Designing AQM Mechanism for Improving Fairness among TCP Connections in Tandem Networks

In recent years, AQM (Active Queue Management) mechanisms, which control the number of packets in the router’s buffer by randomly discarding an arriving packet, have been actively studied. In past studies, most of AQM mechanisms have been designed by taking account of a single router; i.e., few AQM mechanisms have been designed by taking account of multiple routers in the network. In a tandem network with multiple routers and heterogeneous TCP connections, it is known that the bandwidth allocation to TCP connections satisfies F A fairness criterion. This means that the throughput of TCP connection tends to be high when its round-trip time and/or the number of its traversing links is small. In this paper, we focus on such a tandem network, and design an AQM mechanism called FI-RED (Fairness Improvement for RED) for improving the fairness among heterogeneous TCP connections. In FI-RED, ECN (Explicit Congestion Notification) mechanism is used for differentiating the packet marking probability of RED according to the (Congestion Experienced) bit of arriving packets. We analyze the steady state behavior of FI-RED and perform simulation experiments in several network configurations. We quantitatively show that the fairness among TCP connections is significantly improved compared with RED.