Technologism Essay Research Paper The Internet is — страница 8

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imply that every subscriber can transfer data at that rate simultaneously. The effective average bandwidth seen by each subscriber depends on how busy the LAN is. Therefore, a cable LAN will appear to provide a variable bandwidth connection to the Internet Full-time connections Cable LAN bandwidth is allocated dynamically to a subscriber only when he has traffic to send. When he is not transferring traffic, he does not consume transmission resources. Consequently, he can always be connected to the Internet Point of Presence without requiring an expensive dedication of transmission resources. 4.2 Internet Access Via Telephone Company In contrast to the shared-bus architecture of a cable LAN, the telephone network requires the residential Internet provider to maintain multiple

connection ports in order to serve multiple customers simultaneously. Thus, the residential Internet provider faces problems of multiplexing and concentration of individual subscriber lines very similar to those faced in telephone Central Offices. The point-to-point telephone network gives the residential Internet provider an architecture to work with that is fundamentally different from the cable plant. Instead of multiplexing the use of LAN transmission bandwidth as it is needed, subscribers multiplex the use of dedicated connections to the Internet provider over much longer time intervals. As with ordinary phone calls, subscribers are allocated fixed amounts of bandwidth for the duration of the connection. Each subscriber that succeeds in becoming active (i.e. getting

connected to the residential Internet provider instead of getting a busy signal) is guaranteed a particular level of bandwidth until hanging up the call. Bandwidth Although the predictability of this connection-oriented approach is appealing, its major disadvantage is the limited level of bandwidth that can be economically dedicated to each customer. At most, an ISDN line can deliver 144 Kbps to a subscriber, roughly four times the bandwidth available with POTS. This rate is both the average and the peak data rate. A subscriber needing to burst data quickly, for example to transfer a large file or engage in a video conference, may prefer a shared-bandwidth architecture, such as a cable LAN, that allows a higher peak data rate for each individual subscriber. A subscriber who needs

a full-time connection requires a dedicated port on a terminal server. This is an expensive waste of resources when the subscriber is connected but not transferring data.