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. This modem offers a 20-100 Mbps of bandwidth or high speed, making it easier to download large audio/video files. It enables 24-hour Internet connectivity, so, you don’t have to connect or disconnect every time you use the Internet.

Cable modem is faster than dial-up modems, but slower than a 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. However, 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 modem can be internal or external to the computer and can be a part of a set-top box. A coaxial cable brings TV and Internet signals to the homes. A single coaxial cable provides hundreds of megahertz of bandwidth. The cable operator offers many TV channels, but each one needs just 6 MHz. Downloading Internet data needs 6 MHz, while uploading needs 2 MHz.

A splitter is used for a line that goes to the TV, and the coaxial cable line goes to a modem. There is a cable, which is 10 Mbps Ethernet over twisted pair, between the cable modem and the Ethernet card in the PC. The modem can also be connected to the computer through a USB port, in which case you do not require 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 does not 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 these devices get dynamic IP addresses. If you have a digital cable, 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. A link between the CMTS and the modem is encrypted with a DES (Data Encryption Standard) for security purposes. The user can also put a firewall between this type of 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 went bankrupt.

There is a standard for cable modems called the DOCSIS (Data Over Cable Service Interface Specification) that 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 modem from a cable company for a limited period of time, so that when a modem becomes outdated, the user can rent another modem from the cable company.

However, a user can actually save money by buying one. It can be bought from consumer electronics stores, such as Best Buy, or even from online stores. Some of the leading manufacturers are Cisco Systems, Motorola, Philips, 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 modem should have a powerful processor, and video and audio cards. You do not 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 modem, but he cannot operate a server using a connection provided by a cable ISP.