sonet 101

Why Synchronize?
SYNCHRONIZATION HIERARCHY
Digital switches and digital cross-connect systems are commonly employed in the
digital network synchronization hierarchy. The network is organized with a master-slave
relationship with clocks of the higher level nodes feeding timing signals
to clocks of the lower level nodes. All nodes can be traced up to a primary reference
source, a Stratum 1 atomic clock with extremely high stability and accuracy.
Less stable clocks are adequate to support the lower nodes.
The network of Figure 2-1 illustrates the digital network synchronization hierarchy,
with all clocks normally operating at the same frequency as the reference
source. A large network can comprise the interconnection of many such clusters
of nodes, each operating plesiochronously.
24
Nodes
1
Stratum 1
Timing
Signals
2
2
Stratum 2
3
Stratum 3
4
4
4
Stratum 4
Figure 2-1 • Digital Network Synchronization Hierarchy