Powerline adapters: Home networking without rewiring

Three major powerline networking technologies offer high-speed connections simply by plugging small devices into electrical outlets

The concrete and plaster in his Idaho, house blocks Wi-Fi signals. But computer consultant Marc Schoenberg found a way to network the six devices in his house without stringing Ethernet cables: He uses powerline adapters.

"I use them with wireless access points to fill in the various dead spots around the house," Schoenberg said. "Or when the weather is nice, I use them to provide connectivity outside so I can lie in a hammock and, ummm, work."

Indeed, the average house has about 40 power outlets, and with powerline adapters, any of them can be turned into a data port. No additional wiring is necessary.

Powerline adapters were previously limited by interference from the electrical noise generated by appliances and household gadgets using the same circuit, but the latest generation appears to have largely overcome that problem. Also, the adapters offer a theoretical speed of about 200Mbit/sec., which is enough to handle digital video signals, even when actual throughput is less than half the theoretical speed (as is common with Ethernet).

There are three competing (and largely incompatible) technologies on the market: the HomePlug AV standard from the HomePlug Powerline Alliance, the Universal Powerline Association (UPA) standard, and Panasonic's High-Definition Powerline Communications (HD-PLC) specification.

Besides somewhat comparable speed, all of them offer configurable encryption, both to prevent eavesdropping and to avoid crosstalk with other networks of powerline adapters that might reside on the same circuit. (All powerline adapters downstream from the power company's transformer can hear one another.) If they come with any software at all, it is intended primarily to set the encryption key. They support at least 16 units on a circuit, with the units automatically configuring themselves into a network.

With all three technologies, the powerline adapters are a little bigger than a mobile phone. Each has prongs for a power outlet as part of the unit or at the end of an extension line, and each also has an Ethernet port. The user plugs the unit into a power outlet and attaches one end of an Ethernet cable to the Ethernet port and the other end of that cable to a computing device.

After the user does the same with a second adapter and a second computing device (typically a router), the two devices are connected as if via an Ethernet cable. There are usually indicator lights on the adapter to show that it's functioning.

With all three technologies, individual adapters cost less than US$100. Of course, you need at least two. Beyond retail distribution, several power utilities have begun trialling or offering broadband Internet connectivity over power lines, typically using some form of the UPA or HomePlug technologies, and adapters are included with the service.

HomePlug standard

"Data over power line has been kicking around for more than 15 years, but by 2000 nearly all the interference issues had been resolved," explained Matt Theall, Intel's powerline initiative manager and president of the HomePlug Powerline Alliance. The alliance was formed in 2000, and 14Mbit/sec. HomePlug 1.0 adapters began shipping in early 2002, he said. About three years ago, an intermediate Turbo specification offering 85Mbit/sec. reached the market.

"That enabled a new class of applications, not just for data networking, but for things like audio, streaming video and voice over IP," he recalled. "Then, in November 2006, we began shipping the 200Mbit/sec. HomePlug AV standard, geared for video."

Currently, 37 vendors are shipping HomePlug adapters, Theall said, adding that product returns have been less than 1%. Sales of HomePlug units of all sorts have been almost exactly doubling from year to year, and he expects that 11 million units will have shipped during the year ending in October.

In the future, he expects to see them built into or used for televisions, DVD players, speakers, home automation gear, smoke detectors and docking stations to connect iPods to sound systems. A 1Gbit/sec. version is also under development.

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"It's been slow taking off in the US," noted Eric Deming, product marketing manager at Cisco-Linksys, a HomePlug vendor and a division of Cisco Systems. "As with HomePlug 1.0 and Turbo, initial acceptance has been better in Europe, where using wireless is problematic because of the brick and mortar used in home construction. It's also been a little expensive -- it costs US$179 for two, where US$149 will get you wireless card and a wireless adapter. It's also a little bit nonintuitive -- buyers may not understand that they need two, one for each end. That's why we sell them in kits of two."

