In one embodiment, a display panel includes a substrate and a gate driver disposed on the substrate. First and second instances of a performance indicator of the packet traffic are measured respectively during first and second monitoring intervals. The expander comprises a cylindrical cylinder, a rotor which rotates in the cylinder, a vane which divides an expansion space formed between an inner peripheral surface of the cylinder and an outer peripheral surface of the rotor into a plurality of spaces, and a vane groove provided in the rotor for accommodating the vane therein.