Scrubb
Posts: 8
Joined: Sat Jul 07, 2012 2:57 am

Very Low Network Bandwidth with USB Network Dongle

Sat Jul 07, 2012 3:31 am

Greetings,
I have tried two different USB ethernet dongles. One that uses the Pegasus driver, and one that uses the dm9601 driver. Both dongles register as a 100Mb adapter. However, when I attempt an iperf to test the speed I get 3.78 Mb. However, the same iperf test on the native adapter results in 46.5Mb.

I am trying to create a firewall device and need to add a second adapter. I thought USB would allow up to 480Mbs. Assuming overhead, low power, etc, I thought I'd at least get 10Mb. But 3.4Mb is not usable.

Has anyone gotten better results using any specific usb dongle? Is there a reason why I am seeing such miserable transfer rates?

Thanks in advance.

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rpdom
Posts: 14718
Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Very Low Network Bandwidth with USB Network Dongle

Sat Jul 07, 2012 4:31 am

The dm9601 adaptor only supports USB1.1, which runs at 12Mbs, so with the USB overhead I'd doubt you'd get more than 6MBs throughput from it (I have one of those dongles and found it to be dreadfully slow).

The native/on-board adaptor is a true USB2.0 device and runs at 480Mbs and so gets a much higher throughput.

I haven't tried any other dongles, so can't recommend any, sorry :-(

Just make sure that any you do get are USB2 devices.

Scrubb
Posts: 8
Joined: Sat Jul 07, 2012 2:57 am

Re: Very Low Network Bandwidth with USB Network Dongle

Sat Jul 07, 2012 4:37 am

Drat! The dongle was advertised as 2.0. Well, back to the drawing board. Thanks for the insight. I'll see if I can find a real 2.0 dongle. I'll post if it works well.

CCitizenTO
Posts: 83
Joined: Sun May 20, 2012 2:14 am

Re: Very Low Network Bandwidth with USB Network Dongle

Sun Jul 08, 2012 5:58 am

Given you are mentioning 100Mbps wireless dongle I'll assume it is using the Wireless N (802.11n) standard rather than Wireless G (802.11g) standard. However, if you are using a Wireless N dongle to connect to a Wireless G Router it can and will fall back and use Wireless G speeds.

Another thing that may be confusing you is bandwidth vs data rates. Bandwidth is typically measured in BITS (small b) per second such as Mbps while data is measured in BYTES (big B) such as MB/s. A bit is 8 times smaller than a byte. When I need to convert between units I use this tool here: http://web.forret.com/tools/bandwidth.asp

Wireless G = 54 Mbps = 6.75 MB/s
Wireless N = 100 Mbps = 12.5 MB/s

USB1.0 = 12Mbps = 1.5MB/s
USB2.0 = 480Mbps = 60MB/s

Other things to take into consideration.

1) Radio (Wireless) medium is subject to interference. When there is interference speeds go down due to things needing to be retransmitted
2) Radio is also a SHARED medium. Thus if your RPi is connected, your phone, your laptop, your XBox/PS3, etc... each of those is taking a bite out of your bandwidth as well.
3) 2.4 GHz band is heavily populated it includes other peoples wifi, cordless phones, baby monitors, intercoms, etc... all use these frequencies.

Thus before you go out and buy a new dongle. Keep in mind that new dongles might not solve your problems. Especially if it's a USB 2.0 Wireless N Dongle connecting to a Wireless G router.

Also dont forget Ethernet overhead takes up some of the potential as well. Thus even with a 100Mbps connection it wont reach it's full 12.5MB/s.

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rpdom
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Joined: Sun May 06, 2012 5:17 am
Location: Chelmsford, Essex, UK

Re: Very Low Network Bandwidth with USB Network Dongle

Sun Jul 08, 2012 6:17 am

Scrubb wrote:Drat! The dongle was advertised as 2.0. Well, back to the drawing board. Thanks for the insight. I'll see if I can find a real 2.0 dongle. I'll post if it works well.
Yeah, I got caught out the same way. Didn't read the specs carefully enough. These devices are often advertised as USB2.0 compatible. Ie. they work with USB2.0. If you check your system logs after plugging one in, you'll see it referred to as a "full speed" device (which is USB1.1 @ 12Mb/s), not "high speed" (USB2.0 @ 480Mb/s).
CCitizenTO wrote:Given you are mentioning 100Mbps wireless dongle I'll assume...
No, these are wired devices, not wireless.

