SDH digital multiplexing
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Digital multiplexing is SDH’s method of byte mapping tributary signals to a higher
signal rate, which permits economical extraction of a single tributary signal without the
need to demultiplex the entire STM-1 payload. In addition, SDH provides overhead
channels for use by OAM&P groups.
SDH digital multiplexing
The following figure illustrates the SDH technique of mapping tributary signals into
the STM frames.
Transporting SDH payloads
Tributary signals are mapped into a digital signal called a virtual container (VC). The
VC is a structure designed for the transport and switching of STM payloads. There are
various sizes of VCs: VC-11, VC-12, VC-2, VC-3, VC-4, VC-4-4C, VC-4-16C,
VC-4-64C and VC-4-256C.
C-11
C-12
C-2
C-3
STM-0
C-4
C-4-4C
C-4-16C
C-4-64C
C-4-256C
STM-1
STM-4
STM-16
STM-64
STM-256
VC-11
VC-12
VC-2
VC-3
VC-3
Pointer processing
Multiplexing
Aligning
Mapping
AU-3
…
VC-4
VC-4-4C
VC-4-16C
VC-4-64C
VC-4-256C
AU-4
AU-4-4C
AU-4-16C
AU-4-64C
AU-4-256C
TU-11
1
1
1
1
1
1
1
1
1
1
1
1
1
3
3
3
4
4
4
4
4
7
7
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✕
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✕
✕
✕
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TU-12
TU-2
TU-3
TUG-2
TUG-3
AUG-1
AUG-4
AUG-16
AUG-64
AUG-256
An SDH overview
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365-312-801R7.2
Issue 3, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
A-11
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