Multiple PCs are connected via LAN, and one PC calculates the simulation. The calculation results are sent to the other PCs, which then process the images to display. In this system, the machine that calculates the simulation is called "the server" and the machines that receive the calculation results and process the images are called "slave machines". The calculation and processing of images are performed as follows.

1. Simulation is calculated once for each frame.
2. After each calculation, the data required is sent to the slave machines.
3. While the slave machines process these images, the server calculates more data for the next frame.
4. The server will send the data for the next one frame, if the calculation takes less time than the time it takes for the slave machines to process the image.
   This optimization minimizes problems caused by data sending/receiving time. Multicast IP is utilized to send data to the slave machines, so that it minimizes the work load at the server and on the network.
5. After image processing finishes, the server will perform the next calculation and data transmission.

▲Data flow by frame

In the cluster system, one server machine calculates the simulation and the slave machines are used solely to process images. Because of the distributed workload, the performance of the system is improved.

The previous versions of UC-win/Road processed all the calculations except for the traffic in a single thread, but for this multiple display channel function, the calculation and the processing had to be performed independently. As a result of optimized use of multi CPU and multi-core CPU on the standard configuration of the UC-win/Road, we can see the improved performance of 3D trees, flags, clothes, fire and smoke and the animation of MD3 characters.

▲Synchronization of flags, fire and
smoke, vehicles and snow

The data, which server sends to the slave machines, are the information and attributes of moving elements. Each slave machine processes images after receiving data to update the 3D space. When visualizing 3D trees, flags, rain and snow, the processing becomes more complicated, thus, the data becomes larger, and therefore, high speed data transmission over a network becomes nearly impossible. Hence, to process of these objects, server sends minimum parameters for the calculation and the slave machines processes the calculation.

As the functions for the cluster system was added with the standard version of UC-win/Road as the basis, the system has all the features of the standard UC-win/Road. To minimize operations on the slave machines, all the operations except for the initial settings can be done on the server machine. At the time of simulation, operation is done by server machine and visualization is done by slave machines.
The cluster system is operable only when using the following functions with following settings.

We measured the level of performance to check the validity of this system. We found that its performance improved, in comparison with the standard UC-win/Road system, and that the number of clustered PC does not affect the performance. In addition, by comparing 4-channel clustered configuration with the standard configuration, we saw the improvement of 140%. By comparing 15 slave machines and standard 1 channel, we saw the improvement of 20%.