nce, copper wire is lower in cost. 90 TELECOMMUNICATIONS The major advantage to using copper at data rates between 1 and 10 MBS is that it involves a mature, well-understood technology. Connectors are readily available, splices are simple, and both the production of cable and the installation techniques required are well known to manufacturers and users. The major disadvantages of cop- per wire, as compared with optical fiber, are that signal attenuation on copper increases with frequency, while attenuation on an optical fiber is constant up into the 300-MHz region (Fig. 6-7). Copperbased networks are therefore more expensive at high frequencies. Also, copper cable requires a surrounding shield to reduce noise pickup from the environment, as well as to reduce electromagnetic radiation from the copper itself. In light of recent Federal Communications Commission outward-radiation rules, this presents a design problem whose solution requires grounding the shield at both ends of the ca- ble. But this introduces another potential problem: For long cable runs, grounding both ends of a shield can introduce ground currents if the ground voltages at the end points are not equal. Optical fiber is completely immune to such problems. Optical fiber Copper Frequency (MHz) Fig. 6-7. Copper versus fiber. Signal attenuation on the copper medium increases with fre- quency, while on optical fiber it is constant up into the 300-MHz region. NETWORK STRUCTURES 91 In contrast, the drawbacks to optical fiber are the lack of a low- loss optical-fiber connector that can be easily assembled and installed in the field. The splicing techniques also suffer from similar limi- tations. Also, for low-bandwidth applications (below 10 MHz), op- tical fiber is more expensive than copper. This is because optical- fiber cable and components are still manufactured in relatively low volumes. In addition, it is more difficult to find quality installation and maintenance expertise for optical fiber than for copper cable. Disadvantages of optical fiber ar