If you made it through the italicized technical protocol descriptions of the prior page, you encountered numerous references to bit errors and their mitigation; forward error correction approaches, retransmit schemes, hundreds or thousands of discrete transmission channels with independently configured modulation densities, etc. Such workarounds exist because the power grid was never intended for networking purposes and, as such, is a quite unfriendly environment for reliable high-speed data transfers.

Consider, first and foremost, that every AC-fed device creates a momentary dip or surge (however slight) when it first powers up or off. Such situations are usually occasional, and as such can be dealt with packet retransmission (in the case of TCP) or brief loss (with UDP). More egregious, on the other hand, are devices that inject a constant stream of high frequency noise onto the power grid, such as:

  • Switching power supplies (including AC-to-DC converters used in cellphone chargers and the like)
  • Motors in devices such as fans, hair dryers, vacuum cleaners, washers and dryers, furnaces and air conditioners, and refrigerator compressors
  • Illuminated CFLs (compact fluorescent lamps)

Such devices' noise patterns can destructively interfere with one or multiple channels' worth of powerline networking data. And at this point, I should also point out that the active powerline network can itself be a destructive interference source, specifically for shortwave radios, by virtue of the fact that current passing through a wire creates a magnetic field surrounding that wire, thereby turning it into an antenna. Powerline technologies are a longstanding sworn enemy to many 'ham' radio operators, although LAN-based powerline approaches are far less egregious in this regard than are WAN BPL (broadband over powerline) approaches spanning a large region. And powerline adapters are also intentionally designed with notch filters that, when activated, create channels (at the tradeoff of reduced peak bandwidth) that might interfere with other transmitters and receivers in a particular geography.

Next is the issue of networking signal attenuation, which is first and foremost caused by old or otherwise low-quality electrical wiring. Other potential problems include narrow-gauge wiring, with excessively high impedance; poor intra-span connections and variable gauge wiring across the span both result in unwanted reflections. Powerline packet 'jumps' across circuit breakers are performance-problematic; even more so are source-to-destination paths that involve a transition from one 110V (U.S.) phase of the incoming 220V source to the other phase. Even within a particular circuit breaker wiring spur, the presence of GFCI (Ground Fault Circuit Interrupter) outlets can cause problems, even if a powerline adapter isn't directly connected to them.

Don't try to connect a powerline adapter to a surge protector, which will filter out the high frequency data modulated on the 50 or 60 Hz carrier, unless the adapter is three-prong and implements Sigma Designs' ClearPath approach. ClearPath, according to Sigma Designs, alternately routes packets over the earth ground connection, which is normally not filtered. (Atheros also eventually plans to implement a similar approach, called Smart Link.) Keep in mind that surge protection circuitry is increasingly not just included in standalone power strips but also embedded within wall outlets. And a UPS (uninterruptable power supply) also acts as an effective deterrent to powerline packet propagation.

Speaking of circuit breakers, now's as good a time as any to discuss security. Don't worry about your next-door neighbor accessing your LAN if a transformer is in-between your respective street-side power connections. On the other hand, there's a tangible possibility that multiple powerline networking users sharing a common transformer feed (such as, for example, in the same multi-apartment building) could tap into each others' equipment. That's where encryption comes in. HomePlug 1.0 and 1.0 Turbo harness 56-bit DES encryption, while HomePlug AV leverages even more robust 128-bit AES. And altering an adapter's password requires access to a 16-digit unique password stamped on the unit. Just change your equipments' passwords from the 'HomePlug' or 'HomePlugAV' default, and other folks on the same transformer feed won't subsequently have access to them.

