A Cable Modem Is A Device Media Essay

Published: 2021-08-11 02:25:05
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A cable modem is a device that enables you to hook up your PC to a local cable TV line and receive data at about 1.5 Mbps. This data rate far exceeds that of the prevalent 28.8 and 56 Kbps telephone modems and the up to 128 Kbps of Integrated Services Digital Network (ISDN) and is about the data rate available to subscribers of Digital Subscriber Line (DSL) telephone service. A cable modem can be added to or integrated with a set-top box that provides your TV set with channels for Internet access. In most cases, cable modems are furnished as part of the cable access service and are not purchased directly and installed by the subscriber.
A cable modem has two connections: one to the cable wall outlet and the other to a PC or to a set-top box for a TV set. Although a cable modem does modulation between analog and digital signals, it is a much more complex device than a telephone modem. It can be an external device or it can be integrated within a computer or set-top box. Typically, the cable modem attaches to a standard 10BASE-T Ethernet card in the computer.
All of the cable modems attached to a cable TV company coaxial cable line communicate with a Cable Modem Termination System (CMTS) at the local cable TV company office. All cable modems can receive from and send signals only to the CMTS, but not to other cable modems on the line. Some services have the upstream signals returned by telephone rather than cable, in which case the cable modem is known as a telco-return cable modem.
The actual bandwidth for Internet service over a cable TV line is up to 27 Mbps on the download path to the subscriber with about 2.5 Mbps of bandwidth for interactive responses in the other direction. However, since the local provider may not be connected to the Internet on a line faster than a T-carrier system at 1.5 Mpbs, a more likely data rate will be close to 1.5 Mpbs.
Leading companies using cable TV to bring the Internet to homes and businesses are @Home and Time-Warner.
In addition to the faster data rate, an advantage of cable over telephone Internet access is that it is a continuous connection.
How Cable Modems Work
For millions of people, television brings news, entertainment and educational programs into their homes. Many people get their TV signal from cable television (CATV) because cable TV provides a clearer picture and more channels. (See How Cable TV Works for details.)
Many people who have cable TV can now get a high-speed connection to the Internet from their cable provider. Cable modems compete with technologies like asymmetrical digital subscriber lines(ADSL). If you have ever wondered what the differences between DSL and cable modems are, or if you have ever wondered how a computer network can share a cable with dozens of television channels, then read on. In this article, we'll look at how a cable modem works and see how 100 cable television channels and any Web site out there can flow over a single coaxial cable into your home.
Extra Space
You might think that a television channel would take up quite a bit of electrical "space," or bandwidth, on a cable. In reality, each television signal is given a 6-megahertz (MHz, millions of cycles per second) channel on the cable. The coaxial cable used to carry cable television can carry hundreds of megahertz of signals -- all the channels you could want to watch and more. (For more information, see How Television Works.)
In a cable TV system, signals from the various channels are each given a 6-MHz slice of the cable's available bandwidth and then sent down the cable to your house. In some systems, coaxial cable is the only medium used for distributing signals. In other systems, fiber-optic cable goes from the cable company to different neighborhoods or areas. Then the fiber is terminated and the signals move onto coaxial cable for distribution to individual houses.
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 -- data sent from the Internet to an individual computer -- into a 6-MHz channel. On the cable, the data looks just like a TV 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.
Putting both upstream and downstream data on the cable television system requires two types of equipment: a cable modem on the customer end and a cable modem termination system (CMTS) at the cable provider's end. Between these two types of equipment, all the computer networking, security and management of Internet access over cable television is put into place.
Inside the Cable Modem
Cable modems can be either internal or external to thecomputer. In some cases, the cable modem can be part of a set-top cable box, requiring that only a keyboard and mouse be added for Internet access. In fact, if your cable system has upgraded to digital cable, the new set-top box the cable company provides will be capable of connecting to the Internet, whether or not you receive Internet access through your CATV connection. Regardless of their outward appearance, all cable modems contain certain key components:
A tuner
A demodulator
A modulator
A media access control (MAC) device
A microprocessor
Inside the 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. Since the Internet data comes through an otherwise unused cable channel, the tuner simply receives the modulated digital signal and passes it to the demodulator.
