en (low frequencies), fewer people are moved in a given span of time; If the trains arrive more often (higher frequencies), more people will be moved through the system in the same time period. Both copper cabling used for DSL and wireless services carry signals that are made up of wavelengths (frequencies). Low frequencies have longer wavelengths that can carry signals over greater distances. High frequencies have shorter wavelengths that do not travel as far, but they can squeeze more bits into each transmission. To achieve greater capacity, DSL must use high frequencies. However, the shorter wavelengths render high-frequency signals more vulnerable to damage from environmental sources such as magnetic interference. At the same time, vulnerability to attenuation (weakening and fading) means that high speeds are supported only on short lengths of copper cabling. Some carriers use bonding to increase the capacity on DSL. Bonding also has the advantage of increasing the length of cable over which high frequency DSL signals can travel before they fade. www.TechnicalPDF.com Bonding is the use of equipment called inverse multiplexers to increase bandwidth by combining two or more circuits or pairs of copper cabling such that they act as a single circuit. Providers that don't have fiber in an area may double the speed of DSL service by bonding two DSL circuits together using an inverse multiplexer. See Figure 5-4 for an example of bonding on DSL. Bonding is also used to add capacity on direct interconnections to providers' clouds. See the section "Direct Dedicated Interconnections to the Cloud" later in this chapter for information on Dedicated Interconnections. www.TechnicalPDF.com Hospital doctors hospital capacity Figure 5-4 An example of bonding two DSL circuits together to double its capacity. Replacing DSL with Higher-Capacity Fiber and Wireless Carriers are replacing DSL because of its lower capacity and because enterprises and residential subscribers require higher broadband capacity to access cloud-based appl