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<h1>TCSM2 Routing Tests of A-if Circuits</h1>

<p>The TCSM2 test one verifies with very high reliability
the correct operation of the speech coding functions of digital signal processors.</p>


<p>During the test, the TCSM2 loops A and Ater interface timeslots
in its ET2x plug-in units. After the loops are ready, the DSPs serving the
channels generate a test pattern containing a base set of PCM samples into
the A interface direction. The PCM samples are looped back from the ET2E and
encoded with half rate speech coding. The resulting half rate TRAU frames
and located as usual into the 8 kbit/s subchannel, and in case of other circuit
types (16, 32, or 64 kbit/s), the half rate frames are duplicated to the other
sub-channels so that the whole part of the timeslot available is tested. The
DSP decodes the returning TRAU frames and analyses the result. If a corrupted
bit pattern is detected or the comparison between the sent and received frames
fails, the TCSM2 raises an alarm requiring operator actions.</p>


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<img alt="urn:mars:dn0469923:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0469923&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: The TCSM2 test</p>
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<p>The test can be started in two ways:</p>


<ul>
<li><p>The operators start the test with the
diagnostic MML when the TCSM2 in test state.</p>
</li>
<li><p>The operator can schedule the test
so that it will be performed automatically to idle TCSM2 channels without
disturbing busy channels. A parameter defines how many channels (in percent)
have to be free before the BSC activates the test. Therefore, testing does
not cause any unnecessary congestion to the A interface.</p>
</li>
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