cable modem

One of the most popular ways to connect people to the Internet takes advantage of the cable TV infrastructure that already exists in most communities. (For another pervasive alternative, using telephone lines, see Dsl.)

Cable systems offer high-speed access (see broadband) up to about 6 megabits/second (Mb/s), at least 20 times faster than an ordinary telephone modem and generally suitable for receiving today’s multimedia offerings, includ-ing streaming video. (Upload speeds are usually “throttled” to 384 kb/s or fewer.)

In a typical installation, a splitter is used to separate the signal used for cable TV from the one used for data trans-mission. The data cable is then connected to the modem. The modem can then either be connected directly to a com-puter using a standard Ethernet “Cat 5” cable, or connected to a switch (or more commonly, a router) that will in turn provide the Internet connection to computers on the local network. (If the cable modem is connected directly to a computer, additional security against intrusions should also be provided. See firewall.)

A typical cable TV system has from 60 channels to sev-eral hundred, most of which are used for TV programming. A few channels are dedicated to providing Internet service. Users in a given division of the cable network (typically a small neighborhood) thus share a fixed pool of bandwidth, which can reduce speed at times of high usage. The cable system can adjust by reallocating channels from TV to data or by adding new channels.

DOCSIS (Data Over Cable Service Interface Specifica-tion) is the industry standard for cable modems in North America.

Marketing Considerations

As of 2007 there were about 30 million households in North America with cable Internet service. Monthly service fees are $40–$60, though cable providers generally try to bun-dle their cable TV and Internet services. Increasingly they are also offering telephone service over the cable network, using voice over Internet protocol (see voip).

In turn, telephone companies compete with cable com-panies by offering DSL Internet access. Although “tradi-tional” DSL is generally somewhat slower than cable modems, Verizon in 2005 announced a new, much faster fiber-based form of DSL called fios, with speeds of up to 15 Mb/s (see also fiber optics). And just as cable compa-nies can now offer phone service over the Internet, phone companies can offer video content, potentially competing with cable TV services. (Verizon has announced its own Internet-based television network, IPTV.) In general there is likely to be increased competition and more (if sometimes perplexing) choices for consumers.