Specifications

A.14 Fault Tolerance in Trees
FDDI Configuration Capabilities A–33
A.14 Fault Tolerance in Trees
This section describes the fault tolerant safeguards (for trees) that are built into
DEChub 900 network modules.
A.14.1 Maintaining Network Connectivity
When a concentrator or switch in a tree is removed (hot swapped), the FDDI tree
splits into two independent networks, per the FDDI standard.
If the removed module has both M and S ports that are connected to the DEChub 900
backplane, the Hub Manager detects the removal and reconnects the two neighboring
(upstream and downstream) FDDI stations.
If a network module is detected as being unavailable, the Hub Manager will also
patch-out the module (as long as Auto Healing has been enabled). This is a distinct
advantage that FDDI modules, which are configured into a tree in a DEChub, have
over individual nonhub-based FDDI network modules.
NOTE
If the auto-healing function is enabled, MultiChassis Manager prevents the
user from adding or deleting FDDI connections, Ethernet connections,
Ethernet LANs or FDDI LANs via the LAN Interconnect screen. This is
designed to preserve the existing configuration until someone can physically
replace any failed modules. An error message is displayed informing the
user that the requested action cannot be taken, and offers a list of alterna-
tives. If the change is still desired, the user must first disable Auto Healing
by selecting "Disable" from the Auto Healing buttons on the LAN Intercon-
nect screen. This deletes the patched-out connections. Following the recon-
figuration, Auto Healing can be re-enabled. This new configuration is shown
on the screen.