where the intermediate point is in the build- ing basement or just outside a building and the number of end users linked to the same intermediate point is on the order of 20-30. In this case, the intermediate node is generally within 50m from the user. Fiber to the curb (FTTC) is an architecture where the intermediate point collects a few buildings and the number of end users linked to the same intermediate point is on the order of 100. In this case, the intermediate node is generally within 300m from the user. Networks Fundamentals and Present Architectures Building Local exchange Optical Homes Local exchange fiber Optical fiber Local exchange Local exchange Cabinet Building Optical Building Optical fiber fiber Building equipment FIGURE 3.6 Topology of various hybrid fiber-copper access architectures. Fiber to the node (FTTN) or fiber to the cabinet (FTTCab) is an architecture where the inter- mediate point collects many buildings and the number of end users linked to the same intermediate point is on the order of 400. In this case, the intermediate node distance from the user is generally beyond 300m. From a capacity point of view, in principle, a single fiber is largely over-dimensioned with respect to the needs of any group of nearby users: hundreds of multigigabit chan- nels can be transmitted on a single fiber using dense wavelength division multiplex- ing (DWDM). However, DWDM techniques used in the backbone are far too expensive for the access network. In order to reduce costs, the single-fiber capacity is also greatly underused. Thus, adopting a network architecture that optimizes fiber use can be an important issue. Moreover, in several practical cases either the carrier owns a limited number of fibers or it leases fibers from a third party (e.g., a utility company). In this situation, it is a key point to optimize the number of fibers used in the infrastructure. The reduction of the number of fibers arriving at the central office also allows smaller optical patch panels to be deployed. Smaller patch pa