Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 550)

520 Multi-Service IronWare Switching Configuration Guide
53-1003036-02
Signal fail
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Lastly, ERNs 1, 2, and 3 are in the Idle state, and ERN 4 changes the blocking port to the
forwarding state. All ERNs remain in the Idle state. See
Figure 134 .
FIGURE 134 Initializing an ERP topology - VII
Signal fail
Signal fail and signal fail recovery provide the mechanism to repair the ring to preserve connectivity
among customer networks.
ERP guarantees that although physically the topology is a ring, logically it is loop-free. One link,
called the Ring Protection Link (RPL), is blocked to traffic. When a non-RPL link fails in the ring, the
signal failure mechanism triggers and causes the RPL to become forwarding. Later, signal fail
recovery can occur to restore the ring to the original setup.
Convergence time is the total time that it takes for the RPL owner to receive the R-APS (NR)
message and block the RPL port until the ERN with the failed link receives notice and unblocks the
failed link.