Timing and synchronization for modern communications systems

An overview is given of the principles of timing and synchronization for modern communications systems. Sources of frequency and time information include quartz, rubidium and cesium oscillators and a disciplined frequency standard that is referenced either to a cesium standard over a communications net or to a time and frequency service such as Loran-C. The Global Positioning System (GPS), not being fully operational, is not described but will provide an excellent source of accurate time and frequency information using 18 satellites with atomic standards onboard. Services available around the world are noted, and characteristics including equipment cost are tabulated.