28 Jan

Technically, broadband refers to the carrying of multiple communications channels in a single wire or cable. In the broader sense used here, broadband refers to high-speed data transmission over the Internet using a variety of technologies (data communications and telecommubroadband nications). This can be distinguished from the relatively slow (56 Kbps or slower) dial-up phone connections used by most home, school, and small business users until the late 1990s. A quantitative change in speed results in a qualitative change in the experience of the Web, making continuous multimedia (video and sound) transmissions possible.


Broadband Technologies The earliest broadband technology to be developed consists of dedicated point-to-point telephone lines designated T1, T2, and T3, with speeds of 1.5, 6.3, and 44.7 Mbps respectively. These lines provide multiple data and voice channels, but cost thousands of dollars a month, making them practicable only for large companies or institutions.

Two other types of phone line access offer relatively high speed at relatively low cost. The earliest, ISDN (Integrated Services Digital Network) in typical consumer form offers two 64 Kbps channels that can be combined for 128 Kbps. (Special services can combine more channels, such as a 6 channel 384 Kbps configuration for videoconferencing.)

The user’s PC is connected via a digital adapter rather than the usual analog to-digital modem. The most common telephone-based broadband system today is the digital subscriber line (see DSL ). Unlike ISDN, DSL uses existing phone lines.

A typical DSL speed today is 1–2 Mbps, though higher speed services up to about 5 Mbps are now being offered. The main drawback of DSL is that the transmission rate falls off with the distance from the telephone company’s central office, with a maximum distance of about 18,000 feet (5,486.4 m).

The primary alternative for most consumers uses existing television cables (cable modem). Cable is generally a bit faster (1.5–3 Mbps) than DSL, with premium service of up to 8 Mbps or so available in certain areas. However, cable speed slows down as more users are added to a given circuit. With both DSL and cable upload speeds (the rate at which data can be sent from the user to an Internet site) are generally fixed at a fraction of download speed (often about 128 kbps). While this “throttling” of upload speed does not matter much for routine Web surfing, the growing number of applications that involve users uploading videos or other media for sharing over the Internet (user-created content) has led to some pressure for higher upload speeds.

Ultra Broadband Rather surprisingly, the country that brought the world the Internet has fallen well behind many other industrialized nations in broadband speed. In Japan, DSL speeds up to 40 Mbps are available, and at less cost than in the United States. South Korea also offers “ultra broadband” speeds of 20 Mbps or more.

American providers, on the other hand, have tended to focus on expanding their networks and competing for market share rather than investing in higher speed technologies. However, this situation is beginning to improve as American providers ramp up their investment in fiber networks (fiber optics).

For example, in 2005 Verizon introduced Fios, a fiber-based DSL service that can reach speeds up to 15 Mbps. However, installing fiber networks is expensive, and as of 2007 it was available in only about 10 percent of the U.S. market.

Cable and phone companies typically offer Internet and TV as a package—many are now including long-distance phone service (and even mobile phone service) in a “triple play” package. (For long-distance phone carried via Internet, voip).

Wireless Broadband The first wireless Internet access was provided by a wireless access point (WAP), typically connected to a wired Internet router. This is still the most common scenario in homes and public “hot spots” ( Internet cafés and “hot spots”). However, with many people spending much of their time with mobile devices (see laptop, PDA , and smartphone), the need for always-accessible wireless connectivity at broadband speeds has been growing. The largest U.S. service, Nextlink, offered wireless broadband in 37 markets in 2007 (including many large and mid-sized cities) at speeds starting at 1.5 Mbps. An alternative is offered by cell phone companies such as Verizon and Sprint, which “piggy back” on the existing infrastructure of cell phone towers. However, the speed of this “3G” service is slower, from 384 kbps up to 2 Mbps.

wimaxYet another alternative beginning to appear is WiMAX, a technology that is conceptually similar to Wifi but has much greater range because its “hot spots” can be many miles in diameter. WiMAX offers the possibility of covering entire urban areas with broadband service, although questions about its economic viability have slowed implementation as of 2008.

Satellite Internet services have the advantage of being available over a wide area. The disadvantage is that there is about a quarter-second delay for the signal to travel from a geostationary satellite at an altitude of 22,300 km. (Loweraltitude satellites can be used to reduce this delay, but then more satellites are needed to provide continuous coverage.)

Adoption and Applications By mid-2007, 53 percent of adult Americans had a broadband connection at home. This amounts to 72 percent of home Internet users. (About 61 percent of broadband connections used cable and about 37 percent DSL.)

With dial-up connections declining to less than 25 percent, Web services are increasingly designed with the expectation that users will have broadband connections. This, however, has the implication that users such as rural residents and the inner-city poor may be subjected to a “second class” Web experience (see also digital divide).

Meanwhile, as with connection speed, many other countries now surpass the United States in the percentage of broadband users. Broadband Internet access is virtually a necessity for many of the most innovative and compelling of today’s Internet applications. These include downloading media (podcasting, streaming, and music and video distribution, online), uploading photos or videos to sites such as Flickr and YouTube, using the Internet as a substitute for a traditional phone line (voip), and even gaming (online games). Broadband is thus helping drive the integration of many forms of media (see digital convergence) and the continuous connectivity that an increasing number of people seem to be relying on (ubiquitous computing).



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