System : Digital Subscriber Line (DSL)

Digital Subscriber Line (DSL)
Digital subscriber line is the transmission of digital information, usually on a copper wire pair. Although the transmitted information is in digital form, the transmission medium is usually an analog carrier signal (or the combination of many analog carrier signals) that is modulated by the digital information signal.

A DSL network is composed of several key parts; this includes a local access line provider, DSL access provider, backbone network aggregator, ISP provider, and other media providers. DSL services can be provided by a single service provider or may result from the combination of processes from different service providers. The communication network can be divided into several parts; local access lines (copper), voice communications network (PSTN), high-speed digital subscriber line (DSL), aggregator (interconnection), Internet service provider (ISP) and content provider (media source). These network parts and the service providers who operate them, must interact to provide most DSL services.

The physical parts of a DSL network include a subscriber access device, network access lines and digital subscriber line access module (DSLAM). There are many configuration options for a DSL network. They vary from a simple end-user’s modem bridge that connects a single end-user’s computer to the DSL network to complex multi-channel, asynchronous transfer mode (ATM) systems that connect routers and set-top boxes.

Figure 1 shows the functional parts of DSL network. This diagram shows that end user equipment adapts, or converts analog and digital signals to a high-speed DSL transmission signal via a DSL modem (an ATU-R for an ADSL system). The copper wire carries this complex DSL signal to a DSL modem at that connects to the central office (an ATU-C for an ADSL system) where it is converted back to its analog and digital components. The analog POTS portion of the signal (if any) is routed to the central office switching system. The high-speed digital portion is routed to a digital subscriber line access module (DSLAM). The DSLAM combines (concentrates) the signals from several ATU-Cs and converts and routes the signals to the appropriate service provider network.

Figure 1: DSL Network Diagram

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