Steady State Analysis of BBR Using Network Calculus

Recently, Cardwell et. al. proposed the BBR algorithm to improve on TCP variants for congestion control. In contrast to packet loss based congestion control algorithms, BBR attempts to operate at the optimal operating point of a bandwidth constrained network where the delay is minimized and throughput is maximized. However, BBR is in its early stage and has numerous shortcomings. We examine poor performance on throughput in long latency networks in detail. We survey three different techniques from hybrid systems literature, including identifying Piecewise Affine systems, Max Min Plus Scaling systems, and the Min Plus service curve framework from the network calculus literature. We develop an analytical explanation of the performance degradation for longer latencies and design a steady state model for BBR in the network calculus framework. Our analytical explanation also suggests two possible fixes to improve BBR throughput in long latency networks.

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