The client library provides functions to allocate data buffers in shared memory; the stack manages these data buffers and gives the client library access to them. This means that all data transfers must use the provided buffers.
As a result, a class driver must reside on the same physical node as the USB stack. The clients of the class driver, however, can be network-distributed. The advantage of this approach is that no additional memory copy occurs between the time that the data is received by the USB stack and the time that it's delivered to the class driver (and vice versa).