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. Other systems, most often those with more limited capacity for channels, will use the cable modem tuner for downstream data and a dial-up telephone modem for upstream traffic. In either case, after the tuner receives a signal, it is passed to the demodulator.
Inside the Cable 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.
Inside the Cable Modem: 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
Inside the Cable Modem: 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.
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.
Cable Modem Termination System
At the cable provider's head-end, the CMTS provides many of the same functions provided by the DSLAM in aDSL system. The CMTS takes the traffic coming in from a group of customers on a single channel and routes it to an Internet service provider (ISP) for connection to the Internet. At the head-end, the cable providers will have, or lease space for a third-party ISP to have, servers for accounting and logging, Dynamic Host Configuration Protocol (DHCP) for assigning and administering the IP addresses of all the cable system's users, and control servers for a protocol called CableLabs Certified Cable Modems -- formerly Data Over Cable Service Interface Specifications (DOCSIS), the major standard used by U.S. cable systems in providing Internet access to users.
The downstream information flows to all connected users, just like in an Ethernet network -- it's up to the individual network connection to decide whether a particular block of data is intended for it or not. On the upstream side, information is sent from the user to the CMTS -- other users don't see that data at all. The narrower upstream bandwidth is divided into slices of time, measured in milliseconds, in which users can transmit one "burst" at a time to the Internet. The division by time works well for the very short commands, queries and addresses that form the bulk of most users' traffic back to the Internet.
A CMTS will enable as many as 1,000 users to connect to the Internet through a single 6-MHz channel. Since a single channel is capable of 30 to 40 megabits per second (Mbps) of total throughput, this means that users may see far better performance than is available with standard dial-up modems. The single channel aspect, though, can also lead to one of the issues some users experience with cable modems.
Pros and Cons to Cable Modems
If you are one of the first users to connect to the Internet through a particular cable channel, then you may have nearly the entire bandwidth of the channel available for your use. As new users, especially heavy-access users, are connected to the channel, you will have to share that bandwidth, and may see your performance degrade as a result. It is possible that, in times of heavy usage with many connected users, performance will be far below the theoretical maximums. The good news is that this particular performance issue can be resolved by the cable company adding a new channel and splitting the base of users.
Another benefit of the cable modem for Internet access is that, unlike ADSL, its performance doesn't depend on distance from the central cable office. A digital CATV system is designed to provide digital signals at a particular quality to customer households. On the upstream side, the burst modulator in cable modems is programmed with the distance from the head-end, and provides the proper signal strength for accurate transmission.
The History of Cable Modems
In 1993, the first cable modem was developed by a company called Hybrid Networks. The modem provided an asymmetrical Internet connection, meaning that it provided a higher download speed than upload speed. Connections are mostly asymmetrical due to the cost-effectiveness of keeping upload speeds low. Hybrid Networks observed that customers almost always used more of the downstream connection since they mostly were acting as clients, not servers.
History of Cable Modems
In the early 1990s, when the world was just beginning to awaken to the possibilities of digital communications, when the Internet was a tool not of 15-year-olds with web browsers but serious academicians with hulking mainframe computers, a team of enthusiastic engineers were inventing a way to shuttle digital communication streams—the stuff of today's Internet, e-mail, and more—through a new type of "pipe."
This pipe was built, oddly enough, not to deliver e-mail messages and route web pages on request, but to carry television signals. Channels such as Home Box Office, ESPN, and CNN coursed through its high-capacity wires and optical tentacles to a box connected to your television set. It was cable television, of course. Tens of thousands of miles of what the industry called plant, or the physical network of coaxial and fiber-optic cables mounted on wooden utility poles and laced through underground conduits, had been constructed over the last 40 years or so for the single purpose of getting more television to your living room. It worked. Thanks to cable television, by the early 1990s, nearly seven out of ten U.S. homes had access to 60, 70, 80, or more different television channels. The industry ran to big, powerful broadcast networks like ABC, CBS, and NBC, was a $15 billion media titan. Born in the U.S., cable television has migrated to other places; today, cable systems are pumping out dozens and even hundreds of TV channels across every continent.
