Configuring ERP ERP Overview
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 11-4
BPR—The Blocked Port Reference that identifies the ring port (0 for interconnection node or sub-ring, 1
for master ring) that is blocked. The BPR status is used in all R-APS messages.
CCM—When an Ethernet ring contains no ERP capable nodes, CCM (Continuity Check Messages) are
required to monitor the ring-port connectivity across the L2 network.
MEG and MEL—The switches in the Management Entity Group with given priority as MEG level
(MEL).
NR and SF—Not Reachable and Signal Failure specify the status messages that can be sent as part of the
R-APS messages.
ERP Timers
Wait To Restore (WTR) Timer. This timer is used by the RPL to verify stability of the Etherenet ring.
WTR Timer determines the number of minutes the RPL switch waits before returning the RPL ports to a
blocked state after the ring has recovered from a link failure.
Some important points about the WTR Timer are as follows:
• The timer is started when the RPL node receives an R-APS (NR) message that indicates ring protection
is no longer required.
• The timer is stopped when the RPL owner receives an R-APS (SF) message while WTR is running,
which indicates that an error still exists in the ring.
• When the time runs out, the RPL port is blocked and an R-APS (NR, RB) message is transmitted from
both the ring ports to indicate that the RPL is blocked.
• Refer to the “Ethernet Ring Protection Commands” chapter in the OmniSwitch AOS Release 8 CLI
Reference Guide for timer defaults and valid ranges.
Guard Timer. When the failed link recovers, a ring node starts the Guard Timer. The Guard Timer is
used to prevent the ring nodes from receiving outdated R-APS messages that are no longer relevant.
Some important points about the Guard Timer are as follows:
• When the Guard Timer is running, any R-APS messages received are not forwarded.
• The Guard Timer value must be greater than the maximum expected forwarding delay time for which it
takes one R-APS message to circulate around the ring. This calculated value is required to prevent any
looping scenarios within the ring.
• Refer to the “Ethernet Ring Protection Commands” chapter in the OmniSwitch AOS Release 8 CLI
Reference Guide for timer defaults and valid ranges.
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