DSL service was developed in 1989 by a consortium of telecommunication LECs. In its original incarnation, DSL was intended to deliver video on demand (VOD) service across the local access twister-pair cables (telephone lines) already in place and maintained by the telephone company. Although VOD did not quite catch on in the intended time frame, LECs quickly realized that large amounts of data could be delivered to computer users over the bandwidth allocated for video services. This market discovery led to development of the high-speed broadband potential of DSL, setting it on the path to become the Internet access choice it is today. While credit for the development of DSL is sparse and often attributed to one telephone company or another, Joseph Lechleider of Bellcore is generally considered the father of broadband Internet access.
DSL service connects computer users to the Internet across a high-speed connection; this connection is also known as broadband Internet access. The user-level layer (layer one) of DSL physically connects the user’s computer and modem to the telephone company switch over standard two-wire telephone lines; the higher frequency of DSL transmissions allow it to coexist on the same line as concurrent voice conversations.
Layer Two of the DSL model gathers DSL connections from multiple users in a small area in one device. This device, known as a Digital Subscriber Line Access Multiplexer (DSLAM), combines multiple connections from a small town or parts of a city for upstream relay. The connections are then relayed to a PPP aggregator in Layer Three of the DSL operation; this aggregator combines DSL sessions from a larger geographic area, binding the DSL user session to the user’s telephone number, username or other identifying information. The bound data session is then passed upstream to a commercial-grade high speed data device, such as an asynchronous transfer mode (ATM) switch, and, ultimately, out into the Internet backbone. Additional layers of the DSL model allow for logical operation and routing of the DSL traffic.
DSL service was an early version of high speed data, or broadband, Internet access. Deployed across the existing facilities of telephone companies, the service exploited the computer users’ reliance on the public switched telephone network (PSTN) to become an early broadband forerunner. As other higher capacity services, such as cable modems, WiFi and satellite Internet, entered the market, DSL capitalized on its foothold to offer broadband Internet speeds at very low or competitive prices. The single-user line nature of the service also cements a solid throughput speed for DSL users, giving these users an advantage over the shared-bandwidth models of cable and WiFi services. As technology progresses, users increasingly discover new uses–such as home security cameras and voice over Internet protocol–for the low prices and solid telephony foundation of DSL.
The current model DSL service offers broadband Internet access speeds of up to 7 megabits per second (Mbps). As telephone companies add capacity to their networks and the concentration of PPP aggregators grows in key markets, this speed will almost certainly increase to a level competitive with the generally higher-speed cable modems. As the service expands and prices drop, the potential uses for DSL service become less and less limited; already, applications such as IP TV (television over Internet protocol), voice over IP and home security are becoming common on residential and business DSL networks. Future applications of the service may support home monitoring, Jetsons-like communication features and other opportunities limited only by the imagination of DSL users.
The low prices and near ubiquitous penetration of DSL service has forced Internet access competitors, such as cable, into higher speeds, broader markets and lower prices. The availability of DSL has heightened awareness of broadband Internet speeds, and offered these speeds to users whose only other Internet access option may be 56 Kbps dial-up connections.