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What USB devices work through passive hub?



 
 
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  #1  
Old September 17th 17, 04:34 AM posted to alt.comp.hardware
micky
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Posts: 439
Default What USB devices work through passive hub?

What USB devices should work through a passive hub?

My old laptop had 3 USB ports but I needed at least 4. I assumed that
it was better to copy files to a flashdrive without putting a hub in the
middle. Same for my USB speakers.

OTOH, my mouse and keyboard xmit so little that I figured they would
work fine through a passive hub. And they did. Total of 4 devices**,
two going through the hub.

The new-old laptop has only 2 usb ports***. Plus I'm probably getting a
3G or maybe even 3G/4G/hotspot USB dongle.

***Probably USB2, in this Dell Latitud E4300. USB2 is fast enough for
me, but I worry the hub will make it unable to handle some devices.

One less port, one more device, so something will have to give. I will
have to put two more things in the hub. In fact I guess I need a hub
with 5 or 6 ports, not just 4. Which of these, flashdrive, speakers,
3G dongle, plus sometimes I copy photos from the camera or the phone)
will work just fine through a passive hub?


**4 devices all of the time. Sometimes I copy photos from the camera or
the phone. I'm sure the hub will let me copy photos but sometimes there
are 100's of megs. Will a passive hub be much slower than directly
through the USB2 port?

Thanx.
  #2  
Old September 17th 17, 05:00 AM posted to alt.comp.hardware
Paul[_28_]
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Posts: 1,467
Default What USB devices work through passive hub?

micky wrote:
What USB devices should work through a passive hub?

My old laptop had 3 USB ports but I needed at least 4. I assumed that
it was better to copy files to a flashdrive without putting a hub in the
middle. Same for my USB speakers.

OTOH, my mouse and keyboard xmit so little that I figured they would
work fine through a passive hub. And they did. Total of 4 devices**,
two going through the hub.

The new-old laptop has only 2 usb ports***. Plus I'm probably getting a
3G or maybe even 3G/4G/hotspot USB dongle.

***Probably USB2, in this Dell Latitud E4300. USB2 is fast enough for
me, but I worry the hub will make it unable to handle some devices.

One less port, one more device, so something will have to give. I will
have to put two more things in the hub. In fact I guess I need a hub
with 5 or 6 ports, not just 4. Which of these, flashdrive, speakers,
3G dongle, plus sometimes I copy photos from the camera or the phone)
will work just fine through a passive hub?


**4 devices all of the time. Sometimes I copy photos from the camera or
the phone. I'm sure the hub will let me copy photos but sometimes there
are 100's of megs. Will a passive hub be much slower than directly
through the USB2 port?

Thanx.


The passive and active (powered) hubs have the same performance.
For USB2, that would be 35MB/sec out of a possible 60MB/sec, for
USB Mass Storage protocol.

The difference is, in the power available to operate the
subtending devices.

Keyboards and mice, have "config space" ratings of 98mA. The resolution
of the rating is in 2mA steps, and the current is a step below the 100mA
level limit. Devices are either low power or high power, in terms of category,
and even a high power device, needs to take it easy on the power during
the first phase of negotiation.

If a six port device, had 500mA loads on each port, that would be
3 amps of current. The USB cable cannot provide all of that. An active hub
with a 5V @ 3A adapter, could power the ports.

*******

In terms of the ports on an Intel Southbridge or PCH, the ports
are typically "shared". I don't know if this has changed
at all since Intels latest generation of PCH chips (the ones
with only XHCI on them). This is the diagram of an older chip.

Hub0 Hub1
+-+-+-+-+-+ +-+-+-+
| | | | | | | | | |

That's on a desktop motherboard. A laptop might be using
only two of ten ports in that picture.

Now, the thing is, each hub only has 60MB/sec (480Mbit/sec)
of theoretical bandwidth. The first hub shares that over
all six USB2 ports. The second hub shares its 60MB/sec over
four ports.

If the laptop manufacturer took one port from Hub0 set, and
one port from Hub1 set, that would be ideal. You could carry out
two "full rate" connections, without them interfering with one
another. The ports on the hub can still interfere with each
other when bandwidth sharing.

You can use USBTreeView from Uwe Sieber (similar to UVCView from
Microsoft), to figure out what each port is connected to. You
plug your USB stick into each available port, then refresh USBTreeView
display and figure out what hub they're off.

The camera cannot transfer faster than the SD card inside. Maybe 8MB/sec
to 10MB/sec on a typical P&S camera. It could go as fast as 35MB/sec
on USB2, assuming UASP over USB2. But the flash media will see to it, that
the other limits are never reached.

If you had a fast enough Internet connection, that could exceed the
performance level of the USB2 port. But given that it's probably
an expensive plan, with limited data cap, you probably don't want it
running too fast while you're not in the room, anyway.

As a user, you have to worry about the bandwidths involved, as well
as where is the power going to come from. A four port passive can
easily handle four 100mA loads. But if you want to run several
USB coffee cup heaters, you'll need an active hub with a large
5V wall adapter to handle that situation. Same goes for charging
tablets that need 2 amps from a USB3 port. "Not gonna happen in
style" on a USB2 port.

Paul
  #3  
Old September 17th 17, 08:22 AM posted to alt.comp.hardware
VanguardLH[_2_]
external usenet poster
 
Posts: 1,453
Default What USB devices work through passive hub?

micky wrote:

What USB devices should work through a passive hub?


Low-power USB devices (unless it is the *only* USB device attached to a
hub - but then you don't need a hub for a single USB device).

My old laptop had 3 USB ports but I needed at least 4. I assumed that
it was better to copy files to a flashdrive without putting a hub in the
middle.


Flash drives usually take little power.

Same for my USB speakers.


But those are *powered* USB speakers. They have their own separate A/C
power adapter - unless you got some real cheapies that only get their
power from the USB port. The USB power is only going to supply 0.5A X
5V = 2.5W of power for a USB 2 port or 0.9A x 5V = 4.5W for a USB3 port
(which apparently you don't have); however, speakers are never 100%
efficient. That's pretty limp for external speakers - unless you're
"speakers" are actually a USB headset.

OTOH, my mouse and keyboard xmit so little that I figured they would
work fine through a passive hub. And they did. Total of 4 devices**,
two going through the hub.


Yep, those are low-power USB devices.

The new-old laptop has only 2 usb ports***. Plus I'm probably getting a
3G or maybe even 3G/4G/hotspot USB dongle.


Its specifications should tell you how much power it consumes.

One less port, one more device, so something will have to give. I will
have to put two more things in the hub. In fact I guess I need a hub
with 5 or 6 ports, not just 4. Which of these, flashdrive, speakers,
3G dongle, plus sometimes I copy photos from the camera or the phone)
will work just fine through a passive hub?


So get a *powered* USB hub. Just like powered external speakers, a
powered USB hub gets its power from its A/C adapter, not from the USB
port into which it is plugged.

Just remember that *all* of the USB devices on the same hub will have to
share the parent USB port's bandwidth. Something like a USB network
dongle or a USB printer can generate a lot of traffic which means
conflict with any other USB devices on the same hub.
 




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