Conference 7.286::fddi

501.0. "Disaster Tolerant FDDI Configuration" by SYORPD::DEEP (Bob Deep @SYO, DTN 256-5708) Mon Mar 16 1992 11:19

I have a customer who is building defense systems for the US Navy and is 
looking to expand one of their systems in a distributed environment.  The
network must be capable of sustaining itself even if multiple segments
are destroyed.

Using FDDI, the customer has proposed the following configuration (simplified 
version):


                            |---|       |---|
                            |   A1      B1  |   Concentrator 1
                            |   M11     M12 |
                            |   |       |   |
                            |   A2      B2  |   Concentrator 2
                            |   M21     M22 |
                            |   |       |   |
                            |   A3      B3  |   Concentrator 3
                            |   M31     M32 |
                            |___|       |___|
			  Secondary    Primary
			    Ring	Ring


Is this a valid configuiration?   Will the ring initialize?

If so, then lets examine the following failover scenarios...

For Example, the case of a link failure betwee B3 and M22:

                            |---|       |---|
                            |   A1      B1  |   Concentrator 1
                            |   M11     M12 |
                            |   |       |   |
                            |   A2      B2  |   Concentrator 2
                            |   M21     M22 |
                            |   |       *   |
                            |   A3      B3  |   Concentrator 3
                            |   M31     M32 |
                            |___|       |___|

In this scenario, when B3 detects a failure, A3 should activate and pass data?

If a second failure occurs, for example between B2 and M12:


                            |---|       |---|
                            |   A1      B1  |   Concentrator 1
                            |   M11     M12 |
                            |   |       *   |
                            |   A2      B2  |   Concentrator 2
                            |   M21     M22 |
                            |   |       *   |
                            |   A3      B3  |   Concentrator 3
                            |   M31     M32 |
                            |___|       |___|

Now A2 should activate and pass data?

Is the ring still valid after these failures?  (assuming it was valid to begin
with.)

Thanks in advance...   Bob
			

Being discussed offline... this looks like "global hold" which is a Safenet
thing that is allowed by FDDI but way outside the mainline and not a particularly
good solution to the problem.  More later.

	paul