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<h1>Radio Network Fault Recovery</h1>

<p>Radio network maintenance in the BSC provides facilities
for maintaining the radio network operational if a fault occurs in the BSS.</p>


<p>In addition to detection and indication of faults in the
BSS, the BSS executes automatic procedures that minimise the effect on the
quality of the service. The alarm handling system makes decisions on the basis
of alarm indications and activates  the  radio network recovery when necessary.</p>


<p>In case of a fault at a BTS site, the BTS sends an alarm
message to the BSC and indicates the accused object and whether it is operationally
enabled or disabled. Faults in the Abis transmission path (PCM fault, LAPD
signalling link fault) are detected by the BSC. The possibly needed recovery
action depends on the type of the faulty object and its current channel configuration.</p>


<p>An automatic recovery procedure is started if the fault
makes a whole cell in operational. Such faults are</p>


<ul>
<li><p>BCCH TRX fault. The BCCH is reconfigured
into another TRX if one available.</p>
</li>
<li><p>TRX fault in a baseband-hopping cell.
The frequency hopping parameters are recalculated for all the remaining TRXs
of the cell.</p>
</li>
</ul>


<p>If there is a preferred BCCH mark on some TRX, the BCCH
is reconfigured to that TRX. Forced handovers are used to clear the reconfigured
TRX(s) in order to avoid cutting any calls. After the faulty unit has been
repaired or replaced, the failure is cancelled and the radio network configuration
management system allocates the related resources back to service. Also if
the BCCH functionality is not on the preferred BCCH marked TRX, the BCCH functionality
is returned to that TRX.</p>
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