mirror of
https://github.com/permissionlesstech/bitchat.git
synced 2026-07-24 22:45:19 +00:00
jack
1e2717f152
- Probabilistic flooding: Relay probability adapts to network size (30-100%) - Bloom filter duplicate detection: O(1) lookups with 4096-bit filter - Connection pooling: Reuse connections with exponential backoff - Adaptive TTL: Reduces hops based on network size (2-5) - Message aggregation framework: 100ms batching window - BLE advertisements: Include network size/battery hints These optimizations improve capacity from ~20-30 to ~50-100 users while maintaining privacy (no routing tables) and simplicity. The system now adapts automatically to network conditions without configuration. Trade-offs: Slightly higher CPU for bloom filter, probabilistic relay may miss edge cases, but overall much better scaling behavior.
3.5 KiB
3.5 KiB
BitChat Scaling Optimizations
Overview
Implemented practical scaling optimizations to improve BitChat's capacity from ~20-30 users to potentially 50-100 users while maintaining privacy and simplicity.
Optimizations Implemented
1. Probabilistic Flooding
- Messages are relayed with probability based on network density
- Reduces redundant transmissions in dense networks
- Adaptive relay probability:
- ≤5 users: 100% relay (ensure delivery)
- ≤15 users: 80% relay
- ≤30 users: 60% relay
- ≤50 users: 40% relay
-
50 users: 30% relay (minimum)
- Random delay (50-500ms) prevents collision storms
2. Bloom Filter for Duplicate Detection
- 4096-bit bloom filter (512 bytes) for fast duplicate checking
- 3 hash functions for optimal false positive rate
- Resets every 5 minutes to prevent saturation
- Combined with exact set for accuracy
- O(1) lookup time vs O(n) for set membership
3. Connection Pooling & Exponential Backoff
- Reuses existing peripheral connections
- Tracks connection attempts per peripheral
- Exponential backoff: 1s × 2^attempts after failures
- Maximum 3 connection attempts
- Reduces connection churn and battery usage
4. Adaptive TTL
- TTL adjusts based on network size:
- ≤10 users: TTL=5 (maximum reach)
- ≤30 users: TTL=4
- ≤50 users: TTL=3
-
50 users: TTL=2 (limit propagation)
- Prevents message storms in large networks
5. Message Aggregation (Framework)
- 100ms aggregation window
- Groups messages by destination
- Sends with 20ms spacing to prevent collisions
- Ready for future batching optimizations
6. BLE Advertisement Enhancements
- Includes network size hint in manufacturer data
- Battery level in advertisements
- Enables network-aware decisions without connections
- Lightweight presence detection
Performance Impact
Before Optimizations
- Full mesh: O(n²) connections
- Every node relays every message
- Fixed TTL=5 for all messages
- Connection attempts without backoff
- Linear duplicate detection
After Optimizations
- Same mesh topology but smarter behavior
- 30-70% relay reduction in dense networks
- Dynamic TTL reduces unnecessary hops
- Connection failures don't cause storms
- Constant-time duplicate detection
Estimated Capacity
- Small groups (5-10 users): Excellent performance, minimal change
- Medium groups (20-30 users): Good performance, noticeable improvement
- Large groups (50-100 users): Functional but degraded experience
- Very large (100+ users): Not recommended without architectural changes
Future Improvements
- Hierarchical Clustering: Elect cluster heads for inter-cluster routing
- DHT-based Routing: Distributed hash table for targeted message delivery
- True Message Aggregation: Combine multiple messages into single packets
- Adaptive Scanning: Reduce scan frequency based on network load
- Priority Queues: Prioritize direct messages over broadcasts
Trade-offs
- Privacy maintained: No routing tables or persistent node IDs
- Complexity limited: Avoided heavyweight protocols (OLSR/AODV)
- Battery impact: Slightly higher CPU usage for bloom filter
- Reliability: Probabilistic relay may miss some messages in edge cases
Configuration
All parameters are adaptive and require no user configuration. The system automatically adjusts based on:
- Network size (peer count)
- Battery level
- Connection quality
This approach balances scalability improvements with BitChat's core values of simplicity and privacy.