But beginning in the late-1980s, forward-thinking inventors were interested in cable TV for a different reason than just television. It was a time when the concept of computer networks had taken a firm foothold throughout corporate and institutional America. Large organizations had proven that by removing the desktop PC from its isolated berth and making it part of a bigger, more capable collective, they could accomplish some amazing things. Information that once was hidden from view inside one person's machine could be shared, even enhanced, by many users. Documents were released from the prisons of dusty library shelves and published for all to see. Communications changed overnight. Networking protocols—essentially the rules of behavior, etiquette, and language that allowed one computer to talk to another—became codified and widespread and standardized, and as they did, they proliferated. These rules, which went by names such as Novell and Ethernet, became prominent within corporations and institutions, giving rise to the term local-area network (LAN).
Many engineers and inventors who had marveled at these new tools of communications wondered about ways to translate what was going on inside of companies and organizations to a wider geography. What if they could take information stored inside the mainframe computer of a school building, for example, and make it available to another classroom across town? Instead of a local network, there would be a metropolitan network, able to zoom documents, images, and more. (In an attempt to do just that, in 1990, with the support of my colleague and mentor, Bill Elfer, I formed LANcity.) But it was apparent that to build a metropolitan-area network would require a transmission medium, or a physical foundation, over which the information could move. The existing telephone network was a dense labyrinth of copper wires that lacked the pure transmission speed enjoyed by corporate LANs, which used thick cables that could carry more information, faster. DSL hadn't been proven commercially as a broadband data medium. Speedy transmissions were available over a souped-up version of the telephone system, going by names such as T1 and T3 and ISDN, but they were prohibitively expensive.
Happily, the same sorts of cables used for corporate LANs—coaxial cables—had already been buried and strung all across town by the local cable television company. They could, with a bit of tinkering and some careful engineering, serve as a powerful medium of transmission for data communications—the very sort of instrument that, at the time, lots of companies and institutions were demanding. Businesses, schools, hospitals, and municipal agencies wanted ways to transfer computer files, images, and all manner of written and visual materials across town, or even within their buildings, quickly and efficiently. Many built their own pipes, and some rented expensive slices of extra capacity from the local phone company.
But others couldn't shake the notion that a perfectly capable delivery medium—or perhaps even a superior, faster delivery medium—was literally right outside the door. The cable television industry had built, in some ways, an accidental network. A sleek, fast, multibillion dollar data network that was brought up to believe it was a television medium but seemed suspiciously well-suited for data.
It took several years of toil and persistence, and not a small amount of capital, but ultimately the cable television network would be transformed. LANcity invented the foundation technology for what would become the first so-called "cable modems," or the boxes that, attached to a cable TV system, could transform cable from a medium of television to a medium of digital data. As many had hoped, its speed and its affordability were remarkable. In a perfectly happy coincidence, around the time it was launched, a new force in consumer media began to grip the world. It was called the Internet. Coupled with the cable modem technology that was developed, originally, to help businesses and institutions zap files around the office, the Internet's arrival ushered in a new generation of high-speed, connected households.
The road to cable data services has been a long one. As with most useful technologies, cable modems carry an iterative, storied past. They predate the World Wide Web itself—by at least two decades—although the early models would be hard to pick out of a lineup of 1980s-era metal electronics boxes.
For starters, cable modems of yore were bigger than what lines the shelves of today's electronics stores. Much bigger: The size of a toaster, in many cases. They weren't sleekly packaged for residential ambiance because they weren't meant for homes. They were meant for offices, schools, fire stations, city and county buildings—in short, institutions—not homes.
Also, they were used differently. The Internet, at the time, was a complex linking of universities, government facilities, and sundry technologists. Its communicative abilities were mostly dispersed through electronic bulletin boards, with clunky access methods, over very slow, dialup phone lines. These were the monochromatic days of orange or green type on black screens; when PCs were toddlers, and their operating systems immature; when system crashes and inscrutable technical jargon gave rise, sadly, to rampant PC phobia—"I don't want to touch it, I'm afraid I'll ruin something." (It was the DOS days, for those who remember. Not Windows. Not yet.) The Internet had no World Wide Web. It was great for hobbyists and technologists; it was not suitable for most everyone else.
