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When many parties share network resources on an overlay network, mechanisms must exist to allocate the resources and protect the network from overload. Compared to large physical networks such as the Internet, in overlay networks the dimensions of the task are smaller, so new and possibly more effective techniques can be used. In this work we take a fresh look at the problem of flow control in multisender multigroup reliable multicast and unicast and explore a cost-benefit approach that works in conjunction with Internet standard protocols such as TCP. In contrast to existing window-based flow control schemes, we avoid end-to-end per sender or per group feedback by looking only at the state of the virtual links between participating nodes. This produces control traffic proportional only to the number of overlay network links and independent of the number of groups, senders, or receivers. We show the effectiveness of the resulting protocol through simulations and validate the simulations with live Internet experiments. We demonstrate near-optimal utilization of network resources, fair sharing of individual congested links, and quick adaptation to network changes.