequencies, stability (for 2\(hywire audio circuits only),
and noise.
.bp
.sp 2P
.LP
\fBRecommendation\ M.734\fR
.RT
.sp 2P
.ce 1000
\fBEXCHANGE\ OF\ INFORMATION\ ON\ INCOMING\ TEST\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.734''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.734    %'
.ce 0
.sp 1P
.ce 1000
\fBFACILITIES\ AT\ INTERNATIONAL\ SWITCHING\ CENTRES\fR
.ce 0
.sp 1P
.PP
The attention of Administrations is drawn to the need to exchange information
on the incoming test facilities which they have provided at their international
switching centres. The exchange of such information has an
important bearing on maintenance efficiency since it helps to avoid unnecessary
requests for maintenance cooperation and the under utilization of the
facilities which have been provided.
.sp 1P
.RT
.PP
The form to be used for this purpose is shown in Figure 1/M.734. It provides,
for the international switching centre and signalling system
concerned, a description of the available test facilities, their CCITT
.PP
reference (where applicable), the access code to be used, and any necessary
remarks (for example, an outline of the response to be expected where the
facility is not specified by CCITT). Figure\ 2/M.734 shows a hypothetical
example of this form completed for a particular international switching
centre.
.PP
Each Administration should distribute the completed forms to other
Administrations as appropriate. Upon receipt, Administrations should arrange
that the information be distributed to the appropriate points within their
maintenance organization, for example, circuit control station, testing
point (transmission).
.RT
.sp 2P
.LP
    \fBReference\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fICCITT automatic transmission measuring and\fR
\fIsignalling testing equipment ATME No.\ 2\fR ,
Vol.\ IV, Rec.\ O.22.
.LP
.rs
.sp 30P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 1/M.734 [T1.734], p. 3\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 2/M.734 [T2.734], p. 4\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE: PAGE 428 = PAGE BLANCHE\fR
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 4
.ce 0
.sp 1P
.ce 1000
\fBCOMMON\ CHANNEL\ SIGNALLING\ SYSTEMS\fR
.ce 0
.sp 1P
.IP
\fB4.1\ Maintenance of common channel Signalling System No. 6\fR
.sp 1P
.RT
.sp 2P
.LP
\fBRecommendation\ M.750\fR
.RT
.sp 2P
.ce 1000
\fBINTER\(hyADMINISTRATION\ AGREEMENTS\ ON\ COMMON\ CHANNEL\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.750''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.750    %'
.ce 0
.sp 1P
.ce 1000
\fBSIGNALLING\ SYSTEM\ No.\ 6\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
The bringing into service of new telephone circuits and signalling systems
requires that a number of agreements be made in advance by the
Administrations involved. Examples of such agreements are:
.RT
.LP
    \(em
    routing of circuits (cable, satellite, etc.);
.LP
    \(em
    mode of operation (incoming, outgoing, both\(hyway);
.LP
    \(em
    circuit designations;
.LP
    \(em
    order of selection of both\(hyway circuits.
.PP
For common channel signalling systems, a number of agreements are  needed,
in addition to those required for
channel\(hyassociated signalling systems
(e.g.\ R2).
.PP
This Recommendation explains the principal inter\(hyAdministration
agreements which must be made in advance of opening a Signalling System
No.\ 6 service and is provided as guidance to those Administrations intending
to
operate such a service.
.PP
Many of the aspects covered by this Recommendation relate to matters contained
in the specification of Signalling System No.\ 6, as appearing in the Series\
Q Recommendations\ [1]. Where appropriate, cross references to such
Recommendations are given.
.RT
.sp 2P
.LP
\fB2\fR     \fBCommon channel \fR \fBSignalling System No.\ 6 (SS No.\ 6)\fR
.sp 1P
.RT
.PP
The introduction to the specification of SS No.\ 6 and
Recommendation\ Q.251\ [2] provide general and functional descriptions of the
signalling system.
.PP
Recommendation M.760 contains a basic diagram of SS No.\ 6 and a
general description of the (signalling) transfer link.
.bp
.RT
.sp 2P
.LP
\fB3\fR     \fBAspects of SS No. 6 requiring inter\(hyAdministration agreement\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fISignalling links and signalling security arrangements\fR
.sp 9p
.RT
.PP
Signals for a given group of speech circuits between two exchanges may
be \*Qassociated\*U (routed on a signalling link between the two exchanges),
\*Qnon\(hyassociated\*U (routed on two or more signalling links in tandem,
involving one or more signal\(hytransfer\(hypoints) or a mixture of both
(Recommendation\ Q.253, \(sc\ 1.3.1)\ [3]. The possible modes of operation
range from simple arrangements of one signalling link and associated mode
of signalling, to more complex
arrangements, for example, the fully dissociated mode where signals are
transferred via any available path in a signalling \*Qnetwork\*U.
.PP
Before entering detailed discussions on the type of signalling
security arrangements required, it is desirable that the terminal
Administrations exchange information on the type and manufacturer of their
international exchanges and the options available within their existing
software systems. This information will enable each Administration to have
an overall view of available signalling security arrangements; it will
avoid
misunderstandings and thus enable rapid progress in establishing detailed
arrangements. Subsequently, agreement on the following matters will be
required:
.RT
.LP
    i)
    The number of signalling links and reserves to be provided
(Recommendations Q.292 and\ Q.293)\ [4]\ [5]. In general, a choice
will be made between:
.LP
    \(em
    regular link plus synchronized reserve(s);
.LP
    \(em
    regular link plus non\(hysynchronized reserve(s). Such
non\(hysynchronized reserves may be
reserve transfer
links
or nominated speech circuit reserves.
.LP
Where the latter is chosen, the measures to be taken to
ensure that there is a high probability of one of the
chosen speech circuits being free (at both ends) when
required should be discussed between Administrations
(Recommendation\ Q.292, \(sc\ 8.4.3a))\ [4];
.LP
    \(em
    load\(hysharing
.
.LP
    ii)
    The order of selection (ranking order) of regular/reserve
signalling links, reserve transfer links and nominated speech
circuit reserves, as provided. Where non\(hysynchronized reserves
are concerned, the time each terminal exchange will attempt to
regain synchronization (5\ or 7.5\ seconds) must be agreed between
Administrations (Recommendation\ Q.293, \(sc\ 8.6.3.2)\ [5].
.LP
    iii)
    The order of selection between alternative signalling
routes (where more than one has been provided).
.LP
    iv)
    The need to specify an \*Qautomatic load transfer\*U procedure
(Recommendation\ Q.293, \(sc\ 8.6.3.2)\ [5].
.LP
    v)
    Which exchange will act as \*Qemergency restart control
exchange\*U (Recommendation\ Q.293, \(sc\ 8.7c))\ [5].
.sp 1P
.LP
3.2
    \fISignalling link routing and line\(hyup aspects\fR
.sp 9p
.RT
.PP
Administrations must reach agreement on the physical routing and
line\(hyup requirements of the signalling links and reserves. Among the aspects
which are important are:
.RT
.LP
    i)
    diversity of routing for alternative signalling links and
reserves, as required for security purposes;
.LP
    ii)
    the propagation delay of signalling links and reserves.
This should be as low as possible and should not be
significantly greater than that of any speech circuit with which
it is normally associated. By this means the possibility of the
called party being distorted or \*Qclipped\*U is reduced
(Recommendation\ Q.272)\ [6];
.LP
    iii)
    the existence or absence of restoration plans to restore
transmission facilities over which signalling links and reserves
are routed;
.LP
    iv)
    the transmission characteristics and limits to be used for
the transfer links (Recommendation\ M.761).
.sp 1P
.LP
3.3
    \fIMethod of signalling\fR
.sp 9p
.RT
.PP
Signalling System No.\ 6 provides for two basic methods of sending signalling
information namely, \*Qen\(hybloc\*U or \*Qoverlap\*U (Recommendations\
Q.262
and\ Q.265)\ [7]\ [8]. The method to be used for each direction of traffic
should be discussed between Administrations.
.bp
.RT
.sp 2P
.LP
3.4
    \fIUse of optional facilities\fR
.sp 1P
.RT
.sp 1P
.LP
3.4.1
    \fINetwork maintenance signals\fR
.sp 9p
.RT
.PP
Network maintenance signals are specified as an optional facility in the
specification of SS\ No.\ 6 (Recommendation\ Q.295, \(sc\ 9.5)\ [9]. Where
both terminal exchanges are equipped with these facilities, the involved
Administrations may wish to reach agreement on their use, for example to
facilitate recovery from major exchange or signalling system disturbances.
In making such agreements, it must be ensured that any \*Qsignal\(hytransfer\(hypoint\*U
involved between the two terminal exchanges is able to transfer the necessary
network maintenance signals.
