308Alvium USB Cameras User Guide V4.6.1
Performance and troubleshooting
Shared bandwidth on a common USB bus
Ideal setup for two cameras
Preconditions
• Control traffic is ignored.
• The possibility of the host being busy with other tasks is ignored.
• Cameras share 100 percent bus bandwidth.
• Cameras need 100 percent bus bandwidth in total.
• Cameras stream in the same way because they are the same model and have
identical settings.
• No other device is connected.
Result
• Bandwidth is divided by two, cameras get assigned 50 percent bandwidth
each.
For three cameras, the bandwidth is 33.3 percent each.
• If one camera sends no data, the other camera will be assigned 100 percent
bandwidth. To always assign 50 percent to both cameras, they have to be
controlled to use no more than 50 percent bandwidth each.
• If the computer cannot process the images received from a camera, images are
corrupted.
Best practice for bandwidth management
• To assign maximum bandwidth to a camera, make sure your camera is the only
device on the bus.
• Avoid devices, such as a monitor or a mouse, sharing bandwidth with the USB
camera connected to the same bus.
• For maximum bandwidth, use a current version host controller card.
See www.alliedvision.com/en/products/accessories.
• USB3 Vision devices use bulk transfer. Avoid using other transfer modes.
• Control bandwidth by assigning the desired amount to the separate cameras.
Cascading hubs divide bandwidth
The following example applies to standard behavior without individual settings.
The graphics show bandwidth distribution on a common bus. Three cameras try to
use full bandwidth at the same time. If one camera is inactive, the host will provide
its share to the others until this camera sends data again. See Figure 122 on
page 308.
Figure 122: Bandwidth assignment for cascading hubs
Host
adapter
card
Hub 01
Hub 02
Camera 01
Camera 02
Camera 03
100% 50%
50%
25%
25%
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