Copyright 2012 IEEE. Reprinted with permission. 26th IEEE International Conference on Advanced Information Networking and Applications (AINA) Fukuoka, Japan, March 2012 Harsh RED: Improving RED for Limited Aggregate Traffic Ilpo Järvinen, Aaron Yi Ding, Aki Nyrhinen, Markku Kojo Department of Computer Science University of Helsinki Abstract: A bottleneck router typically resides close to the edge of the network where the aggregate traffic is often limited to a single or a few users only. With such limited aggregate traffic Random Early Detection (RED) on the bottleneck router is not able to properly respond to TCP slow start that causes rapid increase in load of the bottleneck. This results in falling back to tail-drop behavior or, at worst, triggers the RED maximum threshold cutter that drops all packets causing undesired break for all traffic that is passing through the bottleneck. We explain how TCP slow start, ACK clock and RED algorithm interact in such a situation, and propose Harsh RED (HRED) to properly address slow start in time. We perform a simulation study to compare HRED behavior to that of FIFO and RED with recommended parameters. We show that HRED avoids tail-drop and the maximum threshold cutter, reduces queue lengths, and provides less bursty drop distribution. IEEE AINA 2012 Conference Proceedings publication DOI.