.RT
.sp 1P
.LP
3.4.2
    \fIAutomatic repeat attempt\fR
.sp 9p
.RT
.PP
The specification for SS No.\ 6 requires that an automatic repeat
attempt be made in a number of specified call failure situations. However,
the potential exists to use an automatic repeat attempt in circumstances
other than those specified. Administrations may wish to discuss the advantages
(if any) of additional application of the automatic repeat attempt facility
(Recommendation\ Q.264)\ [10] and the implications, for example, on the
load on the signalling data link, of such additional use.
.RT
.sp 1P
.LP
3.5
    \fILabel assignment\fR
.sp 9p
.RT
.PP
By agreement between Administrations, each SS No.\ 6 speech circuit must
be assigned a \*Qlabel\*U, comprising a \*Qband number\*U and a \*Qcircuit
number\*U (Recommendation\ Q.257)\ [11]. Any relationship required between
the band
numbering scheme and the physical routing of the speech circuits (via cable,
via satellite, etc.) must also be agreed between Administrations. It may be
noted that there need be no relationship between the circuit number part
of the label and the circuit designation (which would be in accordance
with
Recommendation\ M.140). For convenience, however, it is desirable where
possible to retain an orderly and consistent equivalence between circuit
number and
circuit designation.
.RT
.sp 1P
.LP
3.6
    \fIDouble seizure of both\(hyway circuits\fR
.sp 9p
.RT
.PP
Signalling System No.\ 6 incorporates a procedure for dealing with a situation
where a both\(hyway circuit has been simultaneously seized at both ends
(Recommendation\ Q.263)\ [12]. This procedure requires that control and
.PP
non\(hycontrol exchanges be appointed for each (both\(hyway) circuit. It
may be noted that there need be no relationship between control and non\(hycontrol
exchanges
for double seizure and the circuit control and sub\(hycontrol stations
as defined in Recommendations\ M.723 and\ M.724 (unless so desired by the
involved
Administrations). For convenience, however, it is desirable where possible
that Administrations exercise both dual seizure control and maintenance
control over the same circuits.
.RT
.sp 1P
.LP
3.7
    \fISignal\(hytransfer\(hypoint working\fR
.sp 9p
.RT
.PP
Among the aspects upon which Administrations may need to reach
agreement are:
.RT
.LP
    i)
    label translation and the need for control of label
assignment (Recommendation\ Q.253, \(sc\ 1.3.3.2)\ [3];
.LP
    ii)
    financial accounting. Where the non\(hyassociated mode of
signalling has been adopted, either normally or as a signalling
security arrangement, signalling information will be relayed via
one or more signal\(hytransfer\(hypoints and would typically involve
one or more transit Administrations. Arrangements for any
.LP
necessary financial accounting may need to be discussed between
involved Administrations.
.PP
The inter\(hyAdministration aspects of signal\(hytransfer\(hypoint working
require further study based on the experience of Administrations.
.sp 1P
.LP
3.8
    \fIEngineering test programme\fR
.sp 9p
.RT
.PP
Details of an engineering test programme, to be carried out prior to the
start of the SS No.\ 6 service, should be agreed between Administrations.
This agreement and the resulting test schedule should take account of the
relative experience of the participating Administrations. The following
aspects should be covered in such a programme:
.RT
.LP
    i)
    functional and synchronization aspects of the signalling
links and reserves;
.LP
    ii)
    signalling security arrangements;
.bp
.LP
    iii)
    call processing. Tests should cover normal, abnormal,
transit and signal\(hytransfer\(hypoint signalling sequences;
.LP
    iv)
    system failure response. Both signalling system and
exchange failures should be covered;
.LP
    v)
    tests on individual speech circuits, e.g.\ using
ATME\ No.\ 2;
.LP
    vi)
    limited period, live traffic tests.
.PP
Engineering test programmes require further study. Thus the
programme suggested above should be considered \*Qprovisional\*U and may not be
complete. But in considering the test programme to be implemented, attention
is drawn to the detailed and comprehensive publication cited in \ [13].
.sp 1P
.LP
3.9
    \fIMaintenance and maintenance organization\fR
.sp 9p
.RT
.PP
Inter\(hyadministration agreements necessary for the maintenance of SS
No.\ 6 are the subject of other Recommendations in the M\(hySeries. Reference
should be made to Recommendations\ M.760, M.761, M.762 and\ M.93.
.RT
.sp 2P
.LP
\fB4\fR     \fBTiming of inter\(hyadministration agreements\fR
.sp 1P
.RT
.PP
Due to the differing practices and procedures of Administrations, no specific
timetable for the inter\(hy
administration agreements
necessary on
SS No.\ 6 can be offered. However, experience indicates that initial discussions
between involved Administrations concerning a new SS No.\ 6 service should
preferably commence about two years prior to the required \*Qready for
service\*U date.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fISpecification of Signalling System No.\ 6\fR ,
Vol.\ VI, Recs.\ Q.251\(hyQ.300.
.LP
[2]
    CCITT Recommendation \fIGeneral\fR , Vol.\ VI, Rec.\ Q.251.
.LP
[3]
    CCITT Recommendation \fIAssociation between signalling and speech\fR
\fInetworks\fR , Vol.\ VI, Rec.\ Q.253.
.LP
[4]
    CCITT Recommendation \fIReserve facilities provided\fR , Vol.\ VI,
Rec.\ Q.292.
.LP
[5]
     CCITT Recommendation \fIIntervals at which security measures are to be\fR
\fIinvoked\fR , Vol.\ VI, Rec.\ Q.293.
.LP
[6]
    CCITT Recommendation \fIRequirements for the signalling data link\fR ,
Vol.\ VI, Rec.\ Q.272.
.LP
[7]
    CCITT Recommendation \fIAnalysis of digital information for routing\fR ,
Vol.\ VI, Rec.\ Q.262.
.LP
[8]
    CCITT Recommendation \fISpeed of switching and signal transfer in\fR
\fIinternational exchanges\fR , Vol.\ VI, Rec.\ Q.265.
.LP
[9]
    CCITT Recommendation \fITesting and maintenance \(em Overall tests of\fR
\fISignalling System No.\ 6\fR , Vol.\ VI, Rec.\ Q.295.
.LP
[10]
    CCITT Recommendation \fIPotential for automatic repeat attempt\fR ,
Vol.\ VI, Rec.\ Q.264.
.LP
[11]
    CCITT Recommendation \fIGeneral\fR , Vol.\ VI, Rec.\ Q.257.
.LP
[12]
    CCITT Recommendation \fIDouble seizing with both\(hyway operation\fR ,
Vol.\ VI, Rec.\ Q.263.
.LP
[13]
     CCITT publication \fICCITT Signalling System No. 6 Test Schedule\fR ,
ITU, Geneva, 1982.
.LP
.sp 6
.bp
.sp 2P
.LP
\fBRecommendation\ M.760\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSFER\ LINK\ FOR\ COMMON\ CHANNEL\ SIGNALLING\ SYSTEM\ No. 6\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.760''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.760    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral description of the transfer link\fR
.sp 1P
.RT
.PP
1.1
The transfer link for the common channel Signalling System
No.\ 6 and its relationship with the signalling link and signalling data link
are depicted in Figure\ 1/M.760.
.sp 9p
.RT
.LP
.rs
.sp 22P
.ad r
\fBFigure 1/M.760, p.
.sp 1P
.RT
.ad b
.RT
.PP
1.2
The signalling link may be operated over either an analogue or
a digital transfer link. Analogue transfer links are used to interconnect
data modems located within, or adjacent to, international switching centres,
thus
forming signalling data links. Analogue transfer links are 4\(hywire transmission
channel pairs having no audio terminating units, signalling equipment or
echo suppressors. These channels can be derived from purely analogue, a
combination analogue and digital, or purely digital transmission systems.
Guidance on the setting\(hyup and lining\(hyup of analogue transfer links
is given in
Recommendation\ M.761.
.PP
Digital transfer links are used to interconnect
interface
adaptors
to form
signalling data links
.
.PP
For guidance on the testing and maintenance of Signalling System
No.\ 6, reference should be made to Recommendation\ Q.295\ [1].
.RT
.sp 2P
.LP
\fB2\fR     \fBContinuity of service\fR
.sp 1P
.RT
.PP
2.1
Since the signalling link carries the signals for many speech circuits,
a failure of the link will affect all speech circuits served.
Therefore, arrangements should be made to ensure continuity of service
of the signalling link.
.bp
.sp 9p
.RT
.LP
.PP
2.2
Continuity of service will normally involve the provision of
reserve facilities, which may be one or more of the following:
.LP
    \(em
    quasi\(hyassociated reserve signalling links,
.LP
    \(em
    full\(hytime reserve transfer links,
.LP
    \(em
    nominated direct circuits.
