The ability of transferring very large files in the shortest amount of time is crucial for data-intensive Grid applications. Experimental evidence has shown that the mere availability of high-capacity wide-area networks is not sufficient to obtain adequate performance if vanilla TCP is used to transport data. Consequently, many alternative solutions are being explored, and a variety of data transfer tools have appeared. In this paper we experimentally compare some of these tools in various

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... rk scenarios. Our results show that solutions based on UDP, adopting rate-based algorithms, result in better performance than other alternatives in most cases, while solutions based on TCP are effective only under specific circumstances.