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<h1>Abis Trunk Signalling</h1>

<p>Radio Signalling Link is a logical link between the BSC
and the BTS in Layer 2. The RSL is identified by a functional address known
as Service Access Point, SAPI=0. Radio signalling links over the Abis interface
are addressed to different units by Terminal Endpoint Identifiers, TEI. TEI
values are fixed and correspond to the TRX-id. The TEI management is not used.</p>


<p>One signalling channel is used for each transceiver (TRX)
and one for each BTS base control function (BCF/OMU). Alternative signalling
speeds are available: 16 kbit/s, 32 kbit/s, or 64 kbit/s. The selection of
the signalling speed is done in the commissioning phase on BTS basis. The
same selection is also done on the BSC site when channel configuration is
defined.</p>


<p>Normally, 16 kbit/s TRX signalling speed is recommended
for the FR operation. 32 kbit/s TRX signalling rate is recommended for the
HR use.</p>


<p>At the BCF/OMU signalling rate of 64 kbit/s, the SW downloading
time needed is approximately four times shorter than with 16 kbit/s signalling.</p>
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