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14 Dec 2006 18:19:15 Symmetric Digital Subscriber Line Digital Subscriber Line (DSL) is a class of technology that facilitates high-speed transmission of data over copper cable that runs between a customer's premises and central offices of the telephone companies. DSL allows voice and high-speed data services including swift access to Internet, IP telephony, and videoconferencing over a single pair telephone copper wires. There are a number of variations of DSL. Symmetric Digital Subscriber Line (SDSL) is one such variant of DSL, which is used for transferring data. The term 'Symmetric' means that an SDSL connection has similar maximum upload and download speeds. DSL technologies can make the best use of copper wire infrastructure and deliver broadband services most effectively to a greater number of people. In some instances, they achieve data rates of up to 52 MBPS. They turn the local loop into a multi-service access network that supports Internet access, apart from video and telephony services. For DSL technologies, wiring upgrade is not required. Only the equipment at the users' end and the company's end has to be upgraded. SDSL functions by transmitting digital pulses in the high-frequency area of telephone wires. It is not capable of operating concurrently with voice connections over the same wires. SDSL needs a special modem. SDSL is being developed primarily in Europe. In the US, the other variant of DSL called Asymmetric Digital Subscriber Line (ADSL) is being used widely. SDSL allows equal bandwidth downstream from the central office of the telephone company to the customer's premises and upstream from the subscriber to the central office of the company. SDSL is capable of supporting data only on a single line and does not support analog calls. SDSL uses 2 binary 1 quaternary (2B1Q) line coding and can transmit up to 1.54 MBPS to and from a user. In other words, it can be configured to provide a range of bandwidth of up to 1.54 MBPS. The symmetry that SDSL offers, coupled with the always-on access, which obviates call set up, makes it a favourable WAN technology for small and medium businesses and branch offices. As the traffic is symmetrical, applications such as web hosting, file transfer and distance-learning can be effectively deployed with SDSL. Links: DSL Content Team -- BSNL Portal -- Intelligroup Asia Pvt. Ltd. |
