Presented By:

Bryan Wong

Summary of Paper:

A major problem of networked multiplayer games is caused by transmission delay.  A primary goal is to provide a global consistent state of the game.  One approach is to introduce a local presentation delay.  Simulator-like games such as flight simulators, racing and sports games are most critical because they require smooth movements of the objects.  In this paper, delay is defined as the time between the generation of an event and the resulting update of the game state.  It’s an important issue of how the system handles old state information and how large the difference between the real and expected positions of the players in a game may be due to the delay of messages.  The delay-handling approaches used by two commercial games (Re-Volt and Need-for-Speed) were tested to see how commercial game developers handle the delay problem.  Several tests were carried out:  Start Release, Start Process, Simulated Start, Driving with Constant Speed and Collision Treatment.  The games failed all but the first test.  Next, tests were performed to determine an acceptable amount of delay in terms of the player’s perception of the game.  It was determined that 50ms of delay was acceptable for a racing game and delays of more than 100ms should be avoided.  Also, they consider racing games as a worst case system.  For comparison, lip synchronization requirements for audio and video streams are [-80ms,80ms].  It was concluded that static delay schemes are not well suited for real-time multiplayer games.

Discussion:

• The paper is about two years old (May 2002) so it would be interesting to see if newer games handle delay better than the two games that were tested
• A racing care game is considered as a worst case system, but in previous presentations first person shooters are considered worst case systems
• The value of 100ms delay for first person shooters is consistent with the other papers
• Since most games are closed source, it is difficult to tell exactly how delay is handled within the games and it is difficult to obtain exact measurements

Slides: