According to one aspect of the teachings herein, a system includes first and second modules that respectively anchor host-side and device-side ends of an intermediate transport link that interconnects a USB host to a USB device. The system detects when the host activates an isochronous endpoint in the device for an isochronous IN data transaction, and the second module autonomously generates data requests for the device and forwards the isochronous data output from the device towards the first module. In turn, the first module buffers the data and provides it to the host in response to host's data requests. However, the first module blocks host requests from propagating to the device and it NACKs host requests until forwarded data is available from the second module. Such operation remains transparent to the host and device, while avoiding USB timing violations, even for extended intermediate transport links.