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Old 11-08-2016, 10:48 PM   #1
upnort
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Slow iperf wireless in one direction


Edit: Please refer to the third post for a more correct problem description. I would like to resolve this if possible.

I have an Asus RT-AC66U router. I installed the latest DD-WRT beta. I plan to replace a Linksys WRT54GL running DD-WRT.

Everything thus far configured on the RT-AC66U is working. I can surf the web with wired or wireless.

I run an hourly cron job on all LAN computers to run and log iperf results within my LAN. The LAN server is the iperf server. My wired and wireless iperf results through the WRT54GL are consistent and have been for months. I do not use the iperf tests as throughput tests but only as a nominal method of monitoring network connections.

My WAN/ISP connection speeds with the RT-AC66U are about the same as with the WRT54GL. My iperf tests using wired are a tad faster with the RT-AC66U.

With the WRT54GL I have been seeing about 21 Mbps with my Lenovo T400 wireless. My iperf tests with the T400 through the RT-AC66U are less than half the expected average speed. At best with the RT-AC66U I see about 10 Mbps wireless. Usually I see about 7 to 8 Mbps.

I reverted DD-WRT on the RT-AC66U to Build 25697 v24 SP2 and see the same slow results.

The T400 has an Intel 5100 AGN wireless and should be able to use 802.11n. The WRT54GL only supports 802.11g. The RT-AC66U supports up to 802.11ac. With the RT-AC66U I expected no slower than the WRT54GL average and hopefully something faster.

The T400 has Ubuntu MATE 16.04 and Slackware 14.1 installed. Curiously, the 14.1 system returns the expected average iperf results with the RT-AC66U. Perhaps the difference is NetworkManager, but inconclusive at the moment. I deleted and recreated the Ubuntu NetworkManager system-connections config files. No difference.

I do not have any other wireless devices to help with testing. The RT-AC66U and T400 are about 4 feet apart when testing. I never performed any testing with the Asus firmware.

I tried many different DD-WRT options, including higher and lower transmitter power. I have been searching the web to no avail.

Having run the WRT54GL for the past 10 years, I am unfamiliar with dual band routers. That lack of knowledge could be contributing to the problem. Perhaps I have something configured incorrectly.

Thanks for any help.

Edit: Update the topic title (was "Slow DD-WRT Wireless").

Last edited by upnort; 11-14-2016 at 12:27 PM.
 
Old 11-09-2016, 08:56 PM   #2
jefro
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When I see half then I get to thinking that either half duplex is in or it is not negotiating at same speeds as it was before. Might have fallen back to lower speed band.

Guess you could have changed encryption levels much higher. Disable security and run test.

Might be a setting for B/G protection. Once in a while you can't have legacy devices running without that.

So, find more info on connection on both computer and on router side.
 
Old 11-11-2016, 10:53 PM   #3
upnort
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An update for future readers.

This is only an 802.11n wireless problem with respect to my LAN. Testing iperf with 1 Gbps wired all run at about 950 Mbps. Testing iperf with 802.11g is consistent in either direction. The problem seems to manifest only when moving from 802.11g to 802.11n.

Using 802.11n and running iperf as a client from the T400 laptop to an iperf server on the LAN results in unexpected slow speeds.

Creating an iperf server on a different LAN computer and running the iperf client from the laptop resulted in the same slow speeds.

I reversed roles and created an iperf server on the laptop. When running an iperf client from any other computer I saw expected 802.11n speeds at about 40 MBps or faster.

When testing iperf in either direction, monitoring the NetworkManager Connection Information dialog showed a "Speed" of 72 Mbps or 150 Mbps, which seems to affirm using 802.11n.

The one-way results are not distro dependent. I saw the same directional results in Slackware 14.1 or Ubuntu MATE 16.04.

The results do not seem to be caused by encryption. Removing encryption in the DD-WRT configuration did not change the results.

When running an iperf client at the laptop using the -r option, I saw the same slow speeds going from the laptop to the LAN server but see 40 Mbps or faster from the LAN server to the laptop.

As far as I can tell with these new tests, 802.11n probably is working fine with DD-WRT and the RT-AC66U.

I installed iperf3 on the laptop and LAN server. Same oddball one-way results.

Copying files from the laptop to another computer and vice-versa is not the same as the iperf test, although the copy times in either direction are consistent at about 10 Mbps.

I still do not know the root cause of the problem. An iperf bug? A DD-WRT bug? DD-WRT configuration? RT-AC66U hardware? T400 hardware? An iwlwifi driver problem?

Next week I hope to test iperf and the T400 on a different network.
 
Old 11-23-2016, 06:29 PM   #4
briselec
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seems to be a known problem with iwlwifi
https://wiki.archlinux.org/index.php...ration#iwlwifi
 
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Old 11-25-2016, 06:06 PM   #5
upnort
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Quote:
seems to be a known problem with iwlwifi
Wow. Thanks.

Adding the 11n_disable=8 option dramatically changed my iperf results.

With 2.4 GHz:

From laptop to server: ~33 Mbps
From server to laptop: ~50 Mbps

With 5 GHz:

From laptop to server: ~61 Mbps
From server to laptop: ~95 Mbps

Before the change I was seeing ~45 Mbps from server to laptop using 5 GHz. The improvement is double.

Removing that option returns the system to the same dismal results.

Allegedly there is some kind of trade-off between "stability" and speed. I will watch for packet drops, but I suspect everything will be fine.

Interesting that I still see significant differences depending on which direction I run the iperf test.
 
  


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