Cable Modems to the Rescue?

Despite the hoopla over 56 kb/s technology, dial-up modems have reached an evolutionary dead end. Little more information-carrying capacity can be squeezed out of 3.3 kHz telephone channels. Besides, the promised 56 kb/s can only be achieved in one direction - and then only when all the planets are precisely aligned.

Telcos are promising high-speed alternatives such as ISDN and digital subscriber line. But these technologies suffer from distance limitations, are notoriously difficult to provision and have been slow to arrive. In contrast, cable modems work over existing cable networks, offer throughput well above basic rate ISDN and can configure themselves automatically.

Although the cable TV industry has been thoroughly criticized, it basically has done the right thing. It has researched and tested what were supposed to be lucrative new markets - from highly speculative "interactive television" to cable-based telephony. But the industry never found a market for interactive TV, and plenty of evidence suggests that cable networks were not cut out to deliver POTS. To have retreated on these fronts is a sign of wisdom.

But the Internet presents an entirely different opportunity. Tens of millions of users have become addicted to multimedia content. People were so desperate for untethered access that they were willing to put up with unreliable analog cellular telephone. They want multimedia communications so badly that they are willing to put up with excruciatingly slow dial-up modems. Unlike interactive TV, the market for Internet access is real.

"Even taking into account deployment delays, cable modems are still faster than anything the competition has - or will soon have - to offer," says Leslie Mitts, a consultant with Trident Consulting Group. Cable TV networks pass 90 million U.S. households. And although the majority of cable networks have not been upgraded to two-way, there are cable modem products for every type of cable network.

Cable modems offer qualitatively better performance than either dial-up modems or basic rate ISDN terminal adapters. At speeds measured in megabits per second, Internet access is an entirely different experience. Users can literally flip through Web pages - assuming that cable operators are careful to avoid other bottlenecks (Table 1).

Things are even better for users who can access two-way cable networks. They can remain connected to the Internet all the time - with instant access to on-line information. Two-way networks also offer sufficient upstream throughput for exciting applications such as Internet telephony, Internet videoconferencing and Web page hosting - applications that may be of particular interest to small office/home office users.

Cable modems also offer benefits to business organizations such as the ability for more employees to telecommute. Some manufacturers enable organizations to create virtual private networks, permitting users working from home to access colleagues at home or at the office. Other manufacturers support multiple users, making cable modems attractive to small businesses located in or near residential areas.

Talk to any cable modem vendor and you will get an earful of statistics: the number of households passed by cable networks, the number of households that subscribe to cable TV, the number of households with PCs and the number of households already on-line. Everyone is banking on capturing a "reasonable" fraction of a large number - perhaps 15% of the approximately 90 million homes passed by cable networks, or around 14 million users.

Although the cable TV industry has talked about enhanced services for years, clearly it is reluctant to upgrade to two-way at a time when it faces serious competition from direct broadcast satellite.

Fortunately, it is possible to enter the Internet access market with existing one-way networks. The trick is to use the cable network for the downstream and a telephone "return" for the upstream. This is an asymmetrical solution. But then, Web browsing is an asymmetrical application - most of the data flows from the Web to the user. However, cable operators still must purchase significant headend equipment - spending as much as $75 per PC user.

At last count, more than 40 cable modem commercial trials and launches were taking place in North America, and more than 20 manufacturers were offering cable modems. Tele-Communications Inc., Comcast and Cox are launching data services under the @Home brand at prices ranging from $30 to $50 a month plus a one-time set-up fee. Several industry forecasters believe cable modems will be rolling out in earnest this year and taking off in 1999 or shortly thereafter.

Defining the service Most cable TV networks were built to operate one way. Adapting them to two-way communications is not easy because cable TV networks were designed as "tree-and-branch" networks. While broadcasting to the branches works fine, the noise from all the branches converges at one point when users transmit in the opposite direction.

The typical cable TV network consists of a headend with links to program sources, trunk lines to major service areas, distribution or feeder cables to neighborhoods and cable drops to homes equipped with terminal equipment.

Cable TV networks employ coaxial cable and possess up to 1 GHz of usable bandwidth. The downstream consumes the most bandwidth - from 54 MHz up to the maximum level, which usually is 600, 750 or 1000 MHz. While this is considerable bandwidth, it must carry dozens of full-motion, color video broadcasts.

