OTN – Lesson 12 – APS Features within Atomic Functions – Part 1

This blog post presents a video that discusses the APS features within some of the Atomic Functions that we discussed in Lessons 9 and 10.

Lesson 12 – Video 12 – Detailed Implementation of APS within the Atomic Functions – Video 1

This blog post starts our discussion of the APS Features within various Atomic Functions. In this case, we will present how to implement Automatic Protection Switching in great detail. In particular, we will describe the following:

  • APS Features within the OTUk/ODUk_A_So and OTUk/ODUk_A_Sk functions (OTU-Layer/SNC/I Monitoring)
    • How do we implement the APS features within these Atomic Functions to support OTU-Layered SNC/I Monitoring and Protection-Switching?
    • How do we implement a complete System-Level design (using these atomic functions along with the OTUk_TT_So and OTUk_TT_Sk Atomic Functions)?
      • NOTE: We discussed these atomic functions in Lesson 9. However, we did not discuss the APS features (within those functions) then.
  • APS Features within the ODUkP/ODUj-21_A_So and ODUkP/ODUj-21_A_Sk functions (ODU-Layer/SNC/I Monitoring)
    • How do we implement the APS features within these Atomic Functions to support ODU-Layered SNC/I Monitoring and Protection-Switching?
    • How do we implement a complete System-Level design (using these atomic functions along with the ODUk_TT_So and ODUk_TT_Sk Atomic Functions)?
      • NOTE: We discussed these atomic functions in Lesson 10. However, we did not discuss the APS features (within those functions) then.
  • APS Features of the ODUkP/ODUj-21_A_So and ODUkP/ODUj-21_A_Sk functions (CL-SNCG/I Monitoring)
  • How do we implement the APS features within these Atomic Functions to support CL-SNCG/I Monitoring and Protection-Switching?
  • How do we implement a complete System-Level design (using these atomic functions along with the ODUk_TT_So and ODUk_TT_Sk Atomic Functions)?
    • NOTE: We discussed these atomic functions in Lesson 10. However, we did not discuss the APS features (within those functions) then.

Check Out the Video Below

Continue reading “OTN – Lesson 12 – APS Features within Atomic Functions – Part 1”

OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part ONE

This blog post contains the first of two videos that analyzes how the Multi-Administrative Domain uses Tandem Connection Monitoring to respond to service-affecting defects within the ODU signal passing through it.

Lesson 11 – Video 10 – TCM Multi-Administrative Domain Defect Analysis – Part ONE

This blog post contains a video covering the first part of the Multi-Administrative Domain Walk-Through when defects occur.

In particular, this video discusses how the Multi-Administrative Domain will respond to the presence of defects.

During this video, we assume that we are experiencing a service-affecting defect within the ODU signal (that passes through the Multi-Administrative Domain). However, in this case, we assume that the defect occurs outside any administrative regions. As we analyze the Multi-Administrative Domain’s response to this defect, we will cover the following topics:

  • What exactly occurs within an ODU signal that experiences a service-affecting defect?
  • How do ODU-layer, ODUT-layer, and OTU-layer circuitry respond to such defects?
  • How does each Administrative Domain respond to the presence of a service-affect defect outside of the Service-Requesting (or any other Domain) using Tandem Connection Monitoring?
  • What does the Path Terminating Equipment (at the remote terminal) do in response to this service-affecting defect?

I hope the student will better understand Tandem Connection Monitoring as we go through this and the following video.

Check Out the Video Below.

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part ONE”

OTN – Lesson 10 – Video 2M – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions

This post presents the 2nd of the 6 Videos that covers training on the Peformance Monitoring of the ODUk Layer (for Multiplexed Applications). This post focuses on the Sink Direction ODU-Layer Atomic Functions.

OTN – Lesson 10 – Video 2M – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions

This blog post includes a video that begins our discussion of the Sink (or Receive) Direction Atomic Function/Circuitry for the ODU-Layer/Multiplexed Applications.  

