Practical Industrial Data Networks:Design, Installation and ...

218 Practical Industrial Data Networks: Design, Installation and TroubleshootingOther variations include 1Base5, 10BaseFB, 10BaseFP and 10Broad36 but theseversions would never become commercially viable.10Base5This is the original coaxial cable system and is also called ‘thicknet’. The coaxial cable(50-ohm characteristic impedance) is yellow or orange in color. The naming conventionfor 10Base5 means 10 Mbps, baseband signaling on a cable that will support 500-meter(1640 feet) segment lengths. The cable is difficult to work with, and cannot normally betaken to the node directly. Instead, it is laid in a cabling tray and the transceiverelectronics (medium attachment unit or MAU) are installed directly on the cable. Fromthere, an intermediate cable, known as an attachment unit interface (AUI) cable is used toconnect to the NIC. This cable can be a maximum of 50 meters (164 feet) long,compensating for the lack of flexibility of placement of the coaxial cable. The AUI cableconsists of five individually shielded pairs – two each (control and data) for both transmitand receive, plus one for power.Cutting the cable and inserting N connectors and a coaxial T or more commonly byusing a ‘bee sting’ or ‘vampire’ tap can make the MAU connection to the cable. Thevampire tap is a mechanical connection that clamps directly over the cable. Electricalconnection is made via a probe that connects to the center conductor and sharp teeth thatphysically puncture the cable sheath to connect to the braid. These hardware componentsare shown in Figure 15.1.Coaxial CableTapTransceiver UnitNodeController CardDataControlPower, EarthJabberControlDIX connectorsControlCollisionDetectionDataTransceiver CableTransceiverDrop CableMedia Acesss Control UnitProtocol Control FirmwareMediumAttachmentUnit(MAU)Attachment UnitInterface (AUI)(50m max)CommunicationSubsystem DTEFigure 15.110Base5 componentsThe location of the connection is important to avoid multiple electrical reflections onthe cable, and the cable is marked every 2.5 meters (8 feet) with a black or brown ring toindicate where a tap should be placed. Fan-out boxes can be used if there are a number ofnodes for connection, allowing a single tap to feed each node as though it wasindividually connected. The connection at either end of the AUI cable is made through a25-pin D connector with a slide latch, often called a DIX connector after the originalconsortium.