dems, such as ultra-fast upstream speeds, constant connectivity, and not tying up a subscriber's telephone line. The Cable Modem Termination System (CMTS) is the central device for connecting the cable TV network to the Internet. The CMTS resides at the cable head-end. All the traffic to and from the cable modems in a cable data network travel through the CMTS. The CMTS connects to an IP router that sends and receives the data from the rest of the Internet. The CMTS interprets the data it receives from individual customers and keeps track of the services offered to each of them. The CMTS also modulates the data received from the Internet so that the head-end equipment can send it to a specific subscriber. Some Cable Modem Termination Systems provide the capability to let the MSO create different service packages depending on customers' bandwidth needs (Clark, 1999). For example, a business service can be programmed by the CMTS to receive, as well as transmit, with high bandwidth, while a residential user may be configured by the CMTS to receive high bandwidth downstream traffic and limited to low bandwidth upstream traffic. Cable data network architecture is similar to that of an Ethernet Local Area Network (LAN) (Halfhill, 1996). Current cable modem systems use Ethernet frame format for upstream and downstream transmissions. Basically, the cable operators are building some of the world's largest "intranets". Cable operators are concentrating on providing high-speed intranet access instead of straight Internet access because a network connection is only as fast as its slowest link. The head-end at most MSOs usually connect to the Internet via a T1 line, which has a data rate of 1.5 Mbps, significantly slower than a cable modem, which can theoretically deliver 30 Mbps (Brownstein, 1997). But, the Internet is only as fast as the slowest server. The benefit of a 1.5 Mbps T1 Internet connection is lost if a subscriber tries t...
