Focus on Networking Engine

1. Focus on Networking Engine

2. Contents • “Super IsoBomb” Network Engine Introduction • Game Networking Middleware APIs • Game Networking Issues Overview • “Super IsoBomb” Protocol Messages

3. Original Version: • Jason Winnebeck • Jon Hilliker • Jim Clase • Networking and Upgraded Version: • Peter Mowry

4. Super IsoBomb Networking Paper • http://www.rit.edu/~pem1491/IsoBomb/network.php3 • Game Networking Middleware Selection, General Game Networking Research, Protocol Specification and Issues • Super IsoBomb Home: • http://www.rit.edu/~pem1491/IsoBomb/ • Original Super IsoBomb Home: • http://www.rit.edu/~jpw9607/isobomb/

5. 1: C++ Game Networking Middleware • Research Possibilities • Select from Canidates • 2: Protocol Design Initial • Research Game Networking • Design Protocol • 3: Implementing • Test, Redesign, Re-implement, Targeted Research, etc

6. Game Networking MiddlewarePotential APIs • SDL_net • Component of open source (OpenGL-based) cross platform Simple Direct-Media Layer (SDL) • HawkNL • Low level C-based library; cross platform wrapper for WinSock and Unix Sockets • GNE (Game Networking Engine) • Created from HawkNL; higher level • Quazal Net-Z • Commercial API, cross platform (including console systems); Distributed Objects; only 30 day trial

7. Game Networking MiddlewarePrefered APIs • ReplicaNet • Network shared C++ objects • DirectPlay • DirectX Component; Windows-oriented; integration with DirectVoice • RakNet • C++ Packet-based API

8. RakNet • Has most of the features of DirectPlay, or at least those desired for “Super IsoBomb” • Bonus Features like: • Object IDs, Time Stamping • Intends on adding further optimizations • Such as Packet Combining, Improved Compression • Excellent documentation, tutorials, “Quick Start” • Focused Goals and very well supported

9. TCP vs. UDP • “Lesson two: • TCP is evil. Don’t use TCP for a game.” • “Lesson three: • Use UDP.” • “Lesson four: • UDP is better than TCP, but it still sucks.” http://www.gamasutra.com/features/19990903/lincroft_05.htm

10. How does RakNet Send Packets? • UDP with layers • More efficient than TCP • More customizeable overhead • enum PacketReliability{ UNRELIABLE, // 3, 1, 7 UNRELIABLE_SEQUENCED, // 3, 7 RELIABLE, // 3, 1, 5, 7, 2, 4, 6 RELIABLE_ORDERED, // 1, 2, 3, 4, 5, 6, 7 RELIABLE_SEQUENCED // 3, 5, 7};

11. General Architecture • Server keeps sole authoratative game state • Efficiently synchronize game state • First major step towards Anti-Cheat • Client is “dumb rendering terminal” • Send input requests to server • Not so dumb - Doom to Quake to Unreal • Receive game state and simulate/predict

12. Optimization! • Optimization is a primary concern of real-time game networking! • Minimize traffic for good client simulation • Client simulation – make it look optimized: • Prediction logic • Smoothing algorithms • Server is authority • Sometimes trade-offs between accuracy vs. smoothness

13. Smoothness at the expense of Accuracy Client – simulating smooth local Server – accepting move requests

14. Zero Security Optimization:Client Authority • Perfect Client smoothness for its objects • Each Client has authority over some objects (like its character, its bombs, etc) • Possible methods: • Client sends server updates of its objects;Server relays opponent updates to each Client • Peer to Peer • A fully authoratative server sees the real game • Any authoratative server has the power to cheat,including non-dedicated servers

15. What to send . . . • Send full game state updates? • Send game state updates only for some data? • Ex - 50 world units around the player(assumes player with fixed camera) • Ex – Information for the current small zone • Send input or triggers or deltas?(assume deterministic game logic or partly)

16. Message Groups (by purpose) • Game Setup Triggers:Join, Disc, Start, StartPlayer, Map Change • Character Movement • Thrown Bomb • Homing Bomb • Game Triggers: Powerup, Virus, Damage

17. Messages by Reliability • Server to Client; Reliable; don't need to combine • PlayerJoinedStruct – 1 - server event • PlayerDiscStruct – 2 – server event • GameStartStruct – 3 - server event • GameStartPlayerStruct - 19 – server event

18. Messages by Reliability • Server to Client; Reliable group • ThrownBombSpawnStruct - 24 - server event • ThrownBombHeadBounceStruct - 19 - server update • BombExplodeStruct - 9 - server event • HomingBombSpawnStruct - 28 - server event • PowerupCollisionStruct - 9 - server event • VirusSpawnStruct - 8 - server event • DamagePlayerStruct - 2 - server event

19. Messages by Reliability • Server to Client; Unreliable group • PosVelStruct - 13 - server update • HomingBombUpdateStruct - 16 - server update

20. Messages by Reliability • Client to Server; Reliable group • MapChangeRequest - 2 - client request • MoveRequestStruct - 8 - client request • ThrownBombRequestStruct - 5 - client request • HomingBombRequestStruct - 2 - client request

21. Next Version of RakNet • Easier Packet Combining • Thus, I didn't do it manually in this version • "streaming and a transparent compression / encryption scheme" • Bandwidth optimization • Security improvement

22. Game Setup Triggers:Join, Disc, Start, StartPlayer, Map Change • Create and remove player Ids • StartGame – number of players to expect • StartGamePlayer - Information for one player • Starting Position, Score • MapChangeRequest • List of current requested map for each player • Change when all are same and not current map

23. Character Movement – Possible • Client-side authority over position • Warp cheat • Request/Update • Client sends move requests • Server sends PosVel updates • Client attempts to predict and smooth movement • List of moves with time stamps applied • Gradually reposition over time interval - anti-pop

24. Character Movement – Final • Client-side authority over position verified • Client sends position • Server checks legality of move: • time stamp > current time • distance (use velocity and dt) • height steps (1 tile up per tile change) • *movement through another character *only illegal expected without cheats

25. Thrown Bomb – Possible • Basic – spawn request and spawn • Prediction failed • Hit Floor – basic with single repositioning • ID-based bounce and Hit Floor • Update only when bounce • Non-deterministic logic => Basic fail when no bounce • ID-based continual updates

26. Thrown Bomb – Final • Rewrote more deterministic logic • Update( dt ) – enforce constant dt values • Projectile motion overall equation instead of deltas • Spawn + Deterministic Logic • => accurate client-side prediction • Character positions are unreliable • Update in event of character bounce (not wall bounce)

27. Homing Bomb – Possible • Deterministic AStar path finding • Dynamically finds path to target • Just send Spawn? • Character (target) position is unreliable!

28. Homing Bomb – Final • HomingBombRequest • HomingBombSpawn • (time stamped for prediction) • Continuously sends HomingBombUpdate • (time stamped for prediction) • BombExplode • Ping/2 delay; Could be predicted by sending explode earlier if and only if destination position is known then

29. Game Triggers:Powerup, Virus, Damage • PowerupCollision • Player ID, powerup type, virus type, time stamp • VirusSpawn • Sent if collision with an infected player • Damage event sent • Fatality inferred

30. Additional Questions? (Demo Next)