Mark Claypool

Latency and player actions in online games

Latency determines not only how players experience online gameplay but also how to design the games to mitigate its effects and meet player expectations.

The effects of loss and latency on user performance in unreal tournament 2003

The growth in the popularity of interactive network games has increased the importance of a better understanding of the effects of packet loss and latency on user performance. While previous work on network games has studied user tolerance for high latencies and has studied the effects of latency on user performance in real-time strategy games, to the best of our knowledge, there has been no systematic study of the effects of loss and latency on user performance. In this paper we study user performance for Unreal Tournament 2003 (UT2003), a popular first person shooter game, under varying amounts of packet loss and latency. First, we deduced typical real world values of packet loss and latency experienced on the Internet by monitoring numerous operational UT2003 game servers. We then used these deduced values of loss and latency in a controlled networked environment that emulated various conditions of loss and latency, allowing us to monitor UT2003 at the network, application and user levels. We designed maps that isolated the fundamental first person shooter interaction components of movement and shooting, and conducted numerous user studies under controlled network conditions. We find that typical ranges of packet loss have no impact on user performance or on the quality of game play. The levels of latency typical for most UT2003 Internet servers, while sometimes unpleasant, do not significantly affect the outcome of the game. Since most first person shooter games typically consist of generic player actions similar to those that we tested, we believe that these results have broader implications.

The effect of latency on user performance in Warcraft III

Latency on the Internet is a well-known problem for interactive applications. With the increase in interactive network games comes the increased importance of understanding the effects of latency on user performance. Classes of network games such as First Person Shooters (FPS) and Real Time Strategy (RTS) differ in their user interaction model and hence susceptibility to latency. While previous work has measured the effects of latency on FPS games, there has been no systematic investigation of the effects of latency on RTS games. In this work, we design and conduct user studies that measure the impact of latency on user performance in Warcraft III, a popular RTS game. As a foundation for the research, we separated typical Warcraft III user interactions into the basic components of explore, build and combat, and analyzed each individually. We find modest statistical correlations between user performance and latency for exploration, but very weak correlations for building and combat. Overall, the effect of even very high latency, while noticeable to users, has a negligible effect on the outcome of the game. We attribute this somewhat surprising result to the nature of RTS game-play that clearly favors strategy over the real-time aspects.

WBest: A bandwidth estimation tool for IEEE 802.11 wireless networks

Bandwidth estimation techniques seek to provide an accurate estimation of available bandwidth such that network applications can adjust their behavior accordingly. However, most current techniques were designed for wired networks and produce relatively inaccurate results and long convergence times on wireless networks where capacity can vary dramatically. This paper presents a new wireless bandwidth estimation tool, WBest, designed for fast, non-intrusive, accurate estimation of available bandwidth in IEEE 802.11 networks. WBest is a two-stage algorithm: 1) a packet pair technique estimates the effective capacity over a flow path where the last hop is a wireless LAN (WLAN); and 2) a packet train technique estimates achievable throughput to infer the available bandwidth. WBest parameters are optimized given the tradeoffs of accuracy, intrusiveness and convergence time. The advantage of WBest stems from avoiding a search algorithm to detect the available bandwidth by statistically detecting the available fraction of the effective capacity to mitigate estimation delay and the impact of random wireless channel errors. WBest is implemented and evaluated on an 802.11 wireless testbed. Comparisons with other available bandwidth estimation tools shows WBest to have higher accuracy, lower intrusiveness and faster convergence times. Thus, WBest demonstrates the potential for improving the performance of applications that need bandwidth estimation, such as multimedia streaming, on wireless networks.

An empirical study of realvideo performance across the internet

The tremendous increase in computer power and bandwidth connectivity has fueled the growth of streaming video over the Internet to the desktop. While there have been large scale empirical studies of Internet, Web and multimedia traffic, the performance of popular Internet streaming video technologies and the impact of streaming video on the Internet is still largely unkown. This paper presents analysis from a wide-scale empirical study of RealVideo traffic from several Internet servers to many geographically diverse users. We find typical RealVideos to have high quality, achieving an average frame rate of 10 frames per second and very smooth playout, but very few videos achieve full-motion frame rates. Overall video performance is most influenced by the bandwidth of the end-user connection to the Internet, but high-bandwidth Internet connections are pushing the video performance bottleneck closer to the server.

