Wireless throughput issue using RT-N66U and E4200... I've tried everything :(

[Mikkle]

Long time lurker, first time poster here. I have been struggling to figure out this problem with my wireless throughput these past few days and have tried everything I can think of, with no success. I thought I would ask the community because I am at my wit's end.

I recently replaced three aging routers in an attempt to increase range and simplify my network. We have a two-story home, and the previous setup was as follows: In the living room downstairs, our cable modem was plugged into a Cisco WRT-320N serving as AP. The WRT-320N was configured to use the 802.11 N 5 Ghz band exclusively. Another router, a WRT160N was sitting next to it and configured to provide 2.4 Ghz B/G/N access. The WRT160N was plugged in to the WRT320N so they were on the same network. Upstairs, the office os exactly the room above, where we had a second WRT-320N configured as a wireless bridge over the 5 Ghz band. We then had a couple of PCs attached to said bridge.

This setup was working well, until the WRT160N died last week. I thought this would be a good opportunity to get a true dual-band router downstairs, and increase our wifi range and throughput in the process.

There is now an ASUS RT-N66U in the living room, and a Cisco E4200 in the office upstairs. For now, the RT-N66U is configured to provide two N networks, one at 2.4 Ghz and the other at 5 Ghz. The latter is exclusively used to link to the wireless bridge upstairs, the aforementioned E4200 configured with DD-WRT. I've been doing quite a lot of testing to check what kind of performance increases we're getting over the old setup. Almost right away I noticed that between the AP and wireless bridge, the throughput takes a dive every few seconds. This can be seen in the following graph:

http://i.imgur.com/LzynB.png

Here is a TCP test I just performed using "iperf.exe -c hostname -i 1 -t 60 -w 1M" on a client PC upstairs. As you can see, throughput easily hits 120-130 mbps until something happens and it drops down to 0 mbps for a second or so.

------------------------------------------------------------
Client connecting to htpc, TCP port 5001
TCP window size: 1.00 MByte
------------------------------------------------------------
[ 3] local 10.0.0.112 port 54043 connected with 10.0.0.101 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0- 1.0 sec 4.75 MBytes 39.8 Mbits/sec
[ 3] 1.0- 2.0 sec 14.0 MBytes 117 Mbits/sec
[ 3] 2.0- 3.0 sec 128 KBytes 1.05 Mbits/sec <----- ?
[ 3] 3.0- 4.0 sec 15.5 MBytes 130 Mbits/sec
[ 3] 4.0- 5.0 sec 15.2 MBytes 128 Mbits/sec
[ 3] 5.0- 6.0 sec 128 KBytes 1.05 Mbits/sec <----- ?
[ 3] 6.0- 7.0 sec 15.6 MBytes 131 Mbits/sec
[ 3] 7.0- 8.0 sec 14.8 MBytes 124 Mbits/sec
[ 3] 8.0- 9.0 sec 0.00 Bytes 0.00 bits/sec <------ ?
[ 3] 9.0-10.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 10.0-11.0 sec 14.9 MBytes 125 Mbits/sec
[ 3] 11.0-12.0 sec 15.0 MBytes 126 Mbits/sec
[ 3] 12.0-13.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 13.0-14.0 sec 16.1 MBytes 135 Mbits/sec
[ 3] 14.0-15.0 sec 15.8 MBytes 132 Mbits/sec
[ 3] 15.0-16.0 sec 13.8 MBytes 115 Mbits/sec
[ 3] 16.0-17.0 sec 15.9 MBytes 133 Mbits/sec
[ 3] 17.0-18.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 18.0-19.0 sec 14.1 MBytes 118 Mbits/sec
[ 3] 19.0-20.0 sec 15.1 MBytes 127 Mbits/sec
[ 3] 20.0-21.0 sec 7.38 MBytes 61.9 Mbits/sec
[ 3] 21.0-22.0 sec 1.88 MBytes 15.7 Mbits/sec
[ 3] 22.0-23.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 23.0-24.0 sec 14.9 MBytes 125 Mbits/sec
[ 3] 24.0-25.0 sec 14.8 MBytes 124 Mbits/sec
[ 3] 25.0-26.0 sec 128 KBytes 1.05 Mbits/sec <---- ?
[ 3] 26.0-27.0 sec 15.0 MBytes 126 Mbits/sec
[ 3] 27.0-28.0 sec 14.2 MBytes 120 Mbits/sec
[ 3] 28.0-29.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 29.0-30.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 30.0-31.0 sec 16.4 MBytes 137 Mbits/sec
[ 3] 31.0-32.0 sec 14.6 MBytes 123 Mbits/sec
[ 3] 32.0-33.0 sec 128 KBytes 1.05 Mbits/sec <---- ?
[ 3] 33.0-34.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 34.0-35.0 sec 12.5 MBytes 105 Mbits/sec
[ 3] 35.0-36.0 sec 9.12 MBytes 76.5 Mbits/sec
[ 3] 36.0-37.0 sec 15.6 MBytes 131 Mbits/sec
[ 3] 37.0-38.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 38.0-39.0 sec 128 KBytes 1.05 Mbits/sec <---- ?
[ 3] 39.0-40.0 sec 15.9 MBytes 133 Mbits/sec
[ 3] 40.0-41.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 41.0-42.0 sec 15.0 MBytes 126 Mbits/sec
[ 3] 42.0-43.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 43.0-44.0 sec 16.0 MBytes 134 Mbits/sec
[ 3] 44.0-45.0 sec 15.5 MBytes 130 Mbits/sec
[ 3] 45.0-46.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 46.0-47.0 sec 14.8 MBytes 124 Mbits/sec
[ 3] 47.0-48.0 sec 15.5 MBytes 130 Mbits/sec
[ 3] 48.0-49.0 sec 15.1 MBytes 127 Mbits/sec
[ 3] 49.0-50.0 sec 15.8 MBytes 132 Mbits/sec
[ 3] 50.0-51.0 sec 16.1 MBytes 135 Mbits/sec
[ 3] 51.0-52.0 sec 14.6 MBytes 123 Mbits/sec
[ 3] 52.0-53.0 sec 14.2 MBytes 120 Mbits/sec
[ 3] 53.0-54.0 sec 16.9 MBytes 142 Mbits/sec
[ 3] 54.0-55.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 55.0-56.0 sec 14.5 MBytes 122 Mbits/sec
[ 3] 56.0-57.0 sec 16.4 MBytes 137 Mbits/sec
[ 3] 57.0-58.0 sec 14.6 MBytes 123 Mbits/sec
[ 3] 58.0-59.0 sec 0.00 Bytes 0.00 bits/sec <----- ?
[ 3] 59.0-60.0 sec 15.4 MBytes 129 Mbits/sec
[ 3] 0.0-60.0 sec 676 MBytes 94.5 Mbits/sec