In particular, this video reviews the following Atomic Functions

  • OTUk/ODUk_A_Sk Function
  • ODUk_TT_Sk Function

NOTE:  Even though we did review these functions back in the Non-Multiplexed portion of Lesson 10 Training, I wanted to review the Consequent Equations for these functions (once again) because these equations do impact the signals that the ODUkP/ODUj-21_A_Sk function (downstream) will “see.”

Continue reading “OTN – Lesson 10 – Video 2M – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions”

OTN – Lesson 10 – Video 3N – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions

This post presents the 3rd of the 7 Videos that covers training on the Peformance Monitoring of the ODUk Layer (for Non-Multiplexed Applications). This post focuses on the Sink Direction ODU-Layer Atomic Functions.

OTN – Lesson 10 – Video 3N – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions

This post contains a video that begins our discussion of the Receive (or Sink) Direction circuitry.  

In particular, this video covers the following Atomic Functions.

  • The OTUk/ODUk_A_Sk Atomic Function, and
  • A portion of the ODUk_TT_Sk Atomic Function.

This video covers the following features associated with the ODUk_TT_Sk Atomic Function.

  • Checking for Near-End Errors (e.g., PM-BIP-8 Errors)
  • Checking for Far-End Error Counts (e.g., PM-BEI)

This video also discusses how the ODUk_TT_Sk function will declare and clear the PM-dBDI (Backward Defect Indicator) defect condition.  

Continue reading “OTN – Lesson 10 – Video 3N – The OTUk/ODUk_A_Sk and ODUk_TT_Sk Atomic Functions”

OTN – Lesson 9 – Video 10 – OTUk/ODUk_A_Sk Function

This post presents the 10th of the 11 Videos that covers training on Performance Monitoring at the OTUk Layer. This post focuses on the Sink Direction OTU-Layer Atomic Functions.

OTN – Lesson 9 – Video 10 – OTU Layer Sink Direction Circuitry/Functionality – Part 8

This blog post contains a video that completes much of the Sink (or Receive) Direction Atomic Function circuitry at the OTU Layer.  

In particular, this function will discuss the role/functionality of the OTUk/ODUk_A_Sk Atomic Function.  

As we discuss this Atomic Function, we will focus on the following items.

  • APS (Automatic Protection Switching) features/hooks within the OTUk/ODUk_A_Sk function.
  • Steps to Forcing the OTUk/ODUk_A_Sk function to transmit the ODUk-LCK Maintenance Signal downstream.
  • How the OTUk/ODUk_A_Sk function responds to the upstream OTUk_TT_Sk function asserting the AI_TSF and AI_TSD output signals.
  • Consequent Equation Analysis
  • The ODUk-AIS Maintenance Signal
  • Summary of the OTUk/ODUk_A_Sk Function

And finally, a review of the ODUk-OCI Maintenance Signal.

Continue reading “OTN – Lesson 9 – Video 10 – OTUk/ODUk_A_Sk Function”

What is the OTUk/ODUk_A_Sk Atomic Function?

This post briefly describes the OTUk/ODUk_A_Sk Atomic Function. The OTUk/ODUk_A_Sk function is also known as the OTUk to ODUk Adaptation Sink Function. This function will take an OTUk signal and it will extract/de-map out the ODUk signal within.


What is the OTUk/ODUk_A_Sk Atomic Function?

We formally call the OTUk/ODUk_A_Sk Atomic Function the OTUk to ODUk Adaptation Sink Function.

Introduction

The OTUk/ODUk_A_Sk function performs the exact reverse operation, as does the OTUk/ODUk_A_So function.

NOTE:  We extensively discuss the OTUk/ODUk_A_Sk function within Lesson 9 of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

More specifically, this function will:

  • Accept an OTUk signal (from upstream circuitry) and
  • Extract (or de-map) out an ODUk signal from this signal.

Figure 1 presents a simple illustration of the OTUk/ODUk_A_Sk function.

OTUk/ODUk_A_Sk Function - Adaptation Atomic Function

Figure 1, Simple Illustration of the OTUk/ODUk_A_Sk Function

As the OTUk/ODUk_A_Sk function converts an OTUk signal into an ODUk signal, it will terminate, process, and remove the OTUk-SMOH from this incoming OTUk data stream.  It will also extract the ODUk signal from this OTUk signal and route it to the downstream ODUk circuitry for further processing.

