Figure 3-2 Internet service offering via cable modem in which both the access and ISP service are
provided by the cable company.
Figure 3-3 Internet service offering via cable modem in which access and ISP service are separated.
However, notice that the Frame Relay or ATM networks in which the Internet traffic are being routed may not necessarily belong to the same operator. In this case, the telephone network operators will likely
charge a nominal access fee. This is really an intermediate solution, because it requires multiple overlay networks. There are two possible ADSL deployment scenarios as depicted in Figure 3-4 and Figure 3-5.
Figure 3-4 shows a case where the ADSL technology is integrated into the central office. Figure 3-5, on the other hand, shows a case where an external Digital Subscriber Line Multiplexer DSLAM is used to
separate the Internet traffic from the traditional voice traffic. In this case, no upgrade is required for the existing central office.
Figure 3-4 Integrated ADSL solution.
Figure 3-5 External ADSL Solution.
The third technology solution is the deployment of ATM technology all across to provide both voice and Internet service via the ATM network. The only reason for the intermediate solution using the overlay
Frame Relay or ATM network is the high cost associated with the ATM technology. The transition to a final ATM-based network solution will ultimately be determined by the rate of cost reduction in ATM
technology. We can envision a pure ATM-based telecommunication network across the United States when per user port cost goes down to below the U.S. 100 range. Figure 3-6 illustrates such a pure ATM-
based Internet service offering.
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by Abhijit S. Pandya; Ercan Sen CRC Press, CRC Press LLC
ISBN: 0849331390 Pub Date: 110198
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II. Video on Demand
Video on Demand VOD will be one of the most popular and powerful service offerings through ATM technology. VOD will cause a paradigm shift in terms of how entertainment and education are provided to
the public. Through VOD it will be possible to view an entertainmentnew video piece whenever one wishes. In the education arena, people will be able to access educational videos stored in digital libraries.
Information and entertainment retrieval will be personalized. People will no longer have to adjust their schedule according to a broadcast schedule if they wish to view a particular entertainmentnews
educational program.
A successful VOD operation requires two basic infrastructure elements: high bandwidth for transmission of video content to each destination and a very efficient video server to serve many clients simultaneously
with different timing.
Figure 3-6 Pure ATM-based Internet service offering.
A typical video transmission carries a large amount of information and it is very bursty in nature. ATM technology is well suited for carrying video traffic very efficiently. A high quality video transmission such
as a video in High Definition Television HDTV format requires in the order of 40 to 100 Mbitsec bandwidth capacity without any compression.
At the present time, transmission of high quality TV broadcast through telephony network requires setting up a communication path between the source and destination at DS3 transmission rate 45 Mbits using
Synchronous Transfer Mode. Since the bandwidth is reserved at the peak transfer rate, it wastes bandwidth and it is very expensive. Using the ATM technology it is possible to reserve bandwidth less than the peak
rate. Hence, ATM is better suited for carrying video traffic.
VOD traffic has very asymmetrical characteristics in terms of bandwidth use. Typically, the downstream traffic from the server to clients requires large bandwidth while the upstream traffic from the clients to
server requires very small bandwidth for sending control information such as stop, start, pause, rewind, forward, etc. The STM technology requires equal bandwidth allocation in both directions whereas ATM
allows different bandwidth allocation in both directions. Hence, from accommodating asymmetrical bandwidth for VOD service point of view, ATM is superior to STM technology.
Significant bandwidth reduction for video transmission can be achieved using compression techniques to compress the video information. The most promising video compression technique today is MPEG-2.
In order to provide a successful VOD service, the response time for serving the request has to be real-time or near real-time. Hence, the video server is a crucial piece for implementing a successful VOD service. A
successful video server technology has to be capable of serving many clients viewing different segments of a video program in real-time or near real-time, i.e., the video server has to be operating in the multi-
treading mode.
There are several technological and network architecture problems related to the video server that need to be solved in order to meet the challenge for a successful VOD service offering. Although ATM can
provide a transport environment for point-to-point video transmission, an efficient VOD operation requires a very efficient point-to-multipoint transport environment. Another approach would be to use a cache
system to maintain multiple copies of a video program in different locations closer to the clients.
III. Video Telephony
Video Telephony VT service offering will be among the favorite services provided by the ATM networks both for the general public and business community. It will probably replace the traditional voice
only telecommunication form. Through VT, people will be able to communicate visually. VT will make it possible to communicate person-to-person in private or allow setting up video conferencing.
VT shares some common characteristics with VOD and it also differs from VOD in some other aspects. We will elaborate on these common and divergent characteristics in this section.
VT also requires high bandwidth to carry video signals between the communicating parties. However, the demand for high bandwidth is not as stringent as VOD. During a typical person-to-person VT session as
shown in Figure 3-7, the images change relatively slowly compared to an action scene in a video movie. Also, VT does not suffer from the complexity and difficulty involved in VOD in regards to the video
server.
The traffic between a person-to-person VT session is limited to two nodes and the traffic is symmetrical. Even in the case of video conferencing, as shown in Figure 3-8, in which more than two persons are
involved, the number of clients is fairly small compared to the VOD. In addition, the video transmission is simultaneous, i.e., only one common image is broadcast to all conference participants. Hence, it requires a
relatively simpler conference server. ATM also offers very a cost-effective solution for VT service due to the bursty nature of video traffic. It can be expected that VT service will be provided sooner than VOD
due to its relative simplicity in many aspects as explained above.
IV. Distant LearningMedicine
Distant Learning and Medicine service provided through ATM technology will revolutionize the way
The key requirements for distant learningmedicine are high bandwidth and low bandwidth cost. ATM technology will be able to meet these requirements through efficient use of the bandwidth resources of the
public networks.
High bandwidth is required because both distant learning and medicine rely on high quality video images to be carried over the network to different geographical locations. Distant medicine requires carrying high
definition medical images and medical data across the network. On the other hand, distant learning requires high quality video conferencing capability involving perhaps hundred of students. Interactivity in
real-time will be an important requirement for both distant learning and medicine.
Figure 3-7 Video telephony person-to-person.
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by Abhijit S. Pandya; Ercan Sen CRC Press, CRC Press LLC
ISBN: 0849331390 Pub Date: 110198
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V. Telecommuting
Crowded and inadequate urban infrastructures such as roads are making working in downtown business districts almost impossible. Due to congested roads during busy hours, commuting between work and
home is becoming a nightmare. Workers have to spend a considerable amount of their time i.e., 1 to 3 hours each day for commuting.
