Efficient design of RED routers for TCP/RAP fairness optimization

All real-time applications at present transmit via the UDP transport protocol. This creates a problem of fairness between TCP and UDP flows: in the presence of a high network load and congestion, TCP sources reduce their output traffic while UDP sources continue to transmit in the same way, as if the network were underloaded. In this way, UDP sources monopolize the available bandwidth, strongly penalizing TCP sources. A solution to this problem consists of introducing a congestion control algorithm for UDP sources as well; one of the best known TCP-friendly rate-control algorithms is the rate adaptation protocol (RAP). The target of this paper is twofold: firstly it investigates fairness between TCP and RAP protocols in a real Internet scenario where routers apply a random early detection (RED) active queue management policy; secondly, a set of guidelines for design of RED router parameters in such a way as to optimize fairness is provided.