CUBIC
also: CUBIC TCP, tcp_cubic
CUBIC is a TCP congestion control algorithm designed for high-speed networks that adjusts transmission rates based on packet loss to maximize throughput while maintaining fairness.
CUBIC (CUBIC TCP) is a modern congestion control algorithm used by the Linux kernel to manage how fast data is transmitted over TCP connections. It replaces the older Reno algorithm and is optimized for high-bandwidth, high-latency networks like intercontinental links.
The algorithm uses a cubic function to increase the congestion window (cwnd) during the congestion avoidance phase, allowing faster recovery after packet loss. When packets are dropped, CUBIC reduces the window size but then probes for available bandwidth more aggressively than traditional approaches, making it ideal for networks where latency is high but the connection is stable.
You can check if CUBIC is available on your system with cat /proc/sys/net/ipv4/tcp_available_congestion_control and set it as the default with sysctl -w net.ipv4.tcp_congestion_control=cubic. CUBIC has been the default in the Linux kernel since version 2.6.19 and is widely used in modern networks.