Adding an inactivity timer

Most flows in the Internet are short-lived. If our only mechanism for removing an entry is its expiration after the slice length $t$ and we use a large value for $t$, at any moment in time, most of the entries in the flow memory will belong to flows that are no longer active and just use up memory waiting to expire. On the other hand having a very short slice length can lead to an increase in reporting traffic and loss of accuracy. Adding an inactivity timeout parameter $t_{inactive}$ to flow slices reduces the memory spent on obsolete entries. Experimental results in show that we can significantly reduce the memory requirement by using inactivity timers. An adaptive algorithm for setting the flow slicing rate can turn this reduction in memory usage into an increase in accuracy.