We analyze the composition and layering structure of the synchronization network from the network view point

give the reference link of the clock transporting of the synchronization network

describe the rule on synchronization. It specifies the atomic function building blocks related with the network synchronization and timing

and how the SDH network elements take part in the synchronization of the network. It defines the atomic functions that are part of the two synchronization layers

the Synchronization Distribution （SD） layer and the Network Synchronization （NS） layer from atomic structure view point. It also defines some atomic function

part of the Transport layer

which are related with synchronization. We select the Synchronization Status Messages （SSM） Specifications suitable for applications in China based on the situations in our country.