ed distance of 1 to 2 km among the hub and its serving lasers. A key advantage of this topology is the efficient connection to the core network because all traffic is collected at a single point (hub). The point-to-multipoint topology shares some of the same disadvantages as the point-to-point topology. An additional disadvantage is that the development and setup costs for establishing the hub are high. Figure 9-3 depicts point- to-multipoint configuration. Figure 9-2 Point-to-point free- space (infrared) link. Free space optical link Figure 9-3 Point-to-multipoint configuration. Network Free space optical link Free-Space Optics (FSO) The third network topology in an optical wireless system is a meshed architecture. This topology is sometimes considered an extension of the point-to-multipoint topology. In a meshed FSO system, all transceiving lasers are interconnected or linked together. In other words, rather than linking an individual laser to a hub in the hub-and-spoke topology, this same laser is connected to all other lasers installed in the system in a meshed topology. This type of configuration can also support data rates between 155 and 622 Mbps with a distance limitation of 200 to 450 meters between two lasers. Two key advantages of utilizing this topology are that it offers higher availability from shorter optical links and diverse paths between two endpoints. However, some disadvantages exist, such as the requirement of a large number of over-the-air hops or multiple overlapping rings and the complex requirements for network design and planning. Fig- ure 9-4 shows a meshed FSO system configuration.2 The fourth network topology for an FSO system is called a ring architec- ture. Analogous to fiber-optic cable networks that exist today, a ring topol- ogy uses the same concept except it is done wirelessly. An arbitrary transceiving laser is only configured to communicate with its two neigh- boring lasers. This laser is not set up to exchange data with all other lasers within the network as it is in a meshe