The optimistic approach of involving a third party only in the case of exceptions is a useful technique to build secure, yet practical fair exchange protocols. Previous solutions using this approach implicitly assumed that players had reliable communication channels to the third party. In this paper, we present a set of optimistic fair exchange protocols which tolerate temporary failures in the communication channels to the third party. A central feature of the protocols is that either player can asynchronously and unilaterally bring a protocol run to completion.
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