DSP APPLICATIONS ADSL (Asymmetric Digital Subscriber Line)

Thanks to the widespread popularity of the World Wide Web, Internet traffic is at an all-time high. A study recently conducted by the Wall Street Journal reported 58 million Internet users in the United States and Canada alone. Research firms all predict heavier Internet traffic as more and more people buy PCs and use the Internet for business, academia and recreational purposes. Unless something is done to improve the way we access the Internet, user traffic will ultimately burden the public switched telephone network (PSTN) beyond its original design limits.

Internet users are frustrated by the amount of time it takes to view simple text-based Web sites, especially from 8:00 am to 6:00 pm on business days when congestion and bottlenecks are most prevalent. The problem will only get worse as users attempt to view graphically complex sites, download new video and audio clips, and access other types of multimedia services becoming available over the Internet.

Today’s analog modem and telephone switch technology is simply inadequate. Assuming little or no network delays, a 10 Megabyte data transmission – the equivalent of a four-minute audio/video clip – takes about 95 minutes to download when using a 14.4 Kbps analog modem, 45 minutes when using a 28.8 Kbps modem, and 25 minutes when using a 56Kbps modem. Lengthy on-line calls are tying up telephone systems originally designed to handle short (three-minute) voice calls and switches built to accommodate approximately nine minutes per line during peak hours. How often do you browse the Internet for 10 minutes or less? It now appears that relief, in the form of ADSL (asymmetric digital subscriber line) technology, is on the way. ADSL is a new high-speed digital switching/routing and signal processing technology. It promises to relieve network bottlenecks and provide enough user bandwidth for the Internet explosion. Originally conceived in 1994, ADSL delivers the huge amounts of bandwidth needed for interactive gaming, multimedia services and video-on-demand. These applications, along with videoconferencing, remote schooling and home shopping are still attractive applications. As more and more people use the Internet for electronic commerce in homes around the world, the need for high-speed network access becomes ever more paramount.

ADSL can transfer data over ordinary telephone lines nearly 200 times faster than today’s contemporary modems and 90 times faster than ISDN. Early tests and trials have shown promising results all over the world. And while GTE and other large telephone companies begin to deploy ADSL systems in select regions of the US and abroad, others seek to deploy ADSL-based equipment in 1999 as standards-based systems and modems become commercially available. Due to ADSL’s technical complexity, only a few semiconductor manufacturers are presently developing ADSL silicon chips. Analog Devices is one of them, and is considered a pioneer in ADSL after having produced the first complete ADSL chipset back in 1997. Early adopters of ADSL rallied behind the AD20msp910 chipset after having successfully evaluated its high-speed, long reach capability. Soon thereafter, the world’s most influential industry standards committees (ANSI, ETSI and ITU) approved an advanced discrete multi-tone (DMT) signal processing technique used by the AD20msp910. Today, Analog Devices enjoys the advantages of having the industry’s first standards-based solution, the largest installed customer base, and the most design wins of any semiconductor manufacturer to date.

ADSL is attractive for the following reasons:

• ADSL is fast. The same 10 MB video clip that takes 90 minutes to download using a conventional modem would be downloaded in just 10 seconds using an ADSL modem. Superfast ADSL modems can transmit data at rates as high as 8 megabits per second.

• ADSL is easy to install. It uses existing copper twisted-pair telephone lines from a local exchange carrier (central office) to the subscriber’s home or office. Little or no rewiring is necessary.

• ADSL is cost-effective. It requires no major upgrades in the existing telephone network infrastructure.

• ADSL is viable. Issues that have slowed the deployment of high-speed fiber networks to the home (e.g., prohibitive cost and installation) do not apply.

ADSL works with existing POTS (plain-old telephone service). High-speed data transport can occur simultaneously with voice calls and fax transmissions.
Unlike other high-speed data transmission technologies, ADSL requires no rewiring over the “last mile” of the network. Although commonly referred to as the last mile, transmission length is typically 12,000 to 18,000 feet. That “last mile” (the leg from the central office to a user’s home or office) operates over existing copper loops of twisted-pair telephone wires. But ADSL does require the installation of new equipment at local exchange central offices and major switch offices. However, the technology developed for central office equipment is the same as that used in PC modems and home splitter boxes, thus ensuring interoperability throughout the entire network. A simplified block diagram of an ADSL system is shown in Figure1>>.


About Inna Lyulicheva

4 Responses to DSP APPLICATIONS ADSL (Asymmetric Digital Subscriber Line)

  1. Jerald Minnaert says:

    Telephone systems that are wireless are great like cellphone. ^

    <a href="My blog page

  2. Thresa Tinajero says:

    Telephone systems in the past relied too much on analog technology that is why they have very few features, nowadays, we have digital telephone systems which over so many features.*””.:

    Take care


  4. ammansoor says:

    hi it is Mansoor

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