Digital Subscriber Line (DSL) technology provides high speed connectivity with the capabilities to transmit data at rates of up to 7 Mbps over ordinary copper telephone wire. This is the same wire that is already installed in millions of homes and businesses throughout the world. Dialing an external phone number is no longer required. DSL circuits are always active, connected 24 x 7. DSL solves the front end bottleneck problems often referred to as the "last mile" - the link between the end-user and their network service provider. Before DSL became available, this link was achieved by using dial-up analog modems, ISDN, T1, or Frame Relay connections.
Several years back, legislation was passed requiring telco companies such as Bell Atlantic to share their facilities and infrastructure with third party local exchange carriers (CLEC). The local access point linking their networks to the end user is called the CO (central office). Implementing DSL is a cooperative effort between the CLEC, TELCO, and ISP. A regional CLEC must install a specialized router called a DSLAM at the Telco's CO. This device translates and transmits DSL signals between their larger backbone network (Pipeline) and the customer's copper phone line. The customer must be within 18,000 feet of the CO in order for DSL to work, which is the practical limit over copper before the DSL signal will degrade. Traffic is then switched using ATM and routed a greater distance across a fiber optic pipeline to an Internet Provider (ISP) of choice. SDSL provides virtual circuits across this pipeline, guaranteeing bandwidth, and data privacy. DSL is cheaper to implement, primarily because a single pipeline with virtual circuits has less wire and is easier managed, compared to ISDN and T1 that require physical circuits for each customer from point to point. The ISP then completes the process by routing traffic through their backbone networks to the Internet. The ISP is typically responsible for any value added services and customer interaction. DSL is a mature technology that has been used by telecom carriers for decades. Although DSL technology is not new, the wide scale implementation of DSL did not start until 1998. This is because the amount of time associated with installing DSL equipment at COs every three miles across the country has been lengthily. DSL is now available in most major metropolitan areas.