3  Cable

• Cable television systems were introduced in the USA in the late 1940s as a means of distributing television programs received by a single antenna to users in remote areas with poor reception. Cable systems have now grown in popularity as a means of distributing a wide number of television channels to users within cities without the need for individual homes to have external antenna systems.

Figure 5

• Modern cable systems can provide two-way communication between homes and the cable system operators, and now offer advanced telecommunications services, such as a telephone service and high-speed Internet access, alongside the usual digital cable television.
• Cable system providers traditionally used coaxial cable to connect devices throughout their network. Because of the increase in demand for bandwidth by the service now available to home users, most cable providers use fibre optic cabling within the trunks used to connect together their network and only utilise coaxial cable to provide the link from their local junction box (normally a green, steel street cabinet) to the household. This is called a hybrid fibre-coaxial (HFC) system.

Figure 6 

• Home users are normally provided with a cable modem which connects to the coaxial cable used to deliver the television, telephone and Internet services. The cable modem provides suitable output for the devices required – TV to the television, voice services to the telephone, and data to the home router.
• Typical cable modems use Ethernet to provide the connection to the home router WAN port. Thus, home routers designed for DSL and cable systems are not compatible, as their WAN ports are designed to support different signals.
• Although cable providers generally offer a higher speed Internet service than DSL, the speed depends on the number of local customers, and as the number of users increases, the data rate decreases. Cable customers must use the ISP services of the cable provider as cable operators are not required to open up their network to competitors.