Video-on-Demand Technology Holds Potential to Reshape Distance Learning in Near Future


Just over the technological horizon awaits a multi-million dollar video-on-demand, distance-educational opportunity for educational institutions and companies farsighted enough to take advantage of it. The emerging technology is driven by the Asymmetrical Digital Subscriber Line (ADSL), a relatively new modem technology that allows high-speed data transmittal over existing twisted copper pairs, i.e. telephone lines. 

ADSL technology, which has demonstrated its capability to deliver VHS-quality video over existing unshielded telephone lines, has the potential to drastically reshape the way distance education will be delivered in the future.

ADSL increases the capacity of existing telephone lines with its ability to facilitate the high-speed transmission of data. Combined with video-compression algorithms, ADSL can produce video on demand to virtually anywhere there is a telephone line -- thus bringing interactive-distance learning into every living room. To many individuals, ADSL may be their on-ramp to the information superhighway.

ADSL has demonstrated its capability to deliver VHS-quality video over existing unshielded telephone lines.



The technology is asymmetrical in that the high-capacity is from the source to the subscriber (customer) and lower capacity in both directions.[1] Frequency-division multiplexing supports simultaneous voice and multi-media delivery.[2] 

ADSL circuits, with a modem on each end of the copper telephone line, create a source-to-subscriber high-speed channel (1.5-6 Mbps), a lower-speed duplex channel (16-640 Kbps), and a regular telephone line (4 KHz) split off from the modem by filters. Transmission rates are dependent upon copper line length and wire gauge. The shorter the line and thicker the wire, the better.[3]

Sophisticated signal processing allows the transceiver to optimize performance and correct for changes in temperature and moisture.[1]

The technology employs complimentary algorithms that use frequency-division multiplexing or echo cancellation. Frequency division allocates one band for upstream and one for downstream, with the downstream time-division multiplexed. Echo cancellation overlaps the two bands making better use of the total band width.

Several different transmission techniques have been explored for ADSL. Discrete Multi-Tone Modulation (DMT), a multi-carrier time-division multiplexing technique, has emerged as the preferred method.[4] DMT divides the high bit-rate (6 Mbps) delivery channel into a number of sub-channels.

ADSL, created by J'e Lechleider of Bellcore in the late 1960s, has been tested extensively in the laboratory and in the field by at least 30 telephone companies in the United States, Europe, South East Asia, and Australia.[3,4]


An emerging high-speed version of the technology known as VDSL has the capacity to deliver multi-channel, high-quality broadband multimedia over hybrid fiber-copper networks. VDSL is promising downstream-data rates as high as 55 Mbps over lines up to 1,000 feet in length. Even lengths greater than 4,000 feet can support 13 Mbps.[3]

Because this embryonic technology serves customers rather than geographical areas, it will be a viable, cost-effective way to penetrate the video-on-demand market until fiber becomes ubiquitous.

At 6.144 million bits per second (Mbps) coming into the home, different family members can access the network at the same time. One person can watch a movie. Another might browse a home-shopping service, while a third interacts with a distance-learning source.[5]

In the future there will be lucrative opportunities awaiting educational institutions that can deliver interactive educational video into the home upon demand. Possibly educational institutions will create consortia to offer students a wide variety of options leading to a degree. 

A student could have the choice of studying under professors from various institutions around the world and never leave home. Those wishing to study Nabatean archaeology could attend a seminar in Petra via interactive video; oceanographic students could take a class on the Great Barrier Reef from a researcher in Australia. More than likely, the more esoteric, dangerous and expensive offerings will migrate to dial-in distance learning while the more common courses will be held in typical distance-learning studios or traditional classrooms.

With nearly 600 million copper access lines worldwide and the universal emplacement of fiber a number of years off in the future, ADSL technology will likely open up new video-on-demand markets.[3] How many potential students throughout the world will be willing to take classes from the convenience of their homes? One can conjecture that demand will be enormous. ADSL-related technologies can help educators tap this very large market.

Institutions of higher education that are land-locked and inhibited from physical growth will soon have new venues into which they can penetrate. Those serving sparsely-populated markets will find in ADSL greater utilization of resources to meet their distance-learning demands. A few key leaders in distance learning will likely arise to broker video-on-demand service for other institutions. Colleges and universities should be posturing to be ready for this technological advance that will soon cause a major change in the delivery of distance learning.


[1] Young, G., Foster, K.T. & Cook, J.W. (1995), "Broadband Multimedia Delivery Over Copper," BT Technology Journal, 13(4), pp. 78-96. 

[2] ADSL - An Easy Route to Video On Demand, (1995), Electronics World + Wireless World, 101(1707), pp. 102-105. 

[3] ADSL Forum, May 17,1996. at 

[4] Kyees, Philip J., McConnell, Ronald C. & Sistanizadeh, Kamran (1995), "ADSL: A New Twisted-Pair Access to the Information Superhighway," IEEE Communications Magazine, 33(4), pp. 52-60. 

[5] Young, Gavin (1995), "Asymmetric Digital Subscriber Line (ADSL): From Concept to BT Trial & Beyond," unpublished paper presented at IIR Conference, March 30, 1995.

This article originally appeared in the 12/01/1996 issue of THE Journal.