SDH digital multiplexing

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.

View the figure
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.

Table

The following table shows the mapping possibilities of some digital signals into SDH payloads.

Input tributary

Voice Channels

Rate

Mapped Into

1.5 Mbit/s

24

1.544 Mbit/s

VC-11

2 Mbit/s

32

2.048 Mbit/s

VC-12

6 Mbit/s

96

6.312 Mbit/s

VC-2

34 Mbit/s

672

34.368 Mbit/s

VC-3

45 Mbit/s

672

44.736 Mbit/s

VC-3

140 Mbit/s

2016

139.264 Mbit/s

VC-4

Alcatel-Lucent – Proprietary

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