b. Digital Subscriber Line (DSL)

DSL provides high-speed networking over ordinary phone lines using broadband modem technology. DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections.

DSL Internet services are used primarily in homes and small businesses. DSL Internet service only works over a limited physical distance and remains unavailable in many areas where the local telephone infrastructure does not support DSL technology. All types of DSL Internet service can be categorized as either asymmetric or symmetric.

1. Asymmetric DSL

Asymmetric types of DSL connections provide more network bandwidth for downloading (from the Internet service provider down to the subscriber's computer) than for uploading in the other direction). By reducing the amount of bandwidth available upstream, service providers are able to offer relatively more bandwidth downstream.

Asymmetric DSL technology is popular in residential DSL services as home Internet users predominately use downstream bandwidth. Typical asymmetric DSL services support 5 Mbps for downloads and 1 Mbps for uploads.

Common forms of asymmetric DSL include:

        I.      ADSL (Asymmetric Digital Subscriber Line): ADSL allows more data to be sent over existing copper telephone lines (POTS), when compared to traditional modem lines. A special filter, called a microfilter, is installed on a subscriber's telephone line to allow both ADSL and regular voice (telephone) services to be used at the same time. ADSL requires a special ADSL modem and subscribers must be in close geographical locations to the provider's central office to receive ADSL service. Typically this distance is within a radius of 2 to 2.5 miles.

ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).