1. In 1984, the Exchange Carriers Standards Association ECSA began to work to establish a standard for connecting one fibre system to another which produced system
2. SONET/SDH standard define the basic transmission rates and characteristics, frame formats and testing and an optical interface multiplexing scheme as well as defining OAM&P
3. SONET structure follows a strict definition and hierarchy which maps to electrical hierarchies of many nations
4. SONET structure is then multiplexed to form higher speed transfer circuit that range today to GB and provide alternate to aggregation multiple DS1 and DS3 transmission facilities
5. SONET solves various network management problems associated with DS3
6. SONET defines a hierarchy of electrical signal known as STS
7. Each STS supports a certain data rates specific in Mb per sec
8. The corresponding optical signal are known as optical carriers OCs
9. SDH specifies a similar system known as STM

Path: Information carried end to end

Line: Information carried for STS-n signals between multiplexers

Section: Information caused for communication between adjacent network equipment.