Network synchronization

Network synchronization deals with the problem of distributing time and frequency among spatially remote locations. Network synchronization is an integral part of any large communication system, such as the telephone network. It also plays an important role in many diverse applications like navigation and position determination, computer communication, data gathering, control and command systems, and phased-array antennas. The purpose of this paper is to introduce the reader to the subject of network synchronization by organizing and presenting a tutorial of the theoretical work accomplished to date. Since the subject material is scattered, disconnected, and couched in different notations, the authors have long felt that it would be significant to organize the material and present the reader with an overview of the growth of the subject. A by-product of such a review should serve as an aid to set direction for future studies and research work. The paper begins by providing the classification of networks into plesiochronous (asynchronous) and synchronous. Further breakdown of this basic classification into a tree-structure hierarchy is presented. Since the time and frequency waveforms transmitted between nodes experience propagation delay, some form of ranging system application is usually required in order to compensate for these delays. Several delay compensation techniques are described and incorporated into a more detailed classification of the synchronization systems. This is then followed by presenting functional network models from which a generic and unified mathematical model is formulated. Network performance measures are defined and the mathematical model is used to characterize the synchronization behavior of the network in terms of these measures. Emphasis is placed on characterizing and understanding network stability, steady-state behavior, effects of clock phase noise, and channel thermal noise. The nonlinear behavior of synchronization systems is also explored. Numerous applications are pointed out and a rather complete list (unfortunately nonexhaustive) of the references is provided for the purpose of directing future research work.