For checkpointing to be practical, it has to introduce low overhead for the targeted application. As a means of reducing the overhead of checkpointing, this paper proposes a probabilistic checkpointing method, which uses block encoding to detect the modified memory area between two consecutive checkpoints. Since the proposed technique uses block encoding to detect the modified area, the possibility of aliasing exists in encoded words. However, this paper shows that the aliasing probability is near zero when an 8-byte encoded word is used. The performance of the proposed technique is analyzed and measured by using experiments. An analytic model which predicts the checkpointing overhead is first constructed. By using this model, the block size that produces the best performance for a given target program is estimated. In most cases, medium block sizes, i.e., 128 or 256 bytes, show the best performance. The proposed technique has also been implemented on Unix based systems, and its performance has been measured in real environments. According to the experimental results, the proposed technique reduces the overhead by 11.7% in the best case and increases the overhead by 0.5% in the worst case in comparison with page-based incremental checkpointing.

Previous routing algorithms for mobile ad-hoc networks (MANETs) have focused on finding short-distance path(s) between communicating nodes. However, due to the dynamic and unreliable communication nature of MANETs, previously determined paths can easily become disconnected. Although dynamic routing can be used to circumvent this problem, determining a new route each time a packet needs to be sent involves a lot of overhead. An alternative form of dynamic routing involves maintaining valid routes in routing tables, which can be dynamically updated whenever network changes are detected. This paper proposes a new routing algorithm, referred to as pseudo-distance routing (PDR), that supports efficient routing table maintenance and dynamic routing based on such routing tables.