Online gameplay is impacted by the network characteristics of players connected to the same server. Unfortunately, the
network characteristics of online game servers are not well-understood, particularly for groups that wish to play together
on the same server. As a step towards a remedy, this paper presents analysis of an extensive set of measurements of game
servers on the Internet. Over the course of many months, actual Internet game servers were queried simultaneously by
twenty-five emulated game clients, with both servers and clients spread out on the Internet. The data provides statistics on
the uptime and populations of game servers over a month long period an an in-depth look at the suitability for game servers
for multi-player server selection, concentrating on characteristics critical to playability--latency and fairness. Analysis
finds most game servers have latencies suitable for third-person and omnipresent games, such as real-time strategy, sports
and role-playing games, providing numerous server choices for game players. However, far fewer game servers have the
low latencies required for first-person games, such as shooters or race games. In all cases, groups that wish to play
together have a greatly reduced set of servers from which to choose because of inherent unfairness in server latencies and
server selection is particularly limited as the group size increases. These results hold across different game types and even
across different generations of games. The data should be useful for game developers and network researchers that seek
to improve game server selection, whether for single or multiple players.
KEYWORDS: Video, Computer programming, Video coding, Motion models, Analytical research, Forward error correction, Video compression, Signal attenuation, Signal to noise ratio, Performance modeling
Transmitting high-quality, real-time interactive video over lossy networks is challenging because network data loss can severely
degrade video quality. A promising feedback technique for low-latency video repair is Reference Picture Selection (RPS), whereby
the encoder selects one of several previous frames as a reference frame for predictive encoding of subsequent frames. RPS operates in
two different modes: an optimistic policy that uses negative acknowledgements (NACKs) and a more conservative policy that relies
upon positive acknowledgements (ACKs). The choice between RPS NACK and RPS ACK depends on network conditions, such as
round-trip time and loss probability, and on the video content, such as low or high motion. This paper derives two analytical models to
predict the quality of videos (using Peak Signal to Noise Ration, PSNR) with RPS NACK and RPS ACK. These models are used to
study RPS performance under varied network conditions and with different video contents through a series of experiments. Analysis
shows that the best choice of ACK or NACK greatly depends upon the round-trip time and packet loss, and somewhat depends upon
the video content and Group of Pictures (GOP) size. In particular: 1) RPS ACK performs better than RPS NACK when round-trip
times are low; 2) RPS NACK performs better than RPS ACK when the loss rate is low, and RPS ACK performs better than RPS
NACK when the loss rate is high; 3) for a given round-trip time, the loss rate where RPS NACK performs worse than RPS ACK is
higher for low motion videos than it is for high motion videos; 4) videos with RPS NACK always perform no worse than videos
without repair for all GOP sizes; however, 5) below certain GOP sizes, videos without RPS outperform videos with RPS ACK. These
insights derived from our models can help determine appropriate choices for RPS NACK and RPS ACK under various scenarios.
Computer games are often played on devices with varying display resolutions. While higher resolutions generally provide
more immersive game play they can yield reduced frame rates and/or increased costs, making choosing the optimal resolution
important. Despite this importance, to the best of our knowledge, there has been no extensive study of the effects of
resolution on users playing computer games. This paper presents results from extensive user studies measuring the impact
of resolution on users playing First Person Shooter games. The studies focus on the effects of resolution in conjunction
with low and high contrast virtual environments, full screen and windowed modes and identification of long-range objects.
Analysis indicates resolution has little impact on performance over the range of conditions tested and only matters when
the objects being identified are far away or small and are reduced to too few pixels to be distinguishable.
