Flow Control in High-Speed Networks with Long Delays

The flow control component of a transport layer protocol regulates the natural data transmission rate of an application to match the service rate offered by the network. In this paper, we study the problems that arise when a flow control protocol has to deal with long delays in receiving information about network state, and has large amounts of data transmitted but unacknowledged. We describe three representative flow control protocols, and study their behavior on a suite of three benchmark scenarios. Our simulations indicate that in networks with large delays, protocols that are insensitive to the state of the network, or that require multiple round trip times to attain the optimal transmission rate, will perform poorly. The packet-pair protocol, which avoids these problems, is shown to perform well under rather adverse conditions.