2002 - cesnet

Figure 9.10: Loss rate on Prague–Poděbrady line9.4 TCP Protocol SimulationWhile we focused on experiments for what is known as the passive QoS inthe previous sections, related to the protection of data transmission from theimpact of other data transmissions, we now enter the issue of end-to-end performance,or what is known as the proactive QoS. The objective is to reach thehighest possible throughput between end points, based on their configurationor based on a sutable configuration of the network. The research has not beencompleted; the results presented below are therefore preliminary.More than 95 % of data are currently transmitted via the Internet using the TCPprotocol. This protocol was designed at times when networks operated at muchlower speeds than today. It is therefore obvious that using the TCP protocolwithin extensive high-speed networks can be problematic to a certain extent.One of the possible ways to study these problems is to simulate a protocol andsituations that would be difficult to test in real networks.We have therefore developed a simulation centre based on the ns2 program andcreated an informative Web interface with demonstrations of simple simulationtasks. Ns2 is an open source application. It has been developed since the 1980s.Since then, developers have been intensively trying to improve its simulatingabilities and implement new standards, for example for wireless networks. Theavailability of source code also makes it possible to understand the secrets ofimplementation in various protocols. The basic ns2 package implements almostall of the most frequently used protocols and mechanisms. Thanks to the factthat the ns2 project is open, we are able to implement other protocols, and endapplications or strategies for packet processing in routers.Ns2 includes two programming tools – C++ and the OTcl scripting language.Entities within the data path (agents, queues, lines, etc.) are implemented inC++ with respect to its efficiency. The purpose of the scripting language OTclis to control these entities and specify the topology. This method enables usto change the simulation environment easily and flexibly without any furthercompilation.High-speed National Research Network and its New Applications 2002129