Cable's Metamorphosis
In these days, if PCs were babies, the cable-television business was in its early 30s. A city-to-city sprint in the 1970s to snatch up city-granted franchises, or the rights to string wires and lay cable across the metropolis, had subsided. Dozens of loosely regionalized cable systems existed. Most cable channel lineups topped out at a capacity of 50 channels. Attracting more subscriptions to basic cable services, and luring existing cable customers toward premium channels, such as HBO and Showtime, was the industry's consuming focus.
Cable plant and its basic architecture was also different 20 years ago than it is today. The use of fiber optics—a given today—to shore up transmission lines, reduce the proliferation of noise-inducing amplifiers, and increase reliability was still hotly debated. (There were people who thought fiber latched to coaxial cable would never work.)
Cable systems started, then, and still now, with a headend, which is like the central nervous system, where TV pictures were collected from over-the-air broadcasts (ABC, CBS, NBC) and from satellite (cable channels such as CNN, TNT, the Discovery Channel, and many more.)
At the headend, pictures and sound were captured and placed into an organized channel lineup, then launched out onto miles of coaxial cable, toward homes. Five times or so per mile, the signal would need a boost by an amplifier. But here, as with the telephone network, boosting the signal meant boosting any noise, too. The more amplifiers strung up like Christmas lights, one after the other, the worse the picture at the end of the line.
The topology of the 1980s cable network was tree-and-branch: Fat cables stretched, north, south, east, and west, from the headend to drop-off points, where thinner cable branched out into neighborhoods. From there, one more branching off, to subscribing homes. It was a one-way architecture that did an adequate job of sending lots of TV channels to lots of viewers. But it was in no way suited for the task of data communications, for a variety of reasons.
One of them—probably the key failing at the time—was that cable-television systems could send signals in only one direction: from a central location to a subscriber's home. They lacked a means to send signals in the reverse direction, or back up the network from the home. In order to work for data transmission, there would have to be a way for users to send data back up the pipe, back through the headend, and out to a wider network where they could find their ultimate destination, be it another computer address, or, later, a World Wide Web site.
The vast majority of cable systems in the 1980s hadn't begun lighting up the path from subscribing homes back to headends—called the upstream path or the reverse path, in contemporary lingo—because there wasn't enough user demand to warrant the investment. But that didn't stop developers from marveling at the sheer carrying capacity of a coaxial cable network, and thinking about ways to harness the industry's bandwidth for more than merely video delivery. It would take an enormous effort to rebuild the cable industry's networks to support two-way communications. But it would also require the invention of a new class of electronics devices that could marry the stuff of data communications technology with the wires, amplifiers, and headend architectures of a modern cable system. Cable had big, fat pipes. It needed a special class of data modems, however, to begin its transformation into a data network.
The cable modem of the 1980s wasn't even called a cable modem. Because it was designed and used primarily by engineers, who tend to be succinct, it was just called a modem, or sometimes, an RF modem, where the RF means radio frequency. Itmodulated (imprinted information), and demodulated (extracted imprinted information). The information was digital—1s and 0s—not video, and it moved on the carriers of the frequencies already contained within the cable's spectral boundaries.
Early cable modems served various purposes. Some cable providers agreed, as part of franchise negotiations with a given city, to link up various city buildings—the firehouse, police department, libraries, schools—with what was called an institutional network, or I-net. With an I-net, the attached buildings could send rudimentary messages to one another over a protected swath of the cable system's existing plant. Unlike today's speedy devices, though, cable modems at the time topped out at about 19.2 kbps. This was blazingly fast compared to dial-up telephone modems of the same timeframe, which crawled along at a feeble 1200 bps, but head-shakingly quaint by today's multi-megabit-per-second standards.
Early cable modems were decidedly less complex, and, as usually correlates, less sophisticated, than today's devices. A message from a connected building was sent from a PC, attached to the toaster-sized modem, upstream to the cable headend. There, the message was simply handed to the designated, protected downstream frequency, without any processing, and was broadcast to all connected buildings. The recipient building received the message through its toaster-sized modem. So did everyone else, but their equipment didn't "see" it, because its address didn't correlate. It was the electronic equivalent of writing a note to one person, and applying this logic: I'll assume everyone is John, and send the message to everyone. But because nobody else is uniquely John, he's the only one who will see to receive it.
