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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  • Arbie - Thursday, September 1, 2011 - link

    Yes, it is hard to read. I wasn't going to comment on that until I saw your remark. The style is verbose, with too many words behind every thought, whether or not it's important. "Burrowing through dirty, spider- and snake-infested crawlspaces"? C'mon, that sounds like a 7th grade composition. You've got a good subject and all the smarts; don't mess it up. Reply
  • kmmatney - Thursday, September 1, 2011 - link

    I have a Western Digital Powerline that plugs into the router in my basement, with the other outlet at my TV on the second floor. It works great for streaming video, and it also has 4 ports, so I've hooked up my DirectTV box, BlueRay player, and WD live player, and I still have a spare port for a new internet-enabled TV. Overall, a very good solution for $89 or so. Reply
  • bdipert - Thursday, September 1, 2011 - link

    Quick aside, speaking of WD Livewire...the company's Outlet has a refurb two-adapter kit for $59.99 right now...http://dealnews.com/Refurb-Western-Digital-Livewir... Reply
  • jabber - Thursday, September 1, 2011 - link

    They work well enough in my opinion. As mentioned I only use these as a last resort after physical location/wireless etc. options have failed. Reply
  • abkfenris - Thursday, September 1, 2011 - link

    ... is the house. Reply
  • crimson117 - Thursday, September 1, 2011 - link

    TIL that Anandtech editors' houses are as unique as the editors :)

    Great article!
    Reply
  • edved - Thursday, September 1, 2011 - link

    I've been using the AV 307's for about 3-4 months now and they're great. I'm streaming huge data, HD video and uncompressed audio without a hiccup. Literally plug and play, this is the best way to go! I've now got my Panny Tv, Blu ray player, WDLive, Onkyo 509 all piped-in thanks to the 307's!

    Can't recommend it enough.

    my2cents.
    Reply
  • casteve - Thursday, September 1, 2011 - link

    These $50 powerline adapters are just one LAN connection away from expensive electronics. Since you can't connect them directly to a surge protector, what internal protection do they have for the LAN? Reply
  • edved - Thursday, September 1, 2011 - link

    I paid over $100 for mine, but wasn't ready to start "Burrowing through dirty, spider- and snake-infested crawlspaces"! Reply
  • bobbozzo - Thursday, September 1, 2011 - link

    I had some Logitech security cameras last year, which came with separate powerline adapters; they claimed to have built-in surge suppressors, but no KV or other ratings were specified.

    I put them on some APC surge suppressors, and they worked for several days and then lost the connection, so I had to move them off the APCs.
    Reply

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