In an ideal pervasive computing environment, a large number of connected smart devices are deployed to collaboratively provision seamless services to users. Pervasive computing is enabled by various advanced technologies, particularly wireless technologies and the Internet. It has become a trend for our future lives. A pervasive computing environment can be extremely heterogeneous. We can imagine how many different devices are involved in a smart home: TVs, phones, cameras, coffee makers, or even books and bookshelves. Since these devices are smart and communicate with each other mainly via wireless links, security must be ensured. Otherwise, the smart devices deployed around us would come back to hunt us and the result would be catastrophic. In this abstract we briefly discuss some important security issues in pervasive computing.

Application-layer multicast (ALM) protocols differ in, among other aspects, the topology of the underlying overlay network (e.g., tree, mesh or ring). Therefore, comparing the performance of ALM overlay networks is an important step towards assessing the inherent advantages and/or limitations of each overlay network topology. In particular, ring-based ALM overlay networks have the advantages of (a) providing a constant node degree; i.e., the number of neighbors each group member has on the overlay network is constant and independent of the size of the multicast group and (b) enabling the implementation of secure, reliable and totally-ordered message delivery through the use of a ring with a token that contains ordering and flow control information. Motivated thus, we present in this paper a simulation-based performance evaluation and comparison between two ALM overlay networks. The first connects the multicast group members in a ring overlay network while the second connects them in a tree. Simulation results, which have been conducted in J-Sim, have shown that although a ring overlay network incurs a higher path stretch and a higher link stress than a tree overlay network, it provides a constant and lower node degree and a higher data delivery ratio despite the failure/leaving of a single multicast group member than those provided by a tree overlay network.