Session Nine:
Data Communications
& Cable Communications

Lecture Notes

Lecturette 9 – Data Communications and Cable Communications – and HDTV

	In this session, we will review the technologies employed to originate and terminate high speed transmissions. We will address applications for data communications and cable communications, and take a look at the issues and technologies of high definition television. Slide 1
	Call completion requires a network data circuit. Creating this circuit means having an interface with data terminal equipment. Some examples of such data circuit-termination equipment, or DCE, are modems, NT1 or CSU/DSUs, Channel Service Units/Data Service Units. The newest entrant is the cable modem. Slide 2
	Each of these DCEs performs a series of functions. First, the device performs analog-digital conversion. Second, it is the basis for providing such functions as maintaining required voltage levels, synchronicity, detecting errors, buffering, and compression. The DCE can also be a network testing point. Slide 3

The growth of interest in hybrid or converging systems as a means for new market entrants to reach the "last mile" is creating new architectures. These architectures are further influenced by the need for capacity and speed. The convergence of cable and fiber optics, for instance, requires a new architecture in order to move large volumes of digitized information over coaxial cable. In the past, using NTSC scan rates and repeaters, cable television companies have been able to supply adequate picture quality to the home. Coaxial cable is subject to a problem called "cascading". This term refers to the degradation of the signal as it gets farther from the head end or source. Amplifiers are necessary at relatively close intervals in order to regenerate the strong signal and pass it on.

The implications for data transmission are clear. As the size and volume of the data increases, the need for amplifier capacity increases dramatically. It is cheaper to lay fiber, with its greater bandwidth, than to try to increase the capacity of the coax and to add more amplifiers to handle the volume. So a hybrid system is evolving which uses both media to transmit form the head end to the end user.

Slide 4 shows this hybrid architecture. At the head end, the signal is received from a satellite or another fiber and loaded into the local system. Fiber of indefinite length can carry the signal without degradation. Close to the end user, the signal transfers through an optical node onto coaxial cable. Typically, there will be fewer than 6 amplifiers in the final cascade. The hybrid system provides an acceptable signal quality without the expense of laying fiber all the way to the home and by making use of the existing coaxial cable line.

Critical to the success of these hybrid fiber-cable systems are the development of cable modems. These modems are necessary both for deploying digital television signals and for bringing data over cable lines into your PC. The success of the AT&T merger with TCI/MediaOne hinges upon creating and deploying accepable, affordable cable modems.

 

But as yet, there is no standard, neither regulated nor de facto, for the construction of these modems. And, where before the cable transmission was one way, the new modems must be capable of interfacing across a range of of data types and in both directions. These functions include an interface both upstream and down, analog-digital conversion (as before), modulation of cable radio frequency carrier with encoded data, and demodulation of the cable RF carrier to recover data. Finally, it must filter packet addresses. Slide 5

 

 

 

 

The convergence of telephone and cable technologies allows a number of capabilities which, alone, neither industry would be able to develop and deploy. For example, cable’s advantages include broadband capacity and entertainment content, which telephone systems lack—telephone is narrow band and originates no content. But telephone companies have wide regional coverage, substantial switching competence, reliability, successful billing records, deep pockets (a great deal of which is spent on R&D), excellent name recognition and a large customer base. In contrast, cable falls short in each of these categories. Slide 6

In fact, the cable tv industry’s many issues of reliability, billing problems, and poor reputation kept it firmly in the eye of Congress. Cable Act amendments in 1984 and again with the Telecommunications Act of 1996 placed obligations upon cable providers and curtailed excessive practices. Title VI of the Communications Act of 1934, as amended, delineates those obligations and responsibilities.

 

Slides 7 through 10 outline some of the main features of the Act.

 

Prior to the ’96 Act, cable was barred from interactive communication. Cable operators were covered under "must carry" provisions that required them to provide network—in this case meaning CBS, NBC, ABC, and Fox –to all subscribers. In contrast, Direct Broadcast Satellite providers do not have to provide these services, and many a DBS or other satellite TV subscriber has been chagrined to learn that they cannot receive the basic networks unless they have another antenna or cable service. This, after having paid perhaps three or four thousand dollars to put in the dish and subscribe to the service.

The FCC is encouraging digital television. You perhaps have access to WETA, the PBS station in Arlington, VA. WETA has invested heavily in digitizing its transmission facilities. But so far, few, if any, in their viewing area, have digital receivers. The price of a digital television receiver currently runs above $2000, and given the paucity of programming and the expectation that the price of receivers will go down over time, viewers have been reluctant to become the first to try the new standard.

Slide 11 compare the scanning formats for digital television. The current standard is called NTSC, for National Television Standards Code. The lowest level of digital images, 480X640, compares in quality to the current NTSC standard. Each of the standards above that level increases the resolution, but creates other scanning problems.

But he potential for major market growth in these areas remains high. Each of the major industry players is attempting to improve its technology and make the right speculative investments in order to face the coming competition. When, soon after the millennium, the notion that "bits is bits" shades the differences between and among telephones, computers, and televisions, the major players all want to be prepared and in the forefront.

 

 

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