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I have a TP-Link 500 Mbit/s Gigabit Powerline Adapter linking two computers (one Windows Vista and one Windows 7) in different rooms in the house. As in:

Computer <-Ethernet cord-> Adapter <-Electrical wiring-> Adapter <-Ethernet cord-> Computer

I'm trying to transfer 100 GB of data through this network (there are reasons why I can't use a USB, etc.).

My problem: I get only 3.5 Mbyte/s transfer speed. Aren't I supposed to be getting close to 60 Mbyte/s (500 Mbit/s)?

(NB: limited networking knowledge, may have used incorrect terminology)

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Note, Powerline adapters are not wireless. They use the electrical wiring. I've adjusted your diagram to correct it. –  music2myear Feb 17 '12 at 15:42
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Just to make sure: how do you measure your transfer speed (the 3.5) ??? In the question title you say 3.5MBps, in the text you say 3.5Mbps.... –  woliveirajr Feb 17 '12 at 15:42
    
Yes, I did indeed mean MBps. Corrected in OP :) –  J.B. Feb 17 '12 at 16:00
    
I would wonder what you got hard wired. These powerline adapters are effected by not being on the same circuit , being on the other "phase" of the power, and via power line filtrations that would exist on either of the curcuits , filtration can exist in something as simple as a cheap surge protector. When applying something like this i would do my testing in steps. starting with hard wired, moving to side by side through the adaption, then onto the next room/curcuits. that way you know what is possible, and if or where it goes badly. –  Psycogeek Feb 17 '12 at 16:02
    
@Psycogeek - I would try that, if my desktops were easy to shift about. Unfortunately they're 'stuck' to their current locations :P –  J.B. Feb 17 '12 at 17:00

3 Answers 3

up vote 17 down vote accepted

That's not wireless... those adapters are using your electrical wiring as a medium to transfer the data.

This technology is known for being less than reliable, especially if the two ends of the connection are on different circuits. More than that, a lot of power lines have a lot of noise in the wire that can significantly reduce that actual vs theoretical data throughput.

Now let's look at some other limiting factors. If either computer only has a 100Mbps card, that is as fast as you'll go for the transfer. We also need to mention the uppercase B in MBps vs the lowercase b in Mbps. Whenever you see a lowercase b, you need to divide the number by 8 to get a better idea of how many bytes (vs bits) you can transfer.

So a 100Mbps link from the computer could at most supply your powerline adapter at 12.5MBps, and a certain amount of additional loss is normal for noise, collisions, and TCP overhead. The speed at which your source hard drive is able to read the data may be a factor as well, especially if you're moving data from an older computer to a newer one (which a 100Mbps adapter would suggest). One more potential limitation is the duplex setting of the connection. Most wired connections use two pairs of wires to allow both sides to transmit and receive at the same time. It's possible and even likely that your powerline adapter is only half-duplex, and cannot send and receive at the same time. This will result in more packet collisions that will further slow the transfer. Now factor in high noise in your powerlines, and 3.5MBps seems downright reasonable.

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Thanks for your answer, this is enlightening and I feel slightly silly, but relieved, now :P –  J.B. Feb 17 '12 at 15:57
    
There is also a Tcp/Ip overhead slowing you down by about 10-20% especially on a 'bad' powerline. –  Barfieldmv Feb 17 '12 at 16:06

No. 3.5 isn't too bad.

First, make sure you note whether you're getting 3.5 MBps or 3.5 Mbps. The upper- or lower-case B makes a difference of a factor of 8. Big "B" stands for "Byte", little "b" stands for "bit". There are 8 "bits" in each "Byte", hence the factor of 8 thing. Most internet connections and network connections are measured in "Mega-bits per second" while most file transfers are measured in "Mega-Bytes per second". Just noting, the Powerline adapters use the little "b" in their spec, as is normal for network connection speed ratings.

Then there is network overhead: other things the network has to use to keep the connection working right. This can account for quite a bit of your available bandwidth.

Next, while the Powerline adapter may be capable of 500Mbps, what it actual gets is very very dependent on the quality of your home electrical wiring. Unless the house is very new, has incredibly good wiring, and there are no other electrical junctions, circuit breakers, or large appliance in the circuit between the devices, you're highly unlikely to get anywhere near 500Mpbs total throughput on your network.

Take for example my very nice Gigabit (note: it's not GigaBYTE) network here are work. Transferring between two servers right next to each other on the same switch, I'm fortunate to be 100MBps actual throughput in file transfer speed, which is pretty good, because these servers are each connected to 4 Gigabit ports on that switch.

So, all that to say you're probably seeing an OK network speed.

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Thanks for your answer; it was as useful as the others and particularly educating, but it was pretty hard to decide on the 'correct answer'. I would up-vote your comment if I could :D –  J.B. Feb 17 '12 at 15:59

One of your computers is probably only 100 Mbit/s. After overhead, an ideal connection will get you about 10 Mbyte/s. Your power line adapter probably isn't ideal.

I don't think your numbers are totally off from reality. Up to 500 Mbit/s is certainly under ideal conditions which probably don't exist in reality.

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Thanks for your answer; it was as useful as the others, so it was pretty hard to decide on the 'correct answer'. I would up-vote your comment if I could :D –  J.B. Feb 17 '12 at 15:58

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