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<div class="div">
<h1>BSC System Maintenance</h1>

<p>System Maintenance handles all fault situations and user-initiated
configuration management tasks in the system hardware and software in such
a way that all the availability performance requirements for the whole system
and for individual customers are met.</p>


<p>Fault tolerance is a general requirement set for all software
in the DX 200 BSC network element, but especially System Maintenance controls
this system feature.</p>


<p>System Maintenance is responsible for availability performance
on the network element level, and it should perform its task as automatically
and autonomously as possible. Thus a network element can be maintained remotely,
except in cases when it is necessary to perform a physical action on the hardware.</p>


<p>All MML commands involving System Maintenance can be used
locally as well as remotely from a NetAct exchange.</p>


<a name="mar1241420351" shape="rect"></a>
<div class="topic">
<h2>Supervision</h2>

<p>System supervision is a function group, which consists
of hardware supervision, software supervision, semi-permanent connections
supervision, and real time supervision.</p>
</div>


<a name="mar1241421302" shape="rect"></a>
<div class="topic">
<h2>Hardware
supervision</h2>

<p>Hardware supervision is based on routine tests and on continuous
supervision executed as a background process. Hardware supervision is divided
into supervision of microcomputers and supervision of switching network.</p>


<p>Microcomputer supervision is executed in all computer units
as a background process so that the normal operation of the unit is not disturbed.
Also the supervision of all switching networks in the DX 200 system is executed
as a background process without disturbing the call traffic and by using the
testing properties integrated into the switching network.</p>
</div>


<a name="mar124142263" shape="rect"></a>
<div class="topic">
<h2>Supervision
of software</h2>

<p>Supervision of the software reveals fault conditions in
which the control of the software is lost. The supervision is based on watch-dog
timers and special supervision   messages. All control processors and pre-processors
of the system must set their watch-dog timers at predefined intervals, otherwise
the hardware restarts the processor.</p>
</div>


<a name="mar1241422424" shape="rect"></a>
<div class="topic">
<h2>Supervision
of semi-permanent connections</h2>

<p>Supervision of semi-permanent connections ensures that
the connections defined by user commands are maintained in the switching network.
If a connection that has already been defined is for some reason missing,
it will be redefined. If the restoration of the connection fails or the connection
disappears for the second time, an alarm will be generated.</p>
</div>


<a name="mar1241423235" shape="rect"></a>
<div class="topic">
<h2>Supervision
of real time</h2>

<p>Supervision of real time is executed in a hierarchical
manner so that the NetAct supervises the real time of the systems that are
directly below it in the network hierarchy. At the level of network, the OMU
supervises the time of the other units.</p>


<p>If the time of a system under the NetAct differs from the
times of the other systems more than 5 seconds, the system time is corrected
so that it is the same as the time of the supervisor, or an alarm is given
to the user to check the situation.</p>
</div>


<a name="mar1241423546" shape="rect"></a>
<div class="topic">
<h2>Alarm
Functions</h2>

<p>The tasks of the alarm system are to collect the various
fault observations, to process them, and to inform the user with suitable
alarm printouts and alarm lamp panel controls. Normally, the BSC has a lamp
panel, but the control outputs can   also be used for other purposes. Furthermore,
the alarm system stores the fault observations and the conclusions made on
basis of them and starts up the automatic recovery functions when necessary.</p>


<p>The alarm system tries to localise the fault or disturbance
to a specific functional unit.</p>


<p>Alarm functions include</p>


<ul>
<li><p>Collection of alarm data</p>
</li>
<li><p>Storing of alarms</p>
</li>
<li><p>Output of alarms</p>
</li>
<li><p>Control of alarm outputs</p>
</li>
<li><p>Activation of recovery functions in
connection with a unit failure</p>
</li>
<li><p>Starting of an MML sequence of the
command calendar for predefined faults.</p>
</li>
</ul>


<p>The alarm functions have a user interface to the functions,
which control the set-up of alarm parameters, the examination of the alarm
situation, and alarm history.</p>
</div>


