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What is the pN_DS (Near-End Defect Second) Performance-Monitoring Parameter for the OTUk Layer?  

This blog post aims to briefly define and describe the pN_DS (Near-End Defect Second) Performance-Monitoring parameter that the Sink STE (or OTUk_TT_Sk Atomic Function) will report.

The Sink STE (or OTUk_TT_Sk function) will include information on pN_DS within each Performance Monitoring report it sends to System Management.  

NOTES: 

1. The OTN PTE (ODUP_TT_Sk Atomic Function) also monitors and generates information on the pN_DS (Near-End Defect Second) parameter at the ODUk Layer. Please see the pN_DS at ODUk Layer Post for more details on this parameter.  
2. Throughout this post, I will use the terms:  Sink STE and OTUk_TT_Sk Function interchangeably. In the context of this blog post, these two terms mean the same thing.  

Introduction

At the OTUk Layer, the Sink STE is the entity that is responsible for detecting, flagging, and reporting Near-End Defect Second events.  

As the Sink STE receives and monitors its incoming OTUk signal, it will check for many things. 

It will continuously check the incoming OTUk signal for Service-Affecting Defects (e.g., dTIM, dLOF, dLOM, dLOFLANE, dLOL, dLOS-P, dAIS, etc.) as well as bit (or symbol) errors (e.g., SM-BIP-8 errors, FEC errors, etc.).  

Another thing that the Sink STE will do (as it continuously monitors its incoming OTUk signal) is to divide each second of (monitoring) time into the following two categories:

• Near-End Available (Working) Seconds, and 
• Near-End Defect Seconds

Anytime the Sink STE detects and categorizes a given one-second period as being a Near-End Defect Second. It will increment the pN_DS parameter and report that information to System Management.  

So When does the OTN STE flag a given One-Second Period as being a “Near-End Defect Second”?  

ITU-T G.798 presents the following Performance Monitoring Equation for the OTUk_TT_Sk function.

pN_DS <- CI_SSF or dTIM;

Where: 

CI_SSF is the current state of the CI_SSF input pin to the OTUk_TT_Sk Atomic Function, and

dTIM is the current state of the Trail Trace Identifier Message (or OTUk-TIM) defect condition.  

OK, What Does that Mean in Plain English?

The above equation means that the Sink STE will classify a given one-second period as being a Near-End Defect Second anytime it declares a service-affecting defect within its incoming OTUk signal during even a fraction of that one second.

Conversely, the Sink STE will classify a given one-second period as being a Near-End Available (or Working) second if it is NOT declaring a service-affecting defect within this OTUk signal during this one second.

How to Evaluate the Performance Monitoring Equation for pN_DS?

The Sink STE (or OTUk_TT_Sk function) will continuously evaluate the above-mentioned Performance Monitoring equation as it monitors its incoming OTUk signal.  

Once again, this equation states that the Sink STE will declare a given one-second period as being a “Near-End Defect Second” if it determines that any of the following conditions are (or were ever) TRUE during that one second.

• If the upstream circuitry (e.g., the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk function) asserts the CI_SSF input pin (to the OTUk_TT_Sk function).
  • NOTE: The OTSi/OTUk_A_Sk and OTSiG/OTUk_A_Sk functions will assert their CI_SSF signal if these atomic functions declare any of the following defects conditions.
    • dLOS-P[i], where i represents any of the four electrical lanes in an OTL3.4/OTL4.4 Interface.
    • dLOFLANE[j], where j represents any one of 4 or 20 logical lanes in an OTL3.4/OTL4.4 Interface.
    • dAIS (OTUk-AIS) – for Single-Lane (OTSi/OTUk_A_Sk Function) Applications Only.
    • dLOL – for OTL3.4/OTL4.4 Applications ONLY.
    • dLOF
    • dLOM
• Or if the OTUk_TT_Sk function declares the dTIM (OTUk-TIM) defect condition.

So, for example, if the OTUk_TT_Sk function has determined that the upstream circuitry asserted the CI_SSF input for even a fraction of a given one-second period, then it will classify that one-second period as being a Near-End Defect Second. 

It will also set the parameter pN_DS to 1 and report that information to System Management.  

Conversely, suppose the Sink STE determines that NONE of those conditions were true during the most recent one-second period. In that case, it will declare that one-second period as being a Near-End Available (Working) Second. 

In this case, the Sink STE will not increment the pN_DS parameter.  

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Are there any Times or Conditions during which the OTN STE should NOT tally the pN_DS Parameter?

Yes, ITU-T G.798 states that the OTUk_TT_Sk function (or System Management) should discard the previous and the current one-second period’s measurement of pN_DS whenever it declares the dIAE (Input Alignment Error)(*) defect condition.

NOTE: (*) – Indicates that you need to be a member of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!! to be able to access this link.

We need to discard the previous one-second period reading to account for the propagation delay of the IAE signaling indicator coming from the remote terminal equipment.

Is there such a thing as a Far-End Defect Second?

Throughout this post, we have been using the term Near-End Defect Second. Does this mean that there is another parameter called Far-End Defect Second?

Answer:  Yes, there is such a parameter. Please see the post on Far-End Defect Seconds at the OTUk Layer for more details.  

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