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Synchronous Optical Network (SONET)

Synchronous Optical Network, or SONET. A communication protocol called SONET was created by Bellcore and is used to send a lot of data over relatively long distances using optical fibre. Multiple digital data streams are transmitted simultaneously over the optical fibre with SONET.

Key Ideas

  • Bellcore developed
  • North American usage
  • established by ANSI (American National Standards Institute).
  • SDH (Synchronous Digital Hierarchy), which is utilised in Europe and Japan, is comparable.

Why is SONET referred to as a synchronised network?

Across the entire network, the timing of signal and equipment transmission is controlled by a single clock (the Primary Reference Clock, or PRC).

SONET Network Constituents

Synchronous Optical Network (SONET)

Multiplexer STS:

  • performs signal multiplexing.
  • optical signal from electrical signal is converted.

Demultiplexer STS:

  • performs signal demultiplexing.
  • optical signal to electrical signal conversion.


  • It is a repeater that regenerates (increases the strength of) optical signals.

Drop/Add Multiplexer:

  • It enables the addition of signals from various sources to a particular path or the removal of a signal.

Why is SONET employed?

An electrical signal is changed into an optical signal by SONET so that it can travel farther.

Connections to SONET

  • Section: The portion of the network that connects two nearby devices.
  • Line: A section of the network that links two nearby multiplexers.
  • Path: The network's end-to-end section.

Layers of SONET:

Synchronous Optical Network (SONET)

There are four functional layers in SONET:

1. Step Layer:

  • It is in charge of transferring signals from their optical source to their optical destination.
  • Providing path layer functions is STS Mux/Demux.

2. The Line Layer

  • It is in charge of signal transmission across a real line.
  • Add/Drop Mux and STS Mux/Demux both offer Line layer functions.

3. Stacking Section:

  • It is in charge of signal transmission across a physical region.
  • Each network device performs section layer functions.

4. Optical Layer:

  • It corresponds to the OSI model's physical layer.
  • It includes the optical fibre channel's physical specifications (light is present when 1 and not present when 0).

Benefits of SONET

  • transmits information over long distances
  • very little electromagnetic interference
  • greater data rates
  • Broad Bandwidth

SONET's drawbacks include:

  • No standard that is compatible.
  • SONET mux services are necessary for tributary services.
  • Low cost and efficient for few channels.
  • The SONET/SDH network management system is inadequate for managing and using the DWDM technique.
  • At higher capacities, bandwidth efficiency is a problem.
  • There must be more overhead.

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