  Fast Congestion Notification (FN) is one of the proactive queue management
mechanisms that practices congestion avoidance to help avoid the beginning of
congestion by marking or dropping packets before the routers queue gets full;
and exercises congestion control, when congestion avoidance fails, by
increasing the rate of packet marking or dropping. Technically, FN avoids the
queue overflows by controlling the instantaneous queue size below the optimal
queue size, and control congestion by keeping the average arrival rate close to
the outgoing link capacity. Upon arrival of each packet, FN uses the
instantaneous queue size and the average arrival rate to calculate the packet
marking or dropping probability. FN marks or drops packets at fairly regular
intervals to avoid long intermarking intervals and clustered packet marks or
drops. Too many marked or dropped packets close together can cause global
synchronization, and also too long packet intermarking times between marked or
dropped packets can cause large queue sizes and congestion. This paper shows
how FN controls the queue size, avoids congestion, and reduces global
synchronization by uniformizing marked or dropped packet intervals.
