country to use common long-distance circuits to select their termi- nation points as the data PBX was in turn cabled to several computers Chapter Eight in the data center. This situation worked well until it was decided to open a second data center approximately 500 ft down the hall from the first. With no existing conduit available, the use of conventional multi- plexers that require the installation of a new conduit would have been disruptive, time-consuming, and expensive. Fortunately, a pair of fiber- optic multiplexers were obtained, which became the solution to the previously described problem. The RS-232 connectors on one multiplexer were cabled to a group of eight switch ports, with the group of ports configured on the data PBX for routing to the second data center. The RS-232 ports on the second fiber-optic multiplexer were cabled directly to asynchronous ports on a computer located in the second data center, with a fiber-optic cable strung in the ceiling between the two data centers, obviating the neces- sity to install a conduit. In addition, the use of a pair of fiber-optic multiplexers solved a second problem, one of transmission distance. Because the distance between the two data centers was approximately 500 ft, it was not possible to use conventional multiplexers without inserting at least one repeater between data centers. Because the fiber- optic multiplexer used could easily support a transmission distance of several kilometers, it became possible to simply cable the optical fiber between the two data centers without having to worry about conduits or repeaters. Thus, a fiber-optic multiplexer can represent a versatile communications networking device whose use could solve many com- munications-related requirements. In fact, one interesting network con- figuration that deserves mention is the ability of some products to be configured as a ring, with a self-healing capability similar to that SONET. Thus, before concluding our discussion of fiber-optic modems, let's focus on their self-healing cap