Digital Subscriber Line (DSL)
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Joined: Dec 2008
23-09-2008, 12:36 AM
The accelerated growth of content-rich applications that demand high bandwidth has changed the nature of information networks. High-speed communication is now an ordinary requirement throughout business, government, academic, and "work-at-home" environments. High-speed Internet access, telecommuting, and remote LAN access are three services that network access providers clearly must offer. These rapidly growing applications are placing a new level of demand on the telephone infrastructure, in particular, the local loop portion of the network (i.e., the local connection from the subscriber to the local central office). The local loop facility is provisioned with copper cabling,
which cannot easily support high bandwidth transmission. This environment is now being stressed by the demand for increasingly higher bandwidth capacities. Although this infrastructure could be replaced by a massive rollout of fiber technologies, the cost to do so is prohibitive in today's business models.
More importantly, the time to accomplish such a transition is unacceptable, because the market demand exists today!
This demand for data services has created a significant market opportunity for providers that are willing and able to invest in technologies that maximize the copper infrastructure. Both incumbent and competitive Local Exchange Carriers (ILECs and CLECs) are capitalizing on this opportunity by embracing such technologies. The mass deployment of high-speed Digital Subscriber Line (DSL) has changed the playing field for service providers. DSL, which encompasses several different technologies, essentially allows the extension of megabit bandwidth capacities from the service provider central office to the customer premises. Utilizing existing copper cabling, DSL is available at
very reasonable costs without the need for massive infrastructure replacement.
These new DSL solutions satisfy the business need to provision the network in a fast, cost-effective manner, while both preserving the infrastructure and allowing a planned migration into newer technologies. DSL has the proven ability to meet the customer demand for high bandwidth right now, at costs that make sense. ADSL, or Asymmetric DSL, has emerged as thetechnology of choice for delivering greater throughputto the desktop. Currently, the ADSL Lite specification,also known as g.lite, is expected to be standardized bythe end of June, 1999 as a low-cost, easy-to-installversion of ADSL specifically designed for the consumer marketplace. While g.lite is expected to become the
predominant standard for consumer services, HDSL2 is becoming the protocol of choice for business services
more on HDSL2 to come).
The Telecommunications Infrastructure
The telecommunications industry has developed and deployed cost-effective technologies and created global, high-bandwidth, interoffice networks capable of supporting the demands of the information age. This network infrastructure, however, has been lacking one significant component?a ubiquitous low-cost, high-bandwidth access circuit for the local loop. This fact, more than any other, has slowed the growth and availability of high-bandwidth network services. The pervasive copper cable infrastructure deployed throughout the local loop was historically incapable of supporting the throughput required by growing consumer traffic. In response, the industry embraced DSL, which has proven to be the most significant technological development for solving the local loop demand for higher bandwidth.
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Joined: Jun 2010
14-10-2010, 10:09 PM
Digital Subscriber Line
Digital Subscriber Line (DSL) technology is a modem technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, such as multimedia and video, to service subscribers. The term xDSL covers a number of similar yet competing forms of DSL technologies, including ADSL, SDSL, HDSL, HDSL-2, G.SHDL, IDSL, and VDSL. xDSL is drawing significant attention from implementers and service providers because it promises to deliver high-bandwidth data rates to dispersed locations with relatively small changes to the existing telco infrastructure. xDSL services are dedicated, point-to-point, public network access over twisted-pair copper wire on the local loop (last mile) between a network service provider’s (NSP) central office and the customer site, or on local loops created either intrabuilding or intracampus. Currently, most DSL deployments are ADSL, mainly delivered to residential customers. This chapter focus mainly on defining ADSL.
Asymmetric Digital Subscriber Line
Asymmetric Digital Subscriber Line (ADSL) technology is asymmetric. It allows more bandwidth downstream—from an NSP’s central office to the customer site—than upstream from the subscriber to the central office. This asymmetry, combined with always-on access (which eliminates call setup), makes ADSL ideal for Internet/intranet surfing, video-on-demand, and remote LAN access. Users of these applications typically download much more information than they send. ADSL transmits more than 6 Mbps to a subscriber and as much as 640 kbps more in both directions (shown in Figure 21-1). Such rates expand existing access capacity by a factor of 50 or more without new cabling. ADSL can literally transform the existing public information network from one limited to voice, text, and low-resolution graphics to a powerful, ubiquitous system capable of bringing multimedia, including full-motion video, to every home this century. ADSL will play a crucial role over the next decade or more as telephone companies enter new markets for delivering information in video and multimedia formats. New broadband cabling will take decades to reach all prospective subscribers. Success of these new services depends on reaching as many subscribers as possible during the first few years. By bringing movies, television, video catalogs, remote CD-ROMs, corporate LANs, and the Internet into homes and small businesses, ADSL will make these markets viable and profitable for telephone companies and application suppliers alike.
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Joined: Apr 2012
20-04-2012, 10:23 AM
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