erson makes a call, the network sets up a path between the caller and the dialed party. Importantly, the path is available exclusively for the duration of the call. The path is not shared. Natural pauses in conversation and data transmission are not used for other voice or data calls. Capacity is reserved in the network for the entire duration of the transmission. This exclusivity causes wasteful utilization of network capacity. Circuit switching is being gradually phased out in public and wireless networks. Because of circuit switching's smaller capacity and inefficiencies, advanced, fourth- generation mobile protocols specify non-circuit-switched, IP packet technology. Car- riers increasingly add IP equipment when replacing fully depreciated, older voice switches or when building new infrastructure. Last-mile access networks use a mix of IP and circuit switching to carry voice. Traditional telephone companies, which have investments in older infrastructure, are in the process of transitioning to IP in their last-mile infrastructure as they move cus- tomers to IP voice. When customers select their telephone provider for Internet access and TV services, the provider offers to move the subscriber's voice service to the same Last-Mile Access Networks broadband infrastructure as that used for data and TV. Most of them provide VoIP over the broadband. The Economics of Fiber to Large Apartment Buildings and Enterprises In contrast to the last-mile networks in residential areas, the vast majority of which are made up of twisted-pair copper or hybrid fiber/coaxial, cable TV providers and tradi- tional telephone companies lay fiber to their large business customers. This is because the expense of supplying fiber cable to office and apartment buildings with multiple tenants can be spread across many customers. In addition, fiber is required to handle the large amounts of data traffic that enterprise customers generate. Digital Subscriber Line Access Multiplexers Telephone companies that have not invested in fiber to the p