USB主机负责管理总线的带宽。这是在配置同步和中断端点时的枚举时以及在总线的整个操作过程中完成的。该规范对总线进行了限制，允许为全速总线上的周期传输（中断和同步）分配不超过 90% 的任何帧。在高速总线上，这个限制减少到不超过 80% 的微帧可以分配给周期传输。
因此，如果有一个具有周期性传输的高度饱和的总线，剩余的 10% 将用于控制传输，一旦分配了这些，批量传输将获得剩余的部分。
The host is responsible for managing the bandwidth of the bus. This is done at enumeration when configuring Isochronous and Interrupt Endpoints and throughout the operation of the bus. The specification places limits on the bus, allowing no more than 90% of any frame to be allocated for periodic transfers (Interrupt and Isochronous) on a full speed bus. On high speed buses this limitation gets reduced to no more than 80% of a microframe can be allocated for periodic transfers.
So you can quite quickly see that if you have a highly saturated bus with periodic transfers, the remaining 10% is left for control transfers and once those have been allocated, bulk transfers will get their slice of what is left.