What are the four SONET layers Explain their functions?

Answer 1

The SONET/SDH standard includes a definition of a transmission protocol stack which solves the operation and maintenance problems often found when dealing with networks that have component streams lacking a common clock. The photonic layer is the electrical and optical interface for transporting information over fiber optic cabling. It converts STS electrical signals into optical light pulses (and vice versa, at the receiving end).

The section layer transports STS frames over optical cabling. This layer is commonly compared with the Data-Link layer of the OSI model, which also handles framing and physical transfer. The line layer takes care of a number of functions, including synchronization and multiplexing for the path layer above it. It also provides automatic protection switching, which uses provisioned spare capacity in the event of a failure on the primary circuit. The highest level, the path layer, takes services such as DS-3, T1, or ISDN and maps them into the SONET/SDH format. This layer, which can be accessed only by equipment like an add/drop multiplexer (a device that breaks down a SONET/SDH line into its component parts), takes care of all end-to-end communications, maintenance, and control.