Access Termination Unit (ATU)
5.3.1.8 Radio Frame Demultiplexer
On the receiving side the received composite data stream is demultiplexed and
FEC corrected. The frame alignment function searches and locks the receiver
to the frame alignment bit patterns in the received data stream.
Descrambling and FEC Decoding
Error correction is accomplished using FEC parity bits in combination with a
data quality measurement from the Demodulator. The descrambler transforms
the signal to its original state enabling the Demultiplexer to properly distribute
the received information to its destinations.
Demultiplexing
Demultiplexing is performed according to the used frame format. The
Demultiplexer generates a frame fault alarm if frame synchronization is lost.
The number of bits with errors in the traffic data stream is measured using
parity bits. These are used for BER detection and performance monitoring.
Stuffing control bits are processed for the traffic and service channels.
Traffic
On the receiving side the following is performed to the traffic data:
• AIS insertion (at signal loss or BER10
-3
)
• AIS detection
• Elastic buffering and clock recovery
DCC
On the receiving side, elastic buffering and clock recovery is performed on
the DCC.
HCC
The Hop Communication Channel (HCC) is used for exchange of control and
supervision information between near-end and far-end.
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4/1555-CSH 109 32/1-V1 Uen B 2007-09-14
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