1. Applying Real-time Simulation to Real-time Collaboration Bart Miller

2. Overview Motivation Real-time multiplayer simulation Real-time collaboration GroupDraw Application GroupDraw Protocol Demo/Questions

3. Motivation Multiplayer action games provide responsive, fair simulations across unreliable networks User experience critical for adoption of real-time collaboration Can I apply techniques taken from simulation to collaboration?

4. Real-time Multiplayer Simulation Create a shared environment Environment affected by user input User expects to provide input and see the result of that input rendered onto screen

5. Real-time Multiplayer Simulation Entities o Player vs. non-player o Set of metrics (Position, Health, Ammo) Rules o Movement o Damage Divide time into discrete intervals, Ticks World State, Client State Action

6. Real-time Multiplayer Simulation Client-server design (Synchronous model) o Client simulation loop 1. Gather input, Send input as Actions 2. Receive World State information from server 3. Update Client State 4. Graphically Render World State o Server simulation loop 1. Receive Actions from Clients 2. Consolidate Actions from Clients Conflict resolution 3. Simulate world (generates World State) 4. Send World State snapshot to each Client

7. Real-time Multiplayer Simulation Problems with Synchronous Model o Network interface is the constraining resource  Bandwidth, latency o Latency is unpredictable  Unfair Solution o Buffer input and network traffic o Loop becomes a set of timers  Network send (lowest frequency)  Poll input (in-between)  Simulate (highest frequency)

8. Real-time Multiplayer Simulation

9. Real-time Collaboration Allows multiple users to edit a single file simultaneously Manage access to the file using a Journal Storage System o Server becomes Journal Storage Manager  Log version history of the file Set of Actions  Commitment process resolves conflicts Text data o Series of fixed-length character values o Action data contains location, character buffer

10. GroupDraw Application Client-server program Written in C# Clients share a common canvas Action contains o Player Id o Tick Number o Point Data (X,Y) Timer Periods o Send: 50ms o Input: 33ms o Simulate: 15ms (~67TPS)

11. GroupDraw Protocol Hybrid Protocol o TCP for reliability, latency independent information o UDP for data stream, lowest latency  Reliability, ordering handled by the application, snapshot data acknowledged by the client  No fragmentation TCP Methods o Connect, Disconnect o Join, Leave UDP Methods o AddData, ReceiveData, FullUpdate

12. Demo/Questions Any Questions?