sure that transmit and receive connections are not reversed. Ring Structure Figure 5.3 illustrates how FDDI can compensate for a cable break. The left portion of the figure illustrates the use of the dual-ring structure to interconnect four workstations. Note that the FDDI backbone consists of two separate fiber-optic rings, one of which is active and referred to as the primary ring, while the other ring can be considered to be "on hold," waiting to be activated, and is referred to as the secondary ring. Each device directly connected to the FDDI backbone must be attached to both the primary and secondary rings, resulting in the term dual attach- ment. If a problem occurs on the primary ring, the secondary ring will be used. In fact, FDDI's Station Management (SMT) facility built into each FDDI adapter on either side of a cable break or another impairment on a cable recognizes that communications have failed on the ring. SMT then wraps the communications from the primary ring back out onto the sec- ondary ring in the opposite direction, permitting all stations other than those in that portion of the ring that is broken to resume communica- tions. The middle portion of Figure 5.3 illustrates the occurrence of a Chapter Five break in the FDDI network, while the right portion of that illustration shows how SMT interconnects or wraps communications from the pri- mary ring onto the secondary ring in the opposite direction to re-form the ring. Thus, a break in an FDDI ring can be considered as similar to the battery commercial; that is, like the bunny in the commercial, the FDDI ring keeps on operating. Station Types Two station types are defined under the FDDI standard: class A and class B. Class A stations connect to both primary and secondary rings that make up an FDDI network and are better known as dual-attachment stations. Class B devices are indirectly connected to a ring via a class A device. Thus, a class A station acts as a wiring concentrator that connects several class B stations to the FDDI ring. As you mi