The salient result that emerges from the analyses of polling systems in the previous chapter is the large impact of overhead—particularly at light loading. Because of overhead, performance deteriorates with the number of stations irrespective of the total traffic in the system. On the other hand, as the total traffic in the system increases, the impact of overhead diminishes. All of this may be attributed to the overhead inherent in the action of a central controller. In terms of the effect of overhead on performance similar results apply to TDMA. These properties motivate the consideration of random access techniques in which control is distributed. As we shall see, random access systems are relatively insensitive to the number of active stations in the systems so that performance is best when there are a large number of lightly loaded sources. The difficulty is that these systems are very vulnerable to increases in the level of aggregate traffic.