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TCP CUBIC: The Default Congestion Algorithm

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CUBIC: solving high-bandwidth-delay-product congestion

TCP Reno was designed for the internet of the 1990s: modest speeds, low latency. Modern networks — 10 Gbps links, intercontinental paths, cloud storage — have high bandwidth-delay products: the pipe must hold gigabytes in-flight. Reno's linear window growth fills these too slowly and recovers too slowly after loss.

TCP CUBIC replaces linear growth with a cubic function, growing faster when far from the previous loss point and slowing near it.

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