FDDI dual attachment stations (DAS) are distinguished between those with one connection to both rings and one MAC component- Single MAC Dual Attachment Station (SMDAS) - and those with one connection to both rings and two MAC components - Dual MAC Dual Attachment Station (DMDAS).
Dual Attachment Stations can be inserted directly into the dual ring. Each station of this type contains two ports, designated A and B. Port A is connected to the incoming fiber of the primary ring and the outgoing fiber of the secondary ring, and port B is the other way around. In contrast to Single Attachment Stations ( SAS) and Single Attachment Concentrators( SAC), the DAS station remains in the ring in the event of ring interruptions.