All the existing sender-based message logging (SBML) protocols share a well-known limitation that they cannot tolerate concurrent failures. In this paper, we analyze the cause for this limitation in a unicast network environment, and present an enhanced SBML protocol to overcome this shortcoming while preserving the strengths of SBML. When the processes on different nodes execute a distributed application together in a broadcast network, this new protocol replicates the log information of each message to volatile storages of other processes within the same broadcast network. It may reduce the communication overhead for the log replication by taking advantage of the broadcast nature of the network. Simulation results show our protocol performs better than the traditional one modified to tolerate concurrent failures in terms of failure-free execution time regardless of distributed application communication pattern.

In this paper, we consider the all-to-all broadcast problem in optical broadcast star networks using Wavelength Division Multiplexing. Our network model assumes that receivers are fixed-tuned and transmitters are tunable such that optical lasers assigned to transmitters have limited access to the network bandwidth; hence, each node must be equipped with multiple optical lasers and/or multiple optical filters in order to maintain a single-hop network. This paper is primarily concerned with single-hop networks, in which each node is assigned a single optical filter. Lower bounds are first established on the number of lasers per each node and the minimum schedule length, and a schedule achieving the minimum schedule length is presented. The results are applicable to arbitrary tuning delays, arbitrary numbers of wavelength channels, and optical lasers' arbitrary tuning ranges. Network models with optical devices having limited tuning ranges have not yet been considered in connection with transmission schedules, and this is the first work in this new direction.