Tackling Bufferbloat in capacity-limited networks

Over-provisioned network buffers, often at the Internet edge, induce large queuing delay and high latency; this issue is known as Bufferbloat. In response to this, a set of recently proposed Active Queue Management (AQM) algorithms attempt to reduce standing queues, while maintaining the bottleneck utilisation at an acceptable level. This paper assesses the performance of two AQM schemes (CoDel and FQ-CoDel) over capacity-limited networks with large Round-Trip Time (RTT). In such settings, these AQM schemes have difficulty controlling the buffering level, resulting in both momentarily high queuing delay and low bottleneck utilisation, even if the methods are claimed to be insensitive to link rates and round-trip delays. We explore this issue and show that it is possible to adapt the parameterisation of CoDel and FQ-CoDel to offer a higher bottleneck utilisation while maintaining a low queuing delay. We present experiments over an emulated test bed and a satellite network to confirm that our new parameterisation improves the download time of moderate-size files and reduces the latency for capacity-limited and large-RTT networks.