Metro Ethernet

SONET/SDH Architecture

The SONET/SDH architecture identifies three different layers, each of which corresponds to one level of communication between SONET/SDH equipment. The layers are as follows, starting with the lowest:

• The regenerator section, or section layer

• The multiplex section, or line layer

• The path layer

Figure A-3 shows the three SONET/SDH layers.

Figure A-3. SONET and SDH Layers

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As shown in Figures A-1 and A-2, each of these layers in turn has its own overhead (header). The transport overhead (TOH) of a SONET/SDH frame is mainly subdivided into two parts that contain the section overhead (SOH) and the line overhead ...