Gigabit-class broadband is capturing the imagination of Internet users throughout the country. With Google and other companies bringing fiber-based services that deliver a gigabit of data each second to the home, communities are accelerating their push to get the highest speeds.

A consumer who really needs 1,000 megabits of bandwidth is probably a rare creature, but excitement over fiber deployments shows there is at least some demand for what is a ludicrous speed compared to most home Internet connections.

Cable companies haven't been ignoring this consumer demand… but they haven't done anything to satisfy it, either. Comcast demonstrated the "first ever 1Gbps broadband speed download over a production HFC [hybrid fiber-coaxial] network" two and a half years ago at the NCTA [National Cable and Telecommunications] conference, and the company showed off a 3Gbps technology at this year's cable show.

"Is there anywhere else in the ecosystem where somebody demonstrates something that's really cool and great, and faster and better, and doesn't put it out for more than two years?" Blair Levin, a former FCC official and current executive director of Gig.U , told Ars. "Would Apple ever say, 'here's a phone we're thinking about doing, maybe a couple years from now you'll get it. We could do it today but… no, we're not going to do that'?"

Version 3.1 of DOCSIS (the Data Over Cable Service Interface Specification) is expected to support multiple-gigabit download speeds. DOCSIS 3.1 gear isn't on the market yet, but DOCSIS 3.0 can already support about a gigabit efficiently (or more than a gigabit inefficiently), the organization that manages the spec told Ars.

Yet the fastest cable offering available nationwide from Comcast is 105Mbps down and 20Mbps up. Time Warner Cable's top tier is 100Mbps. Cablevision's Optimum service tops out at 101Mbps.

"We are also trialing a 250/50 Mbps tier using DOCSIS 3.0 in select markets to test consumer interest," Comcast spokesperson Charlie Douglas told Ars. "The interest in these ultra, ultra high-end speed tiers is today still rather limited."

Comcast's data overage fees might put a damper on customer enthusiasm for speeds in the hundreds of megabits. Comcast actually does deliver a half-gigabit to home customers, but that offering relies on fiber to the premises rather than cable. The 505Mbps down and 100Mbps up service is available in some markets for $399.95 a month, nearly six times the price of Google Fiber.

No technological barrier prevents gigabit cable Internet

DOCSIS 3.0 is the dominant specification powering new cable modems today. Matthew Schmitt, director of DOCSIS specifications at CableLabs (the consortium that manages DOCSIS), said 3.0 can comfortably hit about a gigabit. DOCSIS 3.0 gains bandwidth by bonding together 6MHz channels, each of which can carry about 38Mbps. A 24-channel modem could deliver 912Mbps downstream, and 32 channels could boost that to 1.2Gbps.

The DOCSIS 3.1 specification was recently released, and equipment based on it will far outstrip today's products. "There's product development underway to our understanding," Schmitt said. "At this point there are no products out."

3.1 is much more efficient because it uses a new type of "forward error correction" that lets cable equipment pack more data into the same amount of space. But cable providers could offer gigabit bandwidth with today's DOCSIS 3.0 equipment if they really wanted. DOCSIS 3.0 wouldn't be ideal for multi-gigabit Internet connections, but it can provide "around a gigabit" cost-effectively, Schmitt said.

"If you want to go by pure technical capability, you could go to very high speeds with DOCSIS 3.0," he said. "What we think 3.1 brings to the table is a more cost-effective way of getting there."

DOCSIS 3.0 requires modems to support at least four downstream and four upstream channels. In practice, a typical DOCSIS 3.0 modem bonds eight downstream channels and four upstream ones, providing data rates of about 300Mbps down and 100Mbps up.

DOCSIS 3.0 modems with 24 channels have existed for a while, though. Hitron unveiled a 24x8 (24 downstream channels, eight upstream channels) device back in May 2012. Netgear announced the certification of a 24-channel gateway a year ago. Modem manufacturers are dependent upon chipmakers such as Intel and Broadcom, who are now making 24- and 32-channel DOCSIS 3.0 chips that can provide gigabit bandwidth from a single chip.

"16- and 24-channel DOCSIS 3.0 gateways are available and are being deployed in subscribers' homes now," a Cisco spokesperson told Ars. (Cisco's residential gateways combine a cable modem, router, and wireless access point in one device.) "As you would expect, the 16-channel deployments are leading the 24-channel deployments at this point. The overall volumes are low compared to the eight-channel devices at this point. However, we expect to see the 16-channel and 24-channel devices ramping over the next 12 months." 32-channel products are expected to be "available in the second half of next year."

Arris, another prominent modem manufacturer, declined comment.

Even if all customers had gigabit-capable modems, back-end upgrades in cable plants are still required to provide that bandwidth. The industry consensus is that it makes more financial sense to perform those upgrades after 3.1 technology is ready, said John Chapman, CTO of Cisco's cable access business.

Wait till 2016

While DOCSIS 3.1 products may be available next year, the first deployments to home customers aren't expected until at least 2015. A CableLabs presentation says that trends indicate there will be "1Gbps premium offers in 2016 or later."

Besides replacing modems, cable companies would have to address cable modem termination systems (CMTS) that reside in their facilities.

"I can't share what we spend, but we spend an enormous amount of money on CMTSes," RCN VP of network services Peter Jacoby told Ars. Offering gigabit speeds with DOCSIS 3.0 "would be prohibitively expensive," he said.

