The Role of Telecommunication

To delivery multimedia, especially video, the key issue of bandwidth must be addressed first. Bandwidth is communication power - the capacity of an information channel to transmit bits without error in the presence of noise. In fiber optics, in wireless communications, in new dumb switches, and in digital signal processors, bandwidth will expand from 5 to 100 times as fast as the rise of microprocessor speeds. With the rapid spread of national network of fiber and cable, the dribble of kilobits from twisted-pair telephone lines is about to become a firehouse of gigabits.

Broadband bandwidth and video compression are the important technologies to successfully transmit video information. Thus, the focus on this paper is digital video compression and broadband technology such as ADSL, hybrid network, ISDN, ATM, frame rely, and SMDS. In addition, according to Benton Foundation working paper, telephone and cable companies are currently testing delivery systems for video-on-demand and near-video-on demand services. Those interactive testbeds for video-on-demand service will be addressed as well.

Digital Video Compression

MEG (Moving Picture Experts Group) is currently to generate standards for digital video (sequences of images in time) and audio compression. The MPEG format can support full-screen (640*480) 30 frames per second video with audio on computers equipped with hardware MPEG decoders.

In accord with the prevailing MPEG standards, digital compression can produce a bit stream running at between 1.5 and 6 Mbps. The complex and exacting of compressing bits - compensating for motion, comparing blocks of pixels for redundancy, smoothing out the flow of data - entails computer operations running 1,000 times as fast as the raw video bits. This means the video compression algorithm requires a processing speed between 150 and 600 gigabits per second- hundred of times faster than the Pentium. The real time compression process can save time and disk space, and speed transmission, allowing for longer and higher resolution video segments to be captured.

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Broadband Technology

Asymmetric Digital Subscriber Loop (ADSL)

ADSL is a multimedia modem which can transmit more than 6 Mbps over twisted pair copper and permits transmission of a single compressed, high- quality video signal, at a rate of 1.5 Megabits per second, in addition to an ordinary voice phone conversation. It is quick enough to bring remote multimedia - video, audio, graphics, and text - to millions of users. ADSL makes room for Plain Old Telephone Service (POTS) , so the phone line operates as it always did, for voice, facsimile, and computer services. Even if ADSL fails, the line still works for POTS. With ADSL, the following activities can be at the same time:

Since ADSL could convert copper lines to multimedia driveways based on customer request, some telephone companies already appreciate the truth of ADSL. Others have backed off because ADSL seems expensive and does not transmit analog video.

However, ADSL is not yet capable of providing a complete substitute for cable TV, because it can only send one channel at a time and will not serve households where more than one TV is in use at a time.

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Hybrid Network

Networks that reach into the home are hybrids of the fiber-optic cable, existing copper wire and coaxial cable used by telephone and cable television companies. Fiber-optic cables will be used in the major arteries and portions of the distribution system, while existing copper and coaxial cable will be used in the last hundred yards.

Hybrid networks can delivery a full range of high-bandwidth interactive service at a fraction of the cost of fiber to the home. Digital compression, storage, and transmission will reduce the cost of rewiring a neighborhood to a manageable burden. High-capacity video file servers capable of storing thousands of hours of programming will be attached at the regional level. Existing cable systems will be replaced by high-capacity, noiseless fiber-optic cable that will reach from the system's head into each neighborhood.

The "fiber-to-the-node" architecture will serve groups of 200 to 1500 homes. If the networks are engineered properly, every subscriber should be able to view a different program, even if all are watching at the same time. Over time, the network can be expanded to support full two-way communication applications like video telephony.

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Integrated Services Digital Network (ISDN)

ISDN is a technology designed for the public switched telephone network that allows low-cost communication in data, voice, graphics, and video. It is designed to run over the existing copper local loop that connects the telephone company's central office to the home. Some of the characteristics that distinguish ISDN are:

ISDN offers inexpensive dialed service, high-speed data transmission, and the ability to send and receive voice and images through the same fully digital connections. Therefore, it is especially useful for individual and those in smaller companies.

Charge of ISDN

The following is three kinds of ISDN services:

Some of the digitally stored information ISDN can make available includes X-rays, CAT-scans and other medical images, full color photographs and illustrations, general and specialized encyclopedias, film and television image and other visually intensive files.

ISDN, with its end-to-end digital connections, offers giant steps forward in speed-up to 112 Kbps today- with the quantum leap of digital compression still to come.

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Asynchronous Transfer Mode(ATM)

ATM is the most important short-term contributor to the tides of bandwidth. It puts everything into same-sized boxes called cells and each one is 53 byes long, including a five-byte address. Small packets of a uniform 53 bytes can be switched at enormous speeds through an ATM network and dispatched to the end users on a fixed schedule that can accommodate voice, video and data, all at once. ATM also turns networks of small computers into scaleable supercomputers. It combines with fiber-optic links to provide a far simpler, more modular and more scaleable solution than the complex copper backplane buses that perform the same functions in large computers.

The basic principles of ATM:

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Frame Relay

Frame Relay is a packet based on interface standard that has been optimized for the transport of protocol-oriented data. A frame relay network consists of user devices and network devices that implement the standard interface. The user device is responsible for delivering frames to the network in the prescribed format. The network in the prescribed format. The network is responsible for switching or routing the frames to the proper destination user device.

Benefits of Frame Relay

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Switched Multimegabit Data Service (SMDS)

SMDS is a connectionless, cell-switched data transport service that offers total end-to-end application solutions. With SMDS, organizations have the flexibility they need for distributed computing and bandwidth-intensive applications. At the same time, because SMDS supports both existing and emerging technologies, it provides the scalability organizations need to support the application in the future. Because SMDS is able to coexist with dedicated facilities, it enables customers to create hybrid public/ private networks. SMDS also allows for the easy expansion of existing networks, since new sites can be quickly added to a SMDS net without totally reconfiguring the network. Flat rate tariffs for SMDS service range from $350 to $750 per mouth, plus a one-time installation charge per subscriber network interface of $700 to $1000.

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The Developing Delivery Systems

Telephone Company-based Interactive TV Testbeds

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Cable Interactive TV Testbeds

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