Network And Internet Connections

Network And Internet Connections The Internet is a network of networks that interconnects computers around the world, supporting both business and residential users. In 1994, a multimedia Internet application known as the World Wide Web became popular. The higher bandwidth needs of this application have highlighted the limited Internet access speeds available to residential users. Even at 28.8 Kilobits per second (Kbps)the fastest residential access commonly available at the time of this writingthe transfer of graphical images can be frustratingly slow. This report examines two enhancements to existing residential communications infrastructure: Integrated Services Digital Network (ISDN), and cable television networks upgraded to pass bi-directional digital traffic (Cable Modems).

It analyzes the potential of each enhancement to deliver Internet access to residential users. It validates the hypothesis that upgraded cable networks can deliver residential Internet access more cost-effectively, while offering a broader range of services. The research for this report consisted of case studies of two commercial deployments of residential Internet access, each introduced in the spring of 1994: Continental Cablevision and Performance Systems International (PSI) jointly developed PSICable, an Internet access service deployed over upgraded cable plant in Cambridge, Massachusetts; Internex, Inc. began selling Internet access over ISDN telephone circuits available from Pacific Bell. Internex’s customers are residences and small businesses in the “Silicon Valley” area south of San Francisco, California.

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2.0 The Internet When a home is connected to the Internet, residential communications infrastructure serves as the “last mile” of the connection between the home computer and the rest of the computers on the Internet. This section describes the Internet technology involved in that connection. This section does not discuss other aspects of Internet technology in detail; that is well done elsewhere. Rather, it focuses on the services that need to be provided for home computer users to connect to the Internet. 2.1 ISDN and upgraded cable networks will each provide different functionality (e.g. type and speed of access) and cost profiles for Internet connections. It might seem simple enough to figure out which option can provide the needed level of service for the least cost, and declare that option “better.” A key problem with this approach is that it is difficult to define exactly the needed level of service for an Internet connection.

The requirements depend on the applications being run over the connection, but these applications are constantly changing. As a result, so are the costs of meeting the applications’ requirements. Until about twenty years ago, human conversation was by far the dominant application running on the telephone network. The network was consequently optimized to provide the type and quality of service needed for conversation. Telephone traffic engineers measured aggregate statistical conversational patterns and sized telephone networks accordingly.

Telephony’s well-defined and stable service requirements are reflected in the “3-3-3” rule of thumb relied on by traffic engineers: the average voice call lasts three minutes, the user makes an average of three call attempts during the peak busy hour, and the call travels over a bidirectional 3 KHz channel. In contrast, data communications are far more difficult to characterize. Data transmissions are generated by computer applications. Not only do existing applications change frequently (e.g. because of software upgrades), but entirely new categoriessuch as Web browserscome into being quickly, adding different levels and patterns of load to existing networks. Researchers can barely measure these patterns as quickly as they are generated, let alone plan future network 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 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 Hybr …


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