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Digital Subscriber Line | DSL

Digital subscriber line (DSL) is an Internet access method that uses a standard phone line to provide high-speed Internet access. These lines, because they were developed only for voice signals, are restricted in bandwidth and data rate. However, special techniques have been developed to allow very high-speed data transmissions on them. DSL is one of the most popular ways ISPs provide broadband internet access. but is fading in popularity and availability. Because, it is a relatively inexpensive Internet access, it is often found in homes and small businesses, but even there, it is quickly being replaced by fiber Optic. DSL provides dedicated, point-to-point, public network access. This DSL connection is typically between a network service provider (NSP) central office and the customer site. With DSL, a different frequency can be used for digital and analog signals, which means that you can talk on the phone while you upload data. For DSL services, two types of systems exist: asymmetric digital subscriber line (ADSL) and high-rate digital subscriber line (HDSL). ADSL provides a high data rate in only one direction. It enables fast download speeds but significantly slower upload speeds. ADSL is designed to work with existing analog telephone service (POTS). With fast download speeds, ADSL is well suited for home-use Internet access. In contrast to ADSL, HDSL provides, a bidirectional high-data-rate service, that can accommodate services such as videoconferencing, that require high data rates in both directions. A variant of HDSL is very high-rate digital subscriber line (VHDSL), which provides an HDSL service at very high data transfer rates. Before we give a list of the various types of DSL, let us define a few terms. Symmetrical. A service, in which data travel at the same speed in both directions. Downloads and uploads have the same bandwidth. Asymmetrical. A service, that transmits at different rates in different directions. Downloads move faster than uploads. Downstream. Traffic is from the network to the customer. Upstream. Traffic from the customer to the network operating center. DSL arrived on the scene in the late 1990s, and It has different types since 1990. Together, all these variations are known as xDSL: Symmetric DSL (SDSL): A version that offers the same speeds, for uploads and downloads, suitable for business applications, such as web hosting, intranets, and e-commerce. It is not widely implemented in the home or small business environment, and cannot share a phone line. ISDN DSL(IDSL): A symmetric type of DSL, commonly used in environments in which SDSL and ADSL are unavailable. IDSL does not support analog phones. Rate-adaptive DSL(RADSL): A variation on ADSL, that can modify its transmission speeds, based on signal quality. RADSL supports line sharing. Very high-bit-rate DSL(VHDSL): An asymmetric version of DSL, can share a telephone line. VHDSL supports high bandwidth applications such as VoIP. VHDSL can achieve data rates up to approximately 10 Mbps, making it the fastest available form of DSL. To achieve high speeds, VHDSL uses fiber-optic cabling. High-bit-rate DSL(HDSL): A symmetric technology transmission rates, in both directions. HDSL does not allow line sharing with analog phones.