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(DFCA)</a></td>
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<h2>BSC-BSC interface</h2>

<p>The BSCs running the DFCA algorithm are connected to each other with
a BSC to BSC interface (BBI). The interface is used for the transmission of
data that needs to be exchanged between DFCA algorithms in different base
station controllers, when there are DFCA cells that are interfering with each
other and controlled by the different DFCA algorithms.</p>


<p>Data transfer on the inter BSC connection takes place within measurement
relations that have been established between DFCA cells in different BSCs.
The DFCA algorithm in a BSC establishes a measurement relation towards another
DFCA algorithm in another BSC based on the results from the BIM update process.</p>


<p>When a measurement relation between two DFCA cells in different BSCs
exist, the DFCA algorithm of each end updates its counterpart about every
DFCA channel allocation and release that takes place in a DFCA cell of the
relation. The interfered end of the relation sends updates about changes in
the C/I of the relation, as they take place as a result of the BIM update
process. If the operator changes the information used for identifying DFCA
cells, this is updated to the other end of a measurement relation. Also, the
DFCA connection specific power control and neighbour cell C/I data is forwarded
to the DFCA algorithm at the other end of the measurement relation.</p>


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<p>The BSC-BSC interface is physically located in the BCSU unit of the
BSC. The use of MTP3 user adaptation layer (M3UA) and signalling connection
control part (SCCP) allows load sharing between BCSU units. It also supports
BCSU switchovers. If there are links configured in two BCSU units, the system
handles the switchovers without the application noticing it. The DFCA procedures
are an extension of the radio network subsystem application part (RNSAP).
The complete RNSAP has not been implemented as part of DFCA.</p>


<p>Every BSC has been assigned an SCCP Signalling Point Code (SPC) during
the creation of the A interface. This Signalling Point Code is used to identify
and address a BSC through the BSC-BSC interface. The DFCA algorithm finds
out the BSC (SPC) that is controlling a particular external DFCA cell with
the help of a LAC to SPC mapping table. The LAC to SPC mapping table reduces
the needed signalling and processing load in the BSC-BSC interface by giving
the BSC a limited set of neighbour BSCs, from where to search each DFCA cell
that is not under its control.</p>
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