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

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

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

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

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

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

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

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

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

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

Network Security Encryption and Digesting  RSA  Diffie-Hellman  MD5  DES, triple-DES, AES  IPSec References   “Applied Cryptography,” Schneier

Network Address Translation Peer 1 sees:  Peer 2 at : 1000  Peer 3 at : Peer 2 sees:  Peer 1 at : 1000  Peer 3 at : 1000 Peer 3 sees:  Peer 1 at : 1000  Peer 2 at : 1000 Internet NAT Peer 2Peer 3 Peer : : : : : 49155

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

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

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

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

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

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

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