.PP
In the last two cases the transfer links must be equipped with
signalling terminals and modems or interface adaptors to form signalling
links. Reference should also be made to Recommendation\ Q.292\ [2], which
provides a
detailed description of the above reserve arrangements.
.PP
2.3
Whenever possible, the reserve facility to be used should
follow a different route from the route of the regular signalling link.
.sp 9p
.RT
.PP
2.4
In order to reduce the number of interruptions on the
signalling link to a minimum, it is recommended that all equipment associated
with such links (for example, channel translating equipment, modems,
distribution frames,\ etc.) be positively marked to make them readily
identifiable to maintenance staff. Such markings assist maintenance efficiency
and help staff to avoid causing inadvertent interruptions to the link when
carrying out maintenance work in operation centres and switching centres.
.PP
2.5
The proper functioning of Signalling System No.\ 6 is essential
to the operation of the international network and various means are suggested
in order to ensure this operation. If a fault occurs in the normal transfer
link, service will continue (see \(sc\ 2.2). However, a second (or simultaneous)
failure would cause a significant impairment in traffic between centres so
affected.  Therefore, immediate maintenance attention should be given to
transfer link faults and they should be returned to their normal configurations
as rapidly as possible following a failure.
.sp 2P
.LP
\fB3\fR     \fBTransfer link designation\fR
.sp 1P
.RT
.PP
The form of designation to be used for the transfer link and its
nominated reserve is given in Recommendation\ M.140.
.RT
.sp 2P
.LP
\fB4\fR     \fBMaintenance organization\fR
.sp 1P
.RT
.PP
4.1
The maintenance organization for common channel Signalling
System No.\ 6 is in two parts:
.sp 9p
.RT
.LP
    a)
    the maintenance of the overall signalling system with
respect to delivering necessary signalling information between
international centres, and to the functioning of data modems,
signalling terminals and related equipment. The overall
maintenance requirements is a subject for further study;
.LP
    b)
    the maintenance of the transfer link between two centres,
from the output of one data modem to the input of another data
modem. This link does not include data modems.
.PP
4.2
By agreement between Administrations, one terminal
international centre, or an equivalent point specified by the Administration
concerned, will be designated as the overall maintenance control station.
This station will maintain an overview of the performance of Signalling
System No.\ 6 and in general be responsible to ensure that actions are
coordinated when
responsibility for a particular fault is not clearly identified. Additionally,
one terminal international centre should function as the control station
for
transfer link maintenance activities.
.PP
\fINote\fR \ \(em\ For a signalling system this role may be combined with
that of overall maintenance control.
.PP
4.3
Organizational points or stations need to be assigned to
provide for the following functions:
.LP
    a)
    Overall signalling system maintenance
.LP
    i)
    control station
.LP
    ii)
    sub\(hycontrol station
.LP
    iii)
    fault report point
.LP
    iv)
    testing point
.bp
.LP
    b)
    Transfer link maintenance
.LP
    i)
    control station
.LP
    ii
    sub\(hycontrol station
.LP
    iii)
    fault report point
.LP
    iv)
    transmission maintenance point (international line)
(TMP\(hyIL)
.PP
These may be assigned by an Administration as best suited to its individual
needs.
.PP
It is essential that the appropriate contact point information be
exchanged in order to minimize maintenance difficulties. Figure\ B\(hy1/M.93
offers a plan for the exchange of contact point information for the international
telephone service and allows for the exchange of contact point information
Signalling System No.\ 6 maintenance.
.RT
.PP
4.4
This Recommendation relates to the maintenance of the
transfer link. However, maintenance activities on the transfer link should
be controlled in order to preclude interruption of signalling functions,
either
during normal service or while tests initiated by the overall maintenance
control station are being carried out. Furthermore, the TMP\(hyIL for the
transfer link is not likely to be aware of any faults in the signalling
system unless
advised by the overall signalling maintenance control station or transfer
link control station. Therefore, testing of the transfer link will not
be undertaken until advice (or concurrence) is received from the overall
maintenance control station or the transfer link control station.
.PP
4.5
Once a fault is indicated in Signalling System No.\ 6, a possible series
of events is illustrated in Figure\ 2/M.760. In the presentation of the
flowchart it has been necessary to assume a possible organizational arrangement
and assignment of responsibilities [see \(sc\ 4.1, a) above].
.PP
This chart does not go into all possibilities. It is intended to depict
a process toward fault correction, looking first at the most likely
causes of faults in the transfer link with speedy correction in mind, and
then toward more detailed and time\(hyconsuming tests to discover more
elusive faults. It should be noted that some long\(hyterm testing may be
required in this latter process.
.LP
.rs
.sp 28P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
.rs
.sp 47P
.ad r
\fBFigure 2/M.760, p.\fR
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fITesting and maintenance \(em Overall tests of\fR
\fISignalling System No.\ 6\fR , Vol.\ VI, Rec.\ Q.295.
.LP
\fI\fR [2]
    CCITT Recommendation \fIReserve facilities provided\fR , Vol.\ VI,
Rec.\ Q.292.
\v'2P'
.sp 2P
.LP
\fBRecommendation\ M.761\fR
.RT
.sp 2P
.ce 1000
\fBSETTING\ UP\ AND\ LINING\ UP\ A\ TRANSFER\ LINK\ FOR\ COMMON\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.761''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.761    %'
.ce 0
.sp 1P
.ce 1000
\fBCHANNEL\ SIGNALLING\ SYSTEM\ No.\ 6\ (ANALOGUE\ VERSION)\fR
.FS
A
general description of the transfer link for the common channel Signalling
System\ No.\ 6 may be found in Recommendation\ M.760.
.FE
.ce 0
.sp 1P
.LP
\fB1\fR     \fBSetting up and lining up a transfer link\fR
.sp 1P
.RT
.PP
1.1
The method to be used and procedure to be followed in setting up and lining
up a transfer link are similar to those given in
Recommendation\ M.1050\ [1] in so far as it applies. However, in this context,
any reference to national sections in Recommendation\ M.1050 should be
ignored since a transfer link exists between terminal international centres
and
does not include national sections.
.sp 9p
.RT
.PP
1.2
Routing restrictions may be necessary to achieve the
loss/frequency and group\(hydelay distortion limits specified below if
the need to insert equalizers is to be avoided. Factors that may contribute
to difficulties in meeting these limits are the number of through\(hygroup
filters in group links, the use of edge band channels in group links,\
etc.
.PP
In addition, the number of channel translating equipments should be minimized
in order that equalization, if required, may be more easily
achieved, and that the effect of other parameters, such as noise, may be
minimized.
.sp 2P
.LP
\fB2\fR     \fBTransmission characteristics of a transfer link\fR
.sp 1P
.RT
.sp 1P
.LP
2.1
    \fIGeneral\fR
.sp 9p
.RT
.PP
The transmission characteristics of the circuit to be used as the signalling
data link are based on those for international leased circuits
conforming to Recommendation\ M.1020\ [2]. Optionally, the relaxed overall
loss/frequency characteristic and group\(hydelay distortion limits specified in
the Recommendation cited in\ [3] may be applied where agreed between the
Administrations involved and if tests confirm suitability.
.RT
.sp 1P
.LP
2.2
    \fIOverall loss at reference frequency\fR
.sp 9p
.RT
.PP
The overall loss at reference frequency of the channels of a
transfer link is not specified.
.PP
The channels of a transfer link should be set up so that when a test signal
at a level of \(em10\ dBm0 is connected to the input of the transfer
channel, the level received at the output of the transfer channel at the
distant end is as close as possible to \(em10\ dBm0.
.bp
.RT
.sp 1P
.LP
2.3
    \fIVariation with time of the overall loss at reference frequency\fR
.sp 9p
.RT
.PP
The variation with time of the overall loss at reference frequency should
be as small as possible but should not exceed the following
limits:
.RT
.LP
    \(em
    short\(hyterm variation (over a period of a few seconds):
\(+- | \ dB;
.LP
    \(em
    long\(hyterm variation (over long periods including daily and
seasonal variations):\ \(+- | \ dB.
.sp 1P
.LP
2.4
    \fILoss/frequency distortion\fR
.FS
Provisionally the limits of Recommendation M.1020 [2] have been chosen
for the loss/frequency
characteristics although these limits are appropriate for a leased circuit
extending over national plant including local lines to customers' premises.
However, transfer links will only extend between international centres and
their routing will not involve any audio line plant with its inherent
increasing attenuation with frequency. Therefore, further study is needed
concerning the possible need to change the frequency (3000\ Hz), from which
the zero gain restriction extends, to some higher frequency.
.FE
.sp 9p
.RT
.PP
The variation of overall loss with frequency relative to the loss at reference
frequency should not exceed the limits shown in
Figure\ 1/M.761.
.RT
.LP
.rs
.sp 23P
.ad r
\fBFigure 1/M.761, p.
