Outatime: Using Speculation to Enable Low-Latency Continuous Interaction for Cloud Gaming

Gaming is very popular. Cloud gaming – where remote servers perform game execution and rendering on behalf of thin clients that simply send input and display output frames – promises any device the ability to play any game any time. Unfortunately, the reality is that wide-area network latencies are often prohibitive; cellular, Wi-Fi and even wired residential end host round trip times (RTTs) can exceed 100ms, a threshold above which many gamers tend to deem responsiveness unacceptable.

In this paper, we present Outatime, a speculative execution system for mobile cloud gaming that is able to mask up to 250ms of network latency. Outatime produces speculative rendered frames of future possible outcomes, delivering them to the client one entire RTT ahead of time; clients perceive no latency. To achieve this, Outatime combines: 1) future input prediction; 2) state space subsampling and time shifting; 3) misprediction compensation; and 4) bandwidth compression.

To evaluate the prediction and speculation techniques in Outatime, we use two high quality, commercially released games: a twitch-based first person shooter, Doom 3, and an action role playing game, Fable 3. Through user studies and performance benchmarks, we find that players overwhelmingly prefer Outatime to traditional thin-client gaming where the network RTT is fully visible, and that Outatime successfully mimics playing across a low-latency network.

* This work was formerly referred to as DeLorean, which is a trademark of the DeLorean Motor Company.