IETF RFC 9406 PDF

This document describes HyStart⁺⁺, a simple modification to the slow start phase of congestion control algorithms. Slow start can overshoot the ideal send rate in many cases, causing high packet loss and poor performance. HyStart⁺⁺ uses increase in round-trip delay as a heuristic to find an exit point before possible overshoot. It also adds a mitigation to prevent jitter from causing premature slow start exit.