Is It Latency or Do You Just Suck? Latency Can Kill: Precision and - PDF document

12/6/2011 Is It Latency or Do You Just Suck? Latency Can Kill: Precision and Deadline in Online Games http://www.youtube.com/watch?v=r6PwHkhEAkU Mark Claypool and Kajal Claypool ACM MMSys Scottsdale, AZ, USA February 2010 http://www.youtube.com/watch?v=Bn1nBR5jOx8 Is It Latency or Do You Just Suck? Outline � Introduction (done) � What is latency for games? (next) Delayed response � Why does it matter? � How much does it matter? “Magic” bullets http://www.youtube.com/watch?v=r6PwHkhEAkU � Do you have evidence? Server matters http://www.youtube.com/watch?v=Bn1nBR5jOx8 Why Does Latency Matter? What is Network Latency? Game ����� ����� client �������� �������� �������� ���������� ���� Response ��������� ����� time ��������� ������ ������������� ����� ���� Game server • Latency - time to get from source to destination Affects responsiveness – There and back ( round-trip time ) 1

12/6/2011 Example of Unresponsiveness Why Does Latency Matter? ����� Response ����� time �������� �������� Player is pressing left Player is pressing up ������ ���������� ���� ����� ��������� ����� ��������� ���� �������������� �� ���� Affects consistency Running back goes out of bounds! Player curses Example of State Inconsistency Why Does Latency Matter? ��������� ��������� ��������� ��������� ����� ����� ��������� ����� ������������ ����� ��������� ��������� ������������ �� ��������� ����������� ���� Affects fairness How Much Does Latency Matter? Outline � Introduction (done) � What is latency? (done) � Why does it matter? (done) � How much does it matter? (next) � Do you have evidence? Depends upon precision of action 2

12/6/2011 Game Perspectives How Much Does Latency Matter? ������� ������� Third Person Linear First Person Linear ��� ����� ��� ����� (tight deadline) (loose deadline) Depends upon deadline of action Omnipresent Third Person Isometric Player Performance vs. Latency Precision and Deadline ������������������� ����������� ����� ������� ���������� ������� ��������� ��������� �������� �������� �������� ����������� "������� ������������������� ������ ��#$�� �� ��� ������ ��������� �������� ������ ������������� !������� ������� ������ �������� Outline Methodology (1 of 3) � Goal: � Introduction (done) � Vary: precision & � What is latency? (done) deadline of actions � Why does it matter? (done) � Control : latency � How much does it matter? (done) � Measure: performance � Do you have evidence? � Modify open source (next) game � Methodology � BZ Flag � Results http://www.youtube.com/watch?v=xMYkw56t1Gg 3

12/6/2011 Methodology (2 of 3) Methodology (3 of 3) � 8 computer-controlled tanks (bots) � Varying precision – � Steps: � 2 hour runs tank size 1. Made changes � Larger tanks means 2. Verify and validate precision 3. Determined game � Varying deadline – length, number of iterations bullet speed 4. Ran experiments � Slower bullets means 5. Analysis looser deadline Results for Precision (Tank Size) Results for Deadline (Bullet Speed) Generally, higher precision affected more by latency Generally, tighter deadline affected more by latency Summary What to Do About It? � Latency can kill (your fun!) � Network improvements � Responsiveness, Consistency, Fairness � Shift latency “left” � Amount depends upon player action � But mobile, wireless emerging! � Precision – accuracy required to complete action � Server selection successfully � Shift latency “left” � Deadline – time required to achieve the final � But limited selection and/or want to play with friends! outcome of action � And want more players (1000 v 1000)! � Effects grouped based on perspective � Latency compensation techniques - help “ deal � First-person avatar with it ” (so the player doesn’t have to!) � Third-person avatar � Shift curves “up” � But often tradeoffs (e.g. consistency and responsiveness) � Omnipresent 4