Manual Switch

In the absence of a higher priority request in the node, the following Signal Failure (SF) actions are taken.

• An Ethernet ring node detecting an SF condition on one of its ring ports blocks the traffic channel and R-APS channel on the failed ring port.
• The Ethernet ring node detecting an SF condition transmits an R-APS message indicating SF on both ring ports. The R-APS (SF) message informs other Ethernet ring nodes of the SF condition. R-APS (SF) messages are continuously transmitted by the Ethernet ring node detecting the SF condition while this condition persists. (The Periodic timer determines the interval of sending the SF after the first three.) For sub-ring interconnection nodes, the R-APS (SF) message is transmitted on the R-APS channel of the Sub-Ring port.
• Assuming the Ethernet ring node was in an idle state before the SF condition occurred, upon detection of this SF condition the Ethernet ring node triggers a local FDB flush.
• An Ethernet ring node accepting an R-APS (SF) message unblocks any blocked ring port that does not have an SF condition. This action unblocks the traffic channel on the RPL.
• An Ethernet ring node accepting an R-APS (SF) message stops transmission of other R-APS messages.
• An Ethernet ring node accepting an R-APS (SF) message without a DNF indication performs a flush FDB.

An Ethernet ring node that has one or more ring ports in an SF condition (upon detection of clearance of the SF condition) keeps at least one of these ring ports blocked for the traffic channel and for the R-APS channel, until the RPL is blocked as a result of Ethernet ring protection reversion, or until there is another higher priority request (for example, an SF condition) in the Ethernet ring. An Ethernet ring node that has one ring port in an SF condition, and detects clearing of this SF condition, continuously transmits the R-APS (NR) message with its own Node ID as the priority information over both ring ports, informing that no request is present at the Ethernet ring node and initiates a guard timer as described in sub-clause 10.1.5. Another recovered Ethernet ring node (or Nodes) holding the link block receives the message and compares the Node ID information with its own Node ID. If the received R-APS (NR) message has the higher priority, the Ethernet ring node unblocks its ring ports. Otherwise, the block remains unchanged. There is only one link with one-end block. The Ethernet ring nodes stop transmitting R-APS (NR) messages when they accept an R-APS (NR, RB), or when another higher priority request is received