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<h1>Redundant Cold Stand-by TRX</h1>

<p>The BTS may contain a redundant TRX, which can be brought
into traffic in case of a BCCH TRX failure in a 1 TRX BTS. In the sectored
case, a separate stand-by TRX is required for each sector. This stand-by TRX
uses the same Abis transmission resource as the failing unit. Thus there is
no need to reserve any extra capacity for this redundant TRX.</p>


<p>The general operation of the feature is described below.</p>


<p>When the BTS OMU realises that the primary BCCH TRX of
the BTS has failed, it sends the usual alarms to the BSC. Then the following
steps will be taken:</p>


<p>The BIE is reconfigured to divert the traffic of the failing
TRX to the redundant TRX. The combiners are re-tuned, and the CU is given
the appropriate channel number. The OMU switch on the redundant TRX loads
and initialises it. Now the alarm’s rose for the failing unit is cancelled,
and the BSC brings the new TRX into use.</p>


<p>This changeover is transparent to the BSC since it only
receives alarms for the failing TRX and then the cancellation of the alarms.
It does not know that it is now communicating with a different hardware.</p>
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