This figure uses large clouds and small clouds to illustrate six interconnected systems. A key explains that the large clouds represent Provider Networks while the small clouds represent Customer Networks. The large clouds are arranged in a triangle shape; the left point of the triangle is labeled A, the top point is labeled B, and the right point is labeled C. One small cloud, labeled W, appears to the left of, and is connected to, network A. A small cloud, labeled X, appears to the right of, and is connected to, networks B and C. A last small cloud, labeled Y, appears to the right of, and is connected to, network C.