DSL Technology – Broadband via Telephone Lines

Digital subscriber line (DSL) technology transmits broadband data over telephone lines. With approximately 480 million DSL lines in service at the end of 2012, DSL technology is the most popular form of broadband access in the world. The use of existing telephone lines for DSL technology provides several benefits. There are economic benefits from using existing facilities between the network and the home, as well as sharing these facilities with the existing voice/fax services. The fundamental advantage of DSL technology over voice‐band modem technology is the expanded frequency bandwidth of the transmission channel. Specifically, the analog‐to‐digital conversions at the local digital telephone switches are excluded from the DSL transmission channel. Several types of DSL technology have evolved, with a trend toward higher bit rates. The standardized and widely deployed types of DSL technology are described in this chapter.