The Studying of Virtual Token Passing Approach in ControlNet

MAC protocol of ControlNet uses Virtual Token Passing (VTP) to solve the medium access contention, to assure the deterministic and repeatability of message transmission. This paper presents the basic method that VTP uses to transmit real-time I/O message, explicit message and maintenance message in scheduled part, unscheduled part and guardband part respectively. On the basis of analyzing the factors of message transmission delay, the maximum message transmission delay in scheduled part is studied, and the result shows it can be determined, so the deterministic and repeatability of message transmission in ControlNet is validated.