HVAC Control in the New Millennium.pdf - HVAC.Amickracing

Computer Networks and SecurityEthernet is doing well in the industrial marketplace. It has completelytaken over the commercial sector, pushing the former competitionlike ARCnet and token ring aside. Users and vendors have givenEthernet a place in modern control systems.There will soon be an estimated 200 million Ethernet connectionsworldwide. Some control networks may not survive the growth ofEthernet, including controller-to-controller buses such as ControlNet orProfibus-FMS, unless they are modified to use Ethernet.It has become a very inexpensive technology and is well understoodsince it is one of the simplest network technologies to implement(Figure 7-1).Ethernet offers the possibility of a truly open connectivity standardfor distributed control systems along with field-device networks such asProfibus or Foundation Fieldbus.Ethernet technology was originally developed by Xerox in theearly 1980s. It was adopted by the Institute of Electrical and ElectronicsEngineers (IEEE) as standard 802.3 in 1988. Since then it has become thedominant standard for local area networks.Ethernet provides the physical layer and the data-link layer protocolsin the ISO model. The physical layer defines the cable types, connec-Figure 7-1. Basic Ethernet network©2001 by The Fairmont Press, Inc. All rights reserved.