https://blog.margrop.net/en/tag/congestion-control/ Recent content in Congestion Control on Margrop Blog Hugo -- gohugo.io en-US Thu, 02 Jul 2026 20:00:00 +0800 https://blog.margrop.net/en/post/bbr-fix-china-us-vps-slow-network/ Thu, 02 Jul 2026 20:00:00 +0800 https://blog.margrop.net/en/post/bbr-fix-china-us-vps-slow-network/ <blockquote> <p><strong>The short version</strong></p> <p>You&rsquo;re accessing your overseas VPS from within China. SSH feels snappy. <code>curl</code> on a small JSON endpoint returns instantly. But downloading a 2 MB HTML file takes over a minute. Convinced it&rsquo;s &ldquo;peak-hour international link congestion&rdquo;? Probably not — you&rsquo;re being sabotaged by Linux&rsquo;s default CUBIC congestion control. CUBIC treats every packet loss as &ldquo;the road ahead is jammed&rdquo; and immediately backs off. But international links have baseline 5–15% loss from physical-layer imperfections, not congestion. So your TCP flow gets permanently stuck in slow-mo. Switch to Google&rsquo;s <strong>BBR</strong> algorithm and the exact same physical path, same moment, same loss rate delivers <strong>15–24× more throughput</strong>.</p> <p>This post walks through a real mesh-VPN investigation: pulling a 2.3 MB page from a US VPS across a Chinese home connection went from <strong>30 KB/s to 500–1000 KB/s</strong> after four shell commands. It ships three one-shot scripts (Windows 11 / Ubuntu 26.04 / macOS 26), covering both manual execution and AI-agent-driven deployment. All internal IPs, hostnames, and public IPs have been redacted.</p> </blockquote>