CCitizenTO
Posts: 83
Joined: Sun May 20, 2012 2:14 am

Re: Very Low Network Bandwidth with USB Network Dongle

Sun Jul 08, 2012 4:45 pm

Well I havent been able to test a wireless connection but I've done iperf on eth0 and got the following result...

74.1
74.2
74.6

Mbps... This seems to indicate a 25% overhead or data loss on average. This is also a more ideal situation. My wire connection is about 2-3 feet long between the Pi and the router and the wire connection between my router and my computer which was used as the server is about 5-6 feet. I dont know how the first poster is only getting 45-46Mbps on the native interface (eth0). Oh and my RPi is being run headless w/ me sshing into it and with only 32mb towards the GPU. That might be improving performance. If you are running your Pi with X server and graphics it might be slowing your network connection down because the processor is dedicating CPU time to the graphics as well.

Also another issue may be if you are pluging it directly into the Pi it's demanding too much voltage/amps to work properly. You may need a powered USB hub just like if you were to use a USB Wifi Dongle since they suck up too much power for the RPi to give it to them.

Scrubb
Posts: 8
Joined: Sat Jul 07, 2012 2:57 am

Re: Very Low Network Bandwidth with USB Network Dongle

Sun Jul 08, 2012 5:32 pm

Thanks for the posts and comments about the wireless connections. There is some excellent information here.

I did not put it in the subject and probably should have, but I am specifically dealing with wired networking. Unfortunately in the list of tested peripherals there is a dearth information on tested wired USB adapters.

Based on the rpdom's responses, I think my issue is indeed USB 1.1 vs 2.0.

I am trying to find a wired adapter that will give at least 10Mb of bandwidth. It is often not detailed enough on the product specs to tell if an adapter is 2.0 compatible or truly 2.0 speed. In addition, the only ones that truly appear to be 2.0 devices and do 10/100/1000 speeds cost more than the PI itself!

Does anyone have a good recommendation?

I've been trying to get more specs on this one, but I can't find anything usefull: http://www.amazon.com/gp/product/B002Q10UQU/
In addition, I can't determine it's chipset to determine if its supported by debian, let alone the Pi.

Any thoughts on a good USB2.0 network adapater would be welcome.
Thanks again!

Scrubb
Posts: 8
Joined: Sat Jul 07, 2012 2:57 am

Re: Very Low Network Bandwidth with USB Network Dongle

Fri Jul 13, 2012 2:43 am

Ok, so I'm posting this to close out the thread.

I DID finally find a reasonable priced USB 2.0 10/100 dongle ($11.48): http://www.amazon.com/gp/product/B002Q10UQU/

The Pi saw it and loaded a driver happily:

MOSCHIP usb-ethernet driver 1-1.2:1.0: eth1: register 'MOSCHIP usb-ethernet driver' at usb-bcm2708_usb-1.2, MOSCHIP 7830/7832/7730 usb-NET adapter, 00:87:12:67:00:4b
Jul 12 21:46:40 raspberrypi kernel: [ 1319.257579] usbcore: registered new interface driver MOSCHIP usb-ethernet driver

An iperf shows between 80 and 90 Mbps!!!

So thanks for all the thoughts on this thread and I'm good to go for my firewall. If this adapter continues to work and be stable I'll post it to the tested peripherals thread.
Thanks!

CCitizenTO
Posts: 83
Joined: Sun May 20, 2012 2:14 am

Re: Very Low Network Bandwidth with USB Network Dongle

Sat Jul 14, 2012 4:01 pm

Good job!

Also when I tested iperf on my Pi's native 100Mbps interface it showed about 75Mbps (i'm guessing it's common to see anywhere from 10-25% overhead)

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