The cable-television companies themselves recognized the innate, communicative abilities of the plant they'd built, and they made use of early cable modems for their own internal communicating. Headends aren't always near a telephone line. In fact, they're often located in remote, hard-to-reach areas: the tops of mountains or amid miles of fields. Rather than pay the local telephone company to run a line to a remote headend, why not use modems on either end of the cable lines, already strung? So went the logic. It was the early style RF modem that let cable engineers rig up these internal PBX systems. Great grandparents to these units are still used today for residential telephone service.
Where there's phone, there's data (and vice versa). Soon, engineers figured out a cable modem that could latch T1 speed (1.544 Mbps) data communications over cable plant. They used it to offer leased T1 services to businesses, but there was a hitch: Each company that wanted a T1 line used the equivalent of one full television channel, and few cable operators at the time had vacant channels available. Far be it for a thinking cable company to displace the popular HBO, or ESPN, for a private data network that would serve a few office buildings.
Thus, despite the early success indicators, the cable modem would sustain a 15-year wait before it became mainstream. Three difficult realities confronted pioneers in the field. First was a copious lack of two-way plant, needed to move information from homes to headends as well as it could in the other, broadcast direction. It wouldn't be until the late-1990s that the majority of U.S. cable systems were activated for bidirectional signaling, an absolute prerequisite for true high-speed Internet services.
The second obstacle was the niggling matter of a business model. Activating I-nets kept city fathers happy, true. But on the books, it looked unpleasantly like an all-cost, no-revenue endeavor. Ditto for internal communications. Something was needed that would propel the cable modem into the residential marketplace—the cable-television industry's lifeblood.
The third hurdle to overcome was the equipment itself. In many cases, it was custom built for a particular application. In all cases, it was proprietary to each individual supplier, and certainly not interoperable. That meant that cable companies risked putting their investment in a technology that might be usurped, and quickly supplanted, by a rival method. It meant that the modems sitting in one warehouse and intended for a particular market might not work two communities away. The president of Continental Cablevision, Bill Schleyer, was particularly persistent in raising these questions. The answer ultimately would come in the form of DOCSIS—the Data Over Cable Service Interface Specification penned and trademarked by the cable industry's not-for-profit research and development arm, Cable Television Laboratories Inc., in 1997. DOCSIS was an immediate shot-in-the-arm to the development of cable modems on a more economical, volume-driven foundation. But until then, it was a supplier's market: What they had is what cable providers got.
Bicoastal "Eureka!"
There were a few cries of "Eureka!" along the way to interoperable modem technology, or the ability to use the same modem purchased in California with a cable system in Maine, or anywhere else. They occurred across the U.S. geography, from California to Massachusetts to Philadelphia, in the early 1990s.
One happened in the corporate hamlet of Pleasanton, California, then headquarters to Viacom Cable (a company since sold to Tele-Communications Inc., and later, acquired by Comcast Corp. of Philadelphia). As the story goes, Viacom's director of technology development, Doug Semon, a current member of the CableLabs DOCSIS Certification Board (and a hopeless gadget-head, having built himself a computer long before there were computers), happened upon a cable modem in 1993. It was made by a company known as Hybrid Network Technologies, a nearby Silicon Valley neighbor. Semon was smitten by its applicability as an Internet access device for hobbyists. He noted, too, that the cable modem contained a built-in telephone modem—handy for those cable systems not yet upgraded for bidirectional (two-way) signaling. Semon began to muse about its possibilities. The first thing that came to mind was a more socially significant, and potentially more useful, application of the cable system than the industry-standard local franchise giveaway known as a public-access channel.
A requisite of most government-awarded franchises, the public access channel was a standard television channel made available, although usually sparingly used, for local civic groups and schools to produce video programs. Instead, Semon mused, a cable modem installed in schools and libraries could greatly improve the research resources available to students.
