## 2 Related Work
### Geographical Routing and Geocasting
It should also include a routing path between source node and target region. Otherwise, protocols either have to increase the size of the forwarding zone or fall back to simple flooding. An intermediate node forwards a message only if it belongs to the forwarding zone. In [21], the network is partitioned using the Voronoi diagram concept (to define forwarding zone) and each node forwards the packet to the neighbors whose Voronoi regions (as seen by the forwarding node) intersect with the geocast region. The idea is to forward to a neighbor only if it is progressively closer to the target region. In [22], the authors propose a geocasting algorithm detecting routing holes in underwater sensor networks. They use a similar approach to face routing and utilize x-y coordinates of the leaf nodes in the tree for detecting holes and face traversing. Although the authors show in simulations that the proposed protocol achieves handling of node mobility, there is no discussion about the mechanism that performs mobility handling. Interested reader are referred to [23] for a more comprehensive study of the related works. In this paper, we consider the query dissemination problem in a tree-based data collection and dissemination network. Geographical approaches might either fail at dead-ends formed in random networks topologies or require the computation of planar subgraphs of the connectivity graph to tackle routing holes. On the other hand, tree-based approaches work well for random topologies with potential empty areas (_i.e._, holes) in connected networks. Similar to GDSTR protocol [17], we also use a convex hull based approach for packet forwarding. However, the objective of GDSTR protocol is the node-to-node packet delivery realized by the use of multiple spanning trees rooted at different nodes for energy balancing. The main focus of [17] is on the choice of nodes serving as roots of spanning trees. There is not much attention to the construction and maintenance of hull trees. On the other hand, in this work we consider the case where the root of the tree is always the same node, which is a more resource rich device called data sink of the network. In this work, we provide the details of establishing convex hulls in the network and maintaining the routing tree and convex hull definitions in mobile sensor networks. We also compare different maintenance mechanisms (_i.e._, global and local updating). By using convex hull based coverage areas and performing local updates, our approach provides support for sensor mobility. In Section 5.2, we evaluate the performance of our geocasting approach (called GeoCHT), which utilizes coverage areas of sinks and sensors, by comparing it with GEAR protocol. The performance of different geocasting protocols is compared in [3] and GEAR shows the best performance over all the others. Therefore, we chose GEAR for our comparative performance evaluation. Simulation results show that GeoCHT outperforms GEAR in all metrics but query execution ratio in mobile sensor networks. Therefore, execution ratio is further evaluated together with communication overhead to investigate the performances of global and local updates in mobile sensor networks in Sections 5.4 and 5.5.