Please see the post on the ODUk_TT_Sk atomic function for more information on how ITU-T G.798 recommends that we handle and process ODUk signals.

The Interfaces within the OTUk/ODUk_A_Sk Function

Figure 1 shows that this function consists of the following three interfaces.

  • OTUk_AP – The OTUk Access Point:  This is the interface where the function user supplies the OTUk data to the function.  The upstream OTUk_TT_Sk function usually drives the signals within this interface.
  • ODUk_CP – The ODUk Connection Point:  This is where the function outputs ODUk data, clock, frame, and multi-frame signals (of the extracted ODUk data-stream) towards the ODUk-client circuitry.
  • OTUk/ODUk_A_So_MP – The Function Management Point:  This interface permits the function user to exercise control and monitor the activity within the OTUk/ODUk_A_Sk function.  This interface also allows the ODUk-client to access the APS channel (within the ODUk data stream).

Functional Block Diagram

Figure 2 presents the functional block diagram of the OTUk/ODUk_A_Sk function.

OTUk/ODUk_A_Sk Atomic Functional Block Diagram

Figure 2, Functional Block Diagram of the OTUk/ODUk_A_Sk Function

This figure shows the upstream equipment (e.g., the OTUk_TT_Sk function), which we typically connect to the OTUk_AP Interface (of the OTUk/ODUk_A_Sk function), will supply the following signals to this function.

  • AI_D – OTUk data (with the SMOH)
  • AI_CK – The OTUk clock input signal
  • AI_FS – The OTUk Frame Start Input signal
  • AI_MFS – The OTUk Multi-frame Start Input signal

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So What All Does this Atomic Function Do?

The OTUk/ODUk_A_Sk function will perform the following operations on these signals.

It will extract out/de-map the ODUk Data-Stream, the De-Mapping (ODUk) Clock Signal (ODCr), and it will generate the FS (Frame Start) and MFS (Multi-Frame Start) Signals.

The OTUk/ODUk_A_Sk function will de-map out and generate the following signals from the incoming OTUk signal.

  • ODUk Data-Stream – The ODUk Data consists of both the ODUk Overhead (PMOH) and the ODUk payload data
  • The ODUk Clock – The ODUk Clock Output signal
  • ODUk FS – The ODUk Frame Start Output
  • ODUk MFS – The ODUk Multi-frame Start Output

Extract out APS (Automatic Protection Switching) Commands from the APS Channel (within the ODUk-PMOH)

Once the OTUk/ODUk_A_Sk function has extracted the ODUk Data (which consists of the ODUk Overhead and Payload data), this function will now give the user access to the APS Channel (which is available via the APS/PCC field within the ODUk Overhead).

This function will route the APS Command information (within APS/PCC Channel) to the CI_APS output.

Transmits Either a Normal ODUk signal or the ODUk-LCK or ODUk-AIS Maintenance Signals downstream

The user can configure the OTUk/ODUk_A_Sk function to either output Normal (an ODUk signal carrying client-information) data or the ODUk-LCK maintenance signal, depending upon what the user does with the MI_AdminState input (to this function).

The user can also configure this function to automatically generate the ODUk-AIS Maintenance signal (instead of the NORMAL signal) whenever upstream circuitry asserts the AI_TSF input (to this function).

Function Defects

The OTUk/ODUk_A_Sk function does not internally declare any defects.

Consequent Actions

ITU-T G.798 presents the following equations for consequent actions within this particular function.

  • aSSF <- AI_TSF and (NOT MI_AdminState = LOCKED)
  • aAIS <- AI_TSF and (NOT MI_AdminState = LOCKED)
  • aSSD <- AI_TSD and (NOT MI_AdminState = LOCKED)

I will discuss each of these consequent action equations below.

aSSF <- AI_TSF and (NOT MI_AdminState = LOCKED)

This equation means two things.