Semon won approval from his supervisors to launch a trial project. He proceeded with a series of modem tests, still working with Hybrid. Early one afternoon, an executive with Hybrid called, agitated, insisting on an immediate meeting. Semon climbed into his car and headed to Cupertino, wondering what on earth was going on. Inside the company's office, the Hybrid executive typed from his keyboard a long string of letters and numbers, starting with "http://www." Using a pre-Netscape, Mosaic-brand browser, available in prototype form only, the two reached out over the Internet to a graphically oriented page, stored on a computer server physically located in Germany. It was one of six known websites on the planet at the time.
Semon rushed back to Pleasanton to describe the significance of what he'd seen to Viacom Cable's president, John Goddard. The Internet, empowered with a graphical interface and called the World Wide Web, looked intriguing. With a consumer-friendly tool, now known as a web browser, it had the makings of the missing ingredient in the quest for a two-way cable architecture: consumer demand. A residential, cable-delivered service that was a good deal faster than dialup methods could be the economic driver the cable industry had been seeking. Previous experience showed that Americans prefer more to better—witness the huge percentage of VCRs set to extended play to record every possible bit of tape, at the cost of better resolution. Americans would probably also prefer faster (cable modem) to slower (dialup phone modem).
A trial ensued, in 1994, to 50 homes in Viacom's Castro Valley, California system, which had already been upgraded for two-way signaling because of a previous interactive television experiment. Hybrid was joined by Intel Corp. and General Instrument Corp. (now owned by Motorola) to provide equipment. The modems sent data downstream (to homes) at a rate of 10 Mbps; upstream information ran at 128 kbps. The state of the art in telephone modems, at the time, was 28.8 kbps.
The results were almost too astounding; consumer acceptance was almost too high. Relying purely on word-of-mouth marketing, Viacom nursed a backlog of some 200 eager subscribers who wanted to be part of the trial. Phrases were coined: "It changed my life," originated by a Chinese subscriber who couldn't regularly contact his family, in China, without his cable modem. "To get this cable modem back, you'll have to pry it from my cold, dead fingers": origin unknown, but widely circulated in industry circles to this day.
Similar revelations were occurring across the cable television industry, in places like Cambridge, Massachusetts, where Continental Cablevision was putting early generations of cable modems to the test. Dave Fellows, a veteran cable engineering executive who was among the first to explore the data-over-cable connection, recalls Continental's efforts in Cambridge, where the cable company charged its first users $100 a month for a residential Internet link.
"By September of 1994, Continental had wired the entire campus of Boston College to the Internet with LANcity modems, offering Internet access in every dorm room on campus," said Fellows.
"I believe the longest, continuously connected-over-cable site is the Cambridge Public Library."
Cable modem trials and deployments were beginning to build across more companies, and more markets, some involving early-day predecessors of modern Internet service providers such as Prodigy and CompuServe. In Philadelphia, where executives with Comcast Corp. also applauded the notion of a Hybrid/Intel/GI modem, Comcast put the gear to work in 50 trial homes within the company's nearby Lower Merion, PA system. The system was picked for its demographics: More than 60 percent of Comcast's Lower Merion customers owned a PC.
In all cases, the cable modems weren't cheap. Each ran upwards of $500. Without standards, scale economics were difficult. Without standards, no single manufacturer might enjoy the rosy promise of high-production volume, and the development of robust competition—a huge influence in driving down prices—was unlikely to come about.
Yet cable companies believed they were on to something. Not since the introduction of pay television services, such as Home Box Office, in the late 1970s had cable companies enjoyed the sudden boom of incremental business that some saw looming in the form of high-speed data communications. One by one, major cable operating companies rushed to explore the boundaries of this potential new application for their medium. Beginning a multi-billion dollar wave of capital investment that would continue for years, they began raising funds to rebuild their cable systems for a data dawn most believed was now at hand.
By the mid-1990s, two of the three coagulants that had gummed the adoption of cable modems 15 years earlier had, for the most part, been dissolved. Activation of the upstream, home-to-headend path was a perfunctory part of cable system upgrades, coast to coast. The ebullient results from Cambridge, Castro Valley, and Lower Merion were spawning enthusiasm from other cable providers to learn more about the technology, consumer acceptance, and business models.