KEYWORDS: Video, Computer programming, Video coding, Video compression, Quality measurement, Semantic video, Data modeling, Video processing, Distance measurement, Motion measurement
Transmitting high-quality, real-time interactive video over lossy networks is challenging because data loss due to the network can severely degrade video quality. A promising feedback technique for low-latency video repair is Reference Picture Selection (RPS), whereby the encoder selects one of several previous frames as a reference frame for predictive encoding of subsequent frames. RPS can operate in two different modes: an optimistic policy that uses negative acknowledgements (NACKs) and a more conservative policy that relies upon positive acknowledgements (ACKs). The choice between RPS ACK mode and NACK mode to some extent depends upon the effects of reference distance on the encoded video quality. This paper provides a systematic study of the effects of reference distance on video quality for a range of video coding conditions. High-quality videos with a wide variety of scene complexity and motion characteristics are selected and encoded using H.264 with a bandwidth constraint and a range of reference distances. Two objective measures of video quality, PSNR and VQM, are analyzed to show that scene complexity and motion characteristics of the video determine the amount of degradation in quality as reference distance increases. In particular, videos with low motion degrade in quality more with an increase in reference distance since they cannot take advantage of the strong similarity between adjacent frames. Videos with high motion do not suffer as much with higher reference distance since the similarity between adjacent frames is already low. The motion characteristics also determine the initial quality under the bandwidth constraint. The data presented should be useful for selecting ACK or NACK mode or for modeling video repair techniques.
The rates and resolutions for frames rendered in a computer game
directly impact the player performance, influencing both the overall
game playability and the game's 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.
Internet multimedia applications have timing constraints that are often not met by TCP, the de facto Internet transport protocol, hence, most multimedia applications use UDP. Since UDP does not guarantee data arrival, UDP flows often have high data loss rates. Network data loss can be ameliorated by the use of Forward Error Compression (FEC), where a server adds redundant data to the flow to help the client repair lost data. However, the effectiveness of FEC depends upon the network burst loss rates, and current FEC approaches are non-adaptive or adapt without effectively monitoring this rate. We propose a Forward Error Correction protocol that explicitly adapts the redundancy to the measured network burst loss rates. Through evaluation under a variety of network conditions, we find our adaptive FEC approach achieves minimal end-to-end delay and low loss rates after repair.
Quality-of-service (QoS) requirements for the timely delivery of real-time multimedia raise new challenges for today's networks. A key component of QoS is QoS routing which allows the selection of network routes with sufficient resources for requested QoS parameters. Most proposed techniques to compute QoS routes require dynamic update of link-state information. Given the growing size of internets, it is becoming increasingly difficult to gather up-to-date state information. We propose a new technique to compute QoS routes in a fast and efficient manner without any need for dynamic updates. Our method, known as Selective Flooding, checks the state of the links on a set of pre-computed routes from the source to the destination in parallel and based on this information computes the best route and then reserves resources. We implemented Selective Flooding on a QoS routing simulator and evaluated the performance of Selective Flooding compared to source routing for a variety of network parameters. We find Selective Flooding consistently outperforms source routing in terms of call-blocking rate and outperforms source routing in terms of network overhead for some network conditions. The contributions of this work include the design of a new QoS routing algorithm, Selective Flooding, extensive evaluation of Selective Flooding under a variety of network conditions and a working simulator for future research.
Internet multimedia applications have different requirements than do traditional text-based applications, placing new demands on TCP and UDP, the dc-facto Internet transport protocols. We propose a Selective Retransmission Protocol (SRP) to balance the potentially high loss found in UDP with the potentially high latency found in TCP. SRP uses an applicationspecific decision algorithm to determine whether or not to ask for a retransmission for a lost packet, adjusting the loss and latency to the optimum level for the application. We develop and experimentally evaluate an audioconference using SRP on a wide-area network testhed. We find SRP outperforms both TCP and UDP in terms of multimedia application quality.
With rapid progress in both computers and networks, real- time multimedia applications are now possible on the Internet. Sine the Internet was designed to support traditional applications, multimedia applications on the Internet often suffer from unacceptable delay, jitter and data loss. Among these, data loss often has the largest impact on quality. In this paper, we propose a new forward error correction technique for video that compensates for lost packets, while maintaining minimal delay. Our approach transmits a small, low-quality redundant frame after each full-quality primary frame. In the event the primary frame is lost, we display the low-quality frame, rather than display the previous frame or retransmit the primary frame. To evaluate our approach, we simulated the effect of network data loss on MPEG video clips and repaired the data loss by using redundancy frames. We conducted user studies that experimentally measured users' opinions on the quality of the video streams in the presence of data loss, both with and without our redundancy approach. In addition, we analyze the system overhead incurred by the redundancy. We find that video redundancy can greatly improve the perceptual quality of video in the presence of network data loss. The system overhead that redundancy introduces is dependent on the quality of the redundant frames, but a typical redundancy overhead will be approximately 10% that of the original frames.
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