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`NETWORKING (/CATEGORY/NETWORKING-HARDWARE)
`How It Works: Cable Modems
`
` SEARCH
`
`By Andrew Brandt (/author/Andrew-Brandt/), PCWorld
`
`Dec 13, 1999 12:00 AM
`
`How It Works: Cable ModemsThe second in our series of primers explaining today's
`leading technologies. Michael Gowan
`Cable modems: devices that provide high-speed Internet access using cable television
`networks.
`
`Pro: fast data-transmission rates; always-on connection; least expensive broadband
`option.
`Con: no Internet service provider choice; bandwidth is shared with neighbors; not
`available in all areas.
`
`These days, the cable that brings you MTV and CNN can also bring you the Internet.
`Some cable companies have expanded their services to include high-speed Internet
`connections for home users. Like its rival Digital Subscriber Line, cable modem service
`lets you get on the Net without having to dial in.
`
`Cable access theoretically allows downstream speeds of up to 38 megabits per second,
`but actual rates are considerably slower. PC World test results, published in March
`1999, showed that downstream speeds (from the Internet to you) over cable modems
`averaged 382 kilobits per second, while upstream rates (from you to the Internet)
`averaged 315 kbps. But those speeds are still about seven times faster than what you
`get with standard modems.
`
`One reason you'll rarely see the top speeds: Cable modem users must share bandwidth
`with everyone else on the network. The more people online at any moment, the slower
`your access will be. Unlike standard modem access, which creates a one-to-one circuit
`between your PC and your Internet access provider, cable access uses what's called a
`branching network. In such a network, a device called a cable modem termination
`system at your cable company's central office sends out signals along a main line. That
`main line then splits into "feeder lines." All subscribers along a given feeder line must
`share its overall bandwidth. Your cable modem converts the incoming signals into data
`your computer can understand and then sends it to your computer through an Ethernet
`card.
`
`Two types of cable systems are currently in use: coaxial and fiber optic. The older
`coaxial cables max out at 350 MHz and can't send signals upstream. To get around the
`latter problem, the cable company uses the phone line to send data upstream. The
`newer fiber optic networks support rates up to 750 MHz and allow two-way traffic, in
`which the upstream data typically uses some portion of the 5- to 40-MHz frequency
`range. Whichever system is used, cable companies split all available bandwidth into 6-
`MHz channels and assign those channels to individual networks, such as ABC or NBC.
`For Internet access, one of these 6-MHz channels is dedicated to moving data
`downstream; fiber optic systems dedicate another channel to upstream signals.
`
`How It's Sold: Cable Modems
`
`Petitioner Apple Inc. - Exhibit 1071, p. 1
`
`

`

`Cable is ahead of DSL in deployment--more than 1 million people currently surf the Net
`over cable, and another 32 million living in Net-ready cable markets could if they wanted
`to. Forrester Research predicts that about 20 million people will use cable to access the
`Internet by 2003, compared to about 8 million DSL subscribers by the same year.
`
`For now, cable Internet access is restricted primarily to home users; cable companies
`didn't wire downtowns or business parks, so many businesses are out of luck. In most
`markets, service costs from $30 to $40 a month, although in some areas the cheapest
`access will cost $70. Downstream speeds at those price levels range from 256 kbps to
`512 kbps. But the faster you want to go, the more it will cost: 2 mbps downstream, 1
`mbps upstream runs upward of $500 a month in some places.
`
`You first need to find out if your local cable service offers Internet access. If it does and
`you want to get set up, be aware: Unlike DSL and standard modem service, cable
`service gives you no choice in ISPs. Time Warner cable systems, for example, work
`only with a provider called Road Runner; AT&T works only with Excite@Home. Cable
`companies have been reluctant to open their wires to unaffiliated ISPs, claiming they've
`invested too much in the system to lease the lines to other companies. ISPs have filed
`lawsuits to gain access to the lines, and they've won some local cases, which the cable
`companies have appealed. AT&T has recently softened its stance, announcing that it's
`willing to share its lines with other ISPs, though that won't likely happen until 2002.
`
`On your end, you'll need an Ethernet-equipped computer and a cable modem. The
`modems are produced by a number of companies, including 3Com, Motorola, and
`General Instruments. Some cable companies rent modems and include the fee in the
`monthly service charge; others require you to buy them for about $200 to $300.
`
`At this time, it's best to get a modem through your cable company. Different cable
`companies use different modulation schemes, and your modem must use the same
`scheme used by the cable company. While an industry standard called Data Over
`Cable Service Interface Specification has been approved, it won't be fully implemented
`for another year or so. When DOCSIS is universal, you'll supposedly be able to use any
`modem you want.
`
`A cable service technician may need to install your modem and a splitter. If you already
`subscribe to cable television, you need a splitter to separate the lines to the television
`and the computer. You can order cable Net access without having a cable television
`connection, but some companies will charge more for that arrangement.
`
`For additional information, take a look at the sites for the Cable Modem University and
`CableLabs.
`
`Michael Gowan is a staff editor for PC World Online.
`
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`Petitioner Apple Inc. - Exhibit 1071, p. 2
`
`