The effect of latency on user performance in Real-Time Strategy games

Latency on the Internet is a well-known problem for interactive applications. The growth in interactive network games brings an increased importance in understanding the effects of latency on user performance. Classes of network games such as First Person Shooters (FPS) and Real-Time Strategy (RTS) differ in their user interaction model and hence susceptibility to latency. While previous work has measured the effects of latency on FPS games, there has been no systematic investigation of the effects of latency on RTS games. In this work, we design and conduct user studies that measure the impact of latency on user performance on three of the most popular RTS games. As a foundation for the research, we separated typical RTS user interactions into the basic components of explore, build and combat, and analyzed each individually. We find modest statistical correlations between user performance and latency for exploration, but very weak correlations for building and combat. Overall, the effect of even very high latency, while noticeable to users, has a negligible effect on the outcome of the game. We attribute this somewhat surprising result to the nature of RTS game play that clearly favors strategy over the real-time aspects.

The effects of jitter on the peceptual quality of video

Today’s powerful computers and networks present the opportunity for video across the Internet right to the desktop. However, Internet video often suffers from packet loss and jitter, degrading the user’s perceived quality of the video. Understanding the effects of delay, loss and jitter on media quality is critical for choosing delay buffer sizes and packet repair techniques. While the effects of packet loss on perceptual quality are well-understood, to date there have not been careful user studies measuring the impact of jitter on perceptual quality. The major contributions of this work are carefully designed experiments that measure and compare the impact of both jitter and packet loss on perceptual quality of packet video. We find that jitter degrades perceptual quality nearly as much as does packet loss, and that perceptual quality degrades sharply even with low 1eveIs of jitter or packet loss as compared to perceptual quality for perfect video.

Characteristics of streaming media stored on the Web

Despite the growth in multimedia, there have been few studies that focus on characterizing streaming audio and video stored on the Web. This investigation used a customized Web crawler to traverse 17 million Web pages from diverse geographic locations and identify nearly 30,000 streaming audio and video clips available for analysis. Using custom-built extraction tools, these streaming media objects were analyzed to determine attributes such as media type, encoding format, playout duration, bitrate, resolution, and codec. The streaming media content encountered is dominated by proprietary audio and video formats with the top four commercial products being RealPlayer, Windows Media Player, MP3 and QuickTime. The distribution of the stored playout durations of streaming audio and video clips are long-tailed. More than half of the streaming media clips encountered are video, encoded primarily for broadband connections and at resolutions considerably smaller than the resolutions of typical monitors.

The effects of frame rate and resolution on users playing first person shooter games

The rates and resolutions for frames rendered in a computer game directly impact the player performance, influencing both the overall game playability and the games enjoyability. Insights into the effects of frame rates and resolutions can guide users in their choice for game settings and new hardware purchases, and inform system designers in their development of new hardware, especially for embedded devices that often must make tradeoffs between resolution and frame rate. While there have been studies detailing the effects of frame rate and resolution on streaming video and other multimedia applications, to the best of our knowledge, there have been no studies quantifying the effects of frame rate and resolution on user performance for computer games. This paper presents results of a carefully designed user study that measures the impact of frame rate and frame resolution on user performance in a first person shooter game. Contrary to previous results for streaming video, frame rate has a marked impact on both player performance and game enjoyment while resolution has little impact on performance and some impact on enjoyment.

Latency can kill: precision and deadline in online games

The growth in network capacities and availability has been accompanied by a proliferation of online games. While online games perform well under many network conditions, Internet delays can often degrade online game performance. The precise impact that latency has on online gameplay depends upon the game type and the actions within the game. While the effects of latency on specific games has been studied, knowledge about the effects of latency on classes of games and about the effects of latency on different player actions is lacking. This paper presents a broad, perspective-based classification of games based on player control and camera view. The foundation of the game classification are player actions, each of which is defined by its precision and deadline requirements. Experiments with controlled amount of precision, deadline and latency support the classification. This classification of games should prove useful for game designers, network engineers and game players themselves as they build and play on tomorrows networks.