29 CPOS INTERFACE CONFIGURATIONWhen configuring ATM/DSL interface, go to these sections for information you areinterested in:■ “Overview” on page 539■ “Configuring a CPOS Interface” on page 544■ “Configuring an E1 Channel” on page 545■ “Configuring a T1 Channel” on page 545■ “Displaying and Maintaining CPOS Interfaces” on page 546■ “Troubleshooting CPOS Interfaces” on page 546Overview This section covers these topics:■ “SONET/SDH” on page 539■ “SDH Frame Structure” on page 540■ “Terms” on page 540■ “Multiplexing E1/T1 Channels to Form STM-1” on page 541■ “Calculating E1/T1 Channel Sequence Numbers” on page 541■ “Overhead Byte” on page 542■ “CPOS Interface Application Scenario” on page 543SONET/SDH Synchronous optical network (SONET), a synchronous transmission system definedby ANSI, is an international standard transmission protocol. It adopts opticaltransmission.In SDH defined by CCIT (today’s ITU-T), adoption of synchronous multiplexing andflexible mapping allows you to add/drop low-speed tributary signals from SDHsignal without large amount of multiplexing/demultiplexing devices. This reducessignal attenuation and device investment.CPOS Low-speed tributary signals are called channels when they are multiplexed to formSDH signals. CPOS, the channelized POS interface, makes full use of SDH toprovide precise bandwidth division, reduce the number of low-speed physicalinterfaces on devices, enhance their redistribution capacity, and improve theaccess capacity of dedicated lines.CPOS interfaces are mainly used to enhance the devices’ redistribution capacity forlow-speed access. CPOS interfaces are mainly of two rates: STM-1 (155 mbps) andSTM-16c (2.5 Gbps).
