tiple companies produce components for these products. Also, consumers can purchase a wide variety of add-on complementary products. The notions of a plat- form and an open architecture are very general ones, and include networks as well as suites of complementary products, although in the discussion that follows we restrict attention to networks. 5. Unbundled Access Provision of unbundled access to networks to competitors is another matter entirely. Here regulators use the term to refer to the use of the services of inputs used to establish the network. Access to inputs, such as UNEs in the case of a telecom- munications network, corresponds to the antitrust provision of access to what are termed essential facilities. This type of regulated access has significantly different economic consequences. In the case of access to the services of network elements by a competitor, the ability of the network owner to operate the network is likely to be impaired. The network cannot provide the same level of services if network elements are operated independently or are subject to capacity constraints due to use by competitors. As we will see in a later chapter, the economically correct access price depends on what the company could have obtained by using those network services itself or by selling network services to some other party. The proper measure of the value of network access is thus the value of the network services that could otherwise have been provided, which in turn is determined by the value of the network's final output. The types of networks on which we are focusing are physical production facil- ities that encompass factors of production such as land, labor services, capital equipment, and technology. Construction of these facilities requires network own- ers to invest in substantial fixed assets that should be viewed in the same way as other types of capital equipment such as manufacturing plants, office buildings, and commercial structures. Like other long-term assets, the network's physical pro- duction 