1. Game Networking CSE 191A: Seminar on Video Game Programming Lecture 9: Networking UCSD, Spring, 2003 Instructor: Steve Rotenberg Guest Lecturer: Mark Rotenberg

2. Maslow’s Hierarchy of Needs Self Actualization Esteem Social Safety Physiological Offline Games Online Communities Simple Online Games

3. Network Topology ServerClient Peer (Host) Peer Client-Server TopologyPeer-to-Peer Topology

4. Networking Evils Security Cheating Latency (up to 100-300ms round-trip) Bandwidth (64-128 kbps each direction) Packet Loss (2% with 10% bursts) Jitter

5. Lock-Step Simulations Really easy to implement Fully synchronize everything  Initial states  Inputs  Time steps Simulation must be deterministic Some turn-based games use this at a slower sampling rate (Age of Empires) Not suitable for fast Internet games

6. Simulation with Lag Compensation Server-side movement Peer/Client-side movement with Host/Server verification Varying frame rates and latencies Position history with server-side time warping (Half-Life) Interpolation - sliding and skipping Extrapolation – problematic with physics Syncing orientation, position, inputs

7. Networking Protocols TCP (Transport Control Protocol)  Reliable, connection based protocol  Ideal for matchmaking and lobbies but not real- time game play UDP (Unix Datagram Protocol)  Unreliable, unordered datagram oriented  Good for time-sensitive data but not

8. Networking Protocols, cont’d Roll-your-own Protocol  Probably based on UDP  Prioritize and retransmit as necessary  Coalesce or reconstitute packets as necessary  Compression  Encryption  Piggyback Acknowledgements  Heartbeats / Pings / Keep Alive / Network Probes

9. Game-Specific Protocols Positions, Inputs, Orientations Spawning and Removing Game Events Match Configurations State Transitions Complaints, Connection Status Heartbeats (pings) Voice / Chat

10. Game Data Most common transmission modes  Reliable Piggyback ACKs where possible  Unreliable Should be numbered, may arrive out of order Other modes  Most recent only  Fastest / Reliable fastest May transmit multiple times without waiting for ACKs

11. Network Security Encryption and Digesting  RSA  Diffie-Hellman  MD5  DES, triple-DES, AES  IPSec References  http://www.rsasecurity.com/rsalabs/faq/ http://www.rsasecurity.com/rsalabs/faq/  “Applied Cryptography,” Schneier

12. Network Address Translation Peer 1 sees:  Peer 2 at 219.3.16.49 : 1000  Peer 3 at 219.3.16.49 : 49155 Peer 2 sees:  Peer 1 at 198.214.72.29 : 1000  Peer 3 at 10.0.0.3 : 1000 Peer 3 sees:  Peer 1 at 198.214.72.29 : 1000  Peer 2 at 10.0.0.2 : 1000 Internet NAT Peer 2Peer 3 Peer 1 10.0.0.2 : 1000 10.0.0.3 : 1000 198.214.72.29 : 1000 219.3.16.49 : 1000 219.3.16.49 : 49155

13. General Programming Suggestions Always assume networking Separate cause from effect Event-based networking code Multiple levels of state machines Message passing from network layer to game code Monitor everything WAN simulation hardware/software Lots of asserts and debug messages Lots of unit tests Lots of product testing

14. Matchmaking and Community Matchmaking Competitions, Ladders, Leader Boards Friends, Invitations Feedback – both good and bad Content Sharing

15. Online Strategies – Sony vs. Microsoft PS2 Strategy  5 networking stacks to choose from!?  No built-in support for voice, security, authentication  Various middleware vendors  Publishers or users provide servers Xbox Strategy  Very well designed networking stack and APIs  Connect only through Microsoft’s servers  Every packet, machine, user, hard drive, DVD, user can be authenticated  Gamertags work across multiple titles  Consistent billing interface  Strict User Interface Guidelines

16. Deployment Issues Patching Maintenance Who pays for bandwidth? Billing Scalability Monitoring Usage and Statistics Handling Cheaters Detecting Piracy Who “owns” users? “Policing” the Community

17. Massively Multiplayer Online Games Huge Development Costs Virtual Economies Community Server Scalability Keeping content new and interesting

18. Future Considerations IPv6 Handhelds and Cell phones Cross-Title Integration Server-side “Mods” Peer-to-Peer MMOGs? Sony “Cell” Processor

19. Questions? Contact me at mark [at] rockstarsandiego.com.