Technologism Essay Research Paper The Internet is — страница 6

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of aggregate bandwidth to a neighborhood. The result should be cost savings and easier upgrades. ? Cable’s shared bandwidth approach is more flexible at allocating any particular level of bandwidth among a group of subscribers. Since it does not need to rely as much on forecasts of which subscribers will sign up for the service, the cable architecture can adapt more readily to the actual demand that materializes. ? Telephony’s dedication of bandwidth to individual customers limits the peak (i.e. burst) data rate that can be provided cost-effectively. In contrast, the dynamic sharing enabled by cable’s bus architecture can, if the statistical aggregation properties of neighborhood traffic cooperate, give a customer access to a faster peak data rate than the expected average

data rate. 2.2 Why focus on Internet access? Internet access has several desirable properties as an application to consider for exercising residential infrastructure. Internet technology is based on a peer-to-peer model of communications. Internet usage encompasses a wide mix of applications, including low- and high- bandwidth as well as asynchronous and real-time communications. Different Internet applications may create varying degrees of symmetrical (both to and from the home) and asymmetrical traffic flows. Supporting all of these properties poses a challenge for existing residential communications infrastructures. Internet access differs from the future services modeled by other studies described below in that it is a real application today, with growing demand. Aside from

creating pragmatic interest in the topic, this factor also makes it possible to perform case studies of real deployments. Finally, the Internet’s organization as an “Open Data Network” (in the language of (Computer Science and Telecommunications Board of the National Research Council, 1994)) makes it a service worthy of study from a policy perspective. The Internet culture’s expectation of interconnection and cooperation among competing organizations may clash with the monopoly-oriented cultures of traditional infrastructure organizations, exposing policy issues. In addition, the Internet’s status as a public data network may make Internet access a service worth encouraging for the public good. Therefore, analysis of costs to provide this service may provide useful

input to future policy debates. 3.0 Technologies This chapter reviews the present state and technical evolution of residential cable network infrastructure. It then discusses a topic not covered much in the literature, namely, how this infrastructure can be used to provide Internet access. It concludes with a qualitative evaluation of the advantages and disadvantages of cable-based Internet access. While ISDN is extensively described in the literature, its use as an Internet access medium is less well-documented. This chapter briefly reviews local telephone network technology, including ISDN and future evolutionary technologies. It concludes with a qualitative evaluation of the advantages and disadvantages of ISDN-based Internet access. 3.1 Cable Technology Residential cable TV

networks follow the tree and branch architecture. In each community, a head end is installed to receive satellite and traditional over-the-air broadcast television signals. These signals are then carried to subscriber’s homes over coaxial cable that runs from the head end throughout the community Figure 3.1: Coaxial cable tree-and-branch topology To achieve geographical coverage of the community, the cables emanating from the head end are split (or “branched”) into multiple cables. When the cable is physically split, a portion of the signal power is split off to send down the branch. The signal content, however, is not split: the same set of TV channels reach every subscriber in the community. The network thus follows a logical bus architecture. With this architecture, all

channels reach every subscriber all the time, whether or not the subscriber’s TV is on. Just as an ordinary television includes a tuner to select the over-the-air channel the viewer wishes to watch, the subscriber’s cable equipment includes a tuner to select among all the channels received over the cable. 3.1.1. Technological evolution The development of fiber-optic transmission technology has led cable network developers to shift from the purely coaxial tree-and-branch architecture to an approach referred to as Hybrid Fiber and Coax(HFC) networks. Transmission over fiber-optic cable has two main advantages over coaxial cable: ? A wider range of frequencies can be sent over the fiber, increasing the bandwidth available for transmission; ? Signals can be transmitted greater