Performance Analysis of TCP Queues: Effect of Buffer Size and Round Trip Time

In this paper, we demonstrate the effect of buffer size and the round trip time (RTT) on the statistical, dynamical properties of the transport control protocol (TCP) flows. We analyze the queue metrics like link utilization, queue size and packets lost with respect to buffer sizes and RTT. To analyze the network performance, we consider three buffer regimes: large buffer, intermediate buffer, and small buffer. In large buffer regime, we consider the delay bandwidth product gives that buffer size. The intermediate buffer size is determined by scaling the size of large buffer with the square root of the TCP flows using that link. In small buffer regime, fixed length buffer is considered. We study the aggregate traffic flow behaviour of multiple TCP flows and the compound TCP models of traffic flows. The behaviour of fluid models of traffic flows is studied to analyze the dependency of stability, goodput and the magnitude of oscillations when the model is unstable. We perform the packet level simulations of single bottleneck and two bottle neck queues to study the performance parameters like queue size, dropped packets and link utilisation for different buffer sizes and RTTs. We suggest that the buffer sizes can be much smaller than the buffer sizes recommended currently with the support of statistical and control theoretical analysis.