What is the pN_EBC (Near-End Errored Block Count) Performance-Monitoring Parameter for the OTUk Layer?
This blog post aims to briefly define and describe the pN_EBC (Near-End Errored Block Count) Performance Monitoring parameter that the Sink STE (or OTUk_TT_Sk Atomic Function) will compute and tally.
The Sink STE (or OTUk_TT_Sk function) will include information on the pN_EBC parameter within each Performance Monitoring report it sends to System Management.
NOTES:
- The OTN PTE (or ODUP_TT_Sk Atomic Function) also monitors and generates information on the pN_EBC (Near-End Errored Block Count) parameter at the ODUk Layer. Please see the pN_EBC at ODUk Layer Post for more details on this parameter.
- 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 OTN (Sink) STE is the entity that is responsible for detecting and reporting Near-End Errored Block Counts (or SM-BIP-8 Errors).
NOTE: We refer to SM-BIP-8 errors as Near-End errors because these are errors that the Near-End Sink STE is detecting on its end. In contrast, we refer to the SM-BEI parameter as Far-End errors because that parameter reflects errors that a remote (or Far-End) Sink STE is detecting and reporting.
As the Sink STE receives and monitors its incoming OTUk signal, it will check for many things. It will continuously scan the incoming OTUk signal for bit (or symbol) errors (e.g., SM-BIP-8 errors, FEC errors, etc.) as well as Service-Affecting Defects (e.g., dTIM, dLOF, dLOM, dLOS-P, dAIS, etc.).
Definition of Terms:
Before we proceed, we need to define the following terms for this blog post:
- Block: In this case, we define a block as an OTUk frame.
- Errored Block: In this blog post, we define an errored block as any OTUk frame (or block) that contains at least one SM-BIP-8 error.
As the Sink STE checks the incoming OTUk signal for errors and defects, it will also keep a count of the number of errored blocks it detects for each one-second period.
At the end of a given one-second period, the Sink STE will load the total number of errored block counts (detected and tallied in the most recent one-second period) into the variable pN_EBC.
Since each type of OTUk signal (for a given value of k) transmits a different number of OTUk frames than does another OTUk signal (with a different value for k), each OTUk type will transmit a different number of blocks/second, as we show below in Table 1.
Table 1, Number of Blocks/Second for each OTUk Rate
| OTUk Type | Number of Blocks/Second |
|---|---|
| OTU1 | 20,421 |
| OTU2 | 82,026 |
| OTU3 | 329,492 |
| OTU4 | 856,388 |
| OTUCn | n x 860,177 |
So How does the OTN STE tally Errored Blocks for the pN_EBC parameter?
As the Sink STE receives and monitors its OTUk signal, it will continually check for SM-BIP-8 errors.
Anytime the Sink STE receives an OTUk frame that contains at least one SM-BIP-8 error, then it will increment its internal (pN_EBC Counter) by 1.
Conversely, the Sink STE does not increment its internal pN_EBC Counter whenever it receives an OTUk frame that contains 0 SM-BIP-8 errors.
At the end of each one-second period, the Sink STE will load the contents of this internal counter into the pN_EBC parameter and include that information within its Performance Monitor report that it sends to System Management.
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Are there any Times or Conditions during which the OTN STE will NOT tally Errored Block Counts for the pN_EBC parameter?
Yes, ITU-T G.798 states that the OTUk_TT_Sk function will stop tallying Errored Blocks for the pN_EBC parameter whenever the upstream circuitry (e.g., the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk Atomic function) asserts the CI_SSF input of the OTUk_TT_Sk function.
In other words, the OTN STE will not tally any Errored Block Counts (for the pN_EBC parameter) whenever it (e.g., the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk functions) declares any of the following service-affecting defects conditions.
- dLOS-P – Loss of Signal – Path
- dAIS (e.g., OTUk-AIS)
- dLOF – Loss of Frame
- dLOM – Loss of Multi-Frame
- dLOFLANE – Loss of Frame – Logical Lane Signal (for OTL3.4, OTL4.4, or OTL4.10 applications ONLY)(*)
- dLOL – Loss of Lane Alignment (for OTL3.4, OTL4.4, or OTL4.10 applications ONLY)(*)
- Or if the upstream Optical circuitry is asserting the AI_TSF-P input pin to the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk function).
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Additionally, the OTUk_TT_Sk function is not supposed to increment any pN_EBC counts whenever it declares the dIAE (Input Alignment Error) defect condition.
Is there such a thing as Far-End Errored Block Counts?
Throughout this post, we have used the term Near-End Errored Block Count. Does this mean that there is another parameter called Far-End Errored Block Count?
Answer: Yes, there is such a parameter. Please see the Far-End Errored Block Count post at the OTUk Layer for more details.
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