1. The Technology of the Game - Latency and Online Games Mark Claypool Associate Professor Computer Science Director Interactive Media and Game Development Worcester Polytechnic Institute

3. May 7, 2007 Harvard Interactive Media Group3 Software Engineering Human-Computer Interaction Computer Architecture Databases Graphics and Animation Artificial Intelligence Computer Networks

4. May 7, 2007 Harvard Interactive Media Group4 Outline Introduction(done) What is latency?(next) Why does it matter? How much does it matter? What can be done?

5. May 7, 2007 Harvard Interactive Media Group5 What is Network Latency? Internet Game client Game server Latency - time to get from source to destination –There and back (round-trip time)

6. May 7, 2007 Harvard Interactive Media Group6 Why Does Latency Matter? Time User Input Render Input Process and Validate Input Message: User Input Message: Ok User Input Response time Affects responsiveness

7. May 7, 2007 Harvard Interactive Media Group7 Example of Unresponsiveness Player is pressing leftPlayer is pressing upRunning back goes out of bounds! Player curses

8. May 7, 2007 Harvard Interactive Media Group8 Why Does Latency Matter? Affects consistency Time User Input Render Input Process and Validate Input Message: User Input Message: Ok with Update Fix Up Response time

9. May 7, 2007 Harvard Interactive Media Group9 Example of State Inconsistency

10. May 7, 2007 Harvard Interactive Media Group10 Why Does Latency Matter? Time User Input Message: Treasure! Message: Treasure! User Input Message: Get treasure Message: Get treasure Message: Ok Message: Tough luck! Affects fairness

11. May 7, 2007 Harvard Interactive Media Group11 How Much Does Latency Matter? Depends upon precision of task

12. May 7, 2007 Harvard Interactive Media Group12 How Much Does Latency Matter? Depends upon deadline of task

13. May 7, 2007 Harvard Interactive Media Group13 OmnipresentThird-Person Avatar First-Person Avatar Precision and Deadline Deadline Shooting Sniper Racing Casting Area Spell Shooting Machine Gun Shooting Grenades Exploring Drinking Health Potion Moving Building Fighting Combat Running Precision TighterLooser Higher Lower

14. May 7, 2007 Harvard Interactive Media Group14 Player Performance vs. Latency

15. May 7, 2007 Harvard Interactive Media Group15 Outline Introduction(done) What is latency?(done) Why does it matter? (done) How much does it matter?(done) What can be done?(next) –Time Manipulation

16. May 7, 2007 Harvard Interactive Media Group16 Latency Compensation - Time Delay Server delays processing of events –Wait until all messages from clients arrive Server also sends messages to more distant client first, delays messages to closer Time Client 1 command arrives Client 2 command arrives Server processes both client commands Time Delay Disadvantage – decreases responsiveness to that of player with highest latency

17. May 7, 2007 Harvard Interactive Media Group17 Latency Compensation - Time Warp Server rolls-back (warps) to when action taken place on client Disadvantage – user may notice when fix state inconsistency

18. The Technology of the Game - Latency and Online Games Mark Claypool Associate Professor Computer Science Director Interactive Media and Game Development Worcester Polytechnic Institute

19. May 7, 2007 Harvard Interactive Media Group19 References Valve Developer Community. “Source Multiplayer Networking”, Online at: http://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking http://developer.valvesoftware.com/wiki/Source_Multiplayer_Networking Mark Claypool and Kajal Claypool. “Latency and Player Actions in Online Games”, Communications of the ACM, Volume 49, Issue 11, November 2006. Online at: http://www.cs.wpi.edu/~claypool/papers/precision-deadline/ http://www.cs.wpi.edu/~claypool/papers/precision-deadline/ James Nichols and Mark Claypool. “The Effects of Latency on Online Madden NFL Football”, In Proceedings of the 14th ACM International Workshop on Network and Operating Systems Support for Digital Audio and Video (NOSSDAV), Kinsale, County Cork, Ireland, June 16-18, 2004. Online at: http://www.cs.wpi.edu/~claypool/papers/madden/ http://www.cs.wpi.edu/~claypool/papers/madden/ Grenville Armitage, Mark Claypool, and Philip Branch. “Networking and Online Games: Understanding and Engineering Multiplayer Internet Games”, John Wiley and Sons, Ltd., June 2006. ISBN 0470018577. Online at: http://www.cs.wpi.edu/~claypool/papers/book/ http://www.cs.wpi.edu/~claypool/papers/book/