  • The function will NOT declare the SSF (Server Signal Failure) condition if the user configures the MI_AdminState input into the LOCKED position.
  • The function will declare the SSF condition if the upstream OTUk_TT_Sk function drives the AI_TSF input pin TRUE (and if the user has NOT set the MI_AdminState to the LOCKED position).

NOTE:  If the OTUk/ODUk_A_Sk function declares the SSF condition, it will indicate so by asserting the CI_SSF output pin towards downstream circuitry.

The CI_SSF output signal is a crucial signal for Automatic Protection Switching purposes.

aAIS <- AI_TSF and (NOT MI_AdminState = LOCKED)

This equation means two things.

  • Suppose the user sets the MI_AdminState input to the LOCKED position.  In that case, this function will unconditionally generate and transmit the ODUk-LCK Maintenance Signal (via the CI_D output), regardless of the current state of the AI_TSF input to this function.
  • The OTUk/ODUk_A_Sk function will automatically generate and transmit the ODUk-AIS Maintenance Signal (via the CI_D output signal of this function) if the AI_TSF input pin is set to TRUE (provided that the MI_AdminState input is NOT set to the LOCKED position).

This equation also means that this function will only transmit a NORMAL ODUk signal (carrying client data) if the MI_AdminState input is NOT in the LOCKED position and the AI_TSF input pin is set FALSE.

aSSD <- AI_TSD and (NOT MI_AdminState = LOCKED)

This equation means two things.

  • This function will not declare the SSD (Server Signal Degrade) condition if the user configures the MI_AdminState input into the LOCKED position.
  • The function will declare the SSD condition if the upstream OTUk_TT_Sk function drives the AI_TSD input pin TRUE (and if the user has NOT set the MI_AdminState to the LOCKED position).

NOTE:  If the OTUk/ODUk_A_Sk function declares the SSD condition, it will indicate so by asserting the CI_SSD output pin towards downstream circuitry.

The CI_SSD output signal is a crucial signal for Automatic Protection Switching purposes.

How do the AI_TSF and MI_AdminState input signals affect the CI_SSF and CI_D outputs (from this function)?

The Consequent Equations for aSSF and aAIS all show that the function outputs (via the CI_SSF and CI_D pins) depend upon the state of the AI_TSF and MI_AdminState Inputs, as we offer in Table 1 below.

Table 1, Truth Table of the CI_D and CI_SSF Output Signals, based upon the AI_TSF and MI_AdminState Inputs

Relationship between AI_TSF and MI_AdminState inputs and CI_SSF and CI_D Outputs - OTUk/ODUk_A_Sk Function

Defect Correlations

None for this function.

Performance Monitoring

None

Pin Description

Table 2 presents a list and description of each input and output signal for the OTUk/ODUk_A_Sk function.

Table 2, List and Definition for each Input and Output Signal in the OTUk/ODUk_A_Sk function

Signal NameTypeDescription
OTUk_AP Interface
AI_DInputOTUk Adapted Information - OTUk Input:
The upstream OTUk_TT_Sk function is expected to apply a bare-bones OTUk data-stream to this input.

NOTE: This OTUk data will contain the following fields:
- OTUk SMOH data
- The contents of the APS/PCC channel (within the ODUk Overhead) and
- The rest of the OTUk frame.

This OTUk data-stream will not include the FAS, MFAS or FEC fields
AI_CKInputOTUk Adapted Information - Clock Input
This clock signal will sample all data that the user supplies to the AI_D, AI_FS, AI_MFS, AI_TSF and AI_TSD inputs.

The OTUk/ODUk_A_Sk function will also use this clock signal as its base timing source.
AI_FSInputOTUk Adapted Information - Frame Start Input:
The upstream OTUk_TT_Sk function will drive this signal TRUE; coincident to whenever it is supplying the very first bit or byte (of a given OTUk frame) to the AI_D input.

The upstream OTUk_TT_Sk function is expected to assert this signal once for each OTUk frame period.
AI_MFSInputOTUk Adapted Information - Multiframe Start Input:
The upstream OTUk_TT_Sk function will drive this signal TRUE coincident to whenever it is supplying the very first bit or byte (of a given OTUk Superframe) to the AI_D input.

