Understanding the end-to-end packet delay dynamics of the Internet is of crucial importance since it directly affects the QoS (Quality of Services) of applications, and it enables us to design an efficient congestion control mechanism. In our previous work, we have measured round-trip packet delays of the Internet, and have modeled the packet delay dynamics using system identification. As the input and output data for system identification we have used the packet inter-departure time from a source host and the corresponding round-trip time measured by the source host. On the contrary, in this paper, we use the packet transmission rate from the source host, and the average round-trip time measured by the source host for improving an accuracy of the model. Using input and output data measured in LAN and WAN environments. We model the round-trip packet delay dynamics with the ARX (Auto-Regressive eXogenous) model. Through numerical examples, We show that the round-trip time dynamics in LAN environment can be accurately modeled by the ARX model. We also show that the round-trip time dynamics in WAN environment call be accurately modeled when the bottleneck link is shared by a small number of users.
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