New Router Connection Speeds

Some time ago I wrote a shell script to monitor internal LAN connection speeds. Nothing fancy, basically a wrapper to the iperf command but providing me with a desired output. The script updates a text log of the results. I have been running the script as a cron job on all LAN clients. To support the cron jobs I run an iperf server daemon on my LAN server.

All wired systems average about 940 Mbits/second.

With my WRT54GL router using DD-WRT, which supports 802.11g, I saw average wireless iperf speeds with my Thinkpad T400 of about 21 Mbits/second. With the Asus RT-AC66U running DD-WRT I see 802.11g speeds of about 21 Mbits/second.

One reason I bought the new router was to improve my wireless connections. The RT-AC66U supports 802.11ac.

The T400 has an Intel 5100 AGN wireless controller and should be able to use 802.11n. In addition to the device name, the iwconfig command shows IEEE 802.11abgn.

Yet I was unable to obtain 802.11n speeds. I expected something in the neighborhood of 40 to 60 Mbps. Nothing dramatic but something 2 to 3 times faster than 802.11g.

After some tinkering, I discovered I was obtaining increased speeds with 802.11n. I ran into a quirk that misled me.

When I ran iperf as a client from the T400, I saw perplexing 802.11n speeds of less than 10 Mbps. Eventually I reversed the test. I ran an iperf server instance on the T400 and ran iperf as a client on another LAN computer. I then saw better than 40 Mbps.

I saw the same odd dual results with iperf3.

I have no idea what causes this behavior.

I updated my script to support testing from the LAN server or client workstation. The former option allows me to test the T400 and obtain reasonable results. Some SSH magic is needed to start an iperf server instance at the remote system and after the test kill the unneeded iperf daemon process.

After accumulating some data, my T400 wireless speeds are averaging about 38 Mbps, which I understand is typical.

This all on the 2.4 GHz band. With the 5 GHz band I see speeds of about 45 to 50 Mbps. When I use the 2.4 GHz band while the 5 GHz radio is enabled, the speeds dwindle to about 12 Mbps.

Perhaps there are ways to squeeze additional bits per second as well as optimizing both bands. At least now I see faster 802.11n wireless speeds with the laptop.

Posted: Category: Usability Tagged: DD-WRT

Next: Remote Access With DD-WRT

Previous: Using Unique SSIDs