Sonet network can be used as a high-speed backbone carrying loads from other networks such as ATM. The sonet networks is divided into three categories, they are also know as topology network.
Linear network are two types they are
A point-to-point network is normally made of an STS multiplexer, an STS demultiplexer, and zero or more regenerators with no add/drop multiplexers, the signal flow can be unidirectional or bi-directional.
A multipoint network uses ADMs to allow the communications between several terminals. An ADM removes the signal belonging to the terminal connected to it and adds the signal transmitted from another terminal. Each terminal can send data to one or more downstream terminals.
To create protection against failure in linear network, SONET defines automatic protection switching. This APS has three schemes are common for protection in linear channels protocol.
SONET ring can be used in either a unidirectional or bi-directional configuration. In each case we can add extra rings to make the network self-healing, capable or self-recovery from failure.
Mesh network wit h switches probably give better performance; a switch in a network mesh is called as a cross-connect. A cross-connect switches has input and output ports. In input port the switch takes an OC-n signals and change into STS-n signals, demultiplexes it into the corresponding STS-1 signals, and sends each STS-1 signal to the appropriate output port. An output port takes STS-1 signals coming from different input ports, multiplexes them into an STS-n signal and makes OC-n signals for transmission.