What is the difference between SONET and SDH?

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Let us understand what Synchronous Optical Networking (SONET) is.


SONET stands for Synchronous Optical Networking. It is a standardized digital communication protocol that can transmit a large volume of data over relatively long distances using a fiber optic medium. With SONET, several digital data streams are shared simultaneously over optical fiber using LEDs and laser beams.

SONET provides several streams concurrently and supports efficient services in telecommunication systems. It uses standardized line rates, thus all types of organizations can be interconnected using SONET.

The network architecture of a SONET depends on transmitting data even if a section of the network has declined. SONET operate a bidirectional line-switched ring which can be either 2-fiber or 5-fiber modifications, unidirectional path-switched ring, or linear automated protection switching.

The SONET approach was generated to restore the plesiochronous digital hierarchy (PDH) system which moved telephone calls or data in huge amounts over the equivalent fiber. SONET allows for simultaneous transport of multiple circuits of origin within a single framing system. Four multiple layers are defined with SONET. These layers are route, line, section, and photonic. Each layer is responsible for specific jobs or applications. The path layer is responsible for the development of the signal from the optical source until it reaches its destination.

The line layer is where the signal transforms across the cable. The section layer is answerable for the expansion of signals across a physical section. Finally, the photonic layer correlates to the physical layer of the OSI model and contains requirements for the fiber channel.


SDH stands for Synchronous digital hierarchy. It is an international technology standard that uses light-emitting diodes (LED) or lasers for synchronous optical fiber communication. SDH was produced to remove synchronization problems and restore the plesiochronous digital hierarchy (PDH) system for bulk telephone and data exchange.

SDH/SONET specifications are represented in Telcordia Technologies Generic Requirements GR-253-CORE, which is respected by some global standards organizations. Telcordia GR-499-CORE contains general elements associated with SONET and different transmission systems such as asynchronous fiber optic and digital radio.

SDH multiplexing is a technical procedure by which multiple lower-order path layer signals of SDH are modifying into a higher-order direction or the multiple higher-order direction layer signals of SDH are adapting into a multiplex element. The fundamental building block of an SDH frame is an STM signal. It is also the first level of SDH at 155.52Mbps and is referred to as a synchronous transport module (STM).

The SDH is an international standard that is hugely famous and used for its high speed data transmission of the telecommunication and digital signals. This synchronous system has been specially designed to offer a simple and dynamic network infrastructure. This system has deliver a considerable amount of change in the telecommunication networks that were depends on the optical fibers until performance and cost were concerned.

Updated on 22-Nov-2021 05:26:03