What is SONET / SDH Optical Communication

• SONET is  Synchronous Optical Network

• SDH is Synchronous Digital Hierarchy

• SONET/SDH both are ITU (International Telecommunication Union) standards for optical point to point interface that allows

1. Interconnection of fiber optic transmission systems of different carriers and manufacturers 
2.  Easy Access to tributary signals
3.  Direct Optical interfaces at terminals
4.  Synchronous frame structure and TDM digital traffic and network operations

• SONET & SDH are based on digital TDM signal hierarchy where a periodically recurring time frame of 125µs can carry payload traffic of various rates

• Overhead bytes are also included for

• Error Checking
• Network maintenance etc

• SDH support 30 different channels hence it is 1.54 Mbps

• SONET support 24 different channels hence it is 2 Mbps

• SDH and SONET both are circuit switching