HANDOFF BASED SECURE CHECKPOINTING AND LOG BASED ROLLBACK RECOVERY FOR MOBILE HOSTS

An efficient fault tolerant algorithm based on movement-based secure checkpointing and logging for mobile computing system is proposed here. The recovery scheme proposed here combines independent checkpointing and message logging. Here we consider mobility rate of the user in checkpointing so that mobile host can manage recovery information such as checkpoints and logs properly so that a mobile host takes less recovery time after failure. Mobile hosts save checkpoints when number of hand-off exceeds a predefined hand-off threshold value. Current approaches save logs in base station. But this approach maximizes recovery time if message passing frequency is large. If a mobile host saves log in its own memory, recovery cost will be less because log retrieval time will be small after failure. But there is a probability of memory crash of a mobile host. In that case logs can not be retrieved if it is saved only in mobile node. If the failure is transient then logs can be retrieved from the memory of mobile node. Hence in this algorithm mobile hosts also save log in own memory and base station. In case of crash recovery, log will be retrieved from base station and in case of transient failure recovery logs will be retrieved from mobile host. In this algorithm recovery probability is optimized and total recovery time is reduced in comparison to existing works. Logs are very small in size. Hence saving logs in mobile hosts does not cause much memory overhead. Hand-off threshold is a function of mobility rate, message passing frequency and failure rate of mobile hosts. This algorithm describes a secure checkpointing technique as a method for providing fault tolerance while preventing information leakage through the checkpoint data