As the speed and the dynamic range of computer networks evolve, the issue of efficient traffic management becomes increasingly important. This work describes an approach to traffic management using explicit rate information provided to the source by the network. We present an asynchronous distributed algorithm for optimal rate calculation across the network, where optimality is understood in the maxmin sense. The algorithm quickly converges to the optimal rates and is shown to be well-behaved in transience. In the past decade several mechanisms for congestion control have been developed and implemented. DECbit [34] and Slow Start [20] are perhaps the best known. Both of these schemes were developed for connectionless networks with window flow control, in which the routers had no knowledge of the individual flows and their demands, the routes changed frequently and the header space was scarce. With the rapid increase of the ratio of propagation delay to transmission time in the modern networks, window-based schemes face significant challenges [23], [32], [33]. The large window size and long feedback delays cause large bursts of traffic to be injected into the network leading to severe congestion. As a result it has been argued that a rate-based approach may be a viable alternative to windows. A number of rate-based schemes were developed based on the basic idea of DECbit -using a single bit in the packet (cell) header, which is set by the switch in the case of congestion However, the simplicity of the DECbit scheme has its price -slow convergence and rate oscillations, whch can cause large queues and potential data loss in rate-based networks. Even a small overload can cause extremely high queues if sustained for a long time. Since the rate is only adjusted with a period proportional to the endto-end round-trip delay, long-distance networks can no longer afford too many round-trips to determine correct rate allocation. Thus, a scheme with faster convergence properties is extremely desirable. In its simplest form DECbit suffers from unfairness to individual flows. It has been lofig argued that some sort of selective feedback based on individual flow information at the switches is required to provide fairness [37]. Selective Binary Feedback scheme [35] is an enhancement of DECbit in which the switches calculate a fair rate allocation and set the congestion bit for only those flows which exceed the fair allocation. This paper suggests an alternative approach to rate control, in which the switches calculate a rate allocation for the flows, and this allocation is explicitly provided to the sources in control packets or data packet headers. This approach provides significantly reduced convergence time and remarkable robustness. We identify a class of possible switch policies that lead to convergence to the optimal rate allocation. We prove an upper bound to the time of convergence, and show that the scheme is self-stabilizing, in that it will converge from any set of initial conditions. We also show that the expected performance of the algorithm during convergence is well behaved in practice. The scheme described here is primarily suited for connection-oriented networks, in whch the switches
A distributed algorithm is also proposed that is based on the algorithm proposed in REF .
Congestion control with explicit rate indication
Proceedings IEEE International Conference on Communications ICC '95
Proceedings IEEE International Conference on Communications ICC '95
Computer Science