heterogeneity and variability of Internet usage. The shift from text-based applica- tions, such as e-mail, to more bandwidth-intensive applications, such as Web page downloading and file transfers, has dramatically increased the volume of end-user demand. The emergence of applications that are increasingly sensitive to delay, even at the cost of lower accuracy and increased distortion (MacKie-Mason and Varian 1994), such as streaming video and virtual worlds, has created demand for even greater reliability in throughput rates and quality of service and is creating pressure for the deployment of "policy-based routers," which break from TCP/IP by assigning higher priority to packets associated with time-sensitive applications (Clark 1996; Yoo 2004b). Furthermore, as noted in Chapter 2, the unexpected interactions among network components that are the hallmark of complex sys- tems can be quite sensitive to variability of demand. Increases in the variability 14 For a preliminary version of this argument, see Yoo (2004b). 15 Lemley and Lessig (2001); Wu (2004). Networks in Telecommunications of network traffic can thus greatly impede network performance even if, on aver- age, utilization of network capacity remains quite low (Mackie-Mason and Varian 1995b). Furthermore, the packet anonymity inherent in TCP/IP may be interfering with network owners' attempts to add security features designed to foster e-commerce or to protect against viruses and other hostile elements that are proliferating on the Internet. In addition, the Internet's shift away from academically oriented users who enjoyed a similar degree of institutional support and shared certain common institutional norms has increased the justification for moving responsibility for sys- tem maintenance and management away from end users and toward the network's core (Yoo 2004b). These considerations make network management quite challenging. Although it is theoretically possible for network owners to respond to some of these demands by expanding bandwidth (Lessig 