FDDI Stations & Ports

There are different classes of FDDI stations:

> class A - DAS / Dual Attached Station

> class B - SAS / Single Attached Station

> class C - SAS Concentrator

Furthermore, there are various FDDI port types:

> type A - DAS Downstream Port

> type B - DAS Upstream Port

> type S - SAS Slave Port (Workstation or SAS Concentrator)

> type M - SAS Master Port (Concentrators only)

Port Type A

Receives from primary ring,

transmits on secondary ring.

Port Type A

Receives from secondary ring,

transmits on primary ring.

Port Type M / Port Type S

Not connected to main ring / not attached to primary / secondary ring.

Dual Homing

Important FDDI stations (servers etc.) can be attached by two FDDI adapters to one concentrator each (two different concentrators).

In this case port type A will be standby (listening, no transmission of user data), port type B handles all data traffic.

If port type B fails, port type A will continue instead.

This dual homing provides a backup path; switching over to the backup path is done in real time (transparent to applications).