h as 160 Gbps. Free-Space Optics (FSO) 102 Hz 104 Hz 106 Hz 108 Hz 1010 Hz 1012 Hz 1014 Hz 1016 Hz Figure 9-1 Bandwidth capability Radio of various media. Microvave Visible light 102 Hz 104 Hz 106 Hz 108 Hz 1010 Hz 1012 Hz 1014 Hz 1016 Hz Twisted pair Land microwave Telephone Satellite microwave Coaxial cable Radio and TV Optical fiber Note: In general one can get between 2 and 10 bits per baud (hertz) of digital throughput. Note: Maximum bandwidth range for FSO: Terabits per second (1012 bps, or 1 Tbps); actual throughput is significantly lower. 9.1 Technical Aspects of FSO 9.1.1 Network Architecture The network architecture of an optical wireless (FSO) system is categorized by one of the four network topologies that follow: Point-to-point topology Point-to-multipoint topology Meshed topology Ring topology In a point-to-point FSO system, a transmitting laser that sits on a rooftop aims at a receiving laser within its line of sight, and an optical data transport link is set up between the transmitter and the receiver through the air. In ideal atmospheric conditions, this configuration enables data to Chapter 9 reach between 2 to 4 km with a data rate between 155 and 622 Mbps. Two of the advantages of using this configuration are that there is dedicated bandwidth between two endpoints and no complex network architecture or planning requirements. However, two of the disadvantages are that the optical link is the single point of failure and service availability lowers as the distance between the two endpoints increases. Figure 9-2 diagrams a point-to-point topology. Often referred to as a hub-and-spoke architecture, a point-to-multipoint FSO system consists of a transceiving laser that acts as a hub for serving and aggregating optical signals sent from multiple lasers being served by the hub. Because the bandwidth is shared among multiple users (lasers), each laser is able to burst up to higher rates if bandwidth is available. This type of configuration can support data rates between 155 and 622 Mbps with a predefin