Glossary
A logical or physical entity that performs a function. The actual entity described depends on the context of
the reference. At the lowest level, device may refer to a single hardware component, as in a memory device.
At a higher level, it may refer to a collection of hardware components that perform a particular function, such
as a Universal Serial Bus interface device. At an even higher level, device may refer to the function
performed by an entity attached to the Universal Serial Bus; for example, a data/FAX modem device.
Devices may be physical, electrical, addressable, and logical.
Downstream
The direction of data flow from the host or away from the host. A downstream port is the port on a hub
electrically farthest from the host that generates downstream data traffic from the hub. Downstream ports
receive upstream data traffic.
Upstream
The direction of data flow towards the host. An upstream port is the port on a device electrically closest to
the host that generates upstream data traffic from the hub. Upstream ports receive downstream data traffic.
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