Data Communications Networking Devices - 4th Ed.pdf

112 ______________________________ FUNDAMENTAL WIDE AREA NETWORKING CONCEPTSFigure 1.65 Connection to telephone company facilities. Data communications equipmentcan be connected to telephone company facilities by plugging the device into a telephonecompany jackMost communications devices designed for operation on the PSTN interface thetelephone company network via the use of an RJ11C permissive or an RJ45Sprogrammable jack.Figure 1.66 illustrates the conductors in the RJ11 and RJ45 modular plugs. TheRJ11 plug is primarily used on two-wire dial lines. This plug is used in both thehome and of®ce for connecting a single instrument telephone to the PSTN. Inaddition,the RJ11 also serves as an optional connector for four-wire private lines.Although the RJ11 connector is fastened to a cable containing four or six strandedcopperconductors,only two wires in the cable are used for switched networkapplications. When connected to a four-wire leased line,four conductors are used.Figure 1.66RJ11 and RJ45 modular plugsThe development of the RJ11 connector can be traced to the evolution of theswitchboard. The plugs used with switchboards had a point known as the `tip'which was colored red,while the adjacent sleeve known as the ring was coloredgreen.The original color coding used with switchboard plugs was carried over totelephone wiring. If you examine a four-wire two-pair) telephone cable,you willnote that the wires are coloured yellow,green,red and black. The green wire is thetip of the circuit while the red wire is the ring. The yellow and black wires can beused to supply power to the light in a telephone or used to control a secondarytelephone using the same four-wire conductor cable.