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
- Minimizing packet loss and queueing delay,
- Avoiding global synchronization of sources,
- Maintaining high link utilization, and
- 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.
