Question

Write different clock synchronization and leadership algorithms for distributed platforms.

Answer 1

Clock synchronization is a topic in computer science and engineering that aims to coordinate otherwise independent clocks. Even when initially set accurately, real clocks will differ after some amount of time due to clock drift, caused by clocks counting time at slightly different rates.
The Importance of Accurate Time on Computer Networks. The synchronization of time on computers and networks is often vitally important. Without it, the time on individual computers will slowly drift away from each other at varying degrees until potentially each has a significantly different time.

Answer 2

Clock Synchronization of Distributed,

Real-Time, Industrial Data Acquisition Systems

Alessandra Flammini and Paolo Ferrari

University of Brescia, Dept. of Information Engineering

Italy

1. Introduction

In distributed data acquisition systems for industrial applications, the synchronization of the

time references of the nodes is essential to guarantee the right real-time behaviour of the

system. All the modern distributed automation plants require a clock synchronization

mechanism.

The use of distributed architectures in industrial applications based on networks has many

benefits, including high system flexibility and scalability. However, this enhancement does

not come for free; basically, a high-performance network communication among the nodes

is needed and the data exchange across the network requires more complex management

software than centralized systems (Felser, 2005). Moreover, a key point in all distributed

data acquisition systems is the synchronization of the time reference among the nodes

(Eidson & Lee, 2003). A typical automation plant is composed by several distributed nodes,

controllers, sensors and actuators that need to sample and control the system in a

time coordinated fashion. Considering the real-time applications for data-acquisition, the

clock synchronization of the time reference across the network is essential in order to

support:

• Data fusion of the measures obtained using distributed data acquisition system and

sensors (Proft, 2007).

• Distribute signal processing which takes the “time” into account.

• Coordination of the actions across a distributed set of actuators if a control action has to

be taken.

• Optimization of the transmission bandwidth in the network, thanks to channel medium

access control such as TDMA (Time Division Multiple Access), for both wired and

wireless systems (Ueda & Yakoh, 2004).

The scientific community has proposed several types of synchronization algorithms: some

of them are dedicated to wired networks, with different kind of complexity and accuracy;

others are specifically dedicated to satisfy the requirements of wireless networks. The aim of

this chapter is the definition of basic concepts in the field of clock synchronization in order

to better understand the typical applications of clock synchronization techniques to

industrial data acquisition systems.

This chapter is organized as follows. A brief introduction to essential notions regarding the

time keeping and clock performance metrics.