Understanding the network.pdf - Back to Home

SONET/SDH Operation
Although SONET and SDH are strictly OSI-RM Layer 1 activities, (like T-carrier)
there is a definite separation of the transport functions. The separation of functions
into distinct operational areas is common in open standards. Open standards allow
users of the standard to make enhancements to a particular function or combine
functions in their particular implementation. As long as all the functions are met in
accordance to the standard, compatibility will be maintained. SONET and SDH
protocol use a four-layer architecture model (illustrated in Figure 5.7). The four
layers are as follows:
Figure 5.7. The SONET/SDH architecture model.
• Photonic layer
• Section layer
• Line layer
• Path layer