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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  • claytontullos - Thursday, September 01, 2011 - link

    I have a netgear XAV1004 -200 system set up for my ps3.

    When the main unit is on the same breaker as the receiver I get around 35Mb/s. When I had the unit setup a few breakers away I received around 3.1Mb/s. Making the change as made all the difference in the world as I could not stream HD content before.

    You really have to take these 200Mb claims as a joke... my gigabit switch tells me the main unit is connected to it at 100Mb/s... You'd expect if it was truly capable of 200Mbs/ speed it would connect at the gigabit level.
    Reply
  • bersl2 - Thursday, September 01, 2011 - link

    Maybe it only implements Fast Ethernet, and marketing is adding Tx and Rx bandwidth together. Reply
  • fireboy92k - Thursday, September 01, 2011 - link

    It's 100 Mbps full duplex (just like fast ethernet), hence the claim of 200 Mbps as you stat.

    See answer 10 at http://support.netgear.com/app/answers/detail/a_id...
    Reply
  • bdipert - Thursday, September 01, 2011 - link

    Thanks for writing, claytontullos. The '200 Mbps' (or for that matter, '500 Mbps') claims of the powerline folks are analogous to the '54 Mbps' and above claims of the Wi-Fi folks...or for that matter the '100 Mbps' and '1 Gbps' claims of the wired Ethernet folks. The peak theoretical PHY rate (or even close to it) is rarely if ever achievable in real-life usage environments, due to protocol overhead, distance- and otherwise-derived attenuation, destructive interference from other 'transmitters' in the same frequency bands, etc...

    p.s...'200 Mbps' powerline networking adapters usually if not always contain 100 Mbps wired Ethernet transceivers. 'Nuff said ;-) Note, however, that the XAV5001 '500 Mbps' adapters contain GbE transceivers...therefore making it important that I mated them to Endpoint systems (my MacBook and MacBook Pro) which ALSO have GbE capabilities
    Reply
  • JarredWalton - Thursday, September 01, 2011 - link

    I wouldn't lump the 100Mbps and 1Gbps Ethernet stuff in with the WiFi and Powerline networking. I routinely hit >100MBps transfer rates on my GbE setup, and basically peg any 100Mbps connections at 98% of their maximum throughput (around 12.3MBps). And that's using HDDs. Transferring files from an SSD-based system to another SSD over GbE, I can hit around 120MBps. Fastest I've ever managed on WiFi is around 30MBps with a "450Mbps" connection -- or around 53% of the theoretical rate. Reply
  • Per Hansson - Thursday, September 01, 2011 - link

    Yea, I agree, don't talk down Ethernet like that
    I have a 100mbps internet connection and I can routinely hit 12MB/sec transfer speeds...

    I've also used those "Gigabit" Powerline networking devices and they managed an astonishing 5mbps throughput, while at the same time killing my FM reception on my radio, even the cars radio was interferred with when I tried it out to my garage (throughput was then ca 1mbps, somewhat shy of the 1000mbps claim...)
    Reply
  • bdipert - Thursday, September 01, 2011 - link

    Ok, ok, ok...so maybe I was a little harsh on wired Ethernet...;-) In this regard, a compare-and-contrast is perhaps of some value. Wired Ethernet is a media specifically designed to carry network packets. The AC power grid, on the other hand, or the atmosphere, in both cases with who-knows-what attenuators and spectrum contenders in-between transmitter and receiver...

    And even with wired Ethernet, protocol overhead (TCP's handshaking scheme, for example...this is why I REALY wished I could have gotten some meaningful UDP data in this study) will retard the effective transfer rate, even if the media and the transceivers on either end are up to the task. And speaking of the receiver, a slow NAS (for example) does a good job of putting the brakes on things, too...
    Reply
  • el1x - Thursday, September 01, 2011 - link

    As far as i am aware its 100Mbps Full Duplex and the marketing states the Tx & Rx together as bersl2 has said.
    Any chance of looking at the NetComm range of powerline? The NP202, 203, 204 & 206.
    I have a set of the NP204's not only are they a solid reliable unit they have AC passthrough so i don't lose a power point.
    Reply
  • jigglywiggly - Thursday, September 01, 2011 - link

    The problem with this is that it isn't that much better than wifi, lol. Reply
  • akedia - Thursday, September 01, 2011 - link

    My apartment is long, narrow, and fully of radiators. It's also over a century old, and power outlets are distressingly sparse and often tucked half-behind the radiators. Right now I have to have coax strung across half my apartment to get from the bizarre place the cable for my internet connection enters the wall to the only outlet in a good enough position to have my WiFi adapter plugged in and get a signal that's still only serviceable throughout half of my apartment. In a perfect environment, yeah, powerline and WiFi are comparable in performance. In reality, though, there are real advantages and disadvantages to each that can dramatically affect their relative utility. Lots of radiators... only one breaker. Reply

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