Communication Emulation in Real TimeCopyright: RWTH Aachen
In many case the performance of each subsystem and function strongly depends on the communication network performance, to the point that communication bandwidth and availability may become a bottleneck and emerging behaviors may appear. Furthermore, due to this unprecedented interdependence, there is a lack of tools for assessing the integrated performance of power and communication networks.
For these reasons, it is necessary to develop a platform that, leveraging on a realistic representation of the two systems, allows engineers to analyze the two networks simultaneously.
For what concerns off-line, non-real time simulation, an effective solution is offered by the co-simulation approach based on the coordination of discipline specific simulation platforms. In this context, as explained in a dedicated section of this annual report, we developed a co-simulation platform named VPNET based on the Virtual Test Bed (a software for multi-physic simulation) and OpNet (a software for communication network simulation).
For real-time, Hardware In the Loop testing, instead, a custom solution based on a general purpose PC architecture and open-source software (WANem) was developed at ACS. WANem is a Wide Area Network Emulator that allows for the setup of a transparent application gateway, which can be used to emulate WAN characteristics like time delay, Packet loss, Packet corruption, Disconnections, Packet re-ordering, Jitter, etc. Many of these effects can be characterized in a stochastic way, for example in terms of correlation and distribution. All these characteristics can be modified remotely with a web interface.
The set-up of these characteristics is a critical point to obtain realistic results from the evaluation of network controllers. In general these parameters can be determined by experience or through assumptions on the specific network, or through off-line analysis performed via simulation with a software such as OpNet.
By the nature of Wanem is clear that the considered option does not comprise a real time simulation of the communication infrastructure itself, but rather includes an emulation of the real time behavior of a given network as seen from two points of the network.
A general purpose PC running WANem is connected to the Ethernet switch to which all the other devices are also connected. Each of these devices is forced to route its communication messages through the WANem PC. An example of traffic flow in case of communication between a generic controller and RTDS is shown in picture: each packet is forced throw WANem filters.