al inter- ference. The error rate of wireless depends on the prevailing conditions, especially weather and the presence of obstacles, such as foliage and buildings. Yet another characteristic you need to evaluate is the distance required between repeaters. This is a major cost issue for those constructing and operating networks. In the case of twisted-pair deployed as an analog telephone channel, the distance between amplifiers is roughly 1.1 miles (1.8 km). When twisted-pair is used in digital mode, the repeater spacing drops to about 1,800 feet (550 m). With twisted-pair, a great many network elements must be installed and subsequently maintained over their lifetime, and they can be potential sources of trouble in the network. Coax offers about a 25% increase in the distance between repeaters over twisted-pair. With microwave and satellite, the distance between repeaters depends on the frequency bands in which you're operating and the orbits in which the satel- lites travel. In the area of fiber, new innovations appear every three to four months, and, as discussed later in this chapter, some new developments promise distances as great as 4,000 miles (6,400 km) between repeaters or amplifiers in the network. Chapter 2 Traditional Transmission Media Security is another important characteristic. There is no such thing as com- plete security, and no transmission medium in and of itself can provide security. But using encryption and authentication helps ensure security. (Chapter 9, "IP Ser- vices," discusses security in more detail.) Also, different media types have different characteristics that enable rapid intrusion as well as characteristics that enable bet- ter detection of intrusion. For example, with fiber, an optical time domain reflecto- meter (OTDR) can be used to detect the position of splices that could be the result of unwanted intrusion. (Some techniques allow you to tap into a fiber cable with- out splices, but they are extremely costly and largely available only to government security agencies.) Fina