An Asynchronous Recovery Scheme based on Optimistic Message Logging for the Mobile Computing Systems

To provide the fault-tolerance for the mobile computing systems, many checkpointing-based recovery schemes have been proposed. However, considering the nature of the mobile environment in which some mobile hosts (MHs) are often disconnected from the network and the probability of concurrent failures on MHs is high, any kind of coordination during the checkpointing and even during the recovery may not be recommended. In this paper, we propose an asynchronous recovery scheme based on the optimistic message logging. Logging-based schemes have many advantages such as asynchronous recovery, handling of concurrent failures, and independent checkpointing. However, for the efficient implementation, the followings must be considered: First, message logging itself can be a burden on the MHs; and second, the information for the dependency tracking can be a problem, if it has to be added to the message between the MH and the mobile support station (MSS). In the proposed scheme, to cope with such problems, the tasks of logging and dependency tracking are fully performed by the MSSs. MHs are only carrying the minimum information, so that, the mobility of the MHs can properly traced by the MSSs. As a result, with a little overhead, optimistic message logging and asynchronous recovery can be implemented in the mobile environment.