Very poor AP mode speed. Configuration problem?

[rpakdel]

I've been battling this problem for a while and just this last weekend I had it enough and decided to do a thorough investigation. I've spent a lot of time googling for ideas (disable WMM, etc.) but still I came out defeated.

Current Setup

Main router: Asus RT-N66U running Asus firmware (Merlin build).
Two 8 port gigabit switches (TPLink).
All rooms are wired through the switches (thanks to newer townhome).
I have a number of linux machines acting as file servers.

For performance measurement, I used iperf (windows and linux). I've run it probably 100s of times with various configurations. I have InSSIDer home running on laptop for analysing channel and network overlaps.

While everything is wired I can hit 700-900 mbps between desktop, laptop and various file servers.

The main router used to be RT-N16U (tomatoUSB and Merlin firmware), but I recently upgraded it to RT-N66U. Wireless performance from these two were and is good, the RT-N66U obviously is faster and better. The RT-N16U replaced an older WRT54GL (TomatoUSB).

Access Point

The master bedroom has always had very poor wireless reception. It is the furthest away from the main router and one floor up. Of course the wife is not happy since she can't stream...

I've always had some sort of AP in that room. Initially it was an older Linksys WRT54AP, then Linksys WRT54GL, then the Asus RT-N16U as I upgraded the main router. I've also tried a lower-end Linksys without external antennas (E3000? DDWRT).

Anyway, I always would notice the poor performance when connected to the AP. File transfer would be average 1-2 MB/s in Windows. It doesn't seem to matter what hardware is put in place. I simply assumed this was due to something out of my control (perhaps because I was running TomatoUSB, low power NAS, etc.). Anyway, the speeds were good enough to keep the wife happy.

Problem?

Up until now I had low power file servers (pogoplug and WD MyBookLive). I just got an older dual core machine for free and turned it into a fileserver. I noticed huge speed ups when transferring files from desktop and laptop but no difference when hooked through the AP.

I decided to run some numbers with iperf. I hooked up the laptop directly to the AP and wired I can reach 700mbps. But wireless, I can only get 5-15 mbps even when the laptop is next to the AP and inSSIDer shows -25DB signal. I've moved it around, changed channels (making sure not to overlap with main router and with least conflict with neighbors). I even moved the router to another room. Then I tried the older WAP54G (running DD-WRT and then Linksys firmware) in another room and still the same crappy performance.

Is there something obvious I'm missing or are APs just slow? I can understand there being speed limitations between wired <-> wireless modules of the hardware, but these speeds are just way out of whack from what these routers are capable.

I'm leaving out a lot of technical details. I've tried every guide and suggestion I could find online. If there is anything specific I need to provide including actual performance numbers I can do that tonight.

Thanks in advance!

 

[stevech]

APs should be the same speed as the AP built into the WiFi router if they're both 11n or 11g or whatever.
Minus whatever penalty due to how the AP connects to the router.

A -25dBm (not DB) signal is as strong as it gets... this says the path lenth is line of sight and just a few feet. Indeed, some WiFi devices are "overloaded" with such as strong signal and get higher error rates and speed. In real-world, the signal strength is in the range of -80 to -40dBm as typical.

 

[thiggins]

First, what is your wireless client (make, model and type a/b/g/n/ac )? That will limit your maximum throughput.

Second, what link rate is your client reporting?

Third, iperf can provide a wide range of readings, depending on settings. I suggest timing a large single file transfer and calculating speed from there.

You should be using WPA2/AES encryption, WMM enabled and 20 MHz bandwidth mode for 2.4 GHz.

If your client supports 5 GHz, try testing it, too. You can use 40 MHz channels there.

 

[rpakdel]

Thanks for the replies. I played a bit more with different channels and measured bandwidth with 4 different devices.

I've currently setup the RT-N16U in AP mode. Wireless N. Security is AES. Channel 11. The signal strengths below are according to the Asus client status panel (doesn't quite match inSSIDer, but close).

