In this illustration we see a five-layer protocol stack. The layers, from top to bottom, are: Application, Transport, Network, Link, and Physical. The link layer is expanded to the right, and is shown to include "MAC protocol and frame format." The Physical layer is also included, and shown to include six labeled boxes in two rows of three. The top row includes boxes labeled: 100BASE-TX, 100BASE-T2, and 100BASE-FX. The bottom row includes boxes labeled: 100BASE-T4, 100BASE-SX, and 100BASE-BX.