Nortel Networks OPTera Metro 3500 - Manual (Page 52)

2-14 Operation, administration, and maintenance (OAM) features
OPTera Metro 3500 Multiservice Platform NTRN10AN Rel 12.1 Standard Iss 1 Apr 2004
BLSR single span Fiber cut example
Step Action
1 The BLSR ring is clean. Tributaries are added/dropped at Nodes 1 and 4.
2 The signal from Node 4 to Node 3 is degraded.
• Node 3 detects failure.
• Node 4 is unaware there is a problem.
3 Node 3 sends K-byte messages to Node 4 on the Short and Long paths. The
K-byte messages are 2 bytes in the SONET overhead that contain:
• source node (Node 3)
• destination node (Node 4)
• type of switch request (Signal Degrade)
• path direction (Long, Short)
• node status (Short Path sends ‘ RDI’; Long Path sends ‘Idle’)
4 Node 4 receives the message on the Short Path.
Node 4 sends a Signal Degrade switch request back to Node 3 on the Long
Path.
• source node (Node 4)
• destination node (Node 3)
• type of switch request (Signal Degrade)
• path direction (Long)
• node status (’ Idle’)
Node 4 sends a Reverse Request message back to Node 3 on the Short
Path, acknowledging the receipt of the Short Path bridge request (the Signal
Degrade, RDI message).
• source node (Node 4)
• destination node (Node 3)
• type of switch request (Reverse Request)
• path direction (Short)
• node status (’ Idle’)
5 Nodes 1 and 2 enter into a ‘ Passthrough’ state after receiving the message
from Node 3 to Node 4 on the Long Path.
Note: Nodes 1 and 2 check the ‘Destination Node’ attribute of the message
to see if it is addressed to them. They send the message unchanged to the
next node in the ring in the same direction.
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