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<h1>FACCH Call Set-up Due to SDCCH Congestion</h1>

<p>The feature improves the quality of service in the network
in case of the SDCCH congestion. In the FACCH call set-up, the MS is assigned
from a CCCH to a TCH - instead of a SDCCH - with the IMMEDIATE ASSIGNMENT
procedure. The TCH is used for signalling, and thus no assignment procedure
is needed in the Air interface. Instead, only the MODE MODIFY procedure to
the TCH channel is required to change the channel mode from signalling to
speech.</p>


<p>SDCCHs are primarily used when a mobile requests a dedicated
channel from the BSS. Traffic channels can be allocated to mobiles in an immediate
assignment if all SDCCHs are already reserved for signalling, such as call
set-ups, SMS, and supplementary services. For each BSC, the FACCH call set-up
can be set on or off by means of the MMI.</p>
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