## 2 Related Work
### Related Research on Network Simulator and Software Traffic Generators  
Performance measurement and simulation are important approaches for identifying bottlenecks of such systems to predict and improve their performance [16]. Today there is a large number of software tools that allow one to conduct modeling of individual network devices and the whole network as a whole. The main means of modeling, which are used by scientists around the world to test their hypotheses and developments, are: Network Simulator (NS) [17], OPNET [18], NetSim [19], OmNET++ [20]. The listed modeling tools make it possible to investigate the functioning parameters of network nodes, systems, protocols and allow introducing own changes in the configuration of the model of some devices, allows conducting research of own algorithms or protocols developed by scientists. However the listed means are based on a principle of modelling of discrete events [21]. Nevertheless, a significant disadvantage of these tools is that they use statistical methods and analytical dependencies to calculate the state of the system at a certain point in time [22]. Thus, an hour of work of a real network can be simulated within tens of seconds that is not effective when modelling is carried out in real time, for example, modelling of algorithms of work with memory of the network device, formation and service of queues of packages in the router. The authors of [23] offer a solution for traffic modelling in NS-2 network simulator, and whereas [24] is engaged in traffic modelling, the authors of [25] offer a solution for realistic generation of HTTP traffic. Articles [26; 27; 28] analyze the production network traffic behaviour. According to the authors of [26], network traffic can be generated in three ways:  
* stochastic generation,
* replication of production network traffic,
* using list of instructions (communication scenario) for applications in the tested network. The authors of [27] divide network generators according to the layer on which they work:  
* Application-level traffic generators: they emulate the behaviour of specific network applications in terms of the traffic they produce. * Flow-level traffic generators: they are used when the replication of a realistic traffic is requested only at the flow level (e.g., number of packets and bytes transferred, flow duration). For example, Bit-Twist [28] is representative of this group. * Packet-level traffic generators: with this term we refer to generators based on packet's Inter departure time (IDT) and packet size (PS). The size of each packet sent, as well as the time elapsed between subsequent packets, are chosen by the user, typically by setting a statistical distribution for both variables. Most current packet generators belong to this group. In a thesis [29], the author examines the software traffic generators Iperf, Mausezahn, Ostinato in a closed loop physical and virtual environment to evaluate the applicability of the tools and find sources of inaccuracy for a given traffic profile. One can easily find comparisons of some popular tools, such as in [30; 31; 32; 33; 34; 35]. Despite the fact that many tools for the traffic generation are available, none of the reviewed tools fully suits all the requirements on network traffic generator required for network experiments. None of them has not the ability to control the generated stream without synchronizing the input and output interfaces and determine the current delay of packets in real time. Related Research on Problems of Model Adequacy Assessment and Experimental Investigations of Infocommunications System  
In the process of building an information and telecommunication system model, some important dependencies may be missed and may not be included in it. In this case, the model will be inadequate,i.e., the behaviour of the model for these input parameters will not correspond to the behaviour of the real system. It is clear that an inadequate model is practically inexpedient.