1. Plesiochronous Digital Hierarchy (PDH) :
PDH stands for Plesiochronous Digital Hierarchy. It is a telecommunications network transmission technology designed for the transport of large data volumes across large scale digital networks. In PDH, multiplexing of 2 Mbit/s signals into higher order multiplexed signals. The laying cable between switch sites is very expensive. It increases traffic capacity of a cable by increasing bit rate.
2. Synchronous Digital Hierarchy (SDH) :
SDH stands for Synchronous Digital Hierarchy and it refers to as a multiplex technology used in the telecommunication. Synchronous Optical Network is internationally used. It is said to be a variation of SONET and is taken equal to SDH. It characteristics are founded on high order multiplexing. These are the technologies that provide quite fast and low priced network interconnection than PDH which stands for Plesiochronous Digital Hierarchy.
Difference between PDH and SDH :
|1.||Reference clock is not synchronized throughout the network.||Reference clock is synchronized throughout the network.|
|2.||There is no synchronization between payload and frame.||There is synchronization between payload and frame.|
|3.||Its system has different frame structures at different hierarchy levels.||Its system has consistent frame structures throughout the hierarchy.|
|4.||In this, Physical cross-connections are provided on the same level.||In this, Digital cross-connections are provided at different signal levels.|
|5.||In this, rates are derived from basic rate of 1.544 Mbps. The maximum capacity is about 566 Mbps.||In this, rates are derived from basic rate of 155.52 Mbps. The maximum up to 40 Gbps rates can be derived from basic rate mentioned.|
|6.||The implementation cost of PDH is lower.||The implementation cost of SDH is higher.|
|7.||The multiplying method used in PDH is complex.||The multiplying method used in SDH is simple.|
|8.||It is incompatible with other signals such as ATM, FDDI, DQDB etc.||It is compatible with other signals such as ATM, FDDI, DQDB etc.|
|9.||There is no universal standard for PDH.||The universal standard exists for SDH.|
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