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
2.5
    \fIGroup\(hydelay distortion\fR
.sp 9p
.RT
.PP
The group\(hydelay distortion relative to the minimum delay, should
not exceed the limits shown in Figure\ 2/M.761.
.bp
.RT
.LP
.rs
.sp 17P
.ad r
\fBFigure 2/M.761, p.
.sp 1P
.RT
.ad b
.RT
.PP
\fINote\ 1\fR \ \(em\ It is believed that in many cases the limits specified
in \(sc\(sc\ 2.4 and 2.5 may be achieved without the addition of equalizing
equipment.
.PP
\fINote\ 2\fR \ \(em\ The overall loss/frequency characteristic and group\(hydelay
distortion limits are currently under study for the feasibility of more
relaxed limits. However, initial experience indicates that the limits specified
in
\(sc\(sc\ 2.4 and 2.5 are necessary for reliable operation of the signalling
system
data link.
.RT
.sp 1P
.LP
2.6
    \fIRandom noise\fR
.sp 9p
.RT
.PP
The level of the psophometric noise power at the receiving
terminal international centre depends upon the actual length and constitution
of the transfer link. The provisional limit for transfer links of distances
greater than 10 | 00\ km is \(em38\ dBm0p. However, transfer links of shorter
length will have substantially less random noise, as shown in Figure\ 3/M.761.
.PP
Figure 3/M.761 displays random noise versus length and is presented as
a guide to the random noise performance which may be found on a transfer
link.
.RT
.LP
.rs
.sp 19P
.ad r
\fBFigure 3/M.761, p.
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
\fINote\fR \ \(em\ For transfer links routed via satellite, the satellite
section (between earth stations) will contribute approximately 10 | 00\ pW0p
(\(em50\ dBm0p) to the overall circuit noise. Therefore, for the purpose of
determining the noise limits for the Signalling System No.\ 6 transfer
link, the section of the transfer link provided by the satellite may be
considered to be equivalent to a length of 1000\ km. The effective noise
length of such a
transfer link will be 1000\ km plus the total length of the terminal routings.
.sp 1P
.LP
2.7
    \fIImpulsive noise\fR
.sp 9p
.RT
.PP
Impulsive noise should be measured with an instrument complying
with Recommendation\ O.71\ [4]. As a provisional limit, the number of impulsive
noise peaks exceeding \(em21\ dBm0 should not be more than 18 in 15\ minutes.
.RT
.sp 1P
.LP
2.8
    \fIPhase jitter\fR
.sp 9p
.RT
.PP
The value of phase jitter depends upon the actual constitution of the transfer
link (for example, upon the number of modulation equipments
involved). It is expected that any measurement of phase jitter using an
instrument complying with Recommendation\ O.91\ [5] will not normally exceed\
10\(de peak\(hyto\(hypeak. However, for transfer links of necessarily complex
constitution, and where 10\(de peak\(hyto\(hypeak cannot be met, a limit
of up to 15\(de peak\(hyto\(hypeak is permitted. These limits are provisional
and subject to further study.
.RT
.sp 1P
.LP
2.9
    \fIQuantizing noise\fR
.sp 9p
.RT
.PP
If any section of the transfer link is routed over a pulse code
modulation system or through a digital exchange, the signal will be accompanied
by quantizing noise. The minimum ratio of signal\(hyto\(hyquantizing noise
normally expected is 22\ dB.
.RT
.sp 1P
.LP
2.10
    \fISingle tone interference\fR
.sp 9p
.RT
.PP
The level of single tone interference in the band 300\(hy3400\ Hz shall
not exceed a value which is 3\ dB below the circuit noise objective indicated
in Figure\ 3/M.761. This limit is provisional pending further study.
.RT
.sp 1P
.LP
2.11
    \fIFrequency error\fR
.sp 9p
.RT
.PP
The frequency error introduced by the transfer link must not exceed \(+- | \
Hz. It is expected that in actual practice the frequency errors encountered
will be less than 5\ Hz.
.RT
.sp 1P
.LP
2.12
    \fIHarmonic distortion\fR
.sp 9p
.RT
.PP
When a 700\(hyHz test frequency at \(em13 dBm0 is injected at the
transmit end of the transfer link, the level of any individual harmonic
frequency at the receiving end shall provisionally be at least 25\ dB below
the received level of the fundamental frequency.
.RT
.sp 2P
.LP
\fB3\fR     \fBRecording of results\fR
.sp 1P
.RT
.PP
All measurements made in completing the line\(hyup of the transfer
link are valuable as references. These final measurements should be recorded
using an appropriate form.
.PP
If subsequent realignment or adjustment is necessary these records
should be updated.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fILining up an international point\(hyto\(hypoint\fR
\fIleased circuit\fR , Vol.\ IV, Rec.\ M.1050.
.LP
[2]
    CCITT Recommendation \fICharacteristics of special quality\fR
\fIinternational leased circuits with special bandwidth conditioning\fR
, Vol.\ IV, Rec.\ M.1020.
.LP
[3]
    CCITT Recommendation \fIRequirements for the signalling data link\fR ,
Vol.\ VI, Rec.\ Q.272, Annex.
.LP
[4]
     CCITT Recommendation \fIImpulsive noise\fR \fImeasuring equipment for
telephone\(hytype circuits\fR , Vol.\ IV,
Rec.\ O.71.
.LP
[5]
     CCITT Recommendation \fIPhase\fR \fIjitter measuring equipment for telephone
circuits\fR , Vol.\ IV, Rec.\ O.91.
.bp
.sp 2P
.LP
\fBRecommendation\ M.762\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMAINTENANCE\ OF\ COMMON\ CHANNEL\ SIGNALLING\ SYSTEM\ No.\ 6\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.762''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.762    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
1.1
It is essential that a common channel signalling system
perform with very high reliability over the long term. It is also desirable
that maintenance staff perform at the highest practical efficiency. In
order to achieve both of these objectives with regard to common channel
signalling
systems, maintenance responsibilities and actions must be clearly defined
and controlled. Such objectives make it necessary, in some cases, to place
limitations on the freedom of involved maintenance units in performing
independent maintenance actions.
.sp 9p
.RT
.PP
1.2
This Recommendation considers the signalling system as an
integrated system. It is not intended to replace or impose upon any
Recommendation or procedure (national network or otherwise) which might
apply to specific components or sub\(hysystems, for example a signalling
terminal or the transfer
link; rather, it proposes criteria regarding when and how such actions
are to be initiated. Moreover, the general administration of the systems
is considered and not the detailed interworking of its various equipments.
.PP
1.3
Various maintenance organizational units may have functional
responsibility for individual sub\(hysystems which comprise a common channel
signalling system (for example signalling terminals, processors,\ etc.).
As the activities
of any of these units will have an effect on the overall operation of the
signalling system, and because in some cases it may not be possible to
independently determine a need for maintenance attention, one point should
be designated as an overall signalling system control. This point is titled
signalling system administrative control
. The corresponding point at
the distant terminal is known as the
signalling system administrative
sub\(hycontrol
.
.sp 2P
.LP
\fB2\fR     \fBAppointment of administrative control and
sub\(hycontrol\fR
.sp 1P
.RT
.PP
2.1
The appointment of administrative control and sub\(hycontrol will be made
by agreement between the Administrations involved. These two points
must be assigned for each signalling system which is placed in operation.
It is suggested that the most appropriate point to act as administrative
control or sub\(hycontrol is the maintenance unit having responsibility
for the signalling
terminal and processor. However, this matter is left to the discretion
of the Administrations concerned.
.sp 9p
.RT
.PP
2.2
In the case of multiple signalling systems between the same two
points, it may be appropriate to divide control and sub\(hycontrol assignments,
therefore sharing the burden of control responsibility. This is a subject
for agreement between the Administrations concerned; however, this assignment
and that of the control station for the transfer link should be to the
same
Administration.
.sp 2P
.LP
\fB3\fR     \fBFunctions and responsibilities of the administrative control\fR
.sp 1P
.RT
.PP
These responsibilities fall into four main areas:
.RT
.LP
    i)
    day\(hyto\(hyday maintenance of working systems;
.LP
    ii)
    history and long\(hyterm analysis;
.LP
    iii)
    operation under signal transfer point (STP)
configurations;
.LP
    iv)
    implementing a new signalling system, or an existing
signalling system modification.
.sp 2P
.LP
3.1
    \fIDay\(hyto\(hyday maintenance of signalling systems\fR
.sp 1P
.RT
.PP
3.1.1
Except as noted in \(sc\ 3.1.2, maintenance activity on any part of a common
channel signalling system must only be undertaken with the agreement and
knowledge of the administrative control. Such activities might relate to
routine maintenance measurements of the transfer link, service affecting
reconfigurations of transmission systems over which the transfer link is
routed (i.e.\ planned outages), the
temporary removal from service of a signalling terminal, etc.
