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.
- 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:
- STS Multiplexer:
- Performs multiplexing of signals
- Converts electrical signal to optical signal
- STS Demultiplexer:
- Performs demultiplexing of signals
- Converts optical signal to electrical signal
It is a repeater, that takes an optical signal and regenerates (increases the strength) it.
- 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.
- 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 includes four functional layers:
- 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.
- 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.
- Section Layer:
- It is responsible for the movement of signal across a physical section.
- Each device of network provides section layer functions.
- 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