Improving application layer latency for reliable thin-stream game traffic

  • Authors:

  • Andreas Petlund;Kristian Evensen;Pål Halvorsen;Carsten Griwodz

  • Affiliations:

  • Simula Research Laboratory, Norway and University of Oslo, Norway;Simula Research Laboratory, Norway;Simula Research Laboratory, Norway and University of Oslo, Norway;Simula Research Laboratory, Norway and University of Oslo, Norway

  • Venue:
  • Proceedings of the 7th ACM SIGCOMM Workshop on Network and System Support for Games
  • Year:
  • 2008

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Abstract

A wide range of networked games send data with very high interarrival-time between packets and with small payloads in each packet. We call these transmission patterns "thin streams". Reliability, when needed for game traffic, is usually achieved through TCP or by using retransmission schemes modelled on TCP. These retransmission schemes can result in very large delays if the stream is thin [9]. Viewed in the light of the time-dependent nature of game traffic, large delays can be severely impeding to the game experience. In order to reduce application-layer latency when packets are lost, we have implemented modifications to TCP in the Linux kernel. The changes are only active when thin-stream properties are detected, thus not affecting TCP behaviour when the stream is not thin. In this paper, we show the latency improvements from these thin-stream modifications. As a case study, we have used the game BZFlag to test the mechanisms, and present statistics from these tests. The experimental results show that our modifications allow TCP to recover earlier from packet loss. This latency reduction was then shown to improve the difference between perceived and actual player positions in the BzFlag game.