A couple of additional observations:

• Between AP and bridge, Signal is at -44dbm, and noise is at -85dbm. This is quite a bit better signal than I was getting with the two WRT320N.
• The issue is noticeable regardless of what channel I select. I ran inSSIDer and 5 Ghz channels *seem* to be clear. There is only one other visible 5 Ghz network in the area and it is quite weak.
• The issue is noticeable both at 20 Mhz and 40 Mhz channel bandwidth.
• If I run iperf in the other direction, the issue is also noticeable.
• The exact same throughput behavior is noticeable when copying a large file over the network.

I have a laptop with an Intel 5100 A/G/N interface that is 5 Ghz compatible. If I place the laptop where the E4200 bridge is and run the same test in iperf, I do not notice even a hint of this issue and throughput is constant. This leads me to believe I may be dealing with a problem with the E4200 bridge rather than the RT-N66U AP.


Borrowing a couple of additional routers from friends and family this weekend in an effort to troubleshoot, I have been able to try a few additional combinations. Another Cisco E4200 displayed the exact same problem whether serving as AP or Bridge, while using a Netgear WNDR3800 as AP caused the issue to disappear.

AP / Bridge: result

ASUS RT-N66U / Cisco E4200 (friend): Problematic
ASUS RT-N66U / Cisco WRT320N: Problematic
Cisco E4200 (mine) / Cisco E4200 (friend): Problematic
Cisco E4200 (friend) / Cisco E4200 (mine): Problematic
Netgear WNDR3800 / Cisco E4200 (mine): OK


What are your thoughts on this? I feel like I'm close to figuring it out but I've been looking at it for so long I don't know what to try next.

I'm probably forgetting a few things here and this has already gotten too long, but please let me know if there are any additional troubleshooting steps I should take.

Thanks in advance for your help!

 

[patrickgerry]

Can you try rtn66u / Netgear WNDR3800

 

[thiggins]

I would suspect some incompatibility in WDS implementations. Could be the E4200 is adjusting rates a bit too often. Try changing locations. Also be sure any automatic channel adjustment is turned off.

 

[Mikkle]

Thanks for the replies, I appreciate it.

Can you try rtn66u / Netgear WNDR3800

I'll see if I can borrow the router again and give that a shot tonight. I can't recall exactly why I did not try it, off the top of my head I think it was because DD-WRT is not officially supported on WNDR3800, and I couldn't find a wireless bridge mode in the stock Netgear firmware (althout wireless repeater was supported). I will play with it some more.

I would suspect some incompatibility in WDS implementations. Could be the E4200 is adjusting rates a bit too often. Try changing locations. Also be sure any automatic channel adjustment is turned off.

This is the first time I read about WDS as I have never come across the term before. When you mention a possible incompatibility, are we talking about a quirk at the hardware layer, the software layer, or both? Is there any way for me to see if the E4200 is indeed changing rates too often? (The DD-WRT wireless status page shows a constant "450 mbps" link, but it may be that it isn't refreshing quickly enough for me to see it.)


Thanks again for any advice you can provide!

 

[Gingernut]

Are both the E4200 and the WRT320N running DDWrt ?

 

[Mikkle]

Are both the E4200 and the WRT320N running DDWrt ?

Yes they are. I've installed DD-WRT on two E4200 units (mine and my friend's), and two WRT320N units (the two that I own) and the result is the same for all four routers. I am using build 18000 for the E4200 and build 17990 for the WRT320N.

 

[Gingernut]

So that maybe the problem, DDWrt is very feature packed but also very buggy.

You might want to either go back to stock or try out Tomato and retest the whole setup.

If you do, drop back in and tell us your findings.

 

[Mikkle]

So that maybe the problem, DDWrt is very feature packed but also very buggy.

You might want to either go back to stock or try out Tomato and retest the whole setup.

If you do, drop back in and tell us your findings.

Thanks, I will be sure to do that. The reason I haven't been more suspect of DD-WRT itself is twofold: First, it was working flawlessly with the two WRT320N in bridge mode. Second, when pairing a DD-WRT router with the Netgear WNDR3800, the issue cannot be reproduced.

That being said it sounds like there may be some weird incompatibility as thiggins seemed to suggest, so I'll definitely try a few more configurations (including TomatoUSB) tonight.

Thanks again for your help, it is much appreciated!