Management is very inflexible in PDH, So SDH was developed.
Synchronous Digital Hierarchy (SDH) originates from Synchronous Optical Network (SONET) in the US.
It includes capabilities for bandwidth on demand and is also made up of multiples of E1.
STM-1 (155Mb/s) is 63 x E1, STM-4 (622Mb/s) is 4 x STM-1 and STM-16 (2.5Gb/s) is 4 x STM-4.
The benefits of SDH are:
1) Different interfaces or different bandwidths can connect (G708, G781).
2) Network topologies are more flexible.
3) There is flexibility for growth.
4) The optical interface is standard (G957).
5) Network Management is easier to perform (G774 and G784).
Its all about Data and Telecommunication
