Cisco ASR 900 Series Configuration Manual page 85

Configuring SDH on 1-Port OC-192/STM-64 or 8-Port OC-3/12/48/STM-1/-4/-16 Module
SDH Frame Structure
The SDH frame consists of 270 columns. The first nine columns of each frame make up the Section Overhead,
and the last 261 columns make up the VC capacity. The VC plus the pointers (H1, H2, H3 bytes) are called
the Administrative Unit (AU). Carried within the VC capacity, which has its own frame structure of nine rows
and 261 columns, is the Path Overhead and the Container. The first column is for Path Overhead; it is followed
by the payload container, which can itself carry other containers. VCs can have any phase alignment within
the Administrative Unit, and this alignment is indicated by the Pointer in row four. Within the Section Overhead,
the first three rows are used for the Regenerator Section Overhead, and the last five rows are used for the
Multiplex Section Overhead. The STM frame is transmitted in a byte-serial fashion, row-by-row, and is
scrambled immediately prior to transmission to ensure adequate clock timing content for downstream
regenerators.
Figure 6: STM1 Frame Structure
Figure 7: STM1 Section Overhead
1-Port OC-192 or 8-Port Low Rate CEM Interface Module Configuration Guide, Cisco IOS XE Everest 16.7.x (Cisco
ASR 900 Series)
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