The upstream is typically assigned 5 to 42 MHz. Unfortunately, a cable TV network acts like a giant antenna, and many sources of interference and noise are in this part of the spectrum. Those sources include amateur and citizens' band radio, as well as noise generated from household appliances such as vacuum cleaners and TV sets. Poorly constructed drops and bad connections within the home are common points of entry for unwanted signals and noise.

To use cable TV networks for two-way data, operators must circumvent these problems. The simplest solution is the cable modem with telco return. Some models feature integral modems, while others work with external modems. The big drawback to telco return is that it ties up a phone line. But because many users will be upgrading from pure dial-up modem operation, this should not be a big obstacle.

Some applications, however - including Internet videoconferencing - require a high-speed upstream channel. This can be provided by two-way cable modems operating over two-way cable networks. About 15% of U.S. cable TV networks have upgraded to a hybrid fiber/coax (HFC) design supporting two-way transmission. But analog cable networks can also be upgraded at lower cost by converting to bidirectional amplifiers. Some two-way cable modems require HFC networks, while others claim to work over bidirectional analog networks.

Another problem - at least in some peoples' minds - is the lack of a standard permitting any cable modem to work with any headend equipment. Work toward a multimedia cable network system specification was initiated by Cablelabs, a consortium of Time Warner, TCI, Comcast, Cox and Continental Cablevision. This specification defines the physical layer, media access control layer and operational support capabilities. It is being cast in silicon by chipset manufacturer Broadcom Corp. and has received compliance commitments from 3Com, Bay Networks, Cisco Systems, Com21, General Instrument, Hewlett-Packard and Scientific-Atlanta.

But not all cable modem manufacturers are ready to comply with a standard. Some believe they have a superior solution, and others are simply in no rush to let customers incorporate other vendors' cable modems into their headend gear.

Not everyone assumes the major opportunity for cable data is letting PCs borrow cable TV's high-bandwidth infrastructure. Some point out that cable TV networks already are connected to a popular multimedia terminal: the television set. Unlike PCs, TVs are easy to use, not subject to rapid obsolescence and are already hooked up to cable networks.

WebTV is a low-performance way to turn a TV into a network PC. WebTV uses a special set-top box as well as a dial-up modem.

Worldgate Communications has developed a high-performance solution that leverages the cable TV infrastructure. Worldgate uses either a telco return channel or a low-speed cable return channel - originally developed for pay-per-view - to give TV viewers limited access to the Internet. Many TV advertisers now provide their Web address at the end of their commercials. Worldgate permits the viewer to access that Web page with a click of the remote.

When the viewer clicks the remote, a signal is sent to the network's headend. The network knows which channel the viewer is watching. A computer at the headend conducts a database search, matching the channel and time to the scheduled commercial and associated Web address. It then broadcasts that Web page to the TV set. The only prerequisite is that viewers must have either an advanced analog or digital set-top box to properly display computer text on their TV.

The Web page is broadcast at 100 kb/s using the TV signal's vertical blanking interval (VBI). During this time, the scanning beam retraces from the lower right to the upper left corner of the screen. Data may be sent piggyback over a TV signal during part of the VBI. About half of the VBI is reserved for closed captions and frame synchronization. Worldgate supports up to eight simultaneous sessions per VBI channel.

Worldgate is currently running on several systems with "friendly" users. Full commercial service is expected this summer for around $4.95 a month, with ad agencies paying 5› to $2 for each valid click of a viewer's remote. Whether viewers will help subsidize another form of advertising remains to be seen. Worldgate is working with Comcast, Adelphia, Telewest U.K. (Britain's second largest cable operator), Charter Communications and Continental Cablevision to distribute its service.

Another solution, Intel's Intercast, does almost the opposite. With Intercast, the PC receives TV programming plus related data over the VBI. Intercast works with either broadcast TV or cable, but so far only a few program sources support it, including CNN, MTV, NBC and QVC. The basic idea is to transmit the data and cache it at the PC. Users can have virtually instant access to any portion of this information that may interest them.

The virtues of variety One reason to be optimistic about cable modems is the variety of vendor strategies. There are solutions for different types of cable networks and different types of users. Some vendors have found ways to produce surprisingly inexpensive cable modems; others are focusing on added-value features for early adopters and business users.

