OmniSwitch OS6860/OS6900/OS10K Troubleshooting Guide Part No.032996-00 Rev.A
AOS Release 7.X and 8.X January 2015
Alcatel-Lucent Page 133 of 148
Blocked Port Reference (BPR) is a port 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.
Continuity Check Messages (CCM) are messages required to monitor the ring-port connectivity across the L2
network, when an Ethernet ring contains no ERP capable nodes.
Management Entity Group (MEG) are switches given with priority as Management Entity Group Level
(MEL).
Not Reachable (NR) and Signal Failure (SF) are status messages that can be sent as part of the
R-APS messages.
Wait To Restore (WTR) is a timer used by the RPL to verify stability of the Etherenet ring.
Guard Timer (GT) is used to prevent the ring nodes from receiving outdated R-APS messages that are no
longer relevant. A ring node initiates the guard timer when the failed link recovers.
R-APS Messages
R-APS messages are continuously transmitted wherein the first 3 messages are transmitted simultaneously to
ensure fast protection switching (if one or two R-APS messages are corrupted); and after that they are
transmitted periodically with an interval of 5 seconds. Here are the types of messages:
R-APS (Signal Fail) message is continuously transmitted by the node that detects SF (Signal Fail) Condition
until the condition persists and informs other nodes about the condition.
R-APS (No-Request, RPL Blocked) message is continuously transmitted by the RPL node to indicate the other
nodes that there is no failure in the ring and RPL port is blocked.
R-APS (No-Request) message is continuously transmitted by the non RPL node that detects the clearing of SF
(Signal Fail) until the reception of R-APS (NR, RB) from RPL node after WTR expiry.
R-APS (Event) message is transmitted as a single burst of 3 R-APS messages and is not continuously repeated
beyond this burst. The transmission of this R-APS message is done in parallel to other R-APS messages. Flush
messages are R-APS “event” messages transmitted using sub-code field.
State machine of ERP ring
Each ERP enabled ring can be in one of the three states, namely, IDLE, PROTECTION and PENDING.
At initialization, RPL node blocks its RPL port and unblocks its non RPL port and transmits R-APS (NR, RB).
Also, non RPL nodes block one ring port and unblock other ring port. All the ERP nodes then go to the
PENDING state. Then on reception of R-APS (NR, RB) from RPL node, all other non-rpl nodes unblock their
blocked ring ports and all the ERP nodes then go to the IDLE state. So finally in IDLE state all the non RPL
ports are in forwarding state and RPL port is in blocking state.
When the ring port (RPL or non RPL) of any ERP node goes down, then the EVENT "local SF" is detected by
the node and R-APS (SF) is transmitted immediately from the other ring port. If the ring port (RPL or non
RPL) that goes down is already blocked, then the Event "local SF" is detected by the node and R-APS (SF,
DNF) is transmitted immediately from the other ring port. The node then unblocks its blocked port and blocks
the down port. It is important to block the port which is going down so that when the port comes up it will be
To Next Page
Loading...
