On Modeling Round-Trip Time Dynamics of the Internet using System Identi cation

Understanding the end-to-end packet delay dynamics of the Internet is of crucial importance since it directly a ects the QoS (Quality of Services) of realtime services, and it enables us to design an e cient congestion control mechanism. In this paper, we measure the round-trip time, and build a mathematical model representing its dynamics using system identi cation. We rst measure, as the input and output data for system identi cation, the packet inter-departure time from a source host and the corresponding round-trip time measured by the source host. ICMP (Internet Control Message Protocol) is utilized to measure the round-trip time for each packet. We next model the network, seen by a speci c source host, as a dynamic SISO (Single-Input and Single-Output) system. Using measurement results obtained from three di erent network con gurations, we investigate how accurately the round-trip time dynamics of the Internet can be modeled with the system identi cation.