H3C Technologies H3C SR8800 - Manual (Page 35)

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Configuring CPOS interfaces
NOTE:
Only the PIC-CLF2G8L and PIC-CLF4G8L sub-cards have channelized E3/T3 interfaces.
Overview
SONET
Synchronous Optical Network (SONET), a synchronous transmission system defined by the ANSI, is an
international standard transmission protocol. It adopts optical transmission.
SDH
Synchronous Digital Hierarchy (SDH), defined by the CCITT (today’s ITU-T), uses a SONET rate subset.
As SDH uses synchronous multiplexing and a flexible mapping structure, low-speed tributary signals can
be added to or dropped from an SDH signal without a large amount of multiplexing/demultiplexing
devices. This reduces signal attenuation and investment in network devices.
CPOS
The Low-speed tributary signals multiplexed to form an SDH signal are called channels. The channelized
POS (CPOS) interface makes full use of SDH to provide precise bandwidth division, reduce the number
of low-speed physical interfaces on network devices, enhance their aggregation capacity, and improve
the access capacity of leased lines.
The CPOS interface operates at the rate of STM-1.
SDH frame structure
To understand the benefits of CPOS, you need to first understand the frame structure of SDH signal
STM-N.
Low-speed tributary signals should distribute in one frame regularly and evenly for the convenience of
adding them to or dropping them from high-speed signals. The ITU-T specifies that STM-N frames adopt
the structure of rectangle blocks in bytes, as illustrated in Figure 4 :