Triage: Boosting Cross-region Video Conferencing with Proactive FEC on Overlay Network

Video conferencing has become essential for connecting geographically distributed people. Cross-region video conferencing often employs overlay networks to improve long-haul Internet performance. However, transient packet loss can still occur and break the strict real-time latency requirements. Forward Error Correction (FEC) can recover losses without retransmissions, but existing schemes fail under overlay loss patterns. Our large-scale measurements show that overlay losses are sparse, bursty, and short-lived, with most loss events lasting less than one RTT. Under such patterns, the reactive nature of existing FEC schemes-increasing redundancy only after observing losses-leads to both under-protection during prolonged loss-free intervals and protection lag when short-lived loss events occur. Leveraging these insights, we develop a Zero-Inflated Loss Model that decouples loss occurrence from loss severity, and design Triage, a proactive FEC scheme that speculatively adds redundancy before losses are detected. Triage combines a hierarchical predictor for model parameters with an optimizer that balances video latency penalty against bandwidth cost. In evaluations on a five-region real-world testbed, state-of-the-art reactive schemes exhibit 16.6%--25.3% higher average latency penalty (104.0%--178.0% for P99) than Triage, despite only 1.1%--1.7% lower bandwidth cost.