Low Latency Switching in Signal
Article Summary
Signal's team discovered that building encrypted voice calls was easy. Building a VoIP system that actually worked well? That was the hard part.
The Signal team shares how they built RedPhone's low-latency voice infrastructure. They needed to route calls efficiently across the globe while keeping mobile clients simple (no persistent connections, no complex SIP protocols). The cryptography was straightforward, but delivering high-quality voice over pathological mobile NATs required creative solutions.
Key Takeaways
- Multi-connect strategy: clients simultaneously connect to all regional servers, use fastest
- Route 53 latency-based routing costs $5/month versus $500 with Dynect
- Approach eliminates need for dedicated load balancers, clients become the load balancer
- Enables zero-downtime rolling upgrades by draining connections before updates
Critical Insight
By combining DNS-based geographic routing with simultaneous multi-connect logic, Signal built a self-load-balancing VoIP infrastructure that automatically routes to the lowest-latency server.
