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Active Queue Management (AQM) is intended to achieve high link utilization with a low queuing delay. Recent studies show that RED, one of the most well-known AQMs, is difficult to configure and does not provide significant performance gains given the complexity required for proper configuration. Recent variants of RED, such as Adaptive-RED are designed to provide more robust RED performance under a wider-range of traffic conditions but have not yet been evaluated. This paper presents a router queue behavior model (a queue law) for TCP-dropping and TCP-marking control systems, and uses the queue law to illustrate the impact of TCP traffic on the load and queue behavior of congested routers. Through queue law analysis and simulation, this paper confirms that RED-like AQM techniques that employ packet dropping do not significantly improve performance over that of drop-tail queue management. However, when AQM techniques use Explicit Congestion Notification (ECN) as a method to notify TCP sources of congestion rather than packet drops, the performance gains of AQM in terms of goodput and delay can be significant over that of drop-tail queue management.