Page 2 Lecture Notes in Computer Science 2865 Edited by G. Goos ...

232 F.J. Molina, J. Barbancho, and J. LuqueLR - Large range nodeAggregation point(2) Response toLR node point(1) Response(3) Token sentFig. 5. Simultaneously collecting tokens: polling scheme 3.interference are not considered, then collecting time decreases to a factor equalto the number of tokens. Obviously, collisions increase as the number of tokensincrease. Many response tokens travel to the root node, creating an implosionproblem [19] (which is greater near the root node). To avoid this, we propose apolling scheme based on Short range - Long Range topology. The root node mustsend polling tokens to each node in the LR subnet. Each LR node collects datafrom all their sub-trees, aggregating and storing data, without passing them toroot. LR nodes only send data when the UC requests them. The node applicationprotocol does not change significantly with respect to the second schedule, so thisvariant is fundamentally the same one for nodes. As it is shown in figure 5, pollingtokens are passing simultaneously over different areas, so collision probabilityis low. Supposing that all the clusters have approximately the same numberof nodes (long-range and short range densities are homogeneous), neglectingcollisions and second order effects, then:CT 3 =( NSR)CharSize· ATS · NT SR + N · ATS · NT LR ·N LR BaudRateAnd supposing that N SR ≈ N, and applying (equation 2)CT 3CT 1=11+ PTSAT S·1(10)1+ NT SRNT LR(11)Using topology parameters for Seville, this scheme may reach CT 3 = CT 1 /10.