The PI Algorithm

Knobs:

• W -> sampling frequency
• a,b -> weights
• q_ref -> reference queue delay

Other values

• p -> drop probability
• q -> current queue delay
• q_old -> old queue delay

Algorithm:

Every W times per second:

    # calculate q (paper doesn't say how, but PIE uses Little's law

    # calculate drop probability
    p = a*(q-q_ref) + b*(q_old - q_ref) + p_old

    # update p_old and q_old
    q_old = q
    p_old = p