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USB bandwidth utilization is not a feature of the Windows Task Manager so it is not an easy
attribute to measure. The maximum specified bandwidth of USB 2.0 is 480 Mb/sec but in reality
the practical useable bandwidth is about 400 Mb/sec. A typical U170 device runs at about
10Mb/sec at idle and a video stream running between the host PC with vSpace and the U170 will
take up to 130 Mb/sec of bandwidth to support up to 30 frames per second (fps). If the USB
bandwidth does not exist to support 30 fps, then the U170/vSpace system will begin to drop
frames in the video to make up for the lack bandwidth. Our testing has shown that about four
full screen videos (depending upon the video format, size, decoder (player) and USB bus
implementation) can play without a noticeable frames dropping. If your usage pattern is to use a
lot of full screen videos simultaneously then we suggest you implement only up to 4 users per
USB 2.0 bus to ensure better video quality.
Therefore the best set up or topology for nine users is to obtain a host PC with two USB buses
and to divide those buses among the users by having four users on one powered hub and five
users on the second hub. Please refer to the previous table for chip sets with two USB buses or a
USB 2.0 PCI card can be added to the host. A topology that looks like this:
Each U170 kit contains one device that adds a new user to a shared PC. Up to nine U170 devices
may connect to a PC and support ten users (including the host) simultaneously. The U170
combined with a modern PC provides the most affordable and powerful shared computing
environment in the market today.
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