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Synchronous Digital Hierarchy (SDH)

Synchronous Digital Hierarchy (SDH) is a standardized technology for synchronous data transmission on optical media. Here's a brief overview:

1.  Synchronization: SDH uses synchronous transmission, meaning that the sender and receiver are synchronized in time. This synchronization allows for efficient multiplexing of different data streams.


2. Multiplexing: SDH supports multiplexing, enabling the transmission of multiple signals of different capacities over the same optical fiber. This is achieved through a hierarchy of standardized bit rates, such as STM-1 (155 Mbps), STM-4 (622 Mbps), and so on.


3. Optical Fiber Transmission: SDH is designed for optical fiber transmission, providing high bandwidth and low signal attenuation over long distances. It's a key technology in high-capacity, long-haul telecommunications networks.


4. Hierarchical Structure: SDH has a hierarchical structure, where lower-level signals are multiplexed to create higher-level signals. This hierarchy simplifies network management and facilitates the flexible allocation of bandwidth.


5. ADM (Add-Drop Multiplexer): SDH networks often include Add-Drop Multiplexers, allowing the addition or removal of specific signals without affecting the overall network. This flexibility is crucial for dynamic network configurations.


6. Error Detection and Correction: SDH incorporates error detection and correction mechanisms to ensure the integrity of transmitted data. This helps maintain reliable communication in the presence of potential signal impairments.


7.  ITU-T Standards: SDH is defined by international standards developed by the International Telecommunication Union      (ITU-T), primarily under the G.707 and G.783 recommendations.


8.  SONET (Synchronous Optical Networking): In North America, a similar technology known as SONET is used. While SDH and SONET have some differences, they are often considered functionally equivalent and can be interconnected through various methods.


SDH has been widely adopted globally for its efficiency in managing high-capacity data transmission over optical fiber networks.

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