.bp
.sp 9p
.RT
.PP
3.1.2
In the event of total failure of a signalling system due to a
malfunction of one of its parts, immediate steps should be taken to remedy
the fault condition. As soon as possible, the administrative control should
be
informed so that the event can be correlated with other reported events or
known signalling failures. An example of such a fault event might be the
failure of a transmission system over which the transfer link is
routed
.FS
See Recommendation\ M.760, \(sc\ 4 and Figure\ 2/M.760 which illustrate
a possible series of events following the failure of a transfer link of
the
common channel Signalling System No.\ 6.
.FE
.
.PP
3.1.3
Faults which are observable only at a signalling system
terminal, for example intermittent failures resulting from an apparent high
data bit error rate, must be analysed by the administrative control (and
sub\(hycontrol, depending on the direction of the indicated fault) in order to
determine where maintenance attention is required. Such dynamic analysis
might involve terminal diagnostic tests, error performance tests with the
distant
terminal,\ etc. The result of this dynamic analysis and tests will be corrective
action, taken either by the administrative control or the sub\(hycontrol
if under either's jurisdiction, or the referral by the administrative control
to the
indicated part of the maintenance organization, for example the control
station for the transfer link.
.sp 2P
.LP
3.2
    \fIHistory and long\(hyterm analysis\fR
.sp 1P
.RT
.PP
3.2.1
The administrative control should maintain a record of all
recognized or reported faults pertaining to each signalling system for
which it is responsible.
.sp 9p
.RT
.PP
This information includes (but is not limited to) the
following:
.LP
    i)
    date and time a fault was reported or actually occurred;
.LP
    ii)
    the nature of the reported fault;
.LP
    iii)
    the reporting location;
.LP
    iv)
    the location of the fault, when found;
.LP
    v)
    the actual fault condition found and the corrective action
taken.
.PP
This information should become a part of the history record
maintained by the administrative control.
.PP
3.2.2
History records will enable long\(hyterm analysis to identify
repeated faults of a signalling system. Such efforts should improve the
long\(hyterm operation of a signalling system and therefore afford more
economical maintenance.
.sp 9p
.RT
.PP
It is suggested that historical records should be retained for at least
12\ months. From the provision of a new signalling system, the history
record should be initiated and continued until 12\ months have passed. After
analysis, each succeeding month will permit the discarding of records accrued
during that same month of the previous year. Therefore, an administrative
control can examine 13\ months of (possible) events, which should be adequate
to identify persistent faulty conditions.
.sp 2P
.LP
3.3
    \fIOperations under signal transfer point (STP) configurations\fR
.sp 1P
.RT
.PP
3.3.1
With two or more signalling systems in tandem used to convey
signalling information between two international centres, signal transfer
point operation presents possible maintenance complications. Events which
occur in
one system can affect the functioning between centres which have no control
or sub\(hycontrol responsibility for the faulty signalling system. If an
administrative control determines that a fault has occurred in its signalling
system which is part of an STP configuration, it must apprise the
.sp 9p
.RT
.LP
administrative control of the signalling system not directly involved,
that a fault exists that affects (or will affect) signalling processes.
The advice
should also include an estimate of the time necessary to correct the condition
and, when appropriate, the time the condition was actually corrected.
.PP
3.3.2
When a condition affecting signalling via an STP warrants
coordinated testing in order to determine the faulty part of either signalling
system, the administrative control first involved in the fault report should
coordinate testing efforts. Once the fault is localized, referrals can
be made via normal procedures to achieve maintenance action.
.bp
.PP
When the fault is corrected, the administrative control for each of the
signalling systems should be advised and the administrative control
which was first involved should confirm proper signalling via the STP.
.sp 2P
.LP
3.4
    \fIImplementing a new signalling system\fR
.sp 1P
.RT
.PP
3.4.1
The Administrations involved must reach all of the agreements necessary
for the orderly provision of a common channel signalling system, such as
label assignments, constitution of the transfer link routing, security
arrangements, initial testing,\ etc.\ (see also Recommendation\ M.750).
.sp 9p
.RT
.PP
3.4.2
The administrative control should receive and record for future
reference the results of tests carried out prior to putting a
new system into service. In the event of subsequent failures, a reference to
these test results may be valuable to the fault location process and also a
significant factor in assessing signalling system performance and fault
occurrences over the long term.
.sp 2P
.LP
\fB4\fR \fBFunctions and responsibilities of the administrative sub\(hycontrol\fR
.sp 1P
.RT
.PP
In general, the responsibilities of the administrative sub\(hycontrol with
respect to its own terminal are similar to those of the administrative
control. Additionally, the administrative sub\(hycontrol should:
.RT
.LP
    i)
    cooperate with the administrative control in fault
localization and clearing activities as necessary;
.LP
    ii)
    respond with all relevant details of investigations and
fault clearance activities to the administrative control;
.LP
    iii)
    advise the administrative control of any known present or
future event likely to impact on the operation of the signalling
system(s) for which it has responsibility.
.sp 2P
.LP
\fB5\fR     \fBContact point information\fR
.sp 1P
.RT
.PP
It is essential that contact point information be exchanged between Administrations
in order to minimize maintenance difficulties and speed fault localization
and clearance activities, (see Recommendation\ M.93).
.RT
.IP
\fB4.1\ Maintenance of common channel Signalling System No. 7\fR
.sp 1P
.RT
.sp 2P
.LP
\fBRecommendation\ M.770\fR
.RT
.sp 2P
.ce 1000
\fBINTER\(hyADMINISTRATION\ AGREEMENTS\ ON\ COMMON\ CHANNEL\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.770''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.770    %'
.ce 0
.sp 1P
.ce 1000
\fBSIGNALLING\ SYSTEM\ No.\ 7\fR
.ce 0
.sp 1P
.LP
\fB1\fR     \fBIntroduction\fR
.sp 1P
.RT
.PP
The bringing into service of new telephone circuits and signalling systems
requires that a number of agreements be made in advance by the
Administrations involved. Such agreements may concern, for exemple:
.RT
.LP
    \(em
    routing of circuits (cable, satellite, etc.);
.LP
    \(em
    mode of operation (incoming, outgoing, both\(hyway);
.LP
    \(em
    circuit designation;
.LP
    \(em
    order of selection of both\(hyway circuits.
.PP
For common channel signalling systems, a number of agreements are needed
in addition to those required for channel\(hyassociated signalling systems
(e.g.,\ Signalling System\ R2).
.PP
This Recommendation explains the principal inter\(hyAdministration
agreements which must be made in advance of opening a Signalling System
No.\ 7 service and is provided as guidance to those Administrations intending
to
operate such a service.
.bp
.RT
.sp 2P
.LP
\fB2\fR     \fBCommon channel Signalling System No. 7 (SS No. 7)\fR
.sp 1P
.RT
.PP
Many of the aspects covered by this Recommendation relate to
matters contained in the specifications of Signalling System No.\ 7, as
appearing in the Series\ Q Recommendations\ [1]. Where appropriate, cross
references to such Recommendations are given.
.PP
Recommendations Q.701\ [2] and Q.721\ [3] provide functional
descriptions of the Message Transfer Part\ (MTP) and Telephone User
Part\ (TUP) respectively.
.PP
The Q.780 [4] Series of Recommendations provide guidance on how to
test\ SS\ No.\ 7. (Level\ 1, 2 and\ 3).
.RT
.sp 2P
.LP
\fB3\fR     \fBAspects of SS No. 7 requiring inter\(hyAdministration agreement\fR
.sp 1P
.RT
.sp 1P
.LP
3.1
    \fISignalling links and signalling security arrangements\fR
.sp 9p
.RT
.PP
Signals for a given group of speech circuits between two exchanges may
be \*Qassociated\*U (routed on a signalling link between the two exchanges),
or \*Qnon\(hyassociated\*U (routed on two or more signalling links in tandem,
involving one or more signal\(hytransfer points) or a mixture of both (Recommendation\
Q.701, \(sc\ 3.1.2\ [2].
.PP
Before entering into detailed discussions on the type of signalling
security arrangements required, it is desirable that the terminal
Administrations exchange information on the type and manufacturer of their
international exchange and the options available within their existing
software systems. This information will enable each Administration to have
an overall
view of available signalling security arrangements. It will avoid
misunderstandings and thus enable rapid progress in establishing detailed
arrangements. Subsequently, agreement on the following matters will be
required:
.RT
.LP
    i)
    The use of \*Qassociated\*U and/or \*Qnon\(hyassociated\*U modes of
signalling.
.LP
    ii)
    The choice of signalling transfer points (STPs) in the
case where the \*Qnon\(hyassociated\*U mode of signalling is used.
