Powerline Network Adapters: The Next Generation

AC wires can be accessed from multiple spots in any room where a computer is in use. What's more, by deploying what are known as "powerline adapters," system builders can deploy those AC wires inside the walls to replace lengths of Ethernet cable.

Working with powerline adapters can free system builders and their clients from situations where a spot is hard to reach with an Ethernet cable, or when doing so will produce unsightly results. Bottom line: Powerline adapters offer system builders yet another class of product to resell with confidence.

ALL ABOUT POWERLINE ADAPTERS

Powerline adapters function as interfaces between an Ethernet line and an AC line. They convert the Ethernet signals to and from signals that can be sent over the AC lines at frequencies that are unaffected by the power voltage on those lines. Meanwhile, they include processors powerful enough to continually analyze the available bandwidth, to compensate for electrical noise on the AC circuit that might be generated by the electrical motors in appliances, and/or by the jitter of halogen lights.

Proprietary versions of powerline adapters have been around for a couple of decades, offering limited speeds, interoperability, and reliability. But that was then. Today, there's a new generation of powerline adapters on the market. They offer higher speeds than in the past, more robust performance, and greater interoperability.

For this recipe, I reviewed 4 examples of these new-generation powerline adapters. Three of them use the HomePlug AV specification from the California-based HomePlug Powerline Alliance, while the fourth uses a competing spec from the UK-based Universal Powerline Association (UPA). The use of non-proprietary standards can be expected to broaden the market, since users don't have to grapple with interoperability issues.

For me, all 4 worked astonishingly well. For point-to-point connections, installation was simply a matter of plugging them into the power outlet, then using an Ethernet cable to attach them to a device. After about 5 seconds of self-configuration they were working fine, and at a speed approximately equal to that of the Ethernet cable. The Ethernet cable that had previously connected the devices could now be placed in reserve.

Each adapter is quite small, about the size of a band-aid box. And each has 3 indicator lights: 1 for power, 1 for detection of a data path to another adapter, and 1 for detection of a connection to the Ethernet port.

While each adapter has a slightly different shape, all can be plugged into a standard two-plug electric outlet without blocking the second plug the way some adapters and transformers do. (All used a two-prong plug.) None of the tested units had a through-plug, so you could use the plug for power as well. But all worked just as well on an outlet expander, extension cord or power strip.

But the documentation accompanying all four brands warns against plugging them into surge protectors or uninterruptible power supplies, which would obliterate the signal. One of the brands I tested proved nearly incapable of functioning in the presence of line noise, while the others shrugged it off. When using more than 2 adapters on a circuit—that is, for more than a simple point-to-point connection--the situation was more complicated. There were even configurations that did not work well, or at all. I'll discuss in more detail on the following pages. HOMEPLUG UNITS

As I mentioned above, the powerline adapter market is currently split between the UPA and the HomePlug camps. In this section I'll look at HomePlug.

The HomePlug AV specification is the latest in a series of HomePlug powerline adapter specifications. On a quiet line, HomePlug AV can get a throughput of 80 megabits per second (Mbps), which is enough to connect multiple HD-TV sets to a digital set-top box. I found the throughput to be more than adequate to connect multiple computers to a broadband modem.

The HomePlug Powerline Alliance has a Web site listing of products that support the HomePlug AV specification, from more than a dozen vendors. For this recipe, I reviewed three of these vendor products:

• The Actiontec Megaplug HPE200AV Ethernet Adapter from Actiontec Electronics. This adapter retails for just under $170 for a two-unit kit and is a standard direct-plug unit. Here's a look:
• The PLK200 PowerLine AV Ethernet Adapter from Linksys (now a division of Cisco Systems). It costs about $180 for a two-unit kit and is another direct-connect unit. Here's a shot:
• The PLA-400 Ethernet Adapter from ZyXEL Communications. Retailing for about $100 for individual units, it uses a power cord to connect to the outlet, rather than a direct connection. I found this to be convenient, since power outlets are not often conveniently accessible. It has 4 instead of 3 indicators, but 1 was non-functional; apparently, the enclosure was originally intended for some other application. The enclosure also includes mounting holes, so it can be hung on a wall. Here it is:

All of the above products offer 128-bit Advanced Encryption Standard (AES) encryption, with software that lets you set the encryption key. Encryption is important, since the line signal emitted by the adapters will be detectable by anyone using the same power transformer. This was the only time when software was required when using the adapters. However, the upside is that there are also quality-of-service (QoS) settings for use with video equipment.

In point-to-point connections, all 3 adapters worked as described, immediately replacing an Ethernet cable. Even when a hair dryer -- a classic source of electrical noise -- was plugged into the same outlet and turned on, all 3 adapters continued to function without a hitch.

But when more than 2 adapters were in use, the situation became more complicated. When 2 ports on a router are connected to 2 adapters, so that downstream they're connected to 2 different computers, the units interfered with each other. Also, response times rose by a factor of 50. But when 1 adapter was plugged into a port on the router, multiple adapters downstream could use the upstream adapter as if it were a router, with the adapters basically creating their own network.

This ability ran across all 3 brands I tested. The Actiontec unit could be upstream and the Linksys and ZyXEL units could be downstream, or the Linksys or ZyXEL unit could be upstream with the other brands downstream, etc. Apparently, this router functionality is built into the HomePlug AV specification, although it was barely hinted at in the accompanying documentation. In fact, you can use as many as 16 adapters in a network. UPA UNIT

The only example of a UPA adapter I tested was the HDXB101 from Netgear. It costs about $200 for a two-unit set, and it is a direct-plug unit. Here's a look:

In point-to-point use, this unit behaved much like the HomePlug units. It offers about the same speed, too. But there was one difference: A plugged-in and running hair dryer brought the unit to its knees. In fact, once the hair dryer was turned on, using the other plug in the same outlet, response times went up by a factor of about 150. The unit did appear to be trying to adapt, and Web pages eventually did start trickling in rather than timing out. By contrast, as I mentioned, the HomePlug units did not even notice the hair dryer.

Netgear's documentation states that 16 of the units can network in one circuit, similar to the networking achieved by the HomePlug units. Unfortunately, I was unable to test that function, since only 1 pair of adapters was available at the time. However, the documentation indicates that downstream UPA adapters can network to the upstream UPA adapter.

As for coexisting with HomePlug AV units, when UPA units are added to a circuit where HomePlug AV units are already active, the UPA units would not work at all. The computer using the UPA adapter said it could not find the network. The HomePlug units continued working, although response times were lower.

When adding HomePlug devices when the UPA adapters were already active, the UPA adapters continued working fine. The HomePlug adapters also continued working, although as before, with lower response times. The Netgear documentation says that units can coexist with HomePlug 1.0 units, but does not mention HomePlug AV units. This might be because the Netgear unit reached the market ahead of the HomePlug AV units.

In conclusion, it appears the two specifications should not be mixed.

All in all, powerline adapters are suitable in situations where small workgroups need to be networked quickly, or where networking needs to be extended at the spur of the moment to an isolated spot—a spot with a power outlet. In such situations, system builders should find powerline adapters enormously flexible tools.

But powerline adapters do not appear suitable for large-scale installations. In a large building or campus, you don't know who else might be using powerline adapters within the output of the same transformer. Further, if other people are using adapters, they could easily exceed the 16-unit maximum. Even with that variable under control, you still can't use more than 16 adapters on a circuit. Although, again, that should be enough for most small workgroups.

LAMONT WOOD is a freelance writer based in San Antonio, Texas. He has been covering technology for nearly a quarter of a century.