s. The user terminal tries to ac- cess one cell, which is blocked, and is directed to retry another cell. Suppose that we are engineering this system for 2 percent blocking. If we engineer all the cells for 4 percent blocking, then half the traffic will be blocked 4 percent of the time, whereas the other half will have two chances and will see a block- ing rate of 0.16 percent, 4 percent of 4 percent. If half the traffic sees 4 percent block- ing and the other half sees 0.16 percent, then the average blocking for the subscriber community is 2 percent. 14 Thus our example system with 50 percent overflow possibil- ity can be engineered for roughly double the blocking rate. We are relying on the fact that this is a mobile telephone system, that the subscribers are in varying places. A landline system with 4 percent blocking in half its service com- munity would not be able to claim 2 percent blocking, but our subscribers move around and are just as likely, we expect, to be in the good areas as the in the bad areas, so see the average blocking rate. The actual traffic engineering for a system with split cells, overlaid cells, and neigh- bor cells is much more complicated than our example. Often there are many adequate solutions for traffic engineering a system, and the best choice depends on where facili- ties are available or where they can be obtained cheaply. 27.10 Cookie-Cutter Hexagons It is fascinating to explore all these geometric algorithms. During the development of cellular telephone technology in general and of AMPS in particular, many sophisticated studies were done using these cookie-cutter hexagons to represent the cells of a cellu- lar telephone system. These models allowed cellular pioneers to formulate the traffic and reuse models still in use throughout the world today. The reality is quite different. It is important to keep in mind that all these cells are not the lovely, symmetric, equal-sided hexagons we draw in our geometric diagrams. Many analytic and simulation studies also were done using ra