Attaching digital signatures to state update messages in global distributed shared object (DSO) systems is not trivial. If the DSO consists of a number of autonomous local representative that use open, public networks for maintaining the state consistency, allowing a local representative to sign state update messages is not appropriate. More sophisticated schemes are required to prevent unauthorized state updates by malicious local representative or external parties. This paper examines the problem in detail, compares a number of possible solutions, and identifies the most suitable one and demonstrates how the state update messages can be signed using the identified solution.

Reliable multicast protocols on top of the MBone are presently subject to intensive research. In the past, numerous protocols have been developed and their respective performance been analysed. Little progress has been made, though, to compare different approaches. In this paper, we use the network simulator ns-2 to evaluate the performance of three protocols, namely Scalable Reliable Multicast (SRM), Multicast File Transfer Protocol (MFTP) and an enhanced version of the latter, called Multicast File Transfer Protocol with Erasure Correction (MFTP/EC). We also compare the results to each other and test the suitability for multicast file distribution.

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