Sign in with
Sign up | Sign in
Your question

USB Hubs not enough bandwidth for USB products ?

Last response: in Components
Share
Anonymous
January 13, 2001 8:01:09 AM

I understand a 4 port USB hub will SHARE the bandwidth of the USB port I am plugged into. But will this SHARED bandwidth cause much performace difference for my peripherals such as my scanner, mouse, webcam and writing board ?

Or are these devices only required very little bandwidth thus even though 4 USB products are sharing ONE USB port, but the bandwidth is still adequate.

Thanks
Anonymous
March 20, 2001 6:12:15 PM

Here is what I have USB for my computer: Microsoft intellimouse optical, usb radio, usb joystick, usb hook-up for my digi cam, and usb zip drive. I have my mouse plugged into the motherboard, and a 4 port usb hub plugged into the motherboard. My rationale is that my mouse (which is the USB device I use the most) is guaranteed full bandwidth, and the others which I only use one or two at a time are sharing bandwidth. I'm not sure about specifics, about the bandwidth, but speaking from my set-up I have not had any problems.


Jason
Anonymous
March 21, 2001 3:43:14 AM

Speaking from the perspective of a USB hardware designer, your rationale for plugging your mouse into the MB directly so it has max bandwidth isn't quite correct. USB traffic is separated into 1ms frames using a special SOF (start-of-frame) packet which helps keep all the devices on the bus in sync. ALL USB mice are low speed devices (meaning the data transfers at 12MHz) and by definition the fastest they can be polled is once every 10 frames. Additionally, all low speed USB devices on your system will share 10% of the total theoretical bandwidth of the bus. I think this would include your joystick and radio though I am not positive how those devices are designed. High speed devices (your camera, zip drive, plus scanners and printers) transfer their data at 48MHz and must share the remaining 90% of the bandwidth. Some devices request a specific percent of the bandwidth be assigned to them for streaming data at a constant rate (web cams especially) while others will dynamically use what is left over.

Gee, that was more info on USB than anyone probably wanted to read. What was my point? Oh yeah, since your mouse uses such a small percentage of the bandwidth, the only performance gain you get by not using the hub is whatever the hub's delay time is in propagating the signal. For a mouse, I'm fairly certain that not even the most elite Quake III player could notice the difference.

And to address the original poster's question, there is a theoretical maximum of 12mbps of data transfer available to ALL USB devices plugged into the same root port. As long as the devices are designed well, they will negotiate the best possible way to share that limit but yes at some point if you try to scan, print, run a streaming web camera, etc all at the same time, at least one of the devices will have to run slower than it is capable.

BTW, the two USB ports available on most modern motherboards are actually connected to a hub built into the motherboard. Thus all devices connected to BOTH of those ports must share the 12mbps maximum bandwidth. The only way to have more bandwidth is to buy PCI cards with additional root hub controllers on them.
Related resources
March 26, 2001 1:55:46 AM

That's exactly what I was thinking too, without all the numbers. Learned my quota of USB specifications for the day......

Good Call!
March 26, 2001 10:41:42 PM

Atlantix,

Hypothetical question since I don't yet need more bandwidth:

Would the optional "front" USB ports still be sharing the same 12MHz bandwidth with the standard "rear" ports?

My Iwill KK266-R has a separate set of connectors at the front of the board which require an optional harness to connect. The bios allows you to activate/deactivate 2 separate USB ports (maybe called hubs, can't remember). Would one of these bios options be the 2 rear ports and the other be the 2 front ports? If true, I guess that would mean separate "root hubs" and separate bandwidth, correct?

Thanks for the info if my question(s) makes sense.

