This approach affords full redundancy, offering protection against component
failure within a single Fiber-optic Linking Card Set
7.4.2.1 Parallel operation
The cabling and operation of both cards sets is the same as described in 7.4.1
Single card set redundancy.
All card set A units in the linked set are network together forming a redundant
fiber ring. However additionally all card set B units are additionally networked
together to form a parallel redundant fiber ring. There is no fiber linkage
between these two parallel fiber networks.
During normal operation each matrix monitors the number of nodes that are
reachable on each of the two fiber networks. When there is parity between card
set A and card set B then card set A will be used to route audio to and from the
matrix.
7.4.2.2 Loss of fiber connections and nodes
As long all nodes are still deemed to be reachable on Card set A no switchover
will be performed to Card set B.
Therefore, even if fiber connection issues on Card set A that a) result in a switch
to the secondary ring (on Card set A) or b) result is a switch to loopback mode
then Card set A will continue to be used to route audio to and from the matrix.
If sufficient fiber errors occur (either cabling or card failures) that result in the
number of reachable nodes on Card set A dropping below that of Card set B then
the matrix will switch to Card set B.
The currently active fiber card can be identified as it will flash its green status
LED. The current backup (in active) fiber card will not illuminate its green status
LED.
7.4.3 Fault tolerance
In all fault cases involving recoverable cable faults or loss of nodes on one or
both rings the remaining nodes may experience audio breaks or disturbances
and temporary loss of crosspoint information or data.
Audio and data from a failed node will not be available to the remaining nodes
for the duration of the failure. When a ring with non-adjacent failures sub-
divides into two sub-rings, audio and data from the failed nodes will not be
available to the nodes in either sub-ring.
Audio and data will continue to be available to nodes within the same sub-ring
but data may still be available to all nodes that are still functioning if there is an
intact, independent Ethernet connection to those nodes.
If a Matrix, connected as a node of the fiber-optic link is reset, powered down or
failed this will constitute a lost or failed node on both rings and this node will
experience audio breaks or disturbances and loss of crosspoint information or
data for up to 5 seconds after the fault condition is cleared or repaired.
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