SDH is the abbreviation of Synchronous Digital Hierarchy, which refers to multiplexing techniques and technology used in networking and telecommunications. It is the most popular standard being used in the whole world. The SDH proved a high-speed transfer of data and digital signals. Due to synchronization, Synchronous Digital Hierarchy provides a flexible and simple network infrastructure.
Synchronous Digital Hierarchy provides key advantages over plesiochronous digital hierarchy (PDH). Synchronous Digital Hierarchy is interoperable with SONET. SDH is appropriate as a transmission system for broadband ISDN and for transporting ATM cells, PDH signals, Ethernet aggregations, etc.
Synchronous Digital Hierarchy introduces the Synchronous Transport Module (STM) with different levels. The basic level is STM with a data rate of 155.52 Mbps. Other levels are STM-4 (622 Mbps), STM-16(2488 Mbps) or STM-64 (9,953 Mbps).
Advantages of SDH
- Simplified multiplexing and demultiplexing technique.
- Operable with existing PDH system
- Supports of multi-point networking.
- Can transport broadband signals
- Multi-vendor support
- Video conferencing, and interactive multimedia transport capability
- Enhanced administration and maintenance process
- Synchronous Digital Hierarchy provides quick recovery from failure.
Disadvantage of SDH
- Direct adding and dropping of lower-rate signal increases the complexity of the system.
- Usage of Software in Synchronous Digital Hierarchy system is vulnerable to computer viruses.
- The equipment used in Synchronous Digital Hierarchy system is complicated.
- Costly from previously used system PDH.
