[1] Swiss Fed Inst Technol, Comp Engn & Networks Lab, CH-8006 Zurich, Switzerland
[2] Univ Notre Dame, Dept Comp Sci & Engn, Notre Dame, IN 46556 USA
[3] Univ Pittsburgh, Pittsburgh, PA 15260 USA
[4] Swiss Fed Inst Technol, Dept Comp Engn, CH-8006 Zurich, Switzerland