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Virtual Network Configuration Algorithm

The Virtual Network Configuration (VNC) algorithm is an application of a more general mechanism called Time Warp Emulation (TWE). Time Warp Emulation is a modification of Time Warp [17]. The motivation behind TWE is to allow the actual components of a real-time system to work ahead in time in order to predict future behavior and adjust themselves when that behavior does not match reality. This is accomplished by realizing that there are now two types of false messages, those which arrive in the past relative to the process's Local Virtual Time (LVT) and those messages which have been generated which are time-stamped with the current real time, but whose values exceed some tolerance from the component's current value.

The basic Time Warp mechanism is modified by adding a verification query phase. This phase occurs when real time matches the receive time of a message in the output queue of a process. In this phase, the physical device being emulated in time is queried and the results compared with the value of the message. A value exceeding a prespecified tolerance will cause a rollback of the process.



Steve Bush
Tue Nov 12 11:48:31 CST 1996