On the Impact of Delay on Real-Time Multiplayer Games

Authors: Lothar Pantel, Lars C. Wolf

Presented by: Bryan Wong

Outline

Introduction Multiplayer Games Experimental Evaluation Related Work Conclusions

Introduction

Major problem of networked multiplayer games is caused by transmission delay

A primary goal is to provide a global consistent state of the gameOne approach is to introduce a local

presentation delay

Introduction

Simulator-like games such as flight simulators, racing and sports games are most critical because they require smooth movements of the objects

Multiplayer Games

Architectures:Server based with a dynamically

based or central serverDistributed scheme

Influence of Basic System Parameters

Designer must decide which messages are transmitted reliably/unreliably

Delay

The time between the generation of an event and the resulting update of the game state

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

Experiments with Commercial Games

Studied the delay-handling approaches used by two commercial games in two player modeRe-VoltNeed-for-Speed

Examine how commercial game developers handle the delay problem

Start Release

Direct play assigns the role of coordinator to one of the two players

This contains the release of the start Use the start countdown and start

sound to detect correct synchronization

Start Process

As soon as the vehicles begin to move, the first deviations in the positions of the cars can occur

Identical vehicles, motors, etc. are selected to avoid acceleration differences

Expected that both cars remain head to head

Simulated Start

Cars are stopped in the course of the race and are aligned at the beginning of a straight path

Both cars are accelerated simultaneously by one person using both keyboards

Cars should remain side by side

Driving with Constant Speed

Vehicles drive with same constant speed side by side

An identical screen situation should be presented

Occurs only if position consistency is maintained during the game

Collision Treatment

Collision of game objects is detected through a polygon-collision

Only a position difference of 0 of opposing vehicles will cause an identical, local evaluation of the polygon collision

If position consistency is not sufficient, contradictory situations can occur

Observed Results

Games provided very limited handling of delay

Both provided a synchronized start release Start process was not handled correctly –

the local car was always in leadership Both games failed tests 3,4 Neither game provided satisfying treatment

of collisions

Experimental Evaluation of the Impact of Delay Inconsistent state brings several problems

and can be confusing to the players One approach to enhance consistency is to

delay the presentation of the actual game state

How much delay is acceptable for users in real time games?

Delay includes all communication, processing and buffering costs

Principle Setup

Performed steps:

Implementation

Implemented in an RC-Car simulation Driver does not use a cockpit view but

a higher view allowing the user to view the whole area

Virtual RC Racing implements the static delay scheme

The feeling how the car reacts is influenced by the delay between steering and reaction

Experiments

Purpose was to determine acceptable presentation delay

12 candidates performed experiments For each of the following graphs, three

players were selected who were representatives for the following categories: Beginner, Average and Excellent driver

Static presentation delay was increased in 50ms steps up to 500ms

Experiments

Avg time per round in dependence on delayIt becomes more difficult to control the

car, requiring the driver to slow down Best time per round in dependence on

delayReflects the best possible value for

the driver, under the given conditions Frequency of Leaving the Course

Results

Results

Results

Results

Results

View Dependance

Delay value that can be tolerated by the participant depends on the camera perspective

A cockpit view allows at least an additional 50ms of delay to be tolerated

Related Work

MiMaze – distributed 3D Pacman game

Consistency of the is improved by delaying the presentation of the events using buckets

The whole game is 100ms in the past Players with >100ms delay cannot

participate

Conclusions

Delay of 50ms is uncritical for a racing game Delay of >100ms should be avoided Consider the racing game as a worst-case system For other games (first person shooter,…) a delay of

100ms may be acceptable For comparison, lip synchronization requirements for

audio and video streams are [-80ms,80ms] Static delay schemes are not well suited for real-time

multiplayer games