24 March 2020


What is PDH?

PDH is meaning from the plesiochronous digital hierarchy, it is a very popular technology applied in the networks telecommunication technology in order to transport large amounts of data over a digital transport equipment like fiber-optic or microwave radio system. 

What is SDH?

SDH is meaning from the synchronous digital hierarchy, it is a standardized technology that is used for high-speed data transmission of telecommunication and digital signal. It can transfer multiple digital bitstreams synchronously over the optical fiber system using lasers or highly coherent light from LED called as light-emitting diodes. 

Now lets us discuss the main key difference between PDH and SDH

  • PDH stands for a plesiochronous digital hierarchy, SDH stands for synchronous digital hierarchy.
  • In PDH  there is no synchronization between payload and frame while in SDH there is synchronization between payload and frame.
  • Poor administration in PDH, Higher administration in SDH.
  • PDH system has a different frame structure at different hierarchy levels, SDH system has consistent frame strcutre throughout the hierarchy.
  • PDH is a complex system, SDH is a simple system.
  • In PDH system the reference clock is not synchronized throughout the network, but in SDH reference clock is synchronized throughout the network.
  • PDH is incompatible with another signal such as ATM, FDDI, DQDB, etc while in SDH is compatible with other signals such as ATM, FDDI, DQDB, etc.
  • There is no universal standard for PDH, Universal standard exists for SDH.
  • Physical cross-connection are provided on the same level in PDH, Digital cross-connection are provided at the different signal level in SDH.
  • Multiple methods used in PDH is complex, Multiplying method used in SDG is simple.
  • PDH rates are derived from the basic rate of 1.544 Mbps. The maximum capacity is about 566 Mbps while SDH rates are derived from a basic rate of 155.52 Mbps. The maximum up to 40 Gbps rates can be derived from the basic rate mentioned.
  • The implementation cost of PDH is lower while in SDH implementation cost is high.
Explore more information: