ability. RING UTILIZATION Depending on the manufacturer, some vendors, including TC Communications, manufacture both fiber-optic modems and fiber-optic multiplexers that can be configured as a self-healing ring. With this ring structure capability it becomes possible to obtain a high degree of redundancy that can provide a capability equivalent to a mini SONET transmission capability within a building or on a college campus or industrial complex. Figure 8.8 illustrates the configuration of a series of fiber-optic modems and fiber-optic multiplexers in a self-healing ring configura- tion. Both can be used within a ring if they are produced by the same Fiber in the Building Master Figure 8.8 Using a ring with self- healing capability. Slave Slave Slave vendor, have dual-fiber pair connectors, and are manufactured to sup- port a self-healing capability. In this networking environment one device represents a master, while the other devices are slaves. The master periodically polls each slave to determine status. On the detection of a loss of light, the master and slave detecting the loss of signal loop back primary and secondary fiber rings to form a ring. One innovation that warrants attention is the ability to incorporate multiple master optical modems or optical multiplexers into a self-heal- ing ring. This capability increases the reliability of a ring over the use of a single master as it provides the capability to recover from faults occur- ring in both rings at two different locations. Thus, the use of multiple masters promotes integrity in the unlikely event of double faults occur- ring in both the primary and secondary rings. Figure 8.9 illustrates how double breaks in both primary and secondary fibers can be resolved by creating two separate rings. Optical Mode Converters In this concluding section we discuss an optical device that you will rarely use; however, when the need arises, you may swear that it is worth its weight in gold. That device is the optical mode converter. Chapter Eight Master 1 Figure 8.