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

Building Automation, Wireless Technology and the InternetInternet ConnectionsOne of the major uses of modems is Internet access. The Internetconsists of local connections, long-haul connections, routers, servers,and a variety of protocols. These components work together in the followingways.Users connect by dialing in to an Internet Service Provider (ISP) usinga modem over telephone lines. These are often the same kind oftwisted pair, copper wires that have been used since the telephone was invented.At the ISP end is another conventional modem. These modemsconvert the computer’s digital information to analog signals and thenback to digital on the remote end. Connection speed is at best, not countingfactors like line noise, the speed of the slower of the modems.If you are connected to the Internet through a network, your PC ispart of a local area network (LAN). Your PC has a network interface card(NIC) that ties it to the network which is typically Ethernet.The cable coming out of the NIC is either coaxial cable or a largerversion of your telephone wire. Your network will be probably connectedto an ISP not by a modem, but through a higher-speed connectionleased from the local phone company. Newer technologies offerhigh-speed connections to users.Internet GrowthThe Internet was born over decades ago in the form of a U.S.Defense Department network called the ARPAnet. This was an experimentalnetwork designed to support military research in communicationnetworks that could withstand partial outages from military operationsand still function.In the late 1960s most computers were not capable of sendinggraphics across networks or even viewing them. The traffic that traversedthe network was generally text-based in the form of electronic mail messagesand the direct interconnection of one computer with another.In the 1970s the Internet began to be interconnected with largeuniversities and research organizations. The nature of the traffic beganto move towards on-line research, but it was still government-oriented.To send a message on the network, a user only had to put the datain an envelope, called an Internet Protocol (IP) packet, and address thepackets correctly. The communicating computers were also given the©2001 by The Fairmont Press, Inc. All rights reserved.