BW

the more I learn, the less I'm sure I know... :eek: 
Anonymous
March 27, 2001 12:40:46 AM

I think it's a safe bet that the front and rear USB ports are separate root hubs for a total of 24Mbps bandwidth. I have an A7V133 which came with 2 ports on the MB and a ribbon cable leading to a small circuit board that fit over an unused PCI slot with 2 more ports. I checked the Device Manager and I see two root hubs and two host controllers. I haven't actually tried using my system to its full potential yet though. I've only bothered to plug in my USB mouse. The scanner, printer, and web cam are still in the boxes.
March 28, 2001 4:04:21 AM

Thanks for the info. I know the feeling about stuff not yet plugged in. I'm still sitting at the kitchen table as I type this, my wife plunking away on the old machine at the computer desk. Got to get my networking going so I can move over the data files. Then the systems swap places and I get to see if my USB's even work!

BW

the more I learn, the less I'm sure I know... :eek: 
March 1, 2010 11:22:43 PM

Hi all I have been trying to work out whats up with my Razor Megladon was getting error from the USB device requiring to much bandwidth Razor has brought out a new Firmware 2.12 which I have installed. I have been reading up on other forums that the USB controller has trouble keeping up with the USB devices and that the 780i Sli chip could not deliver the required bandwidth for the device, so what I did is got myself a Logitech USB Hub for laptops with its own power source pluged my Razor Mouse, KB, Game pad and printer into it, and the Megladon straight into the pc trying to get it on its own controller so the 780 i would only have 2 usb devices really to control and the usb hub would be taking care of the rest seems to work till now , hope this can help you all out there, and hope I am right, guessing if you have the cash you could get a new P55 chipped board with the 6G/s 3.0 USB on it wouldent have the problem then I guess

MB- 780i Sli
GPU- 2*8800GTX
CPU- 6700 @3.0 G
Ram- Dominator 1066
HD- 640G WD
KB- Razor Acosta
Mouse- Lachisis
Headphones- Megladon
Game Pad- Logitech
Monitor- Samsung 2333
Cooling- Zalman resirator 2
July 20, 2011 1:10:08 PM

okay a slightly different question, I'm trying to make my Logitech g13 wireless and seeing as i picked up some cheap FM radio transmitters i figured why not use FM radio, nobody else is. My question is for, and im sorry for being lazy but i cant check who posted all the information about usb devices, but if they/you know roughly how much data per second per second is being sent from my g13 or if there is a program to measure such information. i found this thread on Google and don't expect anyone to answer but if you could spare the time to email me at biohazard.619@hotmail.com then id be forever grateful
September 17, 2012 9:22:15 PM

Quote:
Speaking from the perspective of a USB hardware designer, your rationale for plugging your mouse into the MB directly so it has max bandwidth isn't quite correct. USB traffic is separated into 1ms frames using a special SOF (start-of-frame) packet which helps keep all the devices on the bus in sync. ALL USB mice are low speed devices (meaning the data transfers at 12MHz) and by definition the fastest they can be polled is once every 10 frames. Additionally, all low speed USB devices on your system will share 10% of the total theoretical bandwidth of the bus. I think this would include your joystick and radio though I am not positive how those devices are designed. High speed devices (your camera, zip drive, plus scanners and printers) transfer their data at 48MHz and must share the remaining 90% of the bandwidth. Some devices request a specific percent of the bandwidth be assigned to them for streaming data at a constant rate (web cams especially) while others will dynamically use what is left over.

Gee, that was more info on USB than anyone probably wanted to read. What was my point? Oh yeah, since your mouse uses such a small percentage of the bandwidth, the only performance gain you get by not using the hub is whatever the hub's delay time is in propagating the signal. For a mouse, I'm fairly certain that not even the most elite Quake III player could notice the difference.

And to address the original poster's question, there is a theoretical maximum of 12mbps of data transfer available to ALL USB devices plugged into the same root port. As long as the devices are designed well, they will negotiate the best possible way to share that limit but yes at some point if you try to scan, print, run a streaming web camera, etc all at the same time, at least one of the devices will have to run slower than it is capable.

BTW, the two USB ports available on most modern motherboards are actually connected to a hub built into the motherboard. Thus all devices connected to BOTH of those ports must share the 12mbps maximum bandwidth. The only way to have more bandwidth is to buy PCI cards with additional root hub controllers on them.


Hello!..And is it possible to connect 4 working webcams to the same usb hub?...
!