Matters also looked good for cable modems on a macro, telecommunications business level. The Internet was on the rise. The cable and telephone industries, which for the better part of 1990-1994 had been arming for a battle to snitch each other's core businesses—the telcos readying residential video service, cable readying residential phone service—put their weapons aside. That mutual retreat, coupled with the rise of the World Wide Web, afforded a nearly perfect environment to nurture a fledgling new business: extremely high-speed Internet access, using cable modems.
Only one barrier remained: equipment interoperability. Without a standard, cable modems would never be interoperable. It was more than an arcane technology concern. Without interoperability, a thriving market for cable modems was unlikely to emerge. For one thing, modem developers were loathe to commit to huge manufacturing volumes if they feared their proprietary techniques might be sideswiped by unforeseeable technology developments. If volume remained slight, prices would remain high—another concern related to consumers.
It was common, even expected, that most consumer electronics equipment would work properly no matter where its user resided. Without interoperable modems, a customer might purchase a whiz-bang cable modem in Tulsa, Oklahoma, only to find it incompatible, and thus useless, when he moved to a suburb served by a different cable television company. If you've ever navigated a confusing array of electrical power outlet incompatibility while traveling abroad, you have a sense of the sour possibility. And retailers, obviously, would never support, or sell, a technology that threatened to spawn angry customers who were burned by incompatibility issues.
Interoperability issues revolved around numerous technology choices that early developers were confronting. Some suppliers made asymmetrical modems, meaning that more information moved more quickly to homes, than from homes. The reasoning: Sending a click to retrieve a web page requires considerably less bandwidth than the page itself.
Other suppliers, including LANcity, were making symmetrical equipment, believing that as broadband activities increased, residential users would want more upstream speed and girth.
As the enthusiasm for cable-delivered, high-speed Internet grew, so did the list of cable modem suppliers, each with a slightly different way of going about it. It was less a case of "one size fits all," and more a case of "all sizes fit many." And the supplier list was growing. Big-name suppliers entered the scene: 3Com, Cisco Systems, Hewlett-Packard Corp., IBM, Motorola, Northern Telecom, and Zenith.
Smaller suppliers—Com21, LANcity, and Terayon, among others—started to tremble a bit, seeing the specter of big manufacturing ready to stamp out modems like cookies, one after the other, for prices much more attractive than they could offer. It was a market share sprint, where everyone moved as quickly as possible in a non-standardized, proprietary environment. Standards, in 1995, were the mantra: Everyone endorsed standards, provided that the standard centered on their technology. (When that didn't work out as intended, from the viewpoint of some of the larger players, such as H-P and IBM, they retreated from the scene.)
In those days—1995—standards were largely a new concern for the cable industry, at least as it related to in-home electronics. During the 1990s, cable had outfitted its headends, plant, and subscribing homes with equipment made by a short list of manufacturers. It made for an innately tense coexistence for both suppliers and cable providers. The lead suppliers held most of the control over pricing and features; namely, when the former would go down, and when the latter would get included.
By late 1995, a small group of cable technologists began to meet privately to discuss a clandestine silicon chip made by a clandestine, Silicon Valley company called MicroUnity. The chip, unlike every chip used up until then, was completely programmable. That meant the chip could be put inside set-tops and cable modems and later be updated with applications as they changed. The alternative was the status quo: new service, new box. New boxes, for cable providers, carry steep capital and operations expenses. There's the extra cost of the box itself, and then there's the cost to send someone out to install it, known in the lingo as a truck roll.
The cable technologists—leaders from Tele-Communications Inc., Time Warner Cable, Comcast Cable, and Cox Communications—thought enough of MicroUnity's programmable silicon idea to both invest in it, and form a private holding company that would steer its use in cable hardware. They called the company MCNS, which stands for Multimedia Cable Network System.
As the discussions matured, it became clear that the driving motivator for MCNS was to attract more hardware suppliers into the cable business, and to be released from the perceived pricing and features stranglehold of the industry's big suppliers. The only way to go about it was to insist on interoperability among cable equipment providers. The only way to garner interoperability was to develop a standard.
