An evaluation of TCP with explicit congestion notification

We study the effect of Explicit Congestion Notification (ECN) on TCP for relatively large but finite file transfers in IP networks, and compare it to other congestion avoidance mechanisms, namely Drop Tail (DT) and Random Early Detection (RED). We use simulation to measure TCP performance for transfers initiated by a varying number of end hosts. In contrast to previous work, we focus on situations in which all nodes in the network operate uniformly under the same mechanism (DT or RED or ECN). Our results show that under such uniform conditions ECN does not necessarily lead to significant improvement in TCP goodput, although in no case does it lead to an actual degradation in performance. Our results also show that, with ECN, TCP flows benefit from lower overhead for unsuccessful transmissions. Furthermore, lockouts are largely avoided In other words, in an all-ECN network resources are shared more fairly. Finally, we show that global synchronization is no longer an issue, and argue that current TCP versions have essentially solved the problem, regardless of the queue management scheme employed.