The upstream OTUk_TT_Sk function is expected to assert this signal once for each OTUk superframe period, or once every 256 OTUk frame periods.
AI_TSFInputOTUk Adapted Information - Trail Signal Fail Indicator
The upsteam equipment (e.g., the OTUk_TT_Sk function) will typically assert this input pin whenever it is declaring one (or more) service-affecting defects wit the data that it is ultimately applying to the AI_D input of this function.

This signal has a similar role to the AIS signal. Please see the blog post on AIS for more information on this topic.
AI_TSDInputOTUk Adapted Information - Trail Signal Degrade Indicator Input:
The upstream equipment (e.g., the OTUk_TT_Sk function) will typically assert this input whenever it is declaring the dDEG (Signal Degrade) defect with the data that it is ultimately applying to the AI_D input of this function.
ODUk_CP Interface
CI_DOutputODUk Characteristic Information - ODUk Data Output:
The OTUk/ODUk_A_Sk function will take the ODUk data (that it has de-mapped from the OTUk signal, applied at the AI_D input) and output this data via this output signal.

However, if the user commands this function to output the ODUk-LCK Maintenance Signal, then it will do so via this output pin.

Finally, this function will also output the ODUk-AIS Maintenance Signal via this output if conditions warrant.
CI_CKOutputODUk Characteristic Information - Clock Output:
As the ODUk_CP Interface outputs data via the CI_D, CI_FS, CI_MFS, CI_APS, CI_SSF and CI_SSD outputs, all of this data will be updated on one of the clock edges of this clock output signal.
CI_FSOutputODUk Characteristic Information - Frame Start Output:
The ODUk_CP interface will pulse this output signal HIGH whenever the ODUk_CP interface outputs the very first bit (or byte) of a new ODUk frame, via the CI_D output.

This output signal will pulse HIGH once for each ODUk frame.
CI_MFSOutputODUk Characteristic Information - Multiframe Start Output:
The ODUk_CP Interface will pulse this output signal HIGH whenever the ODUk_CP interface outputs the very first bit (or byte) of a new ODUk Superframe, via the CI_D output.

This output signal will pulse HIGH once for each ODUk Superframe (or once each 256 ODUk frames).
CI_SSFOutputODUk Characteristic Information - Server Signal Failure Indicator Output:
One can think of this output pin as a buffered version of the AI_TSF input pin. This function will drive this output pin HIGH anytime the AI_TSF input pin (at the OTUk_AP Interface) is driven HIGH.

Conversely, this function will drive this output pin LOW anytime the AI_TSD input pin is driven LOW.
CI_SSDOutputODUk Characteristic Information - Server Signal Degrade Output:
One can think of this output pin as a buffered version of the AI_TSD output pin. This function will drive this output pin HIGH anytime the AI_TSD input pin (at the OTUk_AP Interface) is driven HIGH.

Conversely, this function will drive this output pin LOW anytime the AI_TSD input pin is driven LOW.
CI_APSOutputODUk Characteristic Information - APS Channel Output:
The OTUk/ODUk_A_Sk function will extract out the contents of the APS channel (from the incoming ODUk data-stream) and it will output the contents of the APS/PCC channel (as it applies to the APS Level that this OTUk/ODUk_A_Sk function is operating at).
OTUk/ODUk_A_Sk_MP Interface
MI_AdminStateInputManagement Interface - AdminState Input:
This input permits the function user to configure the OTUk/ODUk_A_Sk function to output either NORMAL ODUk data, or the ODUk-LCK maintenance signal via the CI_D output of this function.

Setting this input pin to the LOCKED state will configure the OTUk/ODUk_A_Sk function to override the NORMAL ODUk data, and the ODUk-AIS maintenance signal with the ODUk-LCK maintenance signal.
MI_APS_EnInputManagement Interface - APS Enable Input
This input permits the function user to either enable or disable APS/PCC Channel extraction from the incoming ODUk data-stream.

