o access content stored on a Web server that is connected to the Internet though a 56-Kbps line. Thus, the bottlenecks for Internet traffic in a cable network system are usually the gateway to the Internet, as well as the Internet itself. The cable companies solution to this problem is to move the Internet content closer to the subscriber. Many popular Web sites are cached on the cable operator's server. So, when a cable modem subscriber goes to access a popular Web page, he will be routed to the server in the head-end at top-speed. If a site isn't cached, however, the head-end server has to go looking for it out on the congested Internet, just as a conventional ISP's server does. Cable modem subscribers should see high speeds (multiple MBit/sec) as long as they stay within the local cable network system. However, data transfer rates can slow down considerably when the user needs to venture out onto the Internet. Like LANs, cable modem systems rely on a shared access platform (Ostergard, 1999). All the cable modem subscribers in a cable loop share available bandwidth to the head-end. Everyone on the local cable loop shares the same cable, which can carry about 30 Mbps total bandwidth. So as more subscribers hook up cable modems, more users will be sharing the same amount of bandwidth. Because of this, there are concerns that cable modem users will see poor performance as the number of subscribers increase on the network. If congestion does begin to occur due to high usage, the cable operators do have the capability to upgrade bandwidth capacity. A cable operator can easily allocate an additional 6 MHz video channel for high-speed data, doubling the downstream bandwidth available to users. Another option for adding bandwidth is to subdivide the physical cable network by running fiber-optic lines deeper into neighborhoods. This reduces the number of cable modems served by each node segment, and thus, increases the amount o...
