My 802.11n home network is maxing out at 2MB/sec and I can't figure out why

[AngelosP]

Hi guys,

I'm having a very hard time figuring this one out and I was wondering if you could help me out.

SETUP

Wireless Router: D-Link DIR-655 (revision A4, firmware 1.34NA)
File server: Gigabit Ethernet (running Windows Home Server)
Laptop: Intel Wireless WiFi Link 4965AGN (running Win7)
Desktop: D-Link DWA-556 XTREME N PCI Express Desktop Adapter (running Win7)

Note: I retrieved the following information using the Xirrus Wi-Fi Inspector.

Router settings: Channel 1, 5 | Frequency: 2412, 2432
On the laptop: Signal strength:-44 dBm | Mode: 802.11n | Encyrption: AES-CCMP | Authentication: WPA2/PSK
On the desktop: Signal strength:-59 dBm | Mode: 802.11n | Encyrption AES-CCMP | Authentication: WPA2/PSK

I have attached a screenshot of all the wireless network areas within range. It's a screenshot from Xirrus Wi-Fi Inspector running on my laptop. The very first network on the list is mine.

ISSUE

My test is to copy a single large file (4GB in size) from my file server to the laptop and the desktop.

• When my laptop or desktop are connected via a cable, I get 70MB/sec+ on both.
• When my laptop is connected via wireless, I get 4MB/sec.
• When my desktop is connected via wireless, I get 2MB/sec.

Note: It doesn't matter where my laptop is located, I still get about the same speed. I can place it right next to the router itself and get -10dBm signal, however the speed will never exceed 4MB/sec.

Any ideas?

 

[overdrive31]

Your laptop is only running at wireless G speeds using WPA TKIP, so roughly 20 Mbps max sorta like what you're seeing. Change it to WPA2 AES and you should see a difference.

 

[AngelosP]

Your laptop is only running at wireless G speeds using WPA TKIP, so roughly 20 Mbps max sorta like what you're seeing. Change it to WPA2 AES and you should see a difference.

Thank you for the suggestion. I have changed the settings on the laptop to WPA2/AES and now the file transfer is averaging at 4MB/sec when the laptop is right next to the router. Although an improvement, this is still only about 32mbits so something else must be wrong too.

I have been having a look through the router's administration screens and I noticed the following (also see screenshot attached):

• While the laptop is copying the large file from the file server, the router is reporting that the signal is 100% (because I have placed the laptop right next to the router) and that the connection speed is 117 Mbps.
• At the same time the signal for my desktop is 70% (it's further away from the router) and the connection speed is 26 Mbps.

This is confusing me even more.

• 117 Mbps is approx 15 MB/sec, yet on the laptop I am only seeing transfer speed of approx 4MB/sec.
• 26 Mbps is approx 3.5MB/sec and on the desktop I am getting approx 2MB/sec which if you consider overheads/etc. is not that bad.

I seem to be having two different issues here:

1. My laptop is not able to transfer the file at the speed it is connected to the router.
2. My desktop is connecting at really low speeds to the router.

I will keep on digging and trying out different settings, but if you guys have any good ideas please throw them my way.

 

[overdrive31]

Using 40MHz mode? What are you expecting?

Your environment is crowded, I hope you're not using 40MHz mode.

Using MIMO alone at 20MHz will get you roughly 60Mbps max at best.

Nothing is consistent with wireless, just like your cellular, you'll lose signal strength(link speed) unexpectedly.

 

[AngelosP]

Using 40MHz mode? What are you expecting?

Your environment is crowded, I hope you're not using 40MHz mode.

Using MIMO alone at 20MHz will get you roughly 60Mbps max at best.

The router is currently configured as 20/40 MHz (Auto). I will change that and force it to use 20MHz only and I will report back the results. What exactly is MIMO though?

 

[overdrive31]

MIMO stands for multiple-input multiple-output, it allows almost double the performance if both the router/ap and client hardware have it.

40MHz mode uses 2/3 the spectrum to accomplish almost double the performance, but shouldn't be used in an area with other 2.4GHz devices nearby. Its generally safe to use 40MHz mode on 5GHz band though.

MIMO = Multiple In Multiple Out(more than one stream/antenna at a time) and in this example it's only 2x(two stream/antenna) MIMO

SGI = Short Guard interval

MIMO(N) 20MHz = 130Mbps(w/ SGI = 150Mbps)

non-MIMO(N) 20MHz = 65Mbps(w/ SGI = 72.2Mbps) = Wireless N base speed(link rate)

MIMO(N) 40MHz = 270Mbps(w/ SGI = 300Mbps)

non-MIMO(N) 40MHz = 130Mbps(w/ SGI = 150Mbps)

 

[stevech]

4MB (bytes) per sec = 32Mbps. That's faster than 11g can do at the IP layer.

In WiFi 802.11, the IP layer speed will be aboutr 60% of the air link bit rate, excluding Internet and remote host server delays (i.e., speed on your LAN)

 

[overdrive31]

Link rate does not directly reflect throughput speeds. Just like wireless G, 54Mbps link rate only nets just about 20Mbps.

In best case scenario, 2x MIMO@40MHz with link rate of 300Mbps will only net you 120Mbps throughput.

Using only 2x MIMO@20MHz because of your crowded spectrum environment, you can probably get up to 150Mbps link rate with a net of maybe 60Mbps.

Also, when transferring data over the wireless, more often than not there is link rate decay resulting in lower transfer rates than expected. It can be caused by a multitude of things, like bad drivers, hardware vendor differences, or antennas and interference.

Just making the change from 20/40MHz auto to 20MHz only should have made an improvement, and it's the best you can do. Mixing the N and G clients could also be a hindrance, but with such a crowded spectrum you may not have the option to put them on a separate access point and channel. Give the laptop some distance from the router too. I have noticed the Intel cards for some reason have issues with being too close.

Wireless buys convenience not speed, I would go wired if worried about speed.