Technology Fundamentals Testing Setup
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  • quiksilvr - Thursday, September 1, 2011 - link

    Have you tried getting a better router and/or perhaps a better wireless card for your laptop? Reply
  • akedia - Thursday, September 1, 2011 - link

    I have a current generation Airport Extreme, which is generally regarded as one of the best wireless routers available, and the built-in WiFi antenna in my Mac mini is not upgradable, as far as I know. My roommate's laptop is an HP dm1z, also not upgradable, and my Droid X is stuck with the antenna it shipped with as well. It's not my hardware, it's my environment. WiFi has limitations, like it or not. Reply
  • bdipert - Thursday, September 1, 2011 - link

    Different tools for different tasks, jigglywiggly. Powerline can make a pretty good 'backbone' technology if, as I state in the article, you want to 'dispense with burrowing through dirty, spider- and snake-infested crawlspaces and drilling holes in walls and floors in order to route Cat5e cable around'. Wi-Fi conversely can be effective across intra-room and few-room spans...and with mobile devices. Reply
  • Paedric - Thursday, September 1, 2011 - link

    Thanks for the article first, that's something I've been interested in for quite some time.

    However, I have a question; you tested it in a "perfect" environment by disabling interfering devices, to test the potential of the system, but what happen if it is not the case?
    Is the performance hit really noticeable?

    I don't want to rout a cable across the whole house, but I'm not really keen on turning off the fridge, lights, and unplugging devices every time I want to connect to the internet.
    Reply
  • Denithor - Thursday, September 1, 2011 - link

    I have the TRENDnet TPL-303E2K Powerline AV Adapter Kit installed in my home, connecting my wireless router in the living room to my office computer about 50 or 60 feet away. Couldn't get a solid enough wireless signal in the office for any kind of gaming, hooked up this kit and within literally 2 minutes was playing everything just fine.

    There's no need to unplug or turn off anything. It just works...
    Reply
  • gariig - Thursday, September 1, 2011 - link

    I bought my parents the same TRENDnet that Denithor has (crazy coincidence) because their wireless router and extra computer are on the other side of a ~2000 SQ FT house. Works flawlessly for normal computer usage (e-mail, Youtube, etc) and printer sharing. I don't know how well it works for large file transfers but I'd imagine you'll at least get 100 mbps Reply
  • bdipert - Thursday, September 1, 2011 - link

    It depends. That's the only meaningful answer I can offer. That's why, after much gnashing of teeth and back-and-forth waffling, I decided to do my testing with everything turned off and disconnected. Otherwise, if (say) I had an especially noisy refrigerator motor, my results might have unfairly undershot some alternative typical-refrigerator reality. Obviously, my data wasn't the absolute best case...as I mentioned, I stuck with DHCP address assignments for the two Endpoints, instead of hard-wiring static IP addresses, and I concurrently ran all available powerline networking adapters although only three were in active use at any point in time, and I chose outlets out of functional meaningfulness to me, intentionally ignoring whether or not they spanned multiple breakers, or jumped across phases, in the process. But I also don't think it would have been right to turn on all potential interference sources, then do the tests.

    With that said, I regularly sling ~20 Mbps Windows Media Center streams (HD ATSC recordings) around my LAN, including through powerline spans, with no problem.
    Reply
  • leexgx - Thursday, September 1, 2011 - link

    just would of been nice if you had done an short test with stuff on to see how it is handled them (just 1 page short tests) as you did it with every thing off

    you could of had an laptop with you to monitor each power plug speeds when stuff came on, last power plugs I used the speeds stated seem close to bandwidth useable (-50 ish % for overhead)

    I found power plugs to be very reliable and how they handle packet loss as well most of the time (last time I played with them)
    Reply
  • Joe Martin - Thursday, September 1, 2011 - link

    Does it work for streaming video or not? Very hard to read article. Reply
  • bdipert - Thursday, September 1, 2011 - link

    It's impossible for me to provide a simple answer to such a question without either undershooting or overshooting the spectrum of possible realities. First off, there's the bandwidth potential of any two powerline nodes in YOUR particular setup to consider...only you can measure and ascertain that. Then you've gotta determine what you mean by 'streaming video'...are we talking about a 20 Mbps encapsulated MPEG-2 (ATSC) HD stream coming from a Windows Media Center server, for example, or a heavily compressed sub-1 Mbps H.264 standard-definition video stream? Protocol? Etc... Reply

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