t issue. The flexible Table 33.1 shows the characteristic impedance of the cables rec- patching leads have to be limited to a maximum length (i.e. 6 ommended to suit the various computer systems. The use of baluns metres) as they tend to have worse high frequency characteristics and media filters enables any of these services to operate over 100 than the solid conductor cable used for the fixed installation. This ohm UTP cable. places a restriction on the patching panel size and hence the number Recent technological improvements in cables and communication of outlets a single patch panel can serve. equipment has led to an increase in the data rates carried by copper cable. Table 33.1 gives an indication of the data rates carried by 33.4.2 Implementation structured cabling systems. At the low end the analogue voice systems have a data rate of 4Kbps (bits per second) while at the high Using the structured cabling system, there are two areas where a end token ring has a bit rate of 4Mb/s or 16Mb/s. computer/communications system may have to be adapted to oper- Higher data rates of 20, 32, 64 and even 100Mb/s over UTP cable ate over an SCS. These are the media and the topology. are being evaluated, although at these high data rates an overall Media conversion is achieved by baluns and filters. Topology shielding cable is used. Table 33.2 shows a data rate comparison conversion is achieved with patch panels, loop wiring concentra- between various media. tors, multi access units and multiport hub units. UTP provides a cost effective solution for the horizontal part of a structured cabling system. However, where these all meet at the System performance hub/wiring closet and travel down the riser, there is a heavy concen- tration of data which can be carried over multi-core UTP or, alter- Structured cabling systems are provided with a system performance natively, it can be multiplexed. specification, which defines the services, data rates, and distances In the preceding sections, the data rates carried by the UTP cable t