The structure of the cluster basically consists of Raspberry Pis interconnected with Ethernet switches and powered by a home-made printed circuit board. This backplane is 6-to-24V powered and features a DC/DC converter to provide the 5V micro USB. It also homes a 16-bit AD7689 analogical to digital converter to evaluate the power consumption of each board. If you want more details about this self-evaluation mechanism, feel free to download the paper on the 'About' page and read section 5.
The backplanes home eight Raspberry Pi each, so that it is possible to have four smaller modules for a lab session. Each module has two 5-port Netgear Ethernet switches (one of which supports Gigabit) and, for these modules to be really independent, a structure was created such that these switches are fixed to the eight Raspberry they are connected to. The two Ethernet switches are connected with each other using an uplink cat. 6 wire.
When willing to work with the whole cluster, all that's needed is to connect each of the routers to a headend full Gigabit switch.