<a name="apr2341630291" shape="rect"></a>
<div class="topic">
<h2>Alarm-specific
printout control</h2>

<p>The new MML commands are used to block and unblock local
printing and the sending of alarms to the NetAct.</p>
</div>


<a name="mar1241427587" shape="rect"></a>
<div class="topic">
<h2>Rule
Base</h2>

<p>By means of a rule base, the behaviour of an alarm system
can be tuned to serve best the operators needs and requirements. As an example,
if the fault or disturbance observation occurs repetitively, a higher class
(2615 ** or 2616 ***) alarm will be automatically sent by the alarm system.</p>
</div>


<a name="mar1241428288" shape="rect"></a>
<div class="topic">
<h2>Recovery</h2>

<p>The task of the recovery block is to control the operating
states of the functional units. The recovery functions are</p>


<ul>
<li><p>Elimination of the effects of faults</p>
</li>
<li><p>Restart control</p>
</li>
<li><p>User interface.</p>
</li>
</ul>


<p>The faults are eliminated by means of the hardware redundancy.
On the functional unit level, processor and pre-processor restarts are also
used.</p>


<p>Recovery has in its possession real-time data about the
states of the functional units. By using this data, it controls the restarting
of the system and its functional units so that the restarts are carried out
in the correct order quickly and reliably.</p>


<p>With the recovery interface commands, the whole system
or its functional units can be restarted, the states of functional units can
be changed, and various inquiries about the states of the units can be made.</p>


<p>The recovery system consists of a centralised part, situated
in the OMU or in the case of an OMU failure, in the MCMU unit, and of a distributed
section in each computer unit. The centralised part controls the recovery
of functional units as a whole, and the distributed part is responsible for
the actions at unit level. The recovery system is implemented so that several
recovery actions can be executed in the system simultaneously.</p>
</div>


<a name="mar124164529" shape="rect"></a>
<div class="topic">
<h2>Fault
recovery</h2>

<p>A unit failure notice from the alarm system functions as
an impulse for the fault recovery. A recovery action to be taken depends on
the type of the unit to be recovered and also on the overall condition of
the system. For instance, if the active unit of a duplicated unit type fails,
either a changeover is made or the operating personnel is called for help,
depending on the availability (state) of the spare unit. In time-slot-based
units, the recovery is responsible for preserving a certain minimum configuration
of the unit type in question in the system at all times.</p>


<p>One of the general principles is that a failed unit is
taken to the test state and fault localisation and testing programs are activated.
On the basis of the diagnosis, the unit is taken to the separated state (fault
detected) or taken automatically into use (no fault).</p>
</div>


<a name="mar1241653110" shape="rect"></a>
<div class="topic">
<h2>Fault
Location</h2>

<p>The task of the fault location function is to refer hardware
faults in the system to one plug-in unit in 70% of cases and to four plug-in
units in 95% of cases. The system complies with the CCITT requirement about
the average active repair time of 30 minutes.</p>


<p>The fault location function has been implemented for every
functional unit (including TCSM2). The function can be divided into the following
subfunctions:</p>


<ul>
<li><p>Fault location for switching network</p>
</li>
<li><p>Fault location for processor units</p>
</li>
<li><p>Fault location for time-slot-based
units</p>
</li>
<li><p>Fault location for pre-processors</p>
</li>
<li><p>Fault location for I/O devices</p>
</li>
<li><p>Fault location for message bus and
supervisory bus</p>
</li>
<li><p>Fault location for clock system.</p>
</li>
</ul>


<p>There can be several diagnostic jobs in progress in the
system at a time. In the diagnostic job queue, there is room for ten jobs,
which can either be running or expecting a certain resource. In addition,
the user can place a job with priority in the queue.</p>


<p>With the commands of the diagnostics handling MML program,
the operator can start the diagnostics for a functional unit or an I/O device,
output individual tests of a functional unit, output the faulty units of the
system (either all of them or just the faulty processor units), inquire the
current test and the waiting tests, and interrupt the current test. The last
command also facilitates the setting of a hold time during which no diagnosis
tests are started up automatically.</p>
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