Enter CableLabs, the Colorado-based research and development arm of the cable television industry. What started as MCNS soon became the Data Over Cable Service Interface Specification, or DOCSIS (pronounced dock-sis). Realizing the strategic importance of cable modems and high-speed Internet services, CableLabs, in November 1996, put the project on fast-track status, girding to have a complete specification written by the end of the year.
By mid-1997, the specification was ready to undergo lab tests of prototype DOCSIS gear at CableLabs. The intent was to provide an ongoing incubator for the vendor community, to sample and test the specification.
In September 1997, CableLabs released a detailed certification program, and formed a Certification Board to review, and ultimately approve, products that met the DOCSIS specifications. It was decided that makers of the headend part of high-speed cable Internet systems, known as Cable Modem Termination Systems (CMTS), would be tested to qualify with the specification, and makers of cable modems would be tested to be certified, for which they received a DOCSIS-certified sticker.
Certification Begins
Two years and three certification test waves would transpire before any vendors' products became DOCSIS-certified. On that fateful day—March 20, 1999—Cisco Systems received qualification for its CMTS. The first certified cable modems came from Toshiba and Thomson Consumer Electronics. A month later, modems made by 3Com, General Instrument, and Arris Interactive passed certification, and in ensuing months, dozens of products made the DOCSIS cut. To this day, many of those who follow broadband's development credit the cable industry's speedy effort to rally around a common standard as the key reason why cable companies currently lead DSL in the U.S. broadband deployment race.
Meanwhile, success stories about cable modems and high-speed Internet services continued to accrue. So-called early adopters were literally lining up for cable modems. The industry itself was thrilled to satisfy the demand, for reasons that went beyond pure economics. In the 1990s, the cable industry's perception as the poster child for poor customer service was at its peak. (Remember the less-than-flattering 1996 movie, The Cable Guy?) Everybody likes some positive attention, sometimes. Water-cooler talk elicited smiling stories of truck chasers, ordinary citizens who ran after cable trucks, arms waving, to beg for cable modem service.
Across the nation, in rollouts of high-speed Internet service, consumer demand far outstretched the supply of technicians who could install the service. (At the time, two were needed: one to handle the cable modem, and one to handle the PC.)
Business models were emerging, some quite dramatic. In Palo Alto, California, the local cable provider, a cooperative known as the Palo Alto Cable Co-Op, sampled the high-end pricing range—and it worked. Reasoning that Pacific Bell (now SBC Communications) charged between $200-$1000/month for ISDN and T1 service, the cable co-op debuted a three-tier pricing card for its high-speed cable modem service: $99/month, $399/month, and $599/month. It immediately signed 60 customers, and vowed that data revenues would exceed video revenues by 2001.
By the end of 1998, the North American cable industry counted 550,000 cable modem subscribers. That grew to 1.6 million by the end of 1999 and five million a year later. At the end of 2002, there were more than 16 million. Over the same time span, the cost of cable modems has declined steadily, from $500 or more in the mid-1990s, to the low $120 range by summer of 2001. The sheer enormity of DOCSIS, and its speed to adoption, is an indisputable success story. The momentum behind cable's new data delivery business spawned entire new companies including Time Warner's RoadRunner high-speed cable modem service, and the much-celebrated but short-lived @Home Corp., a collaboration among investment bankers and several large cable companies. @Home built a sprawling backbone network and an entire service and content infrastructure to support the newborn cable Internet category. The high-flying, high-profile Silicon Valley company ultimately was destroyed by infighting with its partners and the inability to continue service agreements with the cable companies that once supported it. But in its brief history, it provided a jump-start that allowed the cable industry to grab a dominant market share of the broadband residential marketplace.
DOCSIS itself has continued to develop. Cable modem circuitry is now available on slide-in, PC cards, on chips built right into PCs, and in Europe, it's inside set-top cable TV boxes that are connected to TV sets. The successor version, DOCSIS 1.1, folds in the ability to deliver quality-of-service standards that support the next generation of broadband services. These will go beyond mere Internet data to span such services as digital telephony and true video that's layered over a two-way, DOCSIS-paved Internet Protocol path.
In the unfolding story of broadband, cable television has fashioned for itself a prominent role. And DOCSIS can honorably be immortalized as its true beginning.

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