Powerline Networking with the Western Digital Livewire
by Ganesh T S on August 24, 2010 7:50 AM EST- Posted in
- Gadgets
- Networking
- Powerline Adapters
The HomePlug consortium has been around since 2000. It is made up of a number of companies which develop products intending to network the home using the already existing electrical wiring infrastructure. The consortium's technology has been adopted as the baseline for the IEEE P1901 standard due for ratification next month. In this section, we will not talk about standards such as MoCA (Multimedia-over-Coax) and HomePNA which are alternatives to powerline networking for a connected home. The focus will be on standards which aim to compete with the HomePlug base requirements.
Gigle Semiconductors (now, Gigle Networks) was the first to introduce a Gigabit powerline networking chipset by adding proprietary extensions to the base HomePlug AV standards (which correspond to the 200 Mbps PHY). The only product using this chip in the US market is Belkin's GIgabit Powerline Network Adapter Kit, reviewed in detail here. As can be seen, there is an increase in the available bandwidth. However, this increase in performance is not uniform or reliable enough across various locations in the house. The situation with the proprietary extensions to the base standards is such that Gigle Networks is now advertising (PDF link) design wins for their 200 Mbps PHY chipset. Unless Gigle's proprietary extensions become part of the HomePlug / IEEE P1901 standards, it looks likely that we will not be finding many Gigabit powerline adapters in the near future.
The main competitor for the IEEE P1901 standard comes from the ITU. The G.hn standard promoted by the HomeGrid Forum, and also pushed by the ITU, aims to propose a single standard for networking over electrical wires, phone lines and coax cables. While the Wikipedia article suggests that the G.hn standard can network at rates upto 1 Gbps, a detailed perusal reveals that the June 2010 sitting of the ITU committee had decided to reduce the baseband operational spectrum. This further strengthens the criticism of the G.hn standard mentioned towards the end of the article. That said, it would be interesting to see whether Marvell puts its weight behind G.hn, now that it has purchased one of the four initial G.hn silicon vendors, namely, DS2. There are other big companies introducing G.hn silicon too, such as Sigma Designs. However, the fact that there is no proper G.hn standard yet, coupled with the issue of lack of demonstrated silicon, doesn't bode well for the technology.
Having setup the required background for powerline networking products, we now proceed to review the WD Livewire.
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jkostans - Tuesday, August 24, 2010 - link
Ethernet is not twisted to prevent radiation, it's to reduce noise in a differential transmission line. (The fact that ethernet signaling is differential reduces radiation and loss but not the twists) In theory by keeping the wires as close as possible any noise that influences one wire will equally influence the other wire in the same manner. When the subtraction is done to find the voltage, the net result of the noise will have no effect. It's like the equation (5+X) - (0+X) = 5. No matter what value of the noise (X) is, the equation will always equal 5.chromatix - Tuesday, August 24, 2010 - link
The twists have both effects, and effectively isolate the electromagnetic fields of the wires and their surroundings up to a certain frequency and down to a certain distance. It is the isolation which eliminates both emissions and received noise.flgt - Tuesday, August 24, 2010 - link
I think to some extent you're both right. The reduction in emissions comes from the fact that the signal is driven differentially (equal amplitude, opposite polarity) and the control of the electric fields which are generated. In a non-perfect transmission line there is a finite amount of cancellation between the two fields which can be improved with cable construction (Cat 6 > Cat 5 >> Romex). Twisting improves performance but a shield is required optimal emission performance. However the increased costs and installation time of shielded cables make them a less desirable solution as long as regulatory requirements can be met.As stated, differential signaling provides inherent common-mode noise immunity which is aided by the tight coupling of the twisted wires. The twisting helps ensure the radiated noise excites each conductor in the pair equally (again to some finite amount).
I don’t see this being a major issue for radio operators for a number of reasons:
1) The noise immunity provided by differential signaling allows the line to be driven at lower voltage levels, thereby further reducing emissions.
2) The use of OFDM allows each individual frequency channel to be operated at very low signal-to-noise ratios due to the low-order modulation scheme being used. This is the only way they can operate over such a horrible channel in the first place (your power line). They most likely operate each carrier at a very low signal level to make the composite spectrum look more like broadband noise. DSL essentially operates in the same way.
3) The signal will quickly attenuate since the channel is so bad.
Per Hansson - Wednesday, August 25, 2010 - link
I can confirm your suspicionsI recently bought the Belkin Gigabit Powerline HD networking kit
It managed to do 5Mbps over my powerlines, an apartement built 1990
When I turned on my FM radio there was an amazing ammount of noise in the reception when I was transmitting data, less so when I was not transmitting data but still some pops and cracks in the reception
When I unplugged the adapter the reception became perfect
Next test was to run the powerline adapter from the apartement out in to my garage, the speed now dropped to 1Mbps
To my suprise though it managed to even interfere with the FM reception in my car!
The signal got way harder to recieve, it did not crack and pop in the audio tho, but I think that may be simply due to the fact that the stereo in my car is much better at receiving a signal, and the fact that the car itself acts like a faraday cage...
To say the least I returned this "Gigabit" junk
yottabit - Tuesday, August 24, 2010 - link
There's a typo in the second sentence of the summary article on the anandtech home page... :(reckert - Tuesday, August 24, 2010 - link
In most homes, the electric coming in is 240v, and the circuits are split to 2 sets of 120v. I know from past experience power line protocols such as x10 couln't get their signals to jump between the two sides of the wiring without a special bridge.ganeshts - Tuesday, August 24, 2010 - link
reckert, as you mention, x10 needed something to plug in to bridge the legs of the circuits. However, as all Homeplug stuff is on high frequency, they bridge due to the capacitive effect of the bus bars in the circuit breakers. Therefore, you will not have a problem with the configuration you mention as long as you are using HomePlug certified devices.Souka - Tuesday, August 24, 2010 - link
My house build 1984...2 story, 2200 sq/ftCable modem on second floor, tv on 1st with BriteView media player.
Netgear XE-104 (up to 85Mbs claim)... on same curcuit directly plugged into wall I got barely 15Mbps. Different circuit in adjoining rooms 5Mbps. Different circuit on different floors...under 1Mbps and often dropped connection.
BELKIN F5D4073 (up to 85Mbps) Powerline Turbo similar results...
Also tried the kits in my parents 1960's 2 story 3500 sq'ft home....worse results...
I really like the idea of powerline tech, just doesn't deliver for me
ganeshts - Tuesday, August 24, 2010 - link
Souka,Please take a look at the SmallNetBuilder guide here, as it may be of some help to you: http://www.smallnetbuilder.com/lanwan/lanwan-basic...
It is best to buy these type of products from stores which have a good return policy / no restocking fee. Unless the consumer actually tries it out, it is not possible to know in advance as to how well the technology would work, as is evident in your case.
Souka - Tuesday, August 24, 2010 - link
I might give the XAVB5501 or XAVB5001 a shot when they come out....none of the listed retailers (or froogle.com) came up with any units available.I do wish they had dual ports... or at least in kits one of the units had dual ethernet ports.
Yes I can easily hook a switch to it, but rather not.