.LP
    iii)
     Security measures against signalling network link failure, e.g.,\ the
use of load sharing between link sets. If load sharing
between link sets is to be used, agreement must be reached as to
the number of link sets involved.
.LP
    iv)
    Alternative routing within the signalling network in the
event of failure of a link set, i.e.,\ if load sharing is not used,
which \ STPs are available for a given signalling network relation,
and the order of selection of these. Due regard must be paid to the
limitation of the number of\ STPs in tandem in a given signalling
network relation (see Recommendation\ Q.705 \(sc\ 5)\ [5].
.LP
    v)
     The routing of the signalling network links must ensure that the propagation
delay of the links is as low as possible, and not
significantly higher than that of the speech circuits which are
served by Signalling System No.\ 7. This is to minimize the initial
.LP
speech clipping of the verbal answer from the called party. The
above factors must also be considered in any restoration plans,
although the non\(hyavailability of links may force administrations
to accept the possibility of clipping under failure conditions.
.LP
    vi)
    The nature of the signalling network link to be used,
e.g.,\ 4.8\ kbit/s analogue or 64\ kbit/s digital, transmission
routing, etc.
.LP
    vii)
     The method of error correction to be employed in a given signalling relation,
i.e.,\ basic or preventive cyclic
retransmission (see Recommendation\ Q.703 \(sc\ 5)\ [6].
.LP
    viii)
    Emergency restart conditions. (If there is automatic
allocation of signalling terminals or signalling data links
at the end of a signalling link, it must be ensured that the
value\ (T2) of the timeout is different at each end (see
Recommendation\ Q.703, \(sc\ 7.3 and\ Q.704, \(sc\ 3.4.3)\ [6] and\ [7]).
.sp 1P
.LP
3.2
    \fIMode of signalling\fR
.sp 9p
.RT
.PP
Signalling System No. 7 provides for two basic modes of sending
signalling information namely, \*Qen\(hybloc\*U or \*Qoverlap\*U
(Recommendation\ Q.724)\ [8].
.bp
.RT
.sp 1P
.LP
3.3
    \fISignalling network consideration for cross\(hyborder traffic\fR
.sp 9p
.RT
.PP
For cross\(hyborder traffic between signalling points, a bilateral
agreement needs to be made for the routing label assignment of signalling
point codes.
.PP
Two alternative arrangements are described in Recommendation\ Q.705,
\(sc\ 6\ [5]. One arrangement provides for signalling points which are handling
cross\(hyborder traffic to be given signal point codes taken from the
international numbering plan contained in Recommendation\ Q.708\ [9]. The
other provides for these signalling points to be identified by common national
point codes.
.RT
.sp 1P
.LP
3.4
    \fIRouting label assignment\fR
.sp 9p
.RT
.PP
The routing label is that part of the message label which contains the
information necessary to deliver the message to its destination point.
It comprises the following (see Recommendation\ Q.704, \(sc\ 2.2)\ [7]:
.RT
.LP
    \(em
    destination point code (DPC);
.LP
    \(em
    originating point code (DPC);
.LP
    \(em
    signalling link selection (SLS) field or signalling link   code (SLC).
.PP
DPC and OPC labelling will be in accordance with
Recommendation\ Q.708\ [9]. However it may be necessary to have a bilateral
agreement for the\ SLS, so that it can be assigned individually to signalling
links.
.sp 1P
.LP
3.5
    \fICircuit identification code\fR
.sp 9p
.RT
.PP
The circuit identification code (CIC) indicates one speech
circuit among those directly interconnecting the destination and the
originating points. The allocation of\ CICs to individual circuits is determined
by bilateral agreement and/or in accordance with predetermined rules. See
Recommendation\ Q.723, \(sc\ 2.2.3\ [10].
.RT
.sp 1P
.LP
3.6
    \fIReset of circuit and circuit group messages\fR
.sp 9p
.RT
.PP
In systems which maintain status in memory there may be occasions when
the memory becomes mutilated. In such cases the circuits must be reset
to the idle condition in both exchanges to make them available for new
traffic.
Since the exchange with mutilated memory does not know whether the circuits
are idle, busy outgoing, busy incoming, blocked, etc., reset\(hycircuit
signals or a circuit group reset should be sent as appropriate for the
affected circuits
(see Recommendation\ Q.724, \(sc\ 1.15)\ [8].
.PP
Under certain failure conditions however, where a large number of
circuits is involved, it is possible that some realisations of SS\ No.\ 7
terminal equipment will be unable to process the volume of reset messages
generated. It is necessary, therefore, that Administrations agree bilaterally
whether circuit and circuit group messages should both be used.
.RT
.sp 1P
.LP
3.7
    \fIUse of the\fR
\fIcircuit continuity check procedure\fR
.sp 9p
.RT
.PP
Because the SS No. 7 signalling does not pass over the speech path, facilities
should be provided for making a continuity check of the speech paths (see
Recommendation\ Q.724, \(sc\ 1.4)\ [8].
.PP
Use of this procedure on a particular circuit will depend on the type of
transmission system (e.g.,\ analogue, digital, mixed analogue/digital)
which is used for the circuit and whether end\(hyto\(hyend supervision
is provided on the transmission system. It should therefore be bilaterally
agreed.
.RT
.sp 1P
.LP
3.8
     \fIChoice of the time slot to be used within the primary order digital\fR
\fIpath for the signalling link\fR
.sp 9p
.RT
.PP
In the case where time slot 16 is utilized for circuit supervision purposes
(see Recommendation\ Q.33, \(sc\ A.1)\ [11], it is necessary to agree
bilaterally on which time slot within the primary order digital path should
be used for the signalling link.
.RT
.sp 1P
.LP
3.9
    \fIChanging from one specification of the signalling system to\fR
\fIanother\fR
.sp 9p
.RT
.PP
If an Administration changes from one version of the specification of the
signalling system to another, distant Administrations should be informed
as a precautionary measure before the change takes place since potential
interworking problems can then be anticipated. It is desirable therefore,
that Administrations should be aware of the need for, and agree to, this
exchange of information.
.bp
.RT
.sp 2P
.LP
\fB4\fR     \fBTiming on inter\(hyAdministration agreements\fR
.sp 1P
.RT
.PP
Due to the differing practices and procedures of Administrations no specific
timetable for the inter\(hyAdministration agreements necessary on
SS\ No.\ 7 can be offered. However, experience indicates that initial discussions
between Administrations concerning the implementation of a new common channel
signalling system should preferably commence about two years prior to the
required \*Qready for service\*U date.
.RT
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fISpecification of Signalling System No. 7\fR ,
Vol.\ VI, Recommendations\ Q.701\(hyQ.795.
.LP
[2]
     CCITT Recommendation \fIFunctional description of the signalling system\fR
(\fIMessage Transfer Part\fR ), Vol.\ VI,
Recommendation\ Q.701.
.LP
[3]
     CCITT Recommendation \fIFunctional description of the signalling system\fR
(\fITelephone User part (TUP)\fR ), Vol.\ VI,
Recommendation\ Q.721.
.LP
[4]
    CCITT Recommendation \fISignalling System No. 7 test specification,\fR
\fIgeneral description\fR , Vol.\ VI, Recommendation\ Q.780.
.LP
[5]
    CCITT Recommendation \fISignalling network structure\fR , Vol.\ VI,
Recommendation\ Q.705.
.LP
[6]
    CCITT Recommendation \fISignalling link\fR , Vol. VI, Recommendation\ Q.703.
.LP
[7]
    CCITT Recommendation \fISignalling network functions and messages\fR ,
Vol.\ VI, Recommendation\ Q.704.
.LP
[8]
    CCITT Recommendation \fISignalling procedures\fR , Vol. VI,
Recommendation\ Q.724.
.LP
[9]
    CCITT Recommendation \fINumbering of international signalling point\fR
\fIcodes\fR , Vol.\ VI, Recommendation\ Q.708.
.LP
[10]
    CCITT Recommendation \fIFormats and codes\fR ,
Vol.\ VI, Recommendation\ Q.723.
.LP
[11]
    CCITT Recommendation \fIProtection against the effects of faulty\fR
\fItransmission on groups of circuits\fR Vol.\ VI, Recommendation\ Q.33.
.sp 2P
.LP
\fBRecommendation\ M.782\fR
.RT
.sp 2P
.sp 1P
.ce 1000
\fBMAINTENANCE\ OF\ COMMON\ SIGNALLING\ SYSTEM\ No. 7\fR
.EF '%    Fascicle\ IV.1\ \(em\ Rec.\ M.782''
.OF '''Fascicle\ IV.1\ \(em\ Rec.\ M.782    %'
.ce 0
.sp 1P
.LP
\fB1\fR     \fBGeneral\fR
.sp 1P
.RT
.PP
1.1
It is essential that a channel signalling system perform with
very high reliability over the long term. It is also desirable that maintenance
staff perform at the highest practical efficiency. In order to achieve
both of these objectives with regard to common channel signalling systems,
maintenance responsibilities and actions must be clearly defined and controlled.
