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<div class="div">
<h1>Trace Window for Dropped Calls</h1>

<p>This feature provides the operator with detailed information
on the last seconds of a call after the call has been dropped unexpectedly
and thus gives the reasons for possible problems.</p>


<p>The feature is implemented as a new observation type, Dropped
Call Observation (DC_OBS). This observation collects some key parameters of
the call, for example:</p>


<ul>
<li><p>MS Power</p>
</li>
<li><p>BS Power</p>
</li>
<li><p>RX Level and Quality of the BS measured
by the MS</p>
</li>
<li><p>RX Level of the neighbouring cells
measured by the MS</p>
</li>
<li><p>RX Level and Quality of the MS measured
by the BS</p>
</li>
<li><p>MS Speed</p>
</li>
<li><p>the MS's distance (Timing Advance)
from the BS</p>
</li>
<li><p>Handover causes.</p>
</li>
</ul>


<p>Data on the last 16 seconds will be stored in a disk file
if the call drops. If the call is released normally, the data collected will
be discarded. Each call is identified with a reference number. The scope of
the observation is one BTS, but it can be focused down to one TRX to all TSLs.
To activate the observation, use similar MML commands as with other observations.</p>


<p>The benefit of this feature is that information on real
reasons for SDCCH and TCH problems can be found, and the BTS with lower quality
can be detected.</p>
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