What is pF_DS at the OTUk Layer?

This blog post briefly defines the pF_DS (Far-End Defect Second) Performance Monitoring parameter – for the OTUk Layer.

Monitoring

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

This blog post aims to briefly define and describe the pF_DS (Far-End Defect Second) Performance Monitoring parameter that the OTN STE (or OTUk_TT_Sk Atomic Function) will compute and generate.  

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

Performance Monitoring - Another Image

NOTES:

  1. The OTN PTE (ODUP_TT_Sk Atomic Function) also monitors and generates information on the pF_DS (Far-End Defect Second) parameter at the ODUk Layer. Please see the pF_DS at ODUk Layer Post for more details on this parameter.
  2. Throughout this post, I will be using the terms:  OTN 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 OTN (Sink) STE is the entity that is responsible for detecting and reporting Far-End Defect Second events.

As the OTN 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, dLOFLANE(*), dLOL(*), dLOM(*), dAIS (OTUk-AIS), dLOS-P, etc.) as well as bit (or symbol) errors (e.g., SM-BIP-8 errors, SM-BEI errors, FEC errors, etc.).  

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

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

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

Anytime the OTN STE detects and categories a given one-second period as being a Far-End Defect Second, it will increment the pF_DS parameter and report that information to System Management.  

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

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

pF_DS <- dBDI

Where:

dBDI is the current state of the OTUk-BDI or the Backward Defect Indicator Defect (at the OTUk Layer).

The OTN STE (or OTUk_TT_Sk function) will continuously evaluate the above equation as it monitors its incoming OTUk signal.  

This equation states that the OTN STE will declare a given one-second period as being a Far-End Defect Second if it has declared the dBDI defect condition during any portion of that one second.  

A given OTN STE will declare one second as a Far-End Defect Second if the remote OTN STE declares any of the following defect conditions:

  • OTUk-AIS
  • dTIM
  • dLOS-P
  • dLOFLANE
  • dLOL
  • dLOF
  • dLOM

In this case, the OTN STE will increment the pF_DS parameter for each second that it categorizes as a Far-End Defect Second.

Conversely, the OTN STE will declare one second as an Available Second if the remote OTN STE is not declaring any of the defects mentioned above. The OTN STE will NOT increment the pF_DS parameter in this case.

What Does This Mean in English?

Of course, if the OTN STE declares the dBDI defect condition, then this also means that the remote STE is declaring a service-affecting defect condition. In other words, the pF_DS parameter reflects the health of the remote (or Far-End) terminal.

If the remote terminal declares no service-affecting defects, the near-end terminal will not increment the pF_DS parameter. On the other hand, if the remote terminal declares a service-affecting defect, then the near-end terminal will increment the pF_DS parameters.

So, if the OTUk_TT_Sk function has declared the dBDI defect condition for even a fraction of a given one-second period, it will declare it as a Far-End Defect Second. It will also set the parameter pF_DS to 1 and report that information to System Management.  

Conversely, suppose the OTN STE determines that the OTUk_TT_Sk function did not declare the dBDI defect condition during one second period. In that case, it will declare that one-second period as being a Far-End Available (Working) Second.   In this case, the OTN STE will NOT set the parameter pF_DS to 1.  

Are there any Times or Conditions during which the OTN STE should NOT tally the pF_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 the pF_DS parameter whenever it declares either the dIAE (Input Alignment Error)(*) or dBIAE (Backward Input Alignment Error)(*) defect conditions.

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

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 Near-End Defect Second?

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

Answer:  Yes, there is such a parameter. Please see the post on Near-end Defect Seconds (pN_DS) at the OTUk Layer for more details.  

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Author: Darrell Smith

Darrell Smith has more than 30 years of experience as an Electrical Engineer. He has about 20 years of experience as an Applications Engineer and the remainder of his time was spent in Hardware Design and Product Marketing. He will now be sharing his wealth of knowledge on this blog.

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