Much more sophisticated digital transmission techniques than before can now be used over copper wires, because of better electronics, higher density, higher speed, and lower costs. 850M copper `subscriber loops' are already installed world-wide. This article discusses xDSL systems, which are rapidly emerging to use the transmission capacity of copper wires to support new digital services for Intelligent Transport System (ITS) applications. The term `digital subscriber line' ('DSL') is used for high-speed transmission technology applied to telephone twisted pairs, and `x' denotes one of several prefixes that can be added to `DSL'. xDSL signals are designed to work through subclasses of unloaded twisted pairs, using bandwidths that can exceed 1MHz. HDSL (high-speed DSL) has four loop architectures under consideration: dual-duplex, dual-simplex, full-duplex, and provisioned single-loop. ADSL (asymmetric DSL) uses downstream, multipurpose, control, and analog voice channels. SDSL (symmetric DSL) provides bi-directional telecommunications at rates from 160kbs to 2.084Mbps. VDSL (very high rate DSL) can provide data rates of 13Mbps and 26Mbps over short distances. The article has four tables, and concludes that xDSL has important ITS applications, including junction-level activity.
Abstract