CABLE MODEMS

1. CABLE MODEMS AC Adapter USB Connection Ethernet By: Jonathan Montovio

2. Cable Modems • For Millions of people, Cable TV has bought to viewers the news, entertainment, and educational programs. • Now Cable TV has upgraded to have Cable internet service for the viewers all over the US. • Cable modems compete with technologies like asymmetrical digital subscriber lines (ADSL). • And people are wondering what the difference is between Cable modems and DSL. Well you are going to find out. • Cable Modems have fiber-optic cables that comes from the cable to neighborhoods in the area. • When a cable company offers Internet access over the cable, Internet information can use the same cables because the cable modem system puts downstream data.

3. Cable Modems • Data sent from the Internet to an individual computer into a 6-MHz channel.So Internet downstream data takes up the same amount of cable space as any single channel of programming. Upstream data -- information sent from an individual back to the Internet -- requires even less of the cable's bandwidth, just 2 MHz, since the assumption is that most people download far more information than they upload. • Between these two types of equipment, all the computer networking, security and management of Internet access over cable television is put into place. • Some cable modems are either inside the computer or external. Which means that the modem is either inside of the cable box to where you only need a keyboard and a mouse.

4. Inside a cable modem

5. Parts in a Cable Modem • Tuner- The tuner connects to the cable outlet, sometimes with the addition of a splitter that separates the Internet data channel from normal CATV programming. In some cases, the tuner will contain a diplexer , which allows the tuner to make use of one set of frequencies (generally between 42 and 850 MHz) for downstream traffic, and another set of frequencies (between 5 and 42 MHz) for the upstream data. • Media Access Control (MAC)- The MAC sits between the upstream and downstream portions of the cable modem, and acts as the interface between the hardware and software portions of the various network protocols. All computer network devices have MACs, but in the case of a cable modem the tasks are more complex than those of a normal network interface card. For this reason, in most cases, some of the MAC functions will be assigned to a central processing unit (CPU) -- either the CPU in the cable modem or the CPU of the user's system.

6. Parts in a cable modem II • Modulator-In cable modems that use the cable system for upstream traffic, a modulator is used to convert the digital computer network data into radio-frequency signals for transmission. This component is sometimes called a burst modulator, because of the irregular nature of most traffic between a user and the Internet, and consists of three parts: • * A section to insert information used for error correction on the receiving end • * A QAM modulator • * A digital-to-analog (D/A) converter

7. Parts inside a modem • Microprocessor- The microprocessor's job depends somewhat on whether the cable modem is designed to be part of a larger computer system or to provide Internet access with no additional computer support. In situations calling for an attached computer, the internal microprocessor still picks up much of the MAC function from the dedicated MAC module. In systems where the cable modem is the sole unit required for Internet access, the microprocessor picks up MAC slack and much more. In either case, Motorola's PowerPC processor is one of the common choices for system designers.

8. Parts inside a modem Demodulator- The most common demodulators have four functions. A quadrature amplitude modulation (QAM) demodulator takes a radio-frequency signal that has had information encoded in it by varying both the amplitude and phase of the wave, and turns it into a simple signal that can be processed by the analog-to-digital (A/D) converter. The A/D converter takes the signal, which varies in voltage, and turns it into a series of digital 1s and 0s. An error correction module then checks the received information against a known standard, so that problems in transmission can be found and fixed. In most cases, the network frames, or groups of data, are in MPEG format, so an MPEG synchronizer is used to make sure the data groups stay in line and in order.

9. How a cable modem works Computer data is sent along frequencies that lie between the 110 6MHz frequency bands carrying TV programming over hybrid fiber coaxial (HFC) cable. Data is sent as a standard Internet Protocol (IP) packets with error correction and a header identifying which subscriber's PC's they are destined for. The wide bandwidth of fiber optics lets you receive downloads realistically at 3- 10Mb/s, fast enough to download Moby Dick in 4.5 minutes, compared to six minutes for a DSL connection and 14 hours with a V.90 modem. Cable is a broadcast medium. Everyone connected to the same distribution hub receives everyone else's downloads, too. This arrangement raises security issues and could cause a slowdown if everyone connected to the same hub downloads at the same time. A coupler/splitter routes TV programming to television set and computer data to the cable modem. Both may be used simultaneously.

10. More on how a modem works Each cable modem ignores all packets accept those addressed to it. The modem reassembles the packets bound for it into a coherent stream of data it sends to a network interface card in the PC. Data going upstream- from your PC to the Internet- gets only seven bands for transmission, limiting upstream data to a realistic maximum of 2aMb/s. High-speed fiber optic cable links each distrubution hub to the cable supplier's own network, which handies email and routes PC data to the Internet through a 45Mb/s T3 connection. The cable network is flexible so that is one part of it crashes, your data is routed through working sections of the network. Slow servers within the Web with only a 1.5Mb/s TI connection can act as bottleneck, not allowing your cable connection reach its full potential. Cable suppliers may cache popular Web pages on its own servers to avoid bottleneck in the Internet itself.

11. There are many companies that manufacture cable modems • Like • Toshiba • RCA Thomson Consumer Electronics • Philips Electronics There are many types of cable modems that are manufactured in the USA for high speed internet service. I know of some cable companies that have Cable Internet such as COX Communications, Direcway, and Comcast.