Technologism Essay Research Paper The Internet is — страница 2

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capacity based on them. The one generalization that does emerge from studies of both local and wide- area data traffic over the years is that computer traffic is bursty. It does not flow in constant streams; rather, “the level of traffic varies widely over almost any measurement time scale” (Fowler and Leland, 1991). Dynamic bandwidth allocations are therefore preferred for data traffic, since static allocations waste unused resources and limit the flexibility to absorb bursts of traffic. This requirement addresses traffic patterns, but it says nothing about the absolute level of load. How can we evaluate a system when we never know how much capacity is enough? In the personal computing industry, this problem is solved by defining “enough” to be “however much I can

afford today,” and relying on continuous price-performance improvements in digital technology to increase that level in the near future. Since both of the infrastructure upgrade options rely heavily on digital technology, another criteria for evaluation is the extent to which rapidly advancing technology can be immediately reflected in improved service offerings. Cable networks satisfy these evaluation criteria more effectively than telephone networks because: ? Coaxial cable is a higher quality transmission medium than twisted copper wire pairs of the same length. Therefore, fewer wires, and consequently fewer pieces of associated equipment, need to be installed and maintained to provide the same level 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