Consistent Synchronization of Action Order with Least Noticeable Delays in Fast-Paced Multiplayer Online Games

Abstract

When running multiplayer online games on IP networks with losses and delays, the order of actions may be changed when compared to the order run on an ideal network with no delays and losses. To maintain a proper ordering of events, traditional approaches either use rollbacks to undo certain actions or local lags to introduce additional delays. Both may be perceived by players because their changes are beyond the just-noticeable-difference (JND) threshold. In this article, we propose a novel method for ensuring a strongly consistent completion order of actions, where strong consistency refers to the same completion order as well as the same interval between any completion time and the corresponding ideal reference completion time under no network delay. We find that small adjustments within the JND on the duration of an action would not be perceivable, as long as the duration is comparable to the network round-trip time. We utilize this property to control the vector of durations of actions and formulate the search of the vector as a multidimensional optimization problem. By using the property that players are generally more sensitive to the most prominent delay effect (with the highest probability of noticeability P notice or the probability of correctly noticing a change when compared to the reference), we prove that the optimal solution occurs when P notice of the individual adjustments are equal. As this search can be done efficiently in polynomial time ( ∼ 5ms) with a small amount of space ( ∼ 160KB), the search can be done at runtime to determine the optimal control. Last, we evaluate our approach on the popular open-source online shooting game BZFlag.