Scientific-Atlanta is betting that cable modems with telco return will succeed first. The company's dataXcellerator sells for as low as $200 in large quantities - a price that is all the more amazing considering that the unit comes with an integral dial-up modem. Scientific-Atlanta's downlink runs 6 Mb/s over a 3 MHz channel and is split into five 1.2 Mb/s subchannels. The company also plans to introduce a two-way cable modem.

Motorola is making a big push into broadband networks. Its two-way CyberSURFR supports up to eight computers. Motorola has made several innovations, including superior upstream communications thanks to a robust modulation technique and the ability to hop to a different channel to avoid noise.

The CyberSURFR's Auto Provisioning feature permits the headend to "discover" the installed cable modem, relieving the installer from configuring it manually. The CyberSURFR's IP Filtering allows cable operators to offer tiered services such as virtual private networks.

Motorola has announced a deal with Time Warner for 300,000 units and a deal with Comcast for six launches in conjunction with Mountain View, Calif.-based integrator @Home. Motorola also has made about 10 investments in pre- and post-launch vendors such as Worldgate.

Com21 is developing an ATM-based cable data system called ComUnity Access. Its ComPort cable modems run at 30 Mb/s downstream, with up to 12 2.56 Mb/s upstream channels.

GI's Surfboard network interface card, the SB1000, runs at 27 Mb/s downstream, uses a telco return and boasts Windows 95 support. The PC card version is available for as little as $199 in large volumes and eliminates the need for an Ethernet adapter. Most external cable modems require installing an Ethernet adapter in the PC to handle the high-speed communications. The Surfboard works with most existing dial-up modems. Continental Cablevision began offering data services using GI's Surfboard last summer.

Terayon uses a unique technology called synchronous code division multiple access (S-CDMA). S-CDMA is similar to the CDMA used in cellular and personal communication services networks, except it exploits the fact that two-way cable modems communicate over fixed paths (Figure 1).

While wireless - or asynchronous - CDMA networks treat other users on the same channel as noise, Terayon's S-CDMA can eliminate the other users, providing enhanced noise and interference immunity. Terayon claims S-CDMA is superior to the dynamic channel allocation techniques used by other cable modem vendors. Other techniques search for narrow openings, while S-CDMA uses the entire bandwidth.

The big advantage of S-CDMA, however, is that it enables robust two-way transmission - 14 Mb/s in both directions - over existing cable TV networks. While other cable modems struggle to cut through the noise, Terayon's S-CDMA technology renders most of the noise harmless. An upgrade to bidirectional amplifiers is the only requirement. Cisco has invested in Terayon.

Bay Networks' Cable Modem Division also is supporting two-way cable networks with its LANCity products and is extremely bullish on cable data, with more than 50,000 units in use and another 50,000 units in the hands of resellers. The company insists that two-way networks are needed to support high-end applications such as videoconferencing that set cable data apart from its competition.

Bay Networks points out that in many parts of the world, cable TV systems are newer and were built to support two-way transmission. The company has about 400 cable modem installations worldwide, including China, India, Europe and Asia.

Why is the company so bullish? According to Bay Networks, today's two-way cable data technology is more robust and consumer-oriented. While the cable industry has been testing two-way data for years, only now does it have cable modems that outrun ISDN terminal adapters for about the same cost. Like Motorola's CyberSURFR, LANCity products include features to ensure "plug-and-play" operation.

Bay Networks also points out that 5 to 18 MHz is where most noise is found, while 18 to 42 MHz is generally quiet. LANCity products run 10 Mb/s in both directions. In the upstream, Bay Networks' Unilink protocol employs contention techniques under light load, switching to a reservation system under heavy load. This allows the modem to optimize both throughput and response time. Like Terayon, LANCity products require an upgrade to bidirectional amplifiers.

Other cable modem manufacturers include U.S. Robotics, Hayes, Hewlett-Packard, IBM and Intel.

One thing is certain: Cable modems are fast. And as Trident Consulting Group's Mitts points out, "Speed is something people are willing to pay for." But the cable TV industry doesn't have to rely exclusively on home-based users. Many suburban office parks have access to cable TV networks.

The only way to find out if people are willing to pay $30 to $60 a month for high-speed Internet access, however, is to offer it. Once users try it, it will be very difficult to go back to pure dial-up. High-speed Internet access is not just a time-saver. It is an entirely different experience that opens the door to a constellation of new applications.

Ira Brodsky is President of Datacomm Research Co., Wilmette, Ill.