Deming said that a HomePlug AV system might, in an ideal environment, achieve 86Mbit/sec. to 90Mbit/sec., but that extensive testing showed that 35Mbit/sec. is a realistic expectation. However, he noted that 35Mbit/sec. is sufficient for high-definition video, which usually takes 20Mbit/sec. Aluminum house wiring (used three decades ago), halogen lights, long wiring runs and electric motors can also degrade a signal, he noted.

"The biggest problem is consumer education," added Lesley Kirchman, marketing director at ActionTec Electronics. "Many people don't understand how easy it is. Words like 'easy' and 'simple' are overused, and people tend to be jaded. And I think that a lot of people are afraid of networking."

UPA standard

UPA backers tout the fact that UPA got to the market first with 200Mbit/sec., as the first UPA adapters for home use began shipping in January 2005, and volume production began in April 2005, explained Brian Donnelly, president of the UPA Marketing Working Groupand vice president at Corinex Communications Corp. in Vancouver, British Columbia.

"There have been about a dozen firmware upgrades since then, and it's become pretty bulletproof," he said. The chief difference cited between UPA and the other two technologies is a feature that allows an adapter to be placed in a long wire run to boost the signal between one end and the other. Thirty-three adapters can be used in a home network, but some configurations are open-ended, he added. For encryption they use 168-bit DES. Throughput can reach 95Mbit/sec., he said.

Initially, most sales were in Europe, but retail acceptance ballooned last year in North American, with sales rising 800%, he said. He expects that 3.5 million devices will have shipped by year's end.

There are about 15 vendors shipping UPA products, one of which is Netgear. "We chose UPA because of the quality and because UPA was there first. We were on the market a good six to eight months before HomePlug came out," said Jamie Ching, Netgear's powerline product manager. But Netgear also sells HomePlug units, he noted.

"Ninety percent of the time, you can just plug and play," Ching said. "The other 10 percent of the time, the house may have older wiring, or it may have added wiring that doesn't have good connectivity with the older wiring. But the technology is robust enough for most situations." Most appliances do not interfere, he added.

Panasonic HD-PLC

The third technology is Panasonic Corporation of North America's HD-PLC, based on proprietary technology including Panasonic chips, explained Mike Timar, product manager at Panasonic USA in Secaucus, N.J.

The theoretical speed of the units is 190Mbit/sec., and Timar said that users could expect a throughput of 40Mbit/sec. to 45Mbit/sec. for file transfers and up to 80Mbit/sec. for streaming, where lost bits are immaterial. He noted that, by comparison, DVDs output at 6Mbit/sec., and an uncompressed Blu Ray disc uses 33Mbit/sec.

One unit in an HD-PLC network is designated the master by setting a switch. The units use 128-bit AES encryption, and they can be set to use a new random key, without software, by pressing buttons on the master unit, he added. Sixteen adapters can take part in one network.

"We are looking to the time when you can plug your plasma TV into a power outlet, and no other connections are needed," Timar said. "In the meantime, we have come out with these adapters, and they are selling pretty well. But I think that the customers don't appreciate the benefits of higher speeds and security and robustness, since they have nothing to compare it with."

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Panasonic has also promoted the concept of interoperability between the different powerline adapter technologies through its involvement in a consortium called the Consumer Electronics Powerline Communication Alliance (CEPCA). Panasonic has recently agreed to partner with the HomePlug Alliance and submit a joint specification to the IEEE P1901 Working Group, which is working to define an industrywide data-over-powerline technology. Future products using the proposed standard would be interoperable with existing HomePlug AV and Panasonic HD-PLC units, Panasonic and HomePlug jointly announced.

Donnelly said that the UPA has been collaborating with CEPCA on proposed interoperability specifications for the P1901 Working Group. No vote on a new specification is expected until next year, he indicated, and he questioned whether anyone today can predict future compatibility with a standard that remains to be finalized.

"There are multiple proposals, and there are likely to be mergers among the proposals -- this is just Stage 1," Donnelly said. But he foresaw continued involvement by the UPA, leaving open the possibility of three-way interoperability with a future specification.

Read a review of powerline adapters here