Q:

What do "downstream" and "upstream" mean in USB terms?

A:

Universal Serial Bus, or USB, hubs or ports enable a computer user to connect computer peripherals like a monitor to a computer. USB ports distinguish connections by allocating the use of "A" and "B" connectors. "A" connections go upstream toward the computer, while "B" connections move downstream and link to separate peripherals.

For example, an HP flat panel monitor utilizes a USB 2.0 hub. The hub features four downstream ports that connect peripherals to the computer and an upstream port that connects the monitor. An upstream port is always used to connect the monitor, while a downstream port is always utilized to link a USB device.

USB devices are categorized by individual classifications. For instance, microphones and speakers are listed under the audio class, while chip cards and smart cards fall under the classification of a chip card interface device. Communication class USB devices include modems and speakerphones, while keyboards, joysticks and mice belong to the human interface device class of USB peripherals. Composite class items include any devices that contain class-specific details in their interface.

USB attachment points fall under the hub classification, while the mass storage class features hard drives, CD read/write drives, flash memory readers, media players and digital cameras. Video class USB devices include webcams and digital camcorders.


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