Such
objectives make it necessary, in some cases, to place limitations on the
freedom of involved maintenance units in performing independent maintenance
actions.
.sp 9p
.RT
.PP
1.2
This Recommendation considers the signalling system as an
integrated system. It is not intended to replace or supersede any
Recommendation or procedure (national network or otherwise) which might
apply to specific components or sub\(hysystems, for example a signalling
terminal or the signalling data link; rather, it proposes criteria regarding
when and how such actions are to be initiated. Moreover, the general administration
of the
systems is considered and not the detailed interworking of its various
equipments.
.PP
1.3
Various maintenance organizational units may have functional
responsibility for individual sub\(hysystems which comprise a common channel
signalling system (for example signalling terminals, processors,\ etc.).
As the activities of any of these units will have an effect on the overall
operation of the signalling system, and because in some cases it may not
be possible to independently determine a need for maintenance attention,
one point should be designated as an overall signalling system control.
This point is entitled
\fIsignalling system administrative control\fR . The corresponding point
at the distant terminal is known as the
\fIsignalling system administrative\fR
\fIsub\(hycontrol\fR .
.bp
.sp 2P
.LP
\fB2\fR     \fBAppointment of administrative control and sub\(hycontrol\fR
.sp 1P
.RT
.PP
2.1
The appointment of administrative control and sub\(hycontrol will be made
by agreement between the administrations involved. These two points must
be assigned for each signalling system which is placed in operation. It
is
suggested that the most appropriate point to act as administrative control
or sub\(hycontrol is the maintenance unit having responsibility for the
signalling
terminal and processor. However, this matter is left to the discretion
of the Administrations concerned.
.sp 9p
.RT
.PP
2.2
In the case of multiple signalling systems between the same two
points, it may be appropriate to divide control and sub\(hycontrol assignments,
therefore sharing the burden of control responsibility. This is a subject
for agreement between the Administrations concerned; however, this assignment
and that of the control station for the transfer link should be to the
same
Administration.
.sp 2P
.LP
\fB3\fR     \fBFunctions and responsibilities of the\fR
\fBadministrative\fR
\fBcontrol\fR
.sp 1P
.RT
.PP
These responsibilities fall into four main areas:
.RT
.LP
    i)
    day\(hyto\(hyday maintenance of working systems;
.LP
    ii)
    history and long\(hyterm analysis;
.LP
    iii)
    operation under signal transfer point (STP)
configurations;
.LP
    iv)
    implementing a new signalling system or a change to an
existing system.
.sp 2P
.LP
3.1
    \fIDay\(hyto\(hyday maintenance of signalling systems\fR
.sp 1P
.RT
.PP
3.1.1
Except as noted in \(sc\ 3.1.2, maintenance activity on any part of a common
channel signalling system must only be undertaken with the agreement and
knowledge of the administrative control. Such activities might relate to
routine maintenance measurement of the signalling link, services affecting
reconfigurations of transmission systems over which signalling links are
routed (i.e.,\ planned outages), etc.
.sp 9p
.RT
.PP
3.1.2
In the event of total failure of a signalling system due to a
malfunction of one of its parts, immediate steps should be taken to remedy
the fault condition. As soon as possible, the administrative control should
be
informed so that the event can be correlated with other reported events or
known signalling failure.
.PP
3.1.3
Faults which are observable only at a signalling system terminal,
for example intermittent failures resulting from an apparently high data bit
error rate, must be analyzed by the administrative control (and
sub\(hycontrol, depending on the direction of the indicated fault) in order to
determine where maintenance attention is required. Such dynamic analysis
might involve terminal diagnostic tests, error performance tests with the
distant
terminal,\ etc. The result of this dynamic analysis and tests will be corrective
action, taken either by the administrative control, if under its jurisdiction,
or by the sub\(hycontrol, if under its jurisdiction, or the referral by
the
administrative control to the indicated part of the maintenance organization,
for example the control station for the transfer link.
.sp 2P
.LP
3.2
    \fIHistory and long\(hyterm analysis\fR
.sp 1P
.RT
.PP
3.2.1
The administrative control should maintain a record of all
recognized or reported faults pertaining to each signalling system for
which it is responsible.
.sp 9p
.RT
.PP
This information includes (but is not limited to) the
following:
.LP
    i)
    date and time a fault was reported or actually occurred,
.LP
    ii)
    the nature of the reported fault,
.LP
    iii)
    the reported location,
.LP
    iv)
    the location of the fault, when found,
.LP
    v)
    the actual fault condition found and the corrective action   taken.
.PP
This information should become a part of the history record
maintained by the administrative control.
.PP
3.2.2
History records will enable long\(hyterm analysis to identify
repeated faults of a signalling system. Such efforts should improve the
long\(hyterm operation of a signalling system and therefore afford more
economical maintenance.
.bp
.sp 9p
.RT
.PP
It is suggested that historical records should be retained for at least
12\ months. From the provision of a new signalling system, the history
record should be initiated and continue until 12\ months have passed. After
analysis, each succeeding month will permit the discarding of records accrued
during that same month of the previous year. Therefore, an administrative
control can examine 13\ months of (possible) events, which should be adequate
to identify persistent faulty conditions.
.sp 2P
.LP
3.3
    \fIOperations under signal transfer point (STP)\fR \fIconfigurations\fR
.sp 1P
.RT
.PP
3.3.1
With two or more signalling systems in tandem used to convey
signalling information between two international centres, signal transfer
point operation presents possible maintenance complications. Events which
occur in
one system can affect the functioning between centres which have no control
or sub\(hycontrol responsibility for the faulty signalling system. If an
administrative control determines that a fault has occurred in its signalling
system which is part of an STP configuration, it must apprise the
administrative control of the signalling system not directly involved,
that a fault exists that affects (or will affect) signalling processes.
The advice
should also include an estimate of the time necessary to correct the condition
and, when appropriate, the time of correction and the condition actually
corrected.
.sp 9p
.RT
.PP
3.3.2
When a condition affecting signalling via an STP warrants
coordinated testing in order to determine the faulty part of either signalling
system, the administrative control first involved in the fault report should
coordinate testing efforts. Once the fault is localized, referrals can
be made via normal procedures to achieve maintenance action.
.PP
When the fault is corrected, the administrative control for each of the
signalling systems should be advised, and the administrative control
which was first involved should confirm proper signalling via the STP.
.sp 2P
.LP
3.4
    \fIImplementing a new signalling system or a change to an existing\fR
\fIsystem\fR
.sp 1P
.RT
.PP
3.4.1
The Administrations involved must reach all the agreements
necessary such as circuit identification code (CIC) assignments, label
assignment, constitution of the signalling link routing, security
arrangements, testing, etc. (see also Recommendation\ M.750).
.sp 9p
.RT
.PP
3.4.2
It is necessary to conduct tests on those signalling routes which
could be affected by such implementations. The purpose of the tests is to
provide confidence that the software, hardware and data for a signalling
system is correct in that:
.LP
    \(em
    a traffic circuit using that route can enter, or be removed   from service;
.LP
    \(em
    changes made to signalling and traffic routes for which
circuits are already in service function correctly.
.PP
This objective must be achieved without disruption to live
traffic.
.PP
3.4.3
Prior to tests being made, it should be ensured that:
.sp 9p
.RT
.LP
    \(em
    exchange data has been loaded;
.LP
    \(em
    diagnostic checks of the signalling terminals in each
exchange have been made;
.LP
    \(em
    test equipment and facilities are available. (The precise
requirements are a subject for further study.)
.PP
3.4.4
The following situations require tests. The list is not exhaustive since
combinations of situations may occur.
.sp 9p
.RT
.PP
For each situation it is necessary to consider whether or not
traffic circuits are in service and whether they are being added to or
ceased or whether there is no change.
.LP
    i)
    no signalling route existing between two switching centres:
.LP
    \(em
    signalling transfer point (STP) route to be provided
.LP
    \(em
    direct linkset to be provided
.LP
    ii)
    STP signalling route existing between two switching
centres:
.LP
    \(em
    STP route to be added
.LP
    \(em
    STP route to be ceased
.LP
    \(em
    direct linkset to be provided
.bp
.LP
    iii)
    direct signalling route existing between two switching
centres:
.LP
    \(em
    STP route to be added
.LP
    \(em
    STP route to be ceased
.LP
    \(em
    direct linkset to be provided
.LP
    iv)
    direct linkset to be ceased:
.LP
    \(em
    link to be provided
.LP
    \(em
    link to be ceased.
