Sonet network

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
  • Ring network
  • Mesh network

Linear network

Linear network are two types they are

Point-to-point network

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.

Multipoint network

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.

Automatic protection switching

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.

  • One-plus-one APS: In this scheme, there are normally two lines, one is working line and another one is protection line, both lines are active at all the time.
  • One-to-one APS: In this scheme, which looks like the one-plus-one scheme, there is also one working line and one protection line. However, the data are normally sent on the working line until it fails.
  • One-to-many APS: This scheme is similar to the one-to-one scheme expect that there is only one protection line for many working lines. When a failure occurs in one of the working lines, the protection line takes control until the failed line is repaired.

Ring network

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.

  • Unidirectional path switching ring: A unidirectional network with two rings, one ring is used as a working ring and other as a protection ring.
  • Bidirectional line switching ring: Another alternative in SONET ring network is a bidirectional line switching ring, in this case communication is bidirectional which means that we need two working rings and two protection rings. This means BLSR uses four rings.

Mesh network

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.