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.

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.

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.
- In this case, the ODUk-LCK Maintenance Signal will override and replace the Normal ODUk Signal.
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).
- The ODUk-AIS Maintenance Signal will override the Normal ODUk Signal in this case.

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

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 Name	Type	Description
OTUk_AP Interface
AI_D	Input	OTUk 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_CK	Input	OTUk 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_FS	Input	OTUk 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_MFS	Input	OTUk 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_TSF	Input	OTUk 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_TSD	Input	OTUk 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_D	Output	ODUk 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_CK	Output	ODUk 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_FS	Output	ODUk 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_MFS	Output	ODUk 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_SSF	Output	ODUk 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_SSD	Output	ODUk 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_APS	Output	ODUk 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_AdminState	Input	Management 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_En	Input	Management 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_LVL	Input	Management 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 the OTUk/ODUk_A_So Atomic Function?

This post briefly describes the OTUk/ODUk_A_So (OTUk to ODUk Adaptation Source) Function. This function will take an ODUk signal and it will synchronously map it into an OTUk signal.

What is the OTUk/ODUk_A_So Atomic Function?

We formally call the OTUk/ODUk_A_So Atomic Function the OTUk to ODUk Adaptation Source Function.

Introduction

The OTUk/ODUk_A_So function is any circuit that (1) accepts an ODUk signal and (2) adapts (or maps) it into an OTUk signal for transmission to the following Trail Termination Function.

NOTE: If we are working with a Fully-Compliant OTUk frame, then the OTUk/ODUk_A_So function will synchronously map each ODUk frame into the OTUk frame.

On the other hand, if we are working with a Functionally-Compliant OTUkV frame, this mapping might be asynchronous.

In this post, we will assume that we are working with a Fully-Compliant OTUk frame.

NOTE: We discuss the OTUk/ODUk_A_So function in detail in Lesson 9, within THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

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

Figure 1, Simple Illustration of the OTUk/ODUk_A_So function

As the OTUk/ODUk_A_So function converts an ODUk signal into an OTUk signal, it will encapsulate each ODUk frame into an OTUk frame by adding the OTUk Overhead to the ODUk structure.

Please note that the OTUk/ODUk_A_So function will only insert default values for the SMOH (Section Monitoring Overhead) within the OTUk overhead.

Functional Block Diagram for the OTUk/ODUk_A_So Function

Figure 2 presents a Functional Block Diagram for the OTUk/ODUk_A_So function.

Figure 2, Functional Block Diagram for the OTUk/ODUk_A_So function

Interfaces within the OTUk/ODUk_A_So Function

Figure 2 shows that this function consists of three different interfaces.

ODUk_CP – The ODUk Connection Point. The ODUk_CP is the interface where the ODUk-client supplies ODUk characteristic information (CI) to the OTUk/ODUk_A_So function input.
OTUk_AP – The OTUk Access Point. There is where the OTUk/ODUk_A_So function outputs OTUk data, clock, frame, and multi-frame signals (for the outbound OTUk data-stream) to downstream circuitry (towards the OTUk_TT_So function).
OTUk/ODUk_So_MP – The Function Management Point. This interface permits the function user to exercise control of the activity within the OTUk/ODUk_A_So function.

Figure 2 shows that the ODUk-client function (connected to the ODUk_CP Interface – of the OTUk/ODUk_A_So function) will supply the following signals to this function.

CI_D – ODUk Data-Stream
CI_CK – ODUk Clock Signal
CI_FS – ODUk Frame Start Signal
CI_MFS – ODUk Multiframe Start Signal
CI_APS – ODUk APS Communication Channel

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So What Does This Function Do?

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

Optionally Generates the ODUk-LCK Maintenance Signal

The function allows the user to configure the OTUk/ODUk_A_So function to generate the ODUk-LCK maintenance signal upon command internally.

The user can implement this command by setting the MI_AdminState input pin (at the Management Port) into the LOCKED State.

Whenever the user sets the MI_AdminState input into the LOCKED State and commands the OTUk/ODUk_A_So function to generate the ODUk-LCK maintenance signal, the timing, framing, and multi-framing for this ODUk-LCK signal will be based on the CI_CK, CI_FS and CI_MFS inputs (at the ODUk_CP Interface).