Setting this input pin TRUE configures the OTUk/ODUk_A_Sk function to extract the APS Messages from the APS/PCC channel (within the ODUk Overhead of the incoming ODUk data-stream) and output this data via the CI_APS output port.

Conversely, setting this input pin FALSE disables APS Message extraction from the incoming ODUk data-stream.
MI_APS_LVLInputManagement Interface - APS Level Input:
This input permits the user to specify the APS Level for this instantiation of the OTUk/ODUk_A_Sk function.

If the MI_APS_En input is TRUE, then this input pin will select the APS Level (and that portion of the APS/PCC Channel) that this function will output via the CI_APS output. Please see the APS/PCC post on more information about this protocol.

If the MI_APS_En input is FALSE, then this input will be ignored.

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What is an Atomic Function for OTN?

This post briefly introduces the concept of the Atomic Functions that ITU-T G.798 uses to specify the Performance Requirements of OTN systems.


What is an Atomic Function for OTN Applications?

If you have read through many of the ITU standards, particularly those documents that discuss the declaration and clearance of defect conditions, you have come across Atomic Functions.

For OTN applications, ITU-T G.798 is the primary standard that defines and describes defect conditions.

If you want to be able to read through ITU-T G.798 and have any chance of understanding that standard, then you will need to understand what these atomic functions are.

I will tell you that you will have a tough time understanding ITU-T G.798 without understanding these atomic functions.

Therefore, to assist you with this, I will dedicate numerous blog postings to explain and define many of these atomic functions for you.

NOTE:  I also cover these Atomic Functions extensively in Lesson 8 within THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

OK, So What are these Atomic Functions?

You can think of these atomic functions as blocks of circuitry that do certain things, like pass traffic, compute and insert overhead fields, check for, and declare or clear defects, etc.

These atomic functions are theoretical electrical or optical circuits.  They have their own I/O, and ITU specifies each function’s functional architecture and behavior.

It is indeed possible that a Semiconductor Chip Vendor or System Manufacturer could make products that exactly match ITU’s descriptions for these atomic functions.  However, no Semiconductor Chip Vendor nor System Manufacturer does this.  Nor does ITU require this.

ITU has defined these Atomic Functions such that anyone can judiciously connect a number of them to create an Optical Network Product, such as an OTN Framer or Transceiver.

However, if you were to go onto Google and search for any (for example) OTUk_TT_Sk chips or systems on the marketplace, you will not find any.  But that’s fine.  ITU does not require that people designing and manufacturing OTN Equipment make chips with these same names nor have the same I/O as these Atomic Functions.

OK, So Why bother with these Atomic Functions?

The System Designer is not required to design a (for example) OTUk_TT_Sk function chip.  They are NOT required to develop chips with the same I/O (for Traffic Data, System Management, etc.).

However, if you were to design and build networking equipment that handles OTN traffic, you are required to perform the functions that ITU specified for these atomic functions.

For example, if you design a line card that receives an OTUk signal and performs the following functions on this signal.

  • Checks for defects and declare and clear them as appropriate, and
  • Monitors the OTUk signal for bit errors and
  • Converts this OTUk signal into an ODUk signal for further processing

Although you are NOT required to have OTUk_TT_Sk and OTUk/ODUk_A_Sk atomic function chips sitting on your line card, you are required to support all of the ITU functionality defined for those functional blocks.

Therefore, you must understand the following:

  1. Which atomic functions apply to your system (or chip) design, and
  2. What are the requirements associated with each of these applicable atomic functions?

If you understand both of these items, you fully understand the Performance Monitoring requirements for your OTN system or chip.

What type of Atomic Functions does ITU-T G.798 define?

ITU-T G.798 defines two basic types of Atomic Functions:

  • Adaptation Functions and
  • Trail Termination Functions

I will briefly describe each of these types of Atomic Functions below.

Adaptation Functions

Adaptation Functions are responsible for terminating a signal at a particular OTN or network layer and then converting that signal into another OTN or network layer.

For example, an Adaptation function that we discuss in another post is a function that converts an ODUk signal into an OTUk signal (e.g., the OTUk/ODUk_A_So function).

