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Figure 1 shows the classification of the location services proposed so far. Location services can be divided into flooding-based and rendezvous-based approaches. Flooding-based protocols can be further divided into dissemination and reactive approaches. In the dissemination approach, each node periodically floods its location to all nodes in the network. Thus, when a given node requires location information on another node, the information is found in the node’s location table, i.e., the dissemination services usually do not send query messages. They can be classified as an all for-all approach. In the reactive approach, nodes do not send update messages; instead they query location information of a specific node only if needed. The location query is flooded to the whole network. The reactive services belong to all-for some category. In rendezvous-based approach, all nodes agree on the set of location servers. Reactive and dissemination services represent the two extremes of the update strategy and they are not scalable. We focus in the following on the rendezvous based services. Two approaches are used to select the location servers, quorum-based and hashing based (Camp, Boleng, & Wilcox, 2001; Luo, X., Camp, & Navidi, 2005).
Figure 1. Location services classification
One of the main problems in location service problem is time of sending of location update packets. As per available methods, we can classify those to: 1) Time based, 2) Distance based, 3) Distance deviation based, 4) Combination based, 5) Grid based and 6) parametric based methods. The proposed classification is available in Figure 2.
Figure 2. Time of update classification