RPi Mini Wifi Module, very slow download speeds
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RPi Mini Wifi Module, very slow download speeds

by Barackbar on Thu Oct 10, 2013 2:56 pm

Hello,

I recently bought a Miniature USB Wifi Module for Raspberry Pi (http://www.adafruit.com/products/814#Description) and have been consistently getting download speeds of 60kB/s or less. The access point (Apple Airport Extreme 5th Generation) is less than 30 feet away if measured through the single wall that separates them and maybe 40 feet away if measured as a person would walk from one to the other. I am using this Pi as a rudimentary media player that accesses my iMac hard drive through the network using sshfs (http://packages.debian.org/wheezy/sshfs).

Link to screenshots and pictures from testing: http://imgur.com/a/FsaBa#0

I set up the dongle as instructed in Adafruit's tutorial section, it connected fine and never had any signal strength issues.
I first tested download and upload speeds between the iMac and Pi using pv (http://packages.debian.org/stable/utils/pv), and got about 49kB/s download and 62kB/s upload (1st and 2nd picture in album).
Though I failed to take pictures of it, I also tested the speed between the Pi and the internet by downloading various large pictures and got similar results.

Next I tested the speed by connecting the dongle to my iMac, downloading and installing the controller software (http://www.realtek.com.tw/downloads/dow ... loads=true), and using Speedtest.net.
Note, my iMac is literally less than a foot from the Airport Extreme, so signal strength is a non-issue.
Testing connection speed with the dongle gave surprising results: 0.34Mb/s, or 42.5kB/s, download (assuming it is measured in decimal megabits and not binary megabits: 0.34Mb/s * 1000kb/Mb / 8bits/byte = 42.5kB/s) and 3.34Mb/s upload (3rd picture in album).
Testing the iMac's built in Wifi adapter as a control yielded 2.68Mb/s down and 9.52Mb/s up (4th picture in album). Our college town apartment has a less than stellar internet connection that is shared among the entire complex, as such we have always had faster upload speeds.

In conclusion, I believe that either the Wifi adapter is defective on a hardware level or that I have overlooked some software/driver issue that is affecting both my iMac and RPi.

Thanks for your time.
(BTW I love the Adafruit RPi case I got at the same time.)
Barackbar
 
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Re: RPi Mini Wifi Module, very slow download speeds

by adafruit_support_mike on Thu Oct 10, 2013 8:10 pm

What you're seeing is probably a subtle issue we only learned about recently ourselves.

The Realtek driver for that chipset has built-in power management. The RasPi's USB ports can only deliver 140mA, which is toward the lower limit of what the device wants. The combination of those two factors leads to a situation where the driver keeps dropping the device into a low-power state and causing dropped packets. The user-level view of the problem is a weak/slow connection.

We've just added a description of the remedy to our tutorial on setting up network connections for a RasPi: http://learn.adafruit.com/adafruits-ras ... -configure . Basically you need a configuration file for the driver.
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Re: RPi Mini Wifi Module, very slow download speeds

by Barackbar on Sat Oct 19, 2013 12:56 pm

Thanks for the quick response. I applied the power saver fix and the Wifi dongle download speed is now jumping between 3-4Mb/s and 0Mb/s.
Like you said, it seems like a power supply issue. I expect it will work fine once I get an externally powered USB hub.
Barackbar
 
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