t. The layered model underscores the extent to which network neutrality is focused on vertical exclusion. The concern is that owners of the physical layer will use their control over the logical layer to give preferential treatment to proprietary applications and content. Network neutrality thus proposes regulating the logical layer to preserve competition in the applications and content layers. See, e.g., Brown Shoe Co. V. United States, 370 U.S. 294 (1962); White Motor Co. V. United States, 372 U.S. 253 (1963). 12 The layered model is related to the open systems interconnection (OSI) model developed by the International Standards Organization (ISO) in the 1980s, which divides into seven different layers. Because some of these distinctions have greater relevance for technologists than for policy analysts, the four-layer model combines some of these layers (Werbach 2002; Whitt 2004). Note that other versions of the layered approach use different numbers of layers. Benkler (2000) and Lessig (2002) employ a three-layer model of physical, code, and content layers. Solum and Chung (2004) propose a six-layer model. Werbach (2005) has revised his initial our-layer model into a three-layer model. Wu (1999) proposes a different four-layer model. Networks in Telecommunications One of the key insights of vertical integration and vertical restraint theory is that any vertical chain of production will only be efficient if every link is competitive (Yoo 2004b). The intuitions underlying that literature can be easily illustrated through a hypothetical example based on the Supreme Court's landmark Terminal Railroad decision, the seminal case for mandating interconnection to a bottleneck facility. Suppose that a railway company controlled the only bridge across the Mississippi River at St. Louis and that it was using its control of the bridge either to give preferential treatment to its proprietary rolling stock or to forbid competing carriers to use the bridge at all. One might be tempted to require the bridge owner to allow ot