Synchronous Optical Network (SONET)

SONET stands for Synchronous Optical Network. SONET is a communication protocol, developed by Bellcore – that is used to transmit a large amount of data over relatively large distances using optical fibre. With SONET, multiple digital data streams are transferred at the same time over the optical fibre.

Key Points:

• Developed by Bellcore
• Used in North America
• Standardized by ANSI (American National Standards Institute)
• Similar to SDH (Synchronous Digital Hierarchy) which is used in Europe and Japan.

Why SONET is called a Synchronous Network?
A single clock (Primary Reference Clock, PRC) handles the timing of transmission of signals & equipments across the entire network.

SONET Network Elements:

1. STS Multiplexer:
   • Performs multiplexing of signals
   • Converts electrical signal to optical signal
2. STS Demultiplexer:
   • Performs demultiplexing of signals
   • Converts optical signal to electrical signal
3. Regenerator:
   It is a repeater, that takes an optical signal and regenerates (increases the strength) it.
4. Add/Drop Multiplexer:
   It allows to add signals coming from different sources into a given path or remove a signal.

Why SONET is used?
SONET is used to convert an electrical signal into an optical signal so that it can travel longer distances.

SONET Connections:

• Section: Portion of network connecting two neighbouring devices.
• Line: Portion of network connecting two neighbouring multiplexers.
• Path: End-to-end portion of the network.

SONET Layers:

SONET includes four functional layers:

1. Path Layer:
   • It is responsible for the movement of signals from its optical source to its optical destination.
   • STS Mux/Demux provides path layer functions.
2. Line Layer:
   • It is responsible for the movement of signal across a physical line.
   • STS Mux/Demux and Add/Drop Mux provides Line layer functions.
3. Section Layer:
   • It is responsible for the movement of signal across a physical section.
   • Each device of network provides section layer functions.
4. Photonic Layer:
   • It corresponds to the physical layer of the OSI model.
   • It includes physical specifications for the optical fibre channel (presence of light = 1 and absence of light = 0).

Advantages of SONET:

• Transmits data to large distances
• Low electromagnetic interference
• High data rates
• Large Bandwidth

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