The Transmission of multiple digital bit streams syncronously over Optical Fiber using Lasers or LEDs

Also called SDH – Syncronous Digital Network

Basic Unit of Transmission is a STM-1 (Synchronous Transport Module, Level 1) which operates at 155.520 Mbps

SONET is a set of Transport containers that allow transmission of a variety of other protocols like POTS, ATM, Ethernet, etc.

SONET – Synchronous Optical Network