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

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The Line protection switching example shown in Figure 2-26, a single copy of the signal goes 
through the working line of the system.  If the working line fails, then traffic will switch over to 
protection using line layer parameters (K1, K2, and B2).  The ONS 15454 will automatically 
initiate a Line protection switch if any of the following conditions occur: 
 

    Loss of Signal (LOS) 

    Loss of Frame (LOF) 

   Line 

AIS 

    SD (Excessive BIP-8 errors in the Line overhead) 

 

 
 

 
Automatic Protection Switching (APS) is switching that is initiated by the ONS 15454 based on 
built-in algorithms, assisted by Performance Management (PM) threshold settings and protection 
options stored in the TCC database.  The first setting stored in the TCC is the type of SONET 
OC-N) cards that have been installed in the ONS 15454 (i.e., OC-3, OC-12, OC-48, OC-192).  
Each OC-N port has two pre-selected thresholds for protection switching: Signal Fail (SF) and 
Signal Degrade (SD).   
 
SF is a “hard failure” condition detected on the incoming OC-N signal.  The ONS 15454 monitors 
the bit error rate (BER) on the incoming OC-N signal and will switch to the protect span if the BER 
exceeds 1E-3 (one bit error in 1,000 bits) or if the ONS 15454 detects a Loss of Signal (LOS), 
Loss of Frame (LOF), or Alarm Indication Signal (AIS).  If a span goes into the SF condition, the 
ONS 15454 will switch traffic to the protect span, even if that span is in the SD condition.  The 
BER default threshold setting is 1E-4 (one bit error in 10,000 bits), but it may be changed to 1E-3 
or 1E-5. 
 
SD is a “soft failure” condition resulting from the Line BER exceeding 1E-6.  When the ONS 
15454 detects a BER exceeding 1E-6 on the incoming OC-N, it will announce the SD condition 
on that line and switch away from it, if possible.  The BER default setting is 1E-7 (one bit error in 
10,000,000 bits), but it may be changed to 1E-5, 1E-6, 1E-8 or 1E-9.