Synchronous Digital Hierarchy

Synchronous Digital Hierarchy

Synchronous Digital Hierarchy (SDH) is a standardized multiplexing protocol for transferring large amounts of data over optical fiber using time-division multiplexing (TDM). It provides a way to transport multiple digital signals over a single optical fiber while maintaining synchronization between the signals.

Here are some key aspects of Synchronous Digital Hierarchy (SDH):

Synchronization:

SDH is designed to be synchronous, meaning that the transmission of data is based on a common clock signal. This ensures that data from multiple sources can be easily multiplexed and demultiplexed.

Multiplexing and Hierarchy:

SDH uses a hierarchical structure to multiplex different bit rates onto higher bit rate signals. The basic building block is the STM-1 (Synchronous Transport Module level 1), which operates at a rate of 155.52 Mbps. Higher-order structures such as STM-4, STM-16, and STM-64 are created by multiplexing lower-order structures.

Standardized Interfaces:

SDH defines standardized interfaces and rates for various signal levels. These interfaces allow different equipment from various vendors to interoperate seamlessly.

Optical Transmission:

SDH is commonly used for optical fiber transmission. Optical signals carrying multiple digital signals are transmitted over the same fiber using wavelength division multiplexing (WDM) techniques.

International Standards:

SDH is an international standard defined by the International Telecommunication Union (ITU) under the G.707 and G.783 recommendations. These standards ensure the compatibility and interoperability of SDH equipment from different manufacturers..

Error Detection and Correction

SDH incorporates error detection and correction mechanisms to ensure the reliability of data transmission. It uses overhead bytes to carry management, error monitoring, and performance monitoring information.

Add-Drop Multiplexers (ADM):

SDH networks often include add-drop multiplexers that allow the addition or removal of specific signals at intermediate points in the network. This flexibility is crucial for efficiently managing network traffic.

Network Management:

SDH networks include management systems for monitoring and controlling the network. These systems provide capabilities for fault detection, performance monitoring, and configuration management.

Synchronous Transport Modules (STM):

STM-1, STM-4, STM-16, etc., are part of the SDH hierarchy and represent different data rates. For example, STM-1 operates at 155.52 Mbps, and each higher level represents a multiple of the lower level.

SDH has been widely adopted in telecommunications networks, especially in long-distance and high-capacity applications. It has largely replaced the older plesiochronous digital hierarchy (PDH) systems due to its standardized and flexible architecture. SDH provides the foundation for high-speed and reliable digital communication in modern telecommunications networks.