Designers normally constructed FDDI rings in a such as a "dual ring of trees". A small number of devices, typically infrastructure devices such as and concentrators rather than host computers, were "dual-attached" to both rings. Host computers then connect as single-attached devices to the routers or concentrators. The dual ring in its most degenerate form simply collapses into a single device. Typically, a computer-room contained the whole dual ring, although some implementations de.