As for clients:

• Thinkpad T430: Intel Centrino Advanced-N 6205. 2.4Ghz, N, AES, -40dB
• Thinkpad T400: Intel Wifi Link 5100 AGN: 2.4Ghz, N, AES, -41dB
• iPhone 4 running iOS 7: 2.4Ghz, -54dB
• iPad3 running iOS 5.1 (ya, it's the kids iPad): 2.4Ghz, -48dB

Here are the results of running some speed tests. For the laptops, I copied a 2GB file from the new fast fileserver. I'm 6-8 feet away from the router. I waited 5 minutes or so for the speed reported by Windows to stablise. For iPhone and iPad I used the speedtest app. my Internet is 25 Mbps down, 2.5 Mbps up and I can reach those on the desktop.

• T430: file 3.85 MB/second (30.8 Mbps), speedtest: 20.68 Mbps down, 2.59 Mbps up
• T400: file 3.72 MB/second (29.76 Mbps), speedtest: 21.96 Mbps down, 2.65 up.
• iPhone4: speedtest 11.83 Mbps down, 2.66 Mbps up
• iPad3: speedtest 16.28 Mbps down, 2.68 Mbps up

on the T400 then I ran iperf a few times for 30 seconds. The final reported bandwidth was 17.7 Mbps. I then ran it in UDP mode for 30 seconds. 0/2674 datagrams were lost and 1 was sent out of order.

Are these normal?

 

[rpakdel]

Some more numbers

T400 laptop connected wirelessly to RT-N66U in the living room (5Ghz): 20.0 MB/s (160 Mbps) when copying the 2GB file. Using speedtest 26.73 Mbps down and 2.67 Mbps up.

iPhone4 connected to RT-N66U: speedtest 16.83 Mbps down, 2.71 Mbps up.

 

[thiggins]

Both laptop adapters are 2x2 N, so have a maximum 130 Mbps link rate with 20 MHz bandwidth. Our tests, which use very low overhead IxChariot streams, have gotten about 70 Mbps best case with 2x2 clients and routers/APs. So your numbers, particularly uplink, are low.

Do you see a difference when connecting clients to the RT-N66U in 2.4 GHz? Or connecting to the RT-N16 in 5 GHz?

 

[rpakdel]

First, thank you for the help. I'm learning quite a bit about networking

Using the T400 laptop while sitting a few feet away from the RT-N66U router I got the following by transferring a 2GB file

• 2.4Ghz 20Mhz: 7.0MB/s
• 5Ghz single channel 10MB/s
• 5Ghz dual channel 20MB/s

 

[thiggins]

So it looks like slower throughput is through the RT-N16.

How is the N16 configured as an AP and how is it connected to the main router?

 

[rpakdel]

Sorry for the delay. I've been quite busy.

I spent another night fiddling with channels and running more test. We are in a 55 unit townhouse complex and our unit is in the middle. There are quite a bit of wireless devices around us. I think this might be the one reason for really slow speed. Is that a possibility? If so, would upgrading the stock antennas help at all?

As for connection all of the follwing are wired:

Living room: Modem -> RT-N66U WAN -> LAN port -> wall -> switch (TPlink) -> wall -> bedroom: RT-N16 LAN port.

The file server is connected to RT-N66 via another TPlink switch. Both of these switches are 8 port and gigabit.

DHCP and DNS are handled by RT-N66.

I've checked the cables using a cheap cable tester and they all appear fine. Additionaly, as I mentioned, throughput is great when I plug the laptop to the LAN port of RT-N16.

Thanks

 

[thiggins]

Yes, many networks can be a factor if they are constantly busy. That doesn't answer why the N16 performs more poorly than the N66. The way to check this is to move the N66 to the N16 location and run tests.

The only way to get higher throughput with loaded channels is to move to 5 GHz if possible.