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Cable Modem

2.2.8 Cable Modem
Coaxial cable is widely used in urban areas to distribute television signals. Network access is available from some cable television networks. This allows for greater bandwidth than the conventional telephone local loop.
Enhanced cable modems enable two-way, high-speed data transmissions using the same coaxial lines that transmit cable television. Some cable service providers are promising data speeds up to 6.5 times that of T1 leased lines. This speed makes cable an attractive medium for transferring large amounts of digital information quickly, including video clips, audio files, and large amounts of data. Information that would take two minutes to download using ISDN BRI can be downloaded in two seconds through a cable modem connection.
Cable modems provide an always-on connection and a simple installation. An always-on cable connection means that connected computers are vulnerable to a security breach at all times and need to be suitably secured with firewalls. To address security concerns, cable modem services provide capabilities for using Virtual Private Network (VPN) connections to a VPN server, which is typically located at the corporate site.
A cable modem is capable of delivering up to 30 to 40 Mbps of data on one 6 MHz cable channel. This is almost 500 times faster than a 56 Kbps modem.
With a cable modem, a subscriber can continue to receive cable television service while simultaneously receiving data to a personal computer. This is accomplished with the help of a simple one-to-two splitter.
Cable modem subscribers must use the ISP associated with the service provider. All the local subscribers share the same cable bandwidth. As more users join the service, available bandwidth may be below the expected rate.

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