# HSTCP

When an ACK is received (in congestion avoidance), the window is increased by ${\displaystyle a(w)/w}$ and when a loss is detected through triple duplicate acknowledgments, the window is decreased by ${\displaystyle (1-b(w))w}$, where w is the current window size. When the congestion window is small, HSTCP behaves exactly like standard TCP so a(w) is 1 and b(w) is 0.5. When TCP's congestion window is beyond a certain threshold, a(w) and b(w) become functions of the current window size. In this region, as the congestion window increases, the value of a(w) increases and the value of b(w) decreases. This means that HSTCP's window will grow faster than standard TCP and also recover from losses more quickly. This behavior allows HSTCP to be friendly to standard TCP flows in normal networks and also to quickly utilize available bandwidth in networks with large bandwidth delay products.