Serial Line IP Implementation for Linux Kernel TCP/IP Stack | ||
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The communication on the USB is done in two directions and uses four different transfer types. Data directed from the host to a device is called downstream or OUT transfer. The other direction is called upstream or IN transfer. Depending on the device type different transfer variants are used:
Control transfers are used to request and send reliable short data packets. It is used to configure devices and every one is required to support a minimum set of control commands.
Bulk transfers are used to request or send reliable data packets up to the full bus bandwidth. Devices like scanners or scsi adapters use this transfer type.
Interrupt transfers are similar to bulk transfers which are polled periodically. If an interrupt transfer was submitted the host controller driver will automatically repeat this request in a specified interval (1ms - 127ms).
Isochronous transfers send or receive data streams in realtime with guaranteed bus bandwidth but without any reliability. In general these transfer types are used for audio and video devices
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