We consider query slipping and its prevention in wireless sensor networks. The problem happens when a query propagating along a subscribe trajectory moves through a publish trajectory without obtaining the desired information, even though the two trajectories intersect geometrically. There follows resubmission of the query or initiation of another subscribe trajectory. Thus, query slipping results in considerable time delay and, in the worst case, looping in the trajectory or query flooding the network. We address the problem formally and suggest a solution. First, the area where nodes are distributed is logically partitioned into smaller grids, and a grid-based next-hop selection algorithm is proposed. The algorithm not only attempts to make the trajectory straight but also considers the nodal density of recipient nodes and the seamless grid-by-grid multicast. We show that publishing and subscribing using the algorithm eventually eliminates the possibility of slipping. It turns out that our approach dissipates less power at neighbor nodes, compared to a non grid-based method, such as greedy forwarding.

One-to-many connection (i.e., multicast) is an important communication primitive used in parallel processing and high-speed switching in order to simultaneously send data from an input to more than one output. We prove that for even (respectively, odd) n, a multi-log/sub 2/N network is strictly nonblocking for a one-to-many connection traffic if it is designed by vertically stacking at least (/spl delta/n)/4+1((/spl delta//2)(n-1)+1) planes of a log/sub 2/N network together, where N=2/sup n/, /spl delta/=2/sup [n/2]/, and [x] denotes the greatest integer less than or equal to x. We thus give answer to the open problem and introduce yet another strictly nonblocking multicast network. The characterized network has self-routing capability, regular topology, O(2log/sub 2/N+2log/sub 2/(log/sub 2/N)) stages, and fewer crosspoints than the Clos network for N/spl ges/512. We then extend multi log/sub 2/N multicast networks to the fanout restricted nonblocking networks. It turns out that the multi-log/sub 2/N network nonblocking in a strict-sense for a one-to-one connection traffic is also wide-sense nonblocking for a multicast traffic in which the fanout of any connection does not exceed /spl delta/, provided that for even (respectively, odd) n, the fanout capability of each log/sub 2/N network is restricted to stage (n/2)(((n-1)/2)+1) through n-1.