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

Computer Networks and Securityther UTP-3, UTP-4, or STP-3, which is a higher-grade shielded twistedpairwire bundle. The wire itself is typically 24-gauge copper wire witha PVC or Teflon coating.An Ethernet network consists of the cable and connectors. Thereare also terminating resistors, coaxial taps and transceiver drop cables.Transceivers and controllers are used at the node locations. Fan-outs,gateways, repeaters and other equipment are used to expand the system.An Ethernet gateway provides network expansion and conversionamong networks with different protocols.A packet or Ethernet frame is the transmission vehicle. Ethernetacts like a one-line country telephone network since only a single transmissioncan proceed at a time (Figure 7-2). The transmission protocolsare rules for deciding who can transmit.Each node has transmission and reception hardware, which takesthe role of a telephone handset. This hardware controls access to thecommunications channel. Each node builds its message to match therequired Ethernet frame format.Transceivers and ControllersThe transmission-reception hardware is called a transceiver, ortransmitter-receiver. This is analogous to the earphone and microphoneof the telephone headset.The traffic control hardware is called an Ethernet controller, whichis analogous to the dial unit of a phone system. The controller and trans-Figure 7-2. Party-line telephone analogy©2001 by The Fairmont Press, Inc. All rights reserved.