2002 - cesnet

We made sure to set up the simulation environment for a realistic simulationof the TCP protocol, with a possibility of acquiring information concerning theprotocol’s dynamics, i.e., the throughput, changes in congestion control on thesender, changes in RTT and other data.It was necessary to generate a number of scripts and adjust the simulation entitiesin C++. We also focused on the possibility of dynamic parameterization ofthe congestion control, i.e., the possibility to change parameters of the AIMD(Additive Increase Multiplicative Decrease) algorithm in use during the periodof connection. This will enable us to study the behaviour of the TCP protocol inlarge high-speed networks, where the standard algorithm of congestion controlis insufficient due to the large volumes of data along the route.Figure 9.11 shows an example of the development of the congestion window(cwnd, upper part of the picture) and the development of the limit betweenthe slow start and congestion avoidance phases (ssthresh, lower part of thepicture) during a single TCP connection. We are preparing a technical reporton the topic.Figure 9.11: Example of the development of cwnd and ssthresh9.5 Analysis of TCP Protocol Behaviourin High-speed NetworksSender using TCP has to regulate the speed of segment transmission, so that thebuffer does not overflow on the receiver or in any of the routers. Regulation iscarried out by restricting the volume of sent and yet to be acknowledged data(outstanding window, owin), which may be on the way at a given moment. Forthese purposes, the TCP protocol uses two mechanisms (see Figure 9.12).130 High-speed National Research Network and its New Applications 2002