.PP
3.4.5
For the present, tests should be chosen from those specified as
compatibility tests in Recommendations\ Q.781\ [1], Q.782\ [2] and Q.783\
[3] by
agreement between the Administrations concerned. The question of whether
particular tests can be specified for particular situations remains as a
subject of further study. The actual tests chosen will depend on the nature
of the changes which have been made to the signalling network and the relative
experience of the participating Administrations. However, when implementing
a new signalling system, the following aspects should be covered:
.sp 9p
.RT
.LP
    \(em
     Level\ 1 and\ 2 tests which cover normal and failure conditions for synchronization
and Message Transfer Part (MTP) functions;
.LP
    \(em
    Level\ 3 tests which cover the application of failure
conditions in order to test single recovery arrangements;
.LP
    \(em
    Level\ 4 tests which cover Telephone User Part (TUP) call
processing functions and normal STP signalling functions. Test should cover
normal, abnormal, transit and call failure sequences;
.LP
    \(em
    tests on individual speech circuits, e.g. using ATME\ No.\ 2;
.LP
    \(em
    limited period, live traffic tests.
.PP
3.4.6
The test equipment and facilities required remain as a subject for further
study.
.sp 9p
.RT
.PP
3.4.7
After completion of testing, there should be an increased level of
supervision on the route for a period, the duration of which should be
agreed by the Administration concerned. Generally it should not be less
than one week. During this period traffic signalling performance statistics
should be obtained relating to both the Message Transfer Part (MTP) and
Telephone User Part (TUP) in order to confirm that the route performance
is functioning correctly. These should be chosen by agreement between the
Administrations concerned. Those for the MTP should be taken from Recommendation\
Q.791\ [4] (Monitoring and
measurements for the MTP).
.PP
3.4.8
The administrative control should receive and record for future
reference the results of tests carried out. In the event of subsequent
failures, a reference to these test results may be valuable to the fault
location process and also a significant factor in assessing signalling
system performance and fault occurrences over the long term.
.sp 2P
.LP
\fB4\fR \fBFunctions and responsibilities of the administrative sub\(hycontrol\fR
.sp 1P
.RT
.PP
In general, the responsibilities of the administrative sub\(hycontrol with
respect to its own terminal are similar to those of the administrative
control. Additionally, the administrative sub\(hycontrol should:
.RT
.LP
    \(em
    cooperate with the administrative control in fault
localization and clearing activities as necessary;
.LP
    \(em
     respond with all relevant details of investigations and fault clearance
activities to the administrative control;
.LP
    \(em
    advise the administrative control of any known present or
future event likely to affect the operation of the signalling system(s) for
which it has responsibility.
.sp 2P
.LP
\fB5\fR     \fBContact point information\fR
.sp 1P
.RT
.PP
It is essential that contact point information be exchanged between Administrations
in order to minimize maintenance difficulties and speed fault localization
and clearance activities, (see Recommendation\ M.93).
.RT
.sp 2P
.LP
\fB6\fR     \fBMonitoring requirements for maintenance purposes\fR
.sp 1P
.RT
.PP
This section specifies the monitoring requirements for maintenance of the
common channel Signalling System\ No.\ 7.
.bp
.PP
It considers three aspects of monitoring which are as
follows:
.RT
.LP
    \(em
    a monitoring facility for the signalling system which is
realized in the digital exchange software. It would be called into operation
by command when required in order to manually observe signalling sequences.
It is referred to hereafter as a
software monitor
;
.LP
    \(em
     a facility (provided by means of hardware) which allows for the connection
of monitoring equipment to the signalling link, i.e. a
monitoring point;
.LP
    \(em
     the requirements for testing equipment which is connected at the monitoring
point.
.sp 2P
.LP
6.1
    \fIThe software monitor\fR
.sp 1P
.RT
.PP
6.1.1
A software monitor should be provided which will allow signals
handled in the implementation of the signalling system in the SPC exchange,
to be selectively output to an input/output terminal for the purpose of
manually observing signalling sequences.
.sp 9p
.RT
.PP
It is considered that this facility should be the primary means of manually
observing signalling sequences.
.PP
6.1.2
The software monitor should meet the following requirements:
.sp 9p
.RT
.LP
    \(em
     it must be capable of operations without interfering with the operation
of the signalling system;
.LP
    \(em
     it must be capable of monitoring Message Transfer Part (MTP) and Telephone
User Part (TUP) messages. Other User Parts are the subject of
further study;
.LP
    \(em
    it must be capable of displaying all MTP messages which
relate to specified linksets or destinations or both. It should record
registration time, direction, linkset identity, link identity, signal acronym
and any change of signalling link state for all messages. It must be possible
to monitor several destinations and linksets simultaneously. The precise
number of destinations and linksets will depend upon such factors as the
size of the exchange and its position in the network (i.e.\ local, transit,
etc.);
.LP
    \(em
    it must be capable of displaying the contents of all TUP
message signal units sent and received for specified speech circuits or
groups of circuits. It would also be useful to register the link on which
the TUP
signals have been sent and record any changes to the link used. It must be
possible to monitor several circuits simultaneously. The precise number of
circuits will depend on such factors as the size of the exchange and its
position in the network (i.e. local, transit, etc.).
.sp 2P
.LP
6.2
    \fIMonitoring point requirements\fR
.sp 1P
.RT
.PP
6.2.1
A means of connecting independent monitoring equipment to
a\ 64\ kbit/s signalling link should be provided. This facility would be used
either when more information is required than the software monitor is able
to provide or when verification by an independent means is required of
the
information supplied by the software monitor.
.sp 9p
.RT
.PP
The means of connection to a 64 kbit/s signalling link should be either
at the\ 64\ kbit/s level, in which case interface requirements of
Recommendation\ G.703,\ \(sc\ 1\ [5] apply, or at the primary order level,
in which
case the interface requirements of\ G.703,\ \(sc\ 2 (1544\ kbit/s) or\ \(sc\ 6
(2048\ kbit/s) apply.
.PP
6.2.2
The means of connection should be such that:
.sp 9p
.RT
.LP
    \(em
    signals can be monitored in both directions simultaneously;
.LP
    \(em
    the connection of monitoring equipment does not affect the
signals present on the link or on other time slots in the primary order path
which carried the link;
.LP
    \(em
    signals may be monitored irrespective of the current link
status;
.LP
    \(em
     any or all of the protocol levels of any signal units on the link may
be observed.
.bp
.sp 1P
.LP
6.3
    \fIRequirements of test equipment used for monitoring purposes\fR
.sp 9p
.RT
.PP
Requirements for test equipment used for monitoring purposes
are:
.RT
.LP
    \(em
     that the equipment should be self\(hycontained and independent of the
terminal equipment of the system;
.LP
    \(em
    that the equipment should be able to display all signals
which are necessary to be examined in order to detect faults at all levels
of the signalling system;
.LP
    \(em
    that the form in which signals are displayed should enable
them to be easily recognizable to the maintenance staff. In particular it
should be possible to display specified fields of a message or all the fields;
.LP
    \(em
     that the equipment should be capable of storing information from the
link for later off\(hyline examination (amount and extent of this
information has yet to be determined);
.LP
    \(em
    that information should be displayed (and recorded, where
applicable) to allow the operator to determine the time when a signal or
message was received;
.LP
    \(em
    that the equipment should be able to display and store
information on the link at all times;
.LP
    \(em
    that the equipment should have the facility to allow the
maintenance staff to determine which categories of signals or messages
are to be displayed;
.LP
    \(em
    that the equipment should allow the maintenance staff to
specify conditions such as the receipt of messages or signals which would
trigger the commencement of display or storage;
.LP
    \(em
    that when triggered, the equipment should display, in
chronological order the signals which occurred prior to the triggering and
after it. The number of these messages has yet to be determined.
.PP
\fINote\fR \ \(em\ It is intended that a Recommendation in the O\ series
will be developed which will specify this test equipment in detail.
.sp 2P
.LP
    \fBReferences\fR
.sp 1P
.RT
.LP
[1]
    CCITT Recommendation \fIMTP Level\ 2 test specification\fR , | Vol.\ VI,
Recommendation\ Q.781.
.LP
[2]
    CCITT Recommendation \fIMTP Level\ 3 test specification\fR , | Vol.\ VI,
Recommendation\ Q.782.
.LP
[3]
    CCITT Recommendation \fITUP Test specification\fR , | Vol.\ VI,
Recommendation\ Q.783.
.LP
[4]
    CCITT Recommendation \fIMonitoring and measurements for the MTP\fR , |
Vol.\ VI, Recommendation\ Q.791.
.LP
[5]
    CCITT Recommendation \fIPhysical/electrical characteristics of\fR
\fIhierarchical digital interface\fR , | Vol.\ III, Recommendation\ G.703.
.LP
.rs
.sp 22P
.ad r
Blanc
.ad b
.RT
.LP
.bp