Slow 802.11n transfer speeds

[Ranma13]

Here is a description of my setup. I have a DWA-655 router with WPA2-AES, QoS, and SPI enabled. I'm trying to transfer files from my desktop, which is using the DWA-552 PCI card, to my laptop, which uses the Intel 4965. Using Netstat Live, it's reporting that my transfer rate is around 10 mbps. The router reports the link rate to be around 80 for both computers. What could be the problem of the incredibly slow data transfer speed? No B or G clients are connected to the router and it's running on the least-crowded channel with 20/40 Mhz enabled.

Edit: I did some more testing by resetting the router to factory defaults, then moving it into the same room as the desktop and laptop. The only setting I had to change from factory default was to make the router use 20/40 MHz so I can get 300mbps.

Wireless to wireless transfer, I got about 20-30 mbps.
Desktop wired to laptop wireless, I got about 40-50 mbps.
Laptop wired to desktop wireless, I got about 30-40 mbps.

Both the desktop and laptop wired and unwired speeds made sense since the link speed was about 100-120 mbps, half that and subtract a bit and you get about 30-50 mbps. The results are pretty disappointing though, considering that all the advertising says 300 mbps, which means transfer speeds should be at least 100 mbps, but I upgraded from a b router so it's not a complete waste. Any advice on how I can improve this speed would be greatly appreciated.

 

[thiggins]

It could be the measurement tool. What are you using to generate traffic for NetStat Live to measure?

To get a baseline, force the router to 11g mode and run a Netstat test with the router and client in the same room, but at least 10 feet apart. You should get ~20Mbps.

Link rates (the "speed" shown in the Windows Network connection status) are not that directly related to actual, usable speed. My testing has shown that a draft 11n three antenna router and card pair will typically get around 60 Mbps best case in 20 MHz mode and 80 Mbps in 20/40 for an TCP IxChariot test, which is much more efficient than say, a Windows file transfer.

 

[Ranma13]

Oh oops, I forgot to mention. I'm basically copying large video files through simple networking in Windows from the desktop to the laptop, practically the only reason why I'd need something higher than b. I'm measuring the transfer speed using Netstat Live and the wireless status page on the router to see the link speed (it's nice because it updates automatically every few seconds).

Ok, I forced the router into g mode and started transferring some more files. The rate is 54 mbps for both computers as reported by the router and the transfer speed is averaging around 6 mbps. I also tried it on both 802.11n only and mixed 802.11n and g and got around 13 mbps for both. Note that I had to move the router back to its original location since there are a few people in this house who use wireless and I can't exactly be taking away their internet to run some tests.

The main reason why I'm worried is because I read about how you should pair the PCI card with the router, but I also read some pretty bad things about this PCI card (D-Link DWA-552). But from the testing that I did earlier, it seems that it's only slightly slower than the Intel 4965.

 

[thiggins]

If you're getting 6 Mbps with 11g, that's about 30% of typical 11g maximum throughput, which we'll call 20 Mbps. Some of that is due to signal attenuation (since you had to move the router and clients out of the same room) and some due to overhead of the Windows file copy.

If we say typical draft 11n maximum throughput in 20 MHz mode is 60 Mbps, then 30% of that is 18 Mbps. So given the variables, you're not that far off with 13 Mbps.

The D-Link card is a 3 antenna (3T3R card using the same Atheros chipset as in the DIR-655 (AR5416 BB/MAC and AR2133 Transceiver), so the two are "matched". Make sure you upgrade to the latest drivers and firmware if any is available because that could help performance.

Doing large file transfers via wireless is generally going to be unsatisfactory and it's even worse when you're running wireless on both ends of the connection. Remember you're going from the notebook to the DIR-655, then the DIR-655 to the desktop. Since there is only one radio, it has to receive then retransmit, so that cuts available bandwidth in half.

If you could change just one of the connections to wired, you would probably double your throughput.

 

[Ranma13]

I've managed to find a good spot where the router can reach the rest of the house with some help from the Ez-12 design from freeantennas.com. Unfortunately, there's only enough room to put two of them on the 3-antenna router, but it definitely does help the signal. I've also found a way to get a wired connection to my desktop, which is great news for me because now I can save myself the $80 that the DWA-552 PCI card costed.

After running some speed tests, the highest rate I can get for my laptop is around 40 Mbps, which makes sense because half of ~100 is 50. When I bring it upstairs and into another room, it drops to about 20-30, which is still pretty respectable, considering that another laptop with a g card in the same room only gets about 8.

 

[thiggins]

Sounds good. Moving one of the connections to wired was probably the biggest help.