RCN, a cable provider in the northeast US, offers residential service of up to 110Mbps download and 15Mbps upload. Customers won't always get their maximum speed, since bandwidth is shared among neighbors. RCN provides enough to each set of customers that each individual user will get the advertised speed "a statistically very high percentage of the time," Jacoby said.

RCN prioritizes download speeds over upload to match both customer usage patterns and the existing technology. "Cable was built to get a lot of bandwidth to the home because back in the day it was broadcasting a ton of bandwidth and it was only in one direction," Jacoby said. "There's not a ton of RF spectrum allocated for the return."

If customers aren't getting their promised speeds, "we need to upgrade or split that group" so that fewer people are served by the same node, he said. "This capacity management is the key; it's the secret sauce to offering a service that ensures customers get what they want, because the customers are always using more [than they did last year]."

Like many cable providers, RCN offers gigabit or even 10 gigabit service to businesses, running fiber to the premises. Business-class service level agreements provide bandwidth guarantees that residential customers don't get. Technically, residential customers could buy the business-class fiber-to-the-home service, but they'd have to pay a custom price that makes it unlikely anyone would ever want to do so.

"There's no technical reason we couldn't," Jacoby said. As for how much it would cost, "we'd have to look at how far you are from our fiber now. There's fiber to the node and then we dedicate a fiber at that node and we'd build that fiber to your house."

Cable networks are already a mix of fiber and coaxial cable. "We have fiber out on the telephone poles, probably in your neighborhood, and that fiber goes to a node," Jacoby said. "From that node is a media converter that changes it from fiber into coax and the coax then goes to all the houses and MDUs [multi-dwelling unit] etc."

Most Comcast customers pay for 25Mbps or less

Douglas said Comcast's current speeds already satisfy customer demand. Only 34 percent of Comcast residential customers choose a speed tier faster than 25Mbps, he said.

"We’ve increased speeds 12 times in 11 years. As you’ve seen from our track record, we’ll continue to increase speeds well in advance of consumer demand for them," he said.

While Comcast cable tops out at 250Mbps, the company's 505Mbps residential service is a "point to point fiber product that is leveraging commercial grade equipment that we typically use with our business service customers," he said.

Comcast's cable modems use eight channels, making the technical limit a little over 300Mbps. Why not offer 300Mbps?

"A lot of it has to do with the plant and the infrastructure and how many channels we have available to bond in different markets," Douglas said. The number of homes sharing each node affects how much bandwidth Comcast can reliably promise, he noted. "It’s something we do all the time, … split a certain percentage of nodes and increase capacity in different markets and different neighborhoods," he said.

Comcast bandwidth in excess of 505Mbps will have to wait until DOCSIS 3.1 equipment is readily available.

"As the equipment manufacturers begin to make [DOCSIS 3.1] modems that are in that sweet spot for consumers, then we can use our existing plant and our existing infrastructure to deliver speeds far in excess of 505Mbps," Douglas said. Tests and pilots will be necessary before rolling anything out on a broad basis.

Since competition is scarce, why bother matching the speed of fiber?

Although vendors promise that it's coming (eventually), some observers believe there just hasn't been enough competition to spur a large-scale shift to gigabit cable speeds. Cable vendors have been forced to offer better deals or upgrade their marketing in communities with competition from fiber. But fiber deployments are still limited, and most US consumers have little choice among Internet providers.

"I think it is a business model issue," Levin said. "Since the early days of cable Internet service, the model has been scarcity based, designed to sell different packages to different consumers at different price points. Google Fiber is the first package that is designed to sell abundance."

The industry's economics "make it problematic for them to convince Wall Street that it's a good thing to do to deliver that gig," he said.

NCTA CEO Michael Powell has said DOCSIS 3.1 will help cable maintain its competitive edge against Google Fiber and similar services. Some are skeptical of cable's ability to keep pace with fiber, though.

"That DOCSIS limit is purely theoretical and depends on ideal conditions," James Benham, a software company owner and City Council member in College Station, Texas, which is attempting to lure a fiber provider, told Ars.

Fiber, which transmits data using light instead of electrical impulses, has shown itself capable of achieving high throughput both upstream and downstream. With fiber, "a gig can be very easily accomplished with inexpensive hardware on both ends," Benham said.

But that doesn't mean the cable industry should make a wholesale switch to fiber. It makes sense for cable companies to provide fiber to the premises for high-paying business customers, but there's good reason to stick with cable for residential service.

"Everybody would agree that starting from zero, fiber today is probably the most attractive solution," Chapman told Ars. But with the vast amount of infrastructure cable companies already maintain, it's better to "use your existing assets more efficiently" than to make giant fiber investments, he said.

The type of customer who could use an entire gigabit at a time does exist. As one Ars commenter noted, a gigabit could be used up in a household full of HDTVs streaming content from the cloud, computers downloading torrents, video game consoles, personal Web servers, Voice over IP, and computers updating themselves.

That customer is a rare breed, though. "As I understand it, Google Fiber is basically a science experiment," Jacoby said. "I have no doubt that there will come a day that gigabit speeds are necessary in our daily lives, but I'm not sure that day is here yet. When it's here, RCN will be offering it."