A mechanism for TCP-aware Active Queue Management in packet-forwarding devices

Overview & Synopsis

The deployment of Active Queue Management (AQM) policies is known to be a promising solution to bufferbloat, the problem of persistently-full large buffers in Internet routers. However, most AQMs involve tunable parameters, and some require awareness of the characteristics of the transport-layer protocol implemented at the end systems, thereby rendering their deployment infeasible. We consider one such AQM-- a threshold-based queue policy which requires the packet-dropping threshold to be co-designed with relevant TCP parameters. We propose a mechanism that detects network congestion, estimates the congestion window evolution in the end hosts, estimates the required TCP parameter, and produces an optimal value of the packet-dropping threshold. Arguments based on analysis of the TCP fluid model are presented to substantiate the proposed mechanism. A simulation-based performance evaluation reveals the effectiveness of the proposed mechanism, compared to some widely implemented queue policies, in terms of various user- and system-oriented metrics. The proposed mechanism is particularly well-suited for implementation in Software Defined Networks (SDN) where the algorithms can run in the SDN controller and the packet-dropping threshold can be implemented in the data-plane switches through open interfaces.