Encyclopedia of Computer Science and Technology

58 broadbandnications). This can be distinguished from the relativelyslow (56 Kbps or slower) dial-up phone connections used bymost home, school, and small business users until the late1990s. A quantitative change in speed results in a qualitativechange in the experience of the Web, making continuousmultimedia (video and sound) transmissions possible.Broadband TechnologiesThe earliest broadband technology to be developed consistsof 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 thempracticable only for large companies or institutions.Two other types of phone line access offer relativelyhigh speed at relatively low cost. The earliest, ISDN (IntegratedServices Digital Network) in typical consumer formoffers two 64 Kbps channels that can be combined for 128Kbps. (Special services can combine more channels, such asa 6 channel 384 Kbps configuration for videoconferencing.)The user’s PC is connected via a digital adapter rather thanthe usual analog-to-digital modem.The most common telephone-based broadband systemtoday is the digital subscriber line (see DSL). Unlike ISDN,DSL uses existing phone lines. A typical DSL speed todayis 1–2 Mbps, though higher speed services up to about 5Mbps are now being offered. The main drawback of DSL isthat the transmission rate falls off with the distance fromthe telephone company’s central office, with a maximumdistance of about 18,000 feet (5,486.4 m).The primary alternative for most consumers uses existingtelevision cables (see cable modem). Cable is generallya bit faster (1.5–3 Mbps) than DSL, with premium serviceof up to 8 Mbps or so available in certain areas. However,cable speed slows down as more users are added to a givencircuit. With both DSL and cable upload speeds (the rateat which data can be sent from the user to an Internet site)are generally fixed at a fraction of download speed (oftenabout 128 kbps). While this “throttling” of upload speeddoes not matter much for routine Web surfing, the growingnumber of applications that involve users uploading videosor other media for sharing over the Internet (see user-createdcontent) has led to some pressure for higher uploadspeeds.Ultra BroadbandRather surprisingly, the country that brought the world theInternet has fallen well behind many other industrializednations in broadband speed. In Japan, DSL speeds up to40 Mbps are available, and at less cost than in the UnitedStates. South Korea also offers “ultra broadband” speeds of20 Mbps or more. American providers, on the other hand,have tended to focus on expanding their networks andcompeting for market share rather than investing in higherspeed technologies. However, this situation is beginning toimprove as American providers ramp up their investmentin fiber networks (see fiber optics). For example, in 2005Verizon introduced Fios, a fiber-based DSL service that canreach speeds up to 15 Mbps. However, installing fiber networksis expensive, and as of 2007 it was available in onlyabout 10 percent of the U.S. market.Cable and phone companies typically offer Internet andTV as a package—many are now including long-distancephone service (and even mobile phone service) in a “tripleplay” package. (For long-distance phone carried via Internet,see voip).Wireless BroadbandThe first wireless Internet access was provided by a wirelessaccess point (WAP), typically connected to a wired Internetrouter. This is still the most common scenario in homesand public “hot spots” (see also Internet cafés and“hot spots”). However, with many people spending muchof their time with mobile devices (see laptop, PDA, andsmartphone), the need for always-accessible wireless connectivityat broadband speeds has been growing. The largestU.S. service, Nextlink, offered wireless broadband in 37markets in 2007 (including many large and mid-sized cities)at speeds starting at 1.5 Mbps. An alternative is offeredby cell phone companies such as Verizon and Sprint, which“piggy back” on the existing infrastructure of cell phonetowers. However, the speed of this “3G” service is slower,from 384 kbps up to 2 Mbps.Yet another alternative beginning to appear is WiMAX,a technology that is conceptually similar to Wifi but hasmuch greater range because its “hot spots” can be manymiles in diameter. WiMAX offers the possibility of coveringentire urban areas with broadband service, although questionsabout its economic viability have slowed implementationas of 2008.Satellite Internet services have the advantage of beingavailable over a wide area. The disadvantage is that there isabout a quarter-second delay for the signal to travel from ageostationary satellite at an altitude of 22,300 km. (Loweraltitudesatellites can be used to reduce this delay, but thenmore satellites are needed to provide continuous coverage.)Adoption and ApplicationsBy mid-2007, 53 percent of adult Americans had a broadbandconnection at home. This amounts to 72 percent ofhome Internet users. (About 61 percent of broadband connectionsused cable and about 37 percent DSL.)With dial-up connections declining to less than 25percent, Web services are increasingly designed with theexpectation that users will have broadband connections.This, however, has the implication that users such as ruralresidents 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 countriesnow surpass the United States in the percentage ofbroadband users.Broadband Internet access is virtually a necessity formany of the most innovative and compelling of today’sInternet applications. These include downloading media(see podcasting, streaming, and music and video distribution,online), uploading photos or videos to sites