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Chapter 2. Twisted Pair > Twisted Pair Cable Channel Model

2.2. Twisted Pair Cable Channel Model

2.2.1. Wiring Topology

In an office environment, twisted pair cables are wired from each desk to a central location, usually a dedicated wiring closet, where an Ethernet hub is used to connect every incoming cable at the center of a star. This is often called a star wiring configuration. Under this star wiring configuration, a straight twisted cable is used between a port of the hub and a computer NIC. With ideal terminations at both ends of a twisted pair cable, the transfer function of the twisted pair–based transmission channel can be estimated accurately using its propagation constant (Equation 2.8 or 2.9) for an identified distance. The star wiring configuration can also be found in some residences, especially in some newly constructed residential areas where the awareness of data transmission within a household exists. In a majority of existing residential premises, however, twisted pair telephone cables are wired following a daisy-chain fashion. For example, from the NID (Network Interface Device), one twisted pair cable connects a few telephone jacks on the first floor, and a second one connects all phone jacks on the second floor. The homeowner may have added another twisted pair cable to connect the computers, fax machines, and other auxiliary devices at a few different places.

The star daisy-chain telephone in-house wiring configuration in Figure 2.3 shows four phone jacks in this residential premises [6]. The jacks at both ends are marked as station 1 and station 2. Each of the other two are terminated with a capacitor of 500 picofarads (pF) representing an on-hook telephone set. The Central Office is represented by a 100-ohm load at 8000 ft. For this general star daisy-chain wiring configuration, we need to know two-port network representation of all cable sections as well as terminations to estimate the transfer function.


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