Cisco Cisco ONS 15454 SONET Multiservice Provisioning Platform (MSPP) Guía De Diseño

OL-4556-01

 

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Unidirectional 

Each ONS 15454 node bridges it’s transmit information on the working and protect lines.  
When traffic is switched from a bad line, only the receiving node performs a switch.  The 
APS channel (which is carried in the K1 and K2 bytes of the signal on the protection line) is 
used to indicate the local switch action and the mode of operation.  Path Protection 
Configuration is the default mode for 1+1 protection groups in the ONS 15454. 

Bi-directional 

Each ONS 15454 node monitors it’s receive bit stream on the currently active path.  When a 
problem is detected, both nodes transfer their transmit bit stream to the protection line.  
Switching of only one direction is not allowed.  Head end to tail end signaling is 
accomplished using the APS channel.  The ONS 15454 Bi-directional Path Switched Ring 
(BLSR) protection mode is configured by the user during initial turn up of the ring. 

Revertive 

In revertive mode, a failure is detected and the working line temporarily switches to the 
protect line using the K1/K2 bytes.  When the working line is restored and meets the BER 
criteria, a wait-to-restore (WTR) timer is initiated in the ONS 15454 to prevent “switch 
bouncing.”  Traffic is switched back to the working line at both ONS 15454 nodes when the 
working line has recovered from the failure and the WTR interval has been met, or the 
manual switch command is cleared.  Traffic will revert back to the working line again using 
the K1/K2 bytes.  Revertive protection is illustrated in Figure 2-28. 

Non-Revertive 

In non-revertive mode, the ONS 15454 detects a failure and switches the working line to the 
protect line using the K1/K2 bytes.  The protect line now becomes the working line and the 
previous working line will become the protect line.  If the line that failed is restored, traffic will 
not switch back.  There is no WTR setting for non-revertive switching.  Traffic will not be 
switched back unless the current working line develops trouble.  Non-revertive protection is 
illustrated in Figure 2-29. 

 

 
Path protection switching in an ONS 15454 system means, first, discovering that the active path 
is no longer performing as desired, and second, switching the payload to an alternate path that is 
flawless (or at least better than the active path).  In the STS Path level protection example shown 
in Figure 2-25, the path signal is bridged or split at the “head end” or at the source.  Two copies of 
the signal are transmitted to the destination point, where the receiver selects the best signal 
based on Path level parameters (B3 and AIS).  STS Path switching is automatically initiated by 
any of the following conditions: 
 

    Loss of Pointer (LOP) 

    STS or VT Alarm Indication Signal (AIS) 

    STS Payload Defect Indicator (PDI-P) 

    Excessive BIP-8 Errors of STS Path 

    Excessive BIP-2 Errors for VT Path