SDH demultiplexing process
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Demultiplexing is the inverse of multiplexing. This topic describes how to demultiplex
a signal.
Process
The following describes the process for demultiplexing an STM-1 signal to a 2 Mbit/s
signal. The
“SDH digital multiplexing” (p. A-11)
illustrates the demultiplexing process.
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1
The unscrambled STM-1 signal from the optical conversion stages is processed to
extract the path overhead and accurately locate the payload.
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2
The STM-1 path overhead is processed to locate the VCs. The individual VCs are then
processed to extract VC overhead and, via the VC pointer, accurately locate the
2-Mbit/s signal.
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3
The 2-Mbit/s signal is desynchronized, providing a standard 2-Mbit/s signal to the
asynchronous network.
Key points
SDH STM pointers are used to locate the payload relative to the transport overhead.
Remember the following key points about signal demultiplexing:
•
The SDH frame is a fixed time (125 µs) and no bit-stuffing is used.
•
The synchronous payload can float within the frame. This is to permit
compensation for small variations in frequency between the clocks of the two
systems that may occur if the systems are independently timed (plesiochronous
timing).
An SDH overview
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365-312-847R4.0
Issue 4, November 2006
Lucent Technologies - Proprietary
See notice on first page
A-15
