The USB Hub Host Client Driver abstracts the complexities of Hub operation and presents a simple interface to the Host Layer. The interface allows the Host Layer to perform port operations such as port reset, port suspend and port resume. The port interface offered by the Hub Host Client Driver is the same as that offered by the root hub driver. In that, the Host Layer does not differentiate between an external hub and the root hub. 

The USB Hub Host Client Driver does not have any application callable API. It only interacts with the Host Layer. The USB Hub Host Client Driver performs the task of powering up the ports, detecting device attach and detach and notifying the same to the Host Layer and detecting over current conditions. The USB Hub Host Client Driver performs the control transfers required for these tasks.