Information Technology

DSL Technology

By: Tony

xDSL Technology Introduction The accelerated growth of content rich applications and online gaming, which demand high bandwidth, has changed the nature of information networks. High-speed communication is now an ordinary requirement throughout business, government, academic, and home office environments. Internet access, telecommuting, and remote LAN access are three of the clearly defined services that network access providers are offering now. 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) has become a challenge for telephone companies. Historically, this local loop facility has been 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 would be insupportable in today's business models and, more importantly, the time to accomplish such a transition is unacceptable because the market demand exists today! Telephone companies are already faced with growing competition and unprecedented customer demands A new category of companies, Internet Service Providers (ISPs), has emerged in this market as providers of data services. Traditionally ISPs have used the telephone company infrastructure. However, thanks to deregulation, they now have direct access to the physical cable plant. ISPs will be formidable competitors in this quest for the customers. Network service providers around the world fill this moment with great potential for remarkable success. A new technology called high-speed Digital Subscriber Line (xDSL) has emerged onto this scene. xDSL, which encompasses several different technologies, essentially allows the extension of megabit bandwidth capacities from the service provider central office to the customer premises on a customer by customer basis over the existing copper cabling, without the need for massive infrastructure replacement and at very reasonable costs. These new xDSL solutions satisfy the business need to provision the network in a fast, cost effective manner, while preserving the infrastructure and allowing a planned migration into newer technologies. xDSL has the ability to meet the customer demand for high bandwidth right now, at costs that make sense. xDSL is a group of emerging Digital Subscriber Line (DSL) modem technologies for supporting high-rate traffic transmission over POTS lines. X stands for asymmetric in ADSL, rate adaptive in RADSL, high-speed in HDSL, and very high speed in VDSL. xDSL Delivers Broadband over Copper The best thing about xDSL technologies is their ability to transport large amounts of information across existing copper telephone lines. This is possible because xDSL modems leverage signal processing techniques that insert and extract more digital data onto analog lines. The key is modulation, a process in which one signal modifies the property of another. ADSL Development and Deployment Progress Of all the emerging xDSL technologies, ADSL is receiving the most attention because there is a standard (DMT) for it, and its capabilities provide NSPs with a competitive offering to cable modems. But there is increasing interest in symmetrical xDSL offerings such as HDSL and SDSL. As a local access service, ADSL's implementation has no critical drawbacks. It can be deployed as an overlay network where there is subscriber demand, eliminating the need for NSPs to risk building out their infrastructure unnecessarily in the hope that the technology will catch on. ADSL development and deployment is focused primarily in North America, followed by northern Europe and the Pacific Rim. In North America, US West, GTE, Ameritech, SBC, BellSouth, and Edmonton Tel (Canada) are the service providers leading the current wave of ADSL/xDSL deployment. Covad, Northpoint, and a handful of other CLECs are entering high-density metropolitan areas--typically offering a portfolio of xDSL offerings at different classes of service and price points, and competing with incumbent local exchange carriers. Chicago-based InterAccess was the first ISP to offer ADSL. Telia (Sweden), Telenor (Norway), British Telecom (UK), and Telfonica (Spain) are leading xDSL proponents in Europe. In the Pacific Rim, Telstra (Australia), Hong Kong Telecom, and Singtel (Singapore) are deploying xDSL for data and video applications. ADSL modems have been tested successfully by more than 40 telephone companies, and close to 50,000 lines have been installed in various technology trials and commercial deployments. Increasingly, alternative service providers such as enterprises, multi-tenant building owners, hospitality businesses (hotels and resorts), and office park developers are offering or considering offering ADSL to their users as private network operators. Applications In early 90's xDSL technologies were tested by some of the regional Bell operating companies in the United States, as well as several European telephone companies. At that time, the driving applications behind xDSL were video on demand (VOD) and interactive TV (ITV). Those applications were seen as potentially explosive sources of revenue growth for the residential market. In 1995, interest shifted toward the online world and more specifically the World Wide Web. The increasing demand for bandwidth with which to access the Web is one of the primary applications at which xDSL technologies are now targeted. However, xDSL technologies are also being looked at in conjunction with several other applications. These applications may produce a far greater revenue stream in near future compared to broadband Web access for residential market. Listed below are just a few examples of how xDSL technology can be utilized: Internet/Intranet Access Intranet access for organizations that are standardizing on a Web based, client server model is one of primary xDSL applications. An organization that has implemented an Intranet will require higher bandwidth afforded by xDSL in order to link their remote offices and telecommuters to the more demanding business oriented applications running on their private Web servers. LAN to LAN Connectivity xDSL technologies have the potential to prove far more effective in low cost, high throughput, LAN to LAN connectivity than ISDN or traditional leased lines. Frame Relay Access Since xDSL operates at the physical layer, it could emerge as the most cost effective method of carrying frame relay traffic from the service subscriver to the frame relay network. ATM Network Access As with frame relay the xDSL technologies can also be used to carry ATM cells