Abstract
Problem statement: Causal ordering is used in Mobile Distributed Systems (MDS) to reduce the non-determinism induced by four main aspects: host mobility, asynchronous execution, unpredictable communication delays and unreliable communication channels. Some causal protocols have been proposed for MDS. All of these protocols in order to ensure the causal order in unreliable channels use the method of Automatic Repeat Request (ARQ). They detect a lost message and carry out the retransmission of this message. This approach was not recommended in a real time mobile distributed system because it increased the transmission delay of the data and the overhead sent in the communication channels. Approach: In this study, we proposed a protocol that ensured the causal order of messages in unreliable and asynchronous MDS. In our protocol, the detection and recovery of lost messages was achieved by the method of Forward Error Correction (FEC) in a distributed form. One interesting aspect of our Causal-FEC protocol was that the redundant information sent in the wired and wireless communication channels is dynamically adapted to the behavior of the system. Results: Our protocol was efficient in terms of the overhead attached per message, the computational cost and the storage control information at a mobile host. Conclusion: The present study is one of the first works on causal algorithms based on forward error recovery in mobile networks.
Highlights
Some works have been proposed to carry out a information
In order to ensure the causal delivery in the mobile distributed system, we increase the redundancy in the sent control information per message by sending information about causally related messages with a causal distance greater than one
Each time that a message m is received by a base station Base Station (BS) or a mobile host p, we take two corrective represents a message sent by the mobile host pi with logical local clock t = VT(BS)[i] and k =
Summary
Some works have been proposed to carry out a information. The use of causal ordering provides built- causal delivery of messages for mobile. The detection and recovery of lost messages is achieved by the approach of forward error correction proposed in (Pomares et al, 2009) for non mobile constrained systems We apply this FEC scheme to the causal protocol MOCAVI presented in (Lopez et al, 2008) in order to support mobile distributed systems over unreliable wireless channels. One interesting aspect of our Causal-FEC protocol is that the redundant information sent in wireless communication channels is composed by a set of bits, which is dynamically determined according to the behavior of the system and the predetermined causal distance This redundant information greatly increase the probability that causal order delivery will be obtained, even in the presence of lost messages and significant network delays, by moderately increasing the overhead in the wireless channels. The present study is one of the first works on causal algorithms oriented to the forward error recovery over mobile networks
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