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Digital Subscriber Line (DSL)
June 18, 2005 11:36 PM EST | Internet | Email to Friend
Digital Subscriber Line (DSL) is a wireline transmission technology that brings data and information faster over copper telephone lines already installed in homes and businesses. Traditional phone service connects your home or business to a telephone company office via copper wires. A DSL modem accesses the local telephone company's central office where a DSL Access Multiplexer (DSLAM) has been installed. The DSLAM then transmits the signal from the copper telephone line onto a network backbone, and eventually to the Internet. With high-speed Internet access that uses DSL transmission technology, there is no need to "dial in" to a telephone number as with a traditional modem. This service allows consumers and businesses to have an "always-on" dedicated connection to the Internet.
The following are types of DSL transmission technologies that may be used to provide high-speed Internet access:
Symmetrical Digital Subscriber Line (SDSL) - used typically for business applications such as video conferencing. The traffic from the user to the network is upstream traffic, and from the network to the user is downstream traffic. When the data rate in both directions is equal, it is called a symmetric service.
- Asymmetrical Digital Subscriber Line (ADSL) - used primarily by residential users who receive a lot of data but do not send much, such as Internet surfers. ADSL provides faster speed in a downstream direction (from the telephone central office to the customer's premises) than upstream (from customer's premise to the telephone central office). When the upstream data rate is lower than the downstream rate, it is called an asymmetric service.
- ISDN Digital Subscriber Line (IDSL) - provides symmetrical connection with Integrated Services Digital Network (ISDN), and is designed to extend DSL to locations with a long distance to a telephone central office.
- High-data-rate Digital Subscriber Line (HDSL) - provides fixed symmetrical high speed access at T1 rate (1.5 Mbps), and is designed for business purposes.
- Very high-data-rate Digital Subscriber Line (VDSL) - provides both symmetrical and asymmetrical access with very high bit rate over the copper line. Deployment is very limited at this time
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