er a shared network. The same is true for access lines to VPNs. Network Topologies Topology on private lines is a consideration in the following circumstances: Carriers design networks. Organizations design internal networks. Large enterprises lease or build their own private, dedicated line networks. The shape of the network (the configuration in which lines are connected to one another), impacts cost, the ability to scale (add or delete sites), reliability, and accessibility. Consider the multipoint configuration in Figure 5-8. An application for multipoint design is one used by utilities for communications to monitor the control equipment in their plants. They run fiber-optic cabling on their existing rights of way, over which Private Lines, Network Topology, and Frame Relay Multipoint fiber private line connecting large sites Network Operations Center Small sites connected to spokes Figure 5-8 Multipoint private lines connecting large sites. A hub-and-spoke design is used to connect small sites to large sites. signals are sent. If the link to one of the large sites is out of service, the other sites can- not reach the main location. However, recall from the mesh configuration presented in Figure 5-3 that if one link is out of service, traffic can be rerouted over other links. There is a trade-off between designing and constructing the more reliable mesh net- works that are more costly and simply using a less reliable multipoint configuration. The following are common network configurations. Point-to-point One line connects two locations. An example is a hospital with a private line to a medical office where hospital doctors see patients. Multipoint One line connects more than two sites together. This is also referred to as multidrop. (hub-and-spoke) All locations connect to, or "hub into," a central site. Data switches in Local Area Networks (LANs) are configured in star topologies. Another example is a corporation with centralized e-mail, finan- cial, and sales applications. If the central site, the switch, 