High speed bulk data transfer is an important part of many data-intensive scientific applications. The aggressive bulk data transfer algorithm scheme, called Reliable Blast UDP (RBUDP), is intended for extremely high bandwidth, dedicated, or Quality-of-Service enabled networks, such as optically switched networks.

Reliable Blast UDP has two goals.

The first is to keep the network pipe as full as possible during bulk data transfer. The second goal is to avoid TCP’s per-packet interaction so that acknowledgments are not sent per window of transmitted data, but aggregated and delivered at the end of a transmission phase.

Since UDP is an unreliable protocol, some datagrams may become lost due to congestion or an inability of the receiving host from reading the packets rapidly enough. The receiver therefore must keep a tally of the packets that are received in order to determine which packets must be retransmitted. At the end of the bulk data transmission phase, the sender sends a DONE signal via TCP (C in the figure) so that the receiver knows that no more UDP packets will arrive. The receiver responds by sending an Acknowledgment consisting of a bitmap tally of the received packets (D in the figure). The sender responds by resending the missing packets, and the process repeats itself until no more packets need to be retransmitted.