Difference Between SDH and PDH Transmission

     PDH is Plesiochronous Digital Hierarchy and SDH is Synchronous Digital Hierarchy. Both are used in PCM transmission systems. Both use TDM principles for PCM frames.

      Difference Between SDH and PDH Transmission

PDH

The clock used is not the same throughout the transmission network.

Old system used for only point to point communication and interconnectivity between  the system is difficult.

Used in 2Mb, 8Mb, 34Mb and 140 Mb systems only.

No world standard on digital format (three incompatible regional standards  - European,  North American and Japanese).

No world standard for optical interfaces. Networking is impossible at the optical level.

SDH

Synchronous clock is used in the entire Transmission system.

Latest system used in any kind of transmission configuration and interconnectivity between  different systems is very easy.

Used in STM-1 (155.52Mbps,STM-(622.08Mbps),STM-16(2.5Gbps) and STM-64 (10G BPS) transmission systems.

World standard on digital format (three incompatible regional standards - European, North American and Japanese).

World standard for optical interfaces. Networking is possible at the optical level.