CRDT-Based Game State Synchronization in Peer-to-Peer VR

TL;DR

VR presence demands ultra-low latency, and centralized clouds struggle to guarantee it. The authors implement BrickSync, a CRDT-based synchronization framework in Unity, running over WebRTC P2P connections to compare operation-based and state-based CRDTs for real-time VR collaboration. They show substantial latency reductions in P2P configurations (average around $50\,\mathrm{ms}$, best $18\,\mathrm{ms}$) versus remote servers, with state-based MV-Transformer offering robust conflict resolution and support for local-space versus world-space updates. The work addresses challenges such as NAT traversal, global rules like gravity, and oscillations, proposing dynamic strategy switching to adapt to interaction context. Overall, the study demonstrates the practical feasibility of decentralized VR collaboration using CRDTs and provides a foundation for designing open, low-latency digital spaces in VR.

Abstract

Virtual presence demands ultra-low latency, a factor that centralized architectures, by their nature, cannot minimize. Local peer-to-peer architectures offer a compelling alternative, but also pose unique challenges in terms of network infrastructure. This paper introduces a prototype leveraging Conflict-Free Replicated Data Types (CRDTs) to enable real-time collaboration in a shared virtual environment. Using this prototype, we investigate latency, synchronization, and the challenges of decentralized coordination in dynamic non-Byzantine contexts. We aim to question prevailing assumptions about decentralized architectures and explore the practical potential of P2P in advancing virtual presence. This work challenges the constraints of mediated networks and highlights the potential of decentralized architectures to redefine collaboration and interaction in digital spaces.

Figures (11)

• Figure 1: A snapshot of BrickSync in action, showcasing two users collaboratively manipulating virtual objects in a shared VR environment. Real-time synchronization of object states is achieved using CRDTs over a P2P WebRTC connection.
• Figure 2: A Unity GameObject Transform component. Rotation is non-commutative: the order of rotations affects the final orientation. Rotation is a quaternion (4D space to prevent gimbal lock) represented in Euler angles on the UI.
• Figure 3: MV-Transformer synchronization in Local-Space Mode with replicas A and B. A applies 'Move Right' to reach (1,0,0); B applies 'Move Left' twice to (-2,0,0). Solid arrows show local updates, dotted lines indicate state exchanges. The process merges to a final state of (-1,0,0).
• Figure 4: Impact of Connection Type and Architecture on Latency. The x axis displays different network configurations groups that show the different architectures, as expected, P2P is much faster.
• Figure 5: Average latency measurements for different connection types and configurations across all test scenarios.