Whenever you read about atomic functions (in ITU-T G.798), you can also tell that you are dealing with an Adaptation atomic function if you see the upper-case letter A within its name.

For example, I have listed some Adaptation functions that we will discuss within this blog below.

  • OTSi/OTUk-a_A_So – The OTSi to OTUk Adaptation Source Function with FEC (for OTU1 and OTU2 Applications)
  • OTSi/OTUk-a_A_Sk – The OTSi to OTUk Adaptation Sink Function with FEC (for OTU1 and OTU2 Applications)
  • OTSiG/OTUk-a_A_So – The OTSiG to OTUk Adaptation Source Function with FEC (for OTU3 and OTU4 Applications)
  • OTSiG/OTUk-a_A_Sk – The OTSiG to OTUk Adaptation Source Function with FEC (for OTU3 and OTU4 Applications)
  • OTUk/ODUk_A_So – The OTUk to ODUk Adaptation Source Function
  • OTUk/ODUk_A_Sk – The OTUk to ODUk Adaptation Sink Function
  • ODUkP/ODUj-21_A_So – The ODUkP to ODUj Multiplexer Source Atomic Function
  • ODUkP/ODUj-21_A_Sk – The ODUkP to ODUj Multiplexer Sink Atomic Function

Another Way to Identify an Adaptation Function?

ITU in general (and indeed in ITU-T G.798) will identify the Adaptation Function with trapezoidal-shaped blocks, as shown below in Figure 1.

OTUk/ODUk_A_Sk Function - Adaptation Atomic Function

Figure 1, A Simple Illustration of an Adaptation Function (per ITU-T G.798)

Now that we’ve briefly introduced you to Adaptation Functions let’s move on to Trail Termination Functions.

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Trail-Termination Functions

Trail Termination functions are typically responsible for monitoring the quality of a signal as it travels from one reference point (where something called the Trail Termination Source function resides) to another reference point (where another thing is called the Trail Termination Sink function lies).

When you read about atomic functions (in ITU-T G.798), you can also tell that you are dealing with a Trail Termination atomic function if you see the upper-case letters TT within its name.

The Trail Termination functions allow us to declare/clear defects and flag/count bit errors.

I’ve listed some of the Atomic Trail-Termination Functions we will discuss in this blog below.

  • OTUk_TT_So – The OTUk Trail Termination Source Function
  • OTUk_TT_Sk – The OTUk Trail Termination Sink Function
  • ODUP_TT_So – The ODUk Trail Termination Source Function (Path)
  • ODUP_TT_Sk – The ODUk Trail Termination Sink Function (Path)
  • ODUT_TT_So – The ODUk Trail Termination Source Function (TCM)
  • ODUT_TT_Sk – The ODUk Trail Termination Sink Function (TCM)

Another way to Identify a Trail-Termination Function?

In general (and indeed in ITU-T G.798), ITU will identify Trail Termination Function with triangular-shaped blocks.  I show an example of a drawing with a Trail-Termination below in Figure 2.

OTUk_TT_Sk Function - Trail Trace Atomic Function

Figure 2, A Simple Illustration of a Trail Termination Function (per ITU-T G.798)

We will discuss these atomic functions in greater detail in other posts.

 

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What is the ODUk-AIS Signal?

This post defines the ODUk-AIS Maintenance Signal. It also discusses when Network Equipment should transmit this Maintenance Signal. Finally, this post describes how a Sink PTE will declare and clear the dAIS defect.


What is the ODUk-AIS Maintenance Signal, and How does a Network Element declare the dAIS Defect Condition?

What is the ODUk-AIS Maintenance signal?

AIS is an acronym for Alarm Indication Signal.

Another post describes the general purpose/role of the AIS maintenance signal.

For OTN applications, the Network Equipment (NE) will transmit the ODUk-AIS maintenance signal by overwriting the contents of an entire ODUk frame (e.g., ODU Overhead and Payload Data) with an All-Ones pattern.

NOTE:  The variable k in the expression ODUk can be of any of the following values, depending upon the data rate:  0, 1, 2, 2e, 3, 4, and flex.

