Lambda-Grids are richly interconnected collections of plentiful, geographically-distributed computing and storage resources. This rich connectivity is enabled by dedicated dense wavelength division multiplexing (DWDM) optical paths. With abundant bandwidth in the center of the network (many DWDM links), contention and sharing bottlenecks move from the network core to end systems. In such networks, traditional TCP is insufficient to provide acceptable performance. We identify the key communication characteristics of this radically different network, introducing a new multipointto- point communication pattern for data-intensive application. We evaluate several promising rate-based data transport protocols (RBUDP, SABUL/UDT and GTP) for lambda-Grids under a range of communication patterns (single stream, multiple parallel streams, converging streams, and rapid transitions). Our experiments use a range of performance metrics, including sustained throughput and loss rate, inter- and intra-protocol fairness, protocol overhead, and rate adaptation speed to flow transitions. The results provide insights into the capabilities of these three protocols and also for improvements in design and implementation of rate-based protocols.