ess lines to VPNs. Network Topologies-The View from Above Topology refers to the way nodes or circuits in a network are connected together. For example, are all the locations or computers connected in a straight line? Are all devices or locations connected to a central headquarters? Can every location reach every other location without going through a central site? Topology is a consideration in designing private lines in the following: Carriers design of networks Organizations design of internal networks Large enterprises leasing or building 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 access to the lines. Consider the multipoint configuration in Figure 5-6. 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 www.TechnicalPDF.com on their existing rights of way, over which signals are sent. If the link to one of the large sites is out of service, the other sites cannot reach the main location. However, in the mesh configuration presented in Figure 5-8, 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 networks that are more costly and simply using a less reliable multipoint configuration. Network Operations Center connected to spokes Figure 5-6 Multipoint private lines connecting large sites. 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. Star (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 