Unexpected anomalies of isochronous communication over USB 3.1 Gen 1

USB 3.1 is the newest version of the ubiquitous Universal Serial Bus. It is used in various applications such as A/V system, where USB connects a few video cameras to one computer. In this case, quality of service depends not only on task scheduling or computer networks but also on communication interfaces (I/O subsystem). The newest version of USB improves communication efficiency by introducing some new mechanisms such as full-duplex transmission, burst transactions, etc. Thus verification of USB compliance with QoS is an important issue and this article presents a proposal of downstream and upstream scheduling process model. Furthermore, results of QoS guarantee tests have been depicted in three-dimensional Cartesian coordinate system.