Evaluating CoDel, PIE, and HRED AQM techniques with load transients

In the past, networks have been mainly optimized for good system throughput but recently achieving low delay has also gained notable traction. Active Queue Management (AQM) has long been recognized necessary for operating Internet routers with shorter standing queues but only limited deployment has occurred. The recent interest in AQM has resulted in new AQM proposals. In this paper we evaluate CoDel (Controlled Delay) and PIE (Proportional Integral controller Enhanced), both being new AQM proposals, and compare the performance against an aggressive RED (Random Early Detection) variant called HRED (Harsh RED). We focus on AQM behavior during load transients typically occurring at the network edge with the common traffic types of today such as Web transactions. We discover that CoDel auto-tuning does not scale well with the load. With the high-end delays experienced, HRED is better than PIE and CoDel when more than a few simultaneous flows share the bottleneck.