Operating a Network Link at 100%

Internet speed at the edge is increasing fast with the spread of fiber-based broadband technology. The appearance of bandwidth-consuming applications, such as peer-to-peer file sharing and video streaming, has made traffic growth a serious concern like never before. Network operators fear congestion at their links and try to keep them underutilized while no concrete report exists about performance degradation at highly utilized links until today. In this paper, we reveal the degree of performance degradation at a 100% utilized link using the packet-level traces collected at our campus network link. The link has been fully utilized during the peak hours for more than three years. We have found that per-flow loss rate at our border router is surprisingly low, but 30~50 msec delay is added. The increase in delay results in overall RTT increase and degrades user satisfaction for domestic web flows. Comparison of two busy traces shows that the same 100% utilization can result in different amount of performance loss according to the traffic conditions. This paper stands as a good reference to the network administrators facing future congestion in their networks.