Improving the Fairness of Alternative Backoff with ECN (ABE)

Explicit Congestion Notification (ECN) lets a bottleneck's Active Queue Management (AQM) mechanism inform an endpoint about congestion without having to drop a packet. A recently proposed sender-side modification called Alternative Backoff with ECN (ABE) enables reduced latency while maintaining good utilization with ECN. However, under certain circumstances ABE can produce a degree of unfair behavior between ABE-enabled TCP senders and conventional TCP senders. We propose specific guidance for configuring bottleneck AQMs to assist in fairness between ABE-enabled and conventional TCP flows. We evaluate our proposal using RED, then describe how it can be applied to other AQM mechanisms and incrementally introduced into the Internet.