Isdn Vs Cable Essay Research Paper ISDN

Isdn Vs Cable Essay, Research Paper

ISDN VS. cABLE MODEMS1.0 Introduction The Internet is a network of networks that interconnects computersaroundthe world, supporting both business and residential users. In 1994, amultimedia Internet application known as the World Wide Web becamepopular. The higher bandwidth needs of this application havehighlightedthe limited Internet access speeds available to residential users. Evenat 28.8Kilobits per second (Kbps) the fastest residential access commonlyavailable at the time of this writing the transfer of graphical imagescan befrustratingly slow. This report examines two enhancements to existing residentialcommunications infrastructure: Integrated Services Digital Network(ISDN),and cable television networks upgraded to pass bi-directional digitaltraffic(Cable Modems). It analyzes the potential of each enhancement todeliverInternet access to residential users. It validates the hypothesis thatupgradedcable networks can deliver residential Internet access morecost-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 thespring of1994: + Continental Cablevision and Performance Systems International(PSI)jointly developed PSICable, an Internet access service deployed overupgraded cable plant in Cambridge, Massachusetts; + Internex, Inc. began selling Internet access over ISDN telephone circuits available from Pacific Bell. Internex’s customers areresidences andsmall businesses in the “Silicon Valley” area south of San Francisco,California. 2.0 The Internet When a home is connected to the Internet, residential communicationsinfrastructure serves as the “last mile” of the connection between thehome computer and the rest of the computers on the Internet. Thissection describes the Internet technology involved in that connection.This section does not discuss other aspects of Internet technology indetail; that is well done elsewhere. Rather, it focuses on the services that need to be provided for home computer users to connect to theInternet. 2.1ISDN and upgraded cable networks will each provide differentfunctionality(e.g. type and speed of access) and cost profiles for Internetconnections. Itmight seem simple enough to figure out which option can provide theneededlevel of service for the least cost, and declare that option “better.”A keyproblem with this approach is that it is difficult to define exactly theneededlevel of service for an Internet connection. The requirements depend on the applications being run over the connection, but these applicationsareconstantly changing. As a result, so are the costs of meeting theapplications’requirements. Until about twenty years ago, human conversation was by far the dominant application running on the telephone network. The network wasconsequently optimized to provide the type and quality of service neededforconversation. Telephone traffic engineers measured aggregatestatisticalconversational patterns and sized telephone networks accordingly.Telephony’s well-defined and stable service requirements are reflectedin the”3-3-3″ rule of thumb relied on by traffic engineers: the average voicecalllasts three minutes, the user makes an average of three call attemptsduringthe peak busy hour, and the call travels over a bidirectional 3 KHzchannel. In contrast, data communications are far more difficult tocharacterize. Datatransmissions are generated by computer applications. Not only doexistingapplications change frequently (e.g. because of software upgrades), butentirely new categories such as Web browsers come into being quickly,adding different levels and patterns of load to existing networks.Researchers can barely measure these patterns as quickly as they aregenerated, let alone plan future network capacity based on them. The one generalization that does emerge from studies of both local andwide-area data traffic over the years is that computer traffic is bursty. Itdoes notflow in constant streams; rather, “the level of traffic varies widelyoveralmost any measurement time scale” (Fowler and Leland, 1991). Dynamicbandwidth allocations are therefore preferred for data traffic, sincestaticallocations waste unused resources and limit the flexibility to absorbburstsof traffic. This requirement addresses traffic patterns, but it says nothing abouttheabsolute level of load. How can we evaluate a system when we never know how much capacity is enough. In the personal computing industry, thisproblem is solved by defining “enough” to be “however much I can affordtoday,” and relying on continuous price-performance improvements indigitaltechnology to increase that level in the near future. Since both of the infrastructure upgrade options rely heavily on digital technology,anothercriteria for evaluation is the extent to which rapidly advancingtechnologycan be immediately reflected in improved service offerings. Cable networks satisfy these evaluation criteria more effectively thantelephone networks because: + Coaxial cable is a higher quality transmission medium thantwistedcopper wire pairs of the same length. Therefore, fewer wires, andconsequently fewer pieces of associated equipment, need to beinstalled and maintained to provide the same level of aggregatebandwidth to a neighborhood. The result should be cost savings andeasier upgrades. + Cable’s shared bandwidth approach is more flexible a