There are four data transfer types defined in USB（USB中有4种数据传输类型）. Each type is optimized to match the service requirements between the client software and the USB device. The four types are:
- Interrupt Transfers（中断传输） - Small data transfers used to communicate information from the USB device to the client software.（一般应用在少量数据的通信） The Host Controller Driver polls（轮询） the USB device by issuing tokens（令牌） to the device at a periodic interval（周期性间隔） sufficient for the requirements of the device.（USB主控制器驱动通过令牌周期性地轮询USB设备）
- Isochronous Transfers（同步传输） - Periodic data transfers with a constant data rate（数据速率不变的周期性数据传输？）. Data transfers are correlated in time between the sender and receiver.
- Control Transfers（控制传输） - Nonperiodic data transfers used to communicate configuration/command/status type information between client software and the USB device.（用于USB主控制器和USB设备之间“配置、命令、状态等类型”的信息交换？）
- Bulk Transfers（批量传输） - Nonperiodic data transfers used to communicate large amounts of information between client software and the USB device.（大量数据的传输）
In OpenHCI the data transfer types are classified into two categories: periodic and nonperiodic（OpenHCI中，数据传输的类型分为周期性和非周期性两类）.
- Periodic transfers are interrupt and isochronous（周期性传输为中断传输和同步传输） since they are scheduled to run at periodic intervals.
- Nonperiodic transfers are control and bulk（非周期性传输为控制传输和批量传输） since they are not scheduled to run at any specific time, but rather on a time-available basis.
《OpenHCI - Open Host Controller Interface Specification for USB》
OpenHCI - Data Transfer Types
原文：http://www.cnblogs.com/utank/p/4638624.html
