Behavior of TCP-like elastic traffic at a buffered bottleneck router

A major challenge in traffic modeling and performance analysis for the Transmission Control Protocol (TCP) stems from the fact that the incoming traffic is not independent of the congestion level in the network. This paper investigates a queueing model where the traffic essentially shows ON/OFF characteristics, i.e. the number of active TCP connections of finite (probabilistic) duration varies as described by a stochastic process. The essential behavior of TCP-like flow-control mechanisms is captured in the analytic model by the feature that the packet-rate of active connections can be throttled in order to avoid that the overall packet-stream exceeds the output-bandwidth of the bottleneck router. By appropriate adjustment of the connection duration, the number of packets in the connections remains unaffected. However, since TCP reacts to existing congestion, the throttling mechanism is only activated when the buffer-occupancy at the bottleneck router exceeds a certain threshold. The impact of such a flow-control mechanism on the characteristics of the incoming traffic as well as on the performance behavior at the bottleneck router is discussed and illustrated by numerical results of the analytic model. In particular, the use of (truncated) Power-Tail distributions for the ON periods leads to conclusions about the behavior of long-range dependent traffic under the influence of TCP's flow-control mechanism.