ies varying from shoes to cars. The broadband industry fits easily into this vertical structure. The manufac- turing stage is composed of the companies that produce Web page content and Internet-based services, such as e-commerce and VoIP. The retail stage includes DSL providers, cable modem systems, and other last-mile technologies. Conceptu- alizing the chain of distribution in this manner makes clear that the practices toward which network neutrality directs its attention, which are uniformly about last-mile providers favoring proprietary applications and content, are essentially forms of vertical exclusion. The emphasis on vertical exclusion remains clear even if network neutrality is viewed through the "layered model" that has become an increasingly popular way to conceive of the structure of the Internet. The leading approach disaggregates networks into four horizontal layers that cut across different network providers. 12 The bottommost layer is the physical layer, which consists of the hardware infras- tructure used to route and transmit the data packets that make up a particular form of communications. The second layer is the logical layer, which is composed of the protocols used to route packets to their proper destinations and to ensure that they arrive intact. The third layer is the applications layer, which is composed of the particular programs and functions used by consumers. The fourth layer is the content layer, which consists of the particular data being conveyed. The differences between the layers can be illustrated in terms of the most common Internet application: e-mail. The physical layer consists of the telephone or cable lines, e-mail servers, routers, and backbone facilities needed to convey the e-mail from one location to another. The logical layer consists of the SMTP protocol employed by the network to route the e-mail to its destination. The application layer consists of the e-mail program used, such as Microsoft Outlook. The content layer consists of the particular e-mail message sen