On Tolerating Failures of Mobile Hosts and Mobile Support Stations

In this paper, we present two fault-tolerant protocols for mobile computing systems; a causal message logging protocol and a receiver-based pessimistic message logging protocol for tolerating failures of mobile hosts (MHs) and mobile support stations (MSSs) respectively. The systems raise several constraints such as limited life of battery power, mobility and disconnection of hosts and lack of stable storage. Existing causal message logging protocols in distributed systems can efficiently handle some among the constraints. However, they are unable to handle the other constraints such as mobility and disconnection of MHs, and lack of stable storage. Our causal logging protocol can handle all the constraints efficiently and improve asynchrony during recovery. Moreover, it maintains only one checkpoint for each MH. Our receiverbased pessimistic logging protocol reduces the failure-free overhead and improves scalability to a large number of MHs managed by each MSS compared with existing replication-based protocols.