ABSTRACT

The term Distributed Systems is used to describe a system with the following characteristics: i) it consists of several computers that do not share memory or a clock, ii) the computers communicate with each other by exchanging messages over a communication network, iii) each computer has its own memory and runs its own operating system. A mobile computing system is a distributed system where some of processes are running on mobile hosts (MHs), whose location in the network changes with time. The number of processes that take checkpoints is minimized to 1) avoid awakening of MHs in doze mode of operation, 2) minimize thrashing of MHs with checkpointing activity, 3) save limited battery life of MHs and low bandwidth of wireless channels. In minimum-process checkpointing protocols, some useless checkpoints are taken or blocking of processes takes place. To take a checkpoint, an MH has to transfer a large amount of checkpoint data to its local MSS over the wireless network. Since the wireless network has low bandwidth and MHs have low computation power, all-process checkpointing will waste the scarce resources of the mobile system on every checkpoint. Minimum-process coordinated checkpointing is a preferred approach for mobile distributed systems. In this paper, we discuss various existing minimum-process checkpointing protocols for mobile distributed systems.