We propose a multicast protocol for a distributed system that includes mobile hosts. The protocol guarantees reliable delivery, i.e. delivery of every multicast and absence of duplicates. The sender of each multicast may select among three increasingly strong delivery ordering guarantees: FIFO, causal, total. We make loose assumptions on the underlying computing system: (i) we consider an unreliable wireless network i.e. one that provides only incomplete spatial coverage and such that messages could be lost even within cells (e.g., due to physical obstructions); (ii) movements are unpredictable, i.e. a user that leaves a cell may enter any other cell, perhaps after a potentially long disconnection. Our solution does not store any sensible state information at mobile support stations, thus movements do not trigger the transmission query message in the wired network and no notion of hand-off is used. Furthermore, movements at inopportune times can cause only occasional performance penalty but do not affect correctness. Weak assumptions on the underlying computing system, absence of state information at mobile support stations and loose mobility assumptions, contribute to improve the reliability of applications deployed over the proposed protocol.
展开▼
