acity, and reliability. It also prevents any realistic assessment of the impact that different types of access can have on transaction costs. The conceptual framework that developed in Chapter 5 offers a basis for analyzing the impact of various types of access in a way that reflects networks' key attributes, that is, the manner in which the whole exceeds the sum of the parts. Networks in Telecommunications 1. Retail Access Retail access is a right given to customers to use the services provided by the entire network. It has its roots in the common law duty to serve all customers applied to common carriers. Typically, retail access takes the form of a regulatory mandate implemented through public tariffs, which announce the terms under which the carrier will provide service to all comers. In its modern form, retail access normally is justified by the theory of natural monopoly. An industry is a natural monopoly if one firm can serve the entire market demand at lower cost than could two. When that is the case, even markets that begin as competitive will eventually come to be dominated by single players. Retail access protects consumers against denial of service under circumstances where alternative sources of supply are unlikely to exist. To ensure that consumers benefit from the mandated sharing of the monopoly, retail access is often accompanied by rate regulation, typically based on the cost of providing service. Retail access can interfere with a network owner's ability to manage its network. As noted earlier, a network owner will configure its network in a manner that mini- mizes costs, brings capacity into line with demand, and guarantees the appropriate level of reliability based on its prediction of the likely network demand. Should the network demand exceed forecast levels, a network owner has four alternatives for restoring equilibrium. First, the network owner can increase network capac- ity. Because capacity cannot be expanded instantaneously, this solution is typically infeasible in the short run. Sec