If an OTN STE were to map the ODUk-AIS Maintenance signal into an OTUk frame, then the OTN STE will be generating/transmitting a series of OTUk frames in which the FAS, MFAS, and OTUk Overhead fields are all valid.

The STE will compute and generate the FEC field based on the contents within these OTUk frames.

However, these OTUk frames will contain an ODUk Overhead, the OPUk Overhead, and the Payload fields that have been overwritten with an All-Ones pattern.

Figure 1 presents a drawing of an OTUk frame transporting the ODUk-AIS Maintenance signal.

ODUk-AIS Pattern

Figure 1, Drawing of an OTUk frame carrying the ODUk-AIS Maintenance signal.

Please note that the ODUk-AIS pattern differs from the OTUk-AIS pattern (an Unframed PN-11 pattern).

What are the timing/frequency requirements for the ODUk-AIS Maintenance signal?

The OTN STE will need to transmit this ODUk-AIS Maintenance signal at the same nominal bit rate as an ordinary ODUk/OTUk signal.

Like any ordinary OTUk signal, the OTN NE will need to transmit this data at the nominal bit-rate ± 20ppm.

Table 1 presents the nominal bit-rates for the OTUk signals (and, in turn, for the OTUk signal, whenever it is transporting the ODUk-AIS indicator) for each value of k.

Table 1, Required Bit Rates for the OTUk signal – when transporting the ODUk-AIS signal.

OTUk Bit Rate

When would OTN Network Equipment transmit/generate the ODUk-AIS Maintenance signal?

An OTN STE will generate/transmit the ODUk-AIS maintenance signal anytime it has detected and declared a service-affecting defect condition (at the OTUk-layer) within the upstream traffic.

For example:  If an STE declares the dLOS-P (Loss of Signal – Path) or the dLOF (Loss of Frame) defect within its incoming OTUk signal, it will respond to this defect condition by transmitting the ODUk-AIS signal downstream.

Whenever the OTN STE transmits this ODUk-AIS maintenance signal downstream, it is (in effect) replacing the missing (or defective) ODUk signal (that the defective OTUk signal was transporting) with the ODUk-AIS maintenance signal.

In other words, the OTN STE will generate and transmit the ODUk-AIS Maintenance signal downstream rather than de-map out and transmit an ODUk signal that was likely destroyed by the service-affecting defect within its OTUk server signal.   I show this phenomenon below in Figure 2.

Service Affecting Defect at the OTUk Layer results in the tranmission of the ODUk-AIS Maintenance Signal

Figure 2, Drawing of OTN Circuitry transmitting the ODUk-AIS Maintenance Signal downstream, in response to a Service-Affecting Defect occurring within the OTUk-Layer, upstream.  

The OTN STE will generate and transmit the ODUk-AIS maintenance signal towards downstream ODUk client equipment; anytime it declares any of the following service-affecting defects in the upstream signal.

Please see the post on AIS for an in-depth write-up on when the NE will (and will not) generate the AIS pattern downstream.

How does a Sink PTE detect and declare the ODUk-AIS (or dAIS) defect condition?

The Sink PTE downstream from the STE transmitting the ODUk-AIS Maintenance signal will detect and declare the ODUk-AIS defect condition whenever it receives a STAT field value of “1, 1, 1” within three (3) consecutive OTUk/ODUk frames.

NOTE:  The STAT field is a 3-bit field that resides within the PM (Path Monitor) byte-field in the ODUk overhead.

The Upstream NE will set this 3-bit field to the value [1, 1, 1] because it overwrites the ODUk overhead with an All-Ones pattern whenever it transmits the ODUk-AIS Maintenance Signal.

Please see the ODUk Frame post for more information about the STAT field.

How does a Sink PTE clear the ODUk-AIS defect condition?

The Sink PTE will clear the ODUk-AIS defect condition whenever it has accepted a STAT field value of something other than “[1, 1, 1]”.

NOTE:  The Sink PTE should accept a new STAT field value if it receives at least three (3) consecutive ODUk frames that contain a consistent STAT field value.

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