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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  • EarthwormJim - Thursday, September 1, 2011 - link

    You can typically follow other wiring in the house when retrofitting, like telephone wiring or coaxial wiring.

    Competition is probably high in my area, I often see several advertised specials from electricians specifically for cat 5 wiring.
    Reply
  • bobbozzo - Thursday, September 1, 2011 - link

    If you have (wall-to-wall) carpet, it's very easy to lift up the carpet a little and run cat5 under it... I ran a 100' drop in about 15mins.

    Also, you can get baseboard or crown molding which are gapped or routed (cut out) for wires to be hidden in.
    e.g.
    http://www.curbly.com/Chrisjob/posts/3618-Hide-you...
    http://www.wiretracks.com/prod-cm.html
    Reply
  • bobbozzo - Thursday, September 1, 2011 - link

    Also, my alarm guy does cat5 drops through the attic for $30 each, which is a real bargain. He drops them behind curtains, etc., instead of through the walls to a wall box. Reply
  • bdipert - Thursday, September 1, 2011 - link

    Dear bobbozzo, thanks for writing. You do realize, thought, that the feasibility and availability of such wiring options (far from their implementation) are way beyond the comprehension of the consumer masses...right? Versus going down to a nearby consumer electronics store, buying a couple of adapters, and plugging them into power outlets? If consumer electronics manufacturers targeted only the readers (and editors ;-) ) of AnandTech, they'd be able to get away with far less consumer-friendly offerings, because the bleeding-edge early adopters here would figure 'em out anyway. But the potential customer market would be a fraction of the size, as a result. Reply
  • bjacobson - Thursday, September 1, 2011 - link

    can you review it, too? Reply
  • bdipert - Thursday, September 1, 2011 - link

    Glad you all seem to dig my digs. I do, too ;-) Reply
  • bigpow - Thursday, September 1, 2011 - link

    As someone who actually makes a living testing powerline comm, I find your article to be refreshing. Had to close my eyes and bite my tongue, going through the HW section, LOL, but everything after that is quite informative. Reply
  • fausto412 - Thursday, September 1, 2011 - link

    i've been interested in this to run my home network and hookup my PC to the net over wireless..i also have 2 to 3 TIVO's i would love to network over faster speeds than wireless which would allow me to transfer shows real time between boxes.

    anybody able to speak to the capability of these setups in the real world?
    Reply
  • froob - Friday, September 2, 2011 - link

    Did you run any latency tests on these units? I'm interested to know how suitable Powerline networking would be for an Xbox 360 / PS3 etc. Reply
  • bdipert - Friday, September 2, 2011 - link

    Dear froob,
    Yes, IxChariot logs a number of statistics, including latency, packet drop percentage, etc, I didn't explicitly create a table for latency, but you can find the data in the full report files I've archived here (as published in the 'TCP Testing Results' section of the article):

    http://images.anandtech.com/doci/4695/PowerlineBen...
    Reply

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