EE535 Homework 3: Ronald Shamus

ADSLAsymmetrical Digital Subscriber Line (ADSL)

Asymmetric Digital Subscriber Line or ASDL is a newly proposed technology for very high speed transmission of data over twisted pair, telephone cable. Locate any and all information that you can about this technology. Link and Web pages to your report. Summarize the means, the speeds and the state of this new technology. Be sure to search current jounals and magazines for information of a substatial nature in addition to any Web information you locate.


The recent Telecommunications bill approved by Congress and signed off by President Clinton has opened the door to the long awaited "information superhighway". As the Telecommunication providers scramble to develop the new infrastructure, the question on how to connect customers (subscribers) to the high speed fiber optic network available at the telephone company and hense an emerging myriad of services remains. The current popular long term solution appears to be either Hybrid Fiber Coax (HFC) or Fiber-to-the-Curb (FTTC) architecture. However, connecting the majority of the customers with either of those architectures is many years away. How then can consumers "subscribe" to those emerging services now? One proposed solution is Asymmetric Digital Subscriber Line (ADSL). ADSL is important because it can provide near term, high data rate broadband services over the existing copper-based telephone lines. ADSL allows the possibility of such services as high speed Internet access, interactive video (video-on-demand),remote LAN access, interactive information, telecommuting, video teleconferencing, healthcare,and tele-education to home and business users.



In the late 1980's a Bellcore researcher, Joe Lechleider developed the idea for ADSL as a follow on technology to Digital Subscriber Line (DSL), an access technology developed for basic rate ISDN. In 1993, the ANSI accedited Committee T1 Telecommunications, DSL access working group (T1E1.4), began the development of a standard. The development effort was sponsored by the Alliance for Telecommunications Industry Solutions (ATIS). The standard wass assigned the number T1.413 and was approved and published late in 1995.

The ANSI Standard T1.413 looks into:

Although not currently available in most if not all of the libraries, it is available for a fee from ANSI.

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The Means

ADSL utilizes the existing "Plain Old Telephone Service (POTS)" copper Twisted Pair wires currently in place in the Access Loop with ADSL modems attached to both ends to deliver a minimum of 1.5 Mbps "downstream" (to the "subscriber") and receive back a minimum of 16 kbps "duplex" (from the "subscriber") and as much as 6 Mbps "downstream" and 640 kbps "duplex".

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ADSL utilizes modems attached to twisted pair copper wiring that transmit from 1.5 Mbps to 6+ Mbps downstream (to the subscriber) and from 16 Kbps to 640 Kbps upstream, depending on line distance, wire gauge, presence of bridged gaps, and cross coupled interference. However for the sake of comparison and ignoring bridged gaps the speeds are attainable:

Data Rate     Wire Gauge                      Distance 

1.5 or 2 Mbps       24 AWG                   18,000 ft 
1.5 or 2 Mbps       26 AWG                   15,000 ft 
6.1 Mbps            24 AWG                   12,000 ft 
6.1 Mbps            26 AWG                    9,000 ft 
  • Payload channels

  • ADSL Transfer Capacity

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    Late 1980's		Bellcore researcher, Joe Lechleider spawns the idea for ADSL as a follow on
    			technology to Digital Subscriber Line (DSL).  DSL had been developed for 
    			basic rate ISDN.
    22 Nov. 1991		FCC's "Video Dial Tone" ruling allowing the entry of the telephone companies
    			 into the video distribution marketplace.
    1993			ANSI accedited Committee T1 Telecommunications DSL access working group 
    			(T1E1.4), with the sponsorship of the Alliance for Telecommunications\
    			Industry Solutions (ATIS), begins the development of an ADSL standard.
    June 10, 1994		Kansas City, MO.  Draft ADSL standard assembled.
    Late 1994		ADSL Forum formed
    March 1, 1995		Disposition of all comments
    December 1995		ANSI releases the first ADSL Standard: T1.413.

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    The ADSL Forum

    Late in 1994, the ADSL Forum was formed to manage marketing and the standardization of technical issues for this developing technology. The ADSL Forum is comprised of two subgroups:

    More About the ADSL Forum

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    According to the ADSL Forum, there are approximately 600 million copper access lines in the world today with an estimated 750 million by 2001. Some telecom executives estimate that the changeover to FTTC or HFC could take as much as 40 years. To meet the demand for the new broadband services by residences and small businesses, telephone companies around the world will have to use copper access technologies.

    Twisted pair copper wire and ADSL is a current technology that can be used to provide service until replaced by FTTC or HFC. Some in the engineering community believe the push toward greater bandwidth afforded by utilization of the fiber technologies is too quick and unnecessary. In his essay Debunking Bandwidth Nicholas Negroponte makes the point that fiber optic cable is now cheaper than copper. Therefore, the telephone companies will change over to fiber as the copper wears out and as new services are installed. In the meantime, the 6 Mbps provided using ADSL is more than adequate and should be taken advantage of.

    The ADSL Market

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    The following pages describe the 'state-of-the-art':