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Smart Routers

With the volume of network traffic continuing to increase exponentially, the ability of the Internet to share network resources in times of congestion becomes increasingly important. TCP provides such an ability with an end-to-end congestion-control mechanism that enables TCP flows to cooperatively share network resources.

Unfortunately, today's Internet architecture does not provide any incentives to use end-to-end congestion control. As a consequence, many multimedia-based applications rely on UDP, a protocol with no congestion-control mechanism, to achieve high bandwidth and pseudo-real-time delivery of delay-sensitive data. Because these applications are unresponsive to the state of the network, their associated network flows do not reduce their sending rate on congestion notification, e.g., packet loss, thus leading to even higher packet loss in the network. The packet-loss rates increase even further with best-effort applications that increase their sending rate in response to an increased packet-loss rate, thereby exacerbating the severity of the network congestion.

When a packet is dropped before it reaches its destination, all the resources it has consumed in transit are wasted. In the extreme case, this situation can lead to congestion collapse. To fight the increasing packet-loss rates, the Internet Engineering Task Force proposes the deployment of explicit congestion notification (ECN) along with active queue-management techniques such as random early detection (RED).

We are developing an alternative queue-management discipline for intelligent routers which we term GREEN. GREEN either improves or matches RED's performance with respect to

  1. Minimizing packet loss and queueing delay,
  2. Avoiding global synchronization of sources,
  3. Maintaining high link utilization, and
  4. Removing biases against bursty sources.
In addition, GREEN converges to the ideal operating point in nearly all scenarios, even when very small buffers are used in the router.