What is a Cable Modem

A cable modem provides you access to the Internet. The same cable that brings you TV signals allows you to surf the Internet as well. Cable modem offers high speeds or a bandwidth of 1 mbps, which makes it easier to download large audio or video files. A cable modem enables 24-hours Internet connectivity, so you don't have to connect or disconnect every time you want to use the Internet.

Cable modem is faster than dial-up modems, but slower than satellite modem. Dial-up modems use telephone lines and have a speed of 56 kbps. Cable modems compete with DSL modems in the realm of broadband Internet. DSL Internet packages are more expensive than cable Internet packages. DSL Internet service offers dedicated connection, while cable Internet service offers a shared connection, but cable Internet is faster than DSL Internet. Satellite Internet service is faster than cable Internet service, but needs a dial-up modem for uploading data.

A cable modem can be internal or external to the computer, and can also be a part of set-top box. A coaxial cable brings TV and Internet signals to the homes. A single coaxial cable provides hundreds of megahertz. The cable operator offers many TV channels, but each TV channel needs just 6 MHz. Downloading Internet data needs 6 MHz, while uploading Internet data needs 2 MHz. A splitter is used for a line that goes to the TV and the coaxial cable line goes to a cable modem. There is a cable, which is a 10 mbps Ethernet over twisted pair, between the cable modem and the Ethernet card in the PC. The cable modem can also connect to the computer through a USB port, in which case you don't need an Ethernet card. Instead of a coaxial cable, a fiber-optic cable can also be used to bring signals to the whole locality.

Each channel provides a download speed of 27 mbps and an upload speed of 10 mbps. Many users share the same infrastructure without affecting its speed. If more bandwidth is needed, more channels can be used for Internet access. The Internet speed doesn't depend on the distance between the cable operator and the user's home. A cable modem contains a tuner, a demodulator, a modulator, a media access control (MAC) device and a microprocessor. Users of cable modems get dynamic IP addresses. If you have a digital cable, then the set-top box can directly be used to access the Internet.

A device called cable modem termination system (CMTS) is used at the cable operator's end. The link between the CMTS and a cable modem is encrypted with a DES (Data Encryption Standard), for security purposes. The user can also put a firewall between the cable modem and the home network. There is a connection between the CMTS and the cable ISP. One example of cable ISP is the 'Road Runner' provided by Time Warner, and another cable ISP was '@Home', but it has now gone bankrupt.

There is a standard for cable modems called the DOCSIS (Data Over Cable Service Interface Specification), which was created by an organization called CableLabs. Earlier, Motorola hardware would only work with a Motorola modem and was not compatible with any other manufacturer. But now, many modems are tested by CableLabs and are labeled 'CableLabs Certified'. Users can even rent a cable modem from a cable company for a limited period of time, so that when the modem becomes out of date, the user can rent another modem from the cable company. But a user can actually save money by buying a cable modem. A user can buy a cable modem from consumer electronics stores such as Best Buy or even from online stores.The manufacturers of cable modems are Com, Cisco Systems, Com21, Motorola, Nortel Networks, Philips, Thomson, Toshiba, Samsung and Sony.

Businesses that require high-speed Internet connectivity can access the Internet through a cable modem, but they usually get Internet access through a T1 line. The computer using a cable modem should have a powerful processor, video and audio cards. You don't need to have the computer in the same room as the TV. Also it is not necessary to buy cable TV in order to get cable Internet services. The user can send faxes through a cable modem, but he cannot operate a server using a connection provided by a cable ISP.