Abstract-A standard approach to large network visualization is to provide an overview of the network and a detailed view of a small component of the graph centred around a focal node. The user explores the network by changing the focal node in the detailed view or by changing the level of detail of a node or cluster. For scalability, fast force-based layout algorithms are used for the overview and the detailed view. However, using the same layout algorithm in both views is problematic since layout for the detailed view has different requirements to that in the overview. Here we present a model in which constrained graph layout algorithms are used for layout in the detailed view. This means the detailed view has high-quality layout including sophisticated edge routing and is customisable by the user who can add placement constraints on the layout. Scalability is still ensured since the slower layout techniques are only applied to the small subgraph shown in the detailed view. The main technical innovations are techniques to ensure that the overview and detailed view remain synchronized, and modifying constrained graph layout algorithms to support smooth, stable layout. The key innovation supporting stability are new dynamic graph layout algorithms that preserve the topology or structure of the network when the user changes the focus node or the level of detail by in situ semantic zooming. We have built a prototype tool and demonstrate its use in two application domains, UML class diagrams and biological networks.

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Abstract.Broadcasting is an essential and effective data propagation mechanism, with several of important applications such as route discovery, address resolution, as well as many other network services. As data broadcasting has many advantages, also causing a lot of contention, collision, and congestion, which induces what is known as "broadcast storm problems". Broadcasting has traditionally been based on the flooding protocol, which simply overflows the network with high number of rebroadcast messages until the messages reach to all network nodes. A good probabilistic broadcasting protocol can achieve higher saved rebroadcast, low collisions and less number of relays. In this paper, we propose a dynamic probabilistic approach that dynamically fine-tunes the rebroadcasting probability according to the number of neighbour's nodes distributed in the ad hoc network for routing request packets (RREQs). The performance of the proposed approach is investigated and compared with the simple AODVand fixed probabilistic schemes using the GloMoSim network simulator under different mobility models. The performance results reveal that the improved approach is able to achieve higher saved rebroadcast and low collision as well as low number of relays than the fixed probabilistic scheme and simple AODV.

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