Hybrid Slow Start for High-Bandwidth and Long-Distance Networks

Slow Start is a technique to probe for unknown and time-varying available bandwidth of a network path. A sender increases its congestion window by one for each ACK received when ACKs are not delayed, which effectively doubles its congestion window when receiving ACKs for all the packets within a congestion window. Even if an exponential increase of congestion window during Slow Start grabs unused bandwidth quite well, a large number of packet losses within an RTT are inevitable because of its over-shooting. Furthermore, for fast and long distance networks, a large number of packet losses would result in unnecessarily long timeouts and create system performance bottlenecks related to handling the recovery of lost packets.