The form of FDDI interface where a device is connected to Both FDDI token-passing rings, so that uninterrupted operation continues in the event of a failure of either of the rings. All connections to the main FDDI rings are dual-attached. Typically, a small numBer of critical infrastructure devices such as routers and concentrators are dual-attached, whereas host computers are normally single-attached or dual-homed to a router or concentrator. For example, a ring could Be formed Between a single router and two concentrators (all dual-attached) then all other components that need to Be fault-tolerant (typically file servers) can Be dual-homed to Both concentrators. (1994-12-13)