NOTE: In this case, the ODUk-LCK maintenance signal will replace the ODUk traffic carrying user/client data.

This function will, in turn, map this replacement signal into an OTUk data stream.

Please see the post on the ODUk-LCK maintenance signal for more details about the ODUk-LCK maintenance signal.

Allows User to Insert APS (Automatic Protection Switching) Commands into the APS Channel (within the ODUk-PMOH).

The OTUk/ODUk_A_So function permits the user to access the APS channel (within this ODUk signal) via some inputs (at both the OTUk/ODUk_A_So_MP and the ODUk_CP Interfaces).

More specifically, this function allows the user to enable or disable the APS Channel and configure this function to operate at a specific APS Level through the MI_APS_En and MI_APS_LVL inputs (via the OTUk/ODUk_A_So_MP Interface).

Additionally, this function permits the user to insert their own APS Commands into the APS/PCC Channel within the ODUk Overhead via the CI_APS input (at the ODUk_CP Interface).

NOTE: Please see the relevant post on the APS/PCC Channel to learn more about the APS Channel.

Generates OTUk Clock, FS (Frame Start), and MFS (Multi-Frame Start) Signals via the OTUk_AP Interface

The OTUk/ODUk_A_So function will synthesize the clock (AI_CK), frame start (AI_FS), and multi-frame start (AI_MFS) signals for the outbound OTUk signal via the OTUk_AP Interface.

The OTSiG/OTUk_A_So or OTSi/OTUk_A_So function (downstream) will use these signals to generate and insert the FAS and MFAS fields into the correct locations within the outbound OTUk data stream.

Generates the IAE (Input Alignment Error) Indicator for the downstream OTUk_TT_So function

The OTUk/ODUk_A_So function will generate the IAE (Input Alignment Error) indicator anytime it detects a frame-slip within the incoming ODUk signal (e.g., CI_FS) via the ODUk_CP Interface.

In other words, if this function detects the CI_FS signal pulsing TRUE during an unexpected clock cycle (CI_CK), then this function will drive the AI_IAE output pin HIGH.

Whenever the OTUk/ODUk_A_So function drives the AI_IAE output pin HIGH, it signals an Input Alignment Error Event. The OTUk/ODUk_A_So function will drive the AI_IAE output signal to the downstream OTUk_TT_So function.

The downstream OTUk_TT_So function will accept and perform another process with this AI_IAE output signal.

The OTUk/ODUk_A_So function will keep the AI_IAE output pin HIGH until the upstream (ODUk-circuitry) starts to assert the CI_FS input indicator during the correct (or expected) CI_CK period, once again.

Generate and Route the OTUk Data-Stream to downstream circuitry

This function will output a data stream via the AI_D output, which I will call a partial OTUk data stream.

This data stream will not contain the FAS, MFAS, or the FEC fields.

It will include the ODUk-portion of the OTUk frame and the default values for the various OTUk Overhead Fields (e.g., the Section Monitoring Overhead – SMOH).

We will then route this data stream to other circuitry (e.g., the OTUk_TT_So function) for further processing.

List of Input and Output Signals for the OTUk/ODUk_A_So Function

Table 1 presents a list and description for each OTUk/ODUk_A_So function input and output ports.

Table 1, List and Definition for each Input and Output Signal in the OTUk/ODUk_A_So function

Signal Name	Type	Description
ODUk_CP Interface
CI_D	Input	ODUk Characteristic Information - Data Input: The ODUk-client is expected to input the ODUk data via this input. This ODUk data will contain all portions of the ODUk frame.
CI_CK	Input	ODUk Characteristic Information - Clock Input: This clock signal will sample all data that the ODUk-client supplies to the CI_D, CI_FS, CI_MFS and CI_APS inputs. The OTUk/ODUk_A_So function will also use this clock signal as its timing source.
CI_FS	Input	ODUk Characteristic Information - Frame Start Input: The ODUk-client equipment will drive this signal TRUE; coincident to whenever it is supplying the very first bit or byte (of a given OTUk frame) to the CI_D input. The ODUk-client is expected to assert this signal once for each ODUk frame period. The OTUk/ODUk_A_So function will also use this input signal to determine if it should declare the IAE condition, via the AI_IAE output pin.
CI_MFS	Input	ODUk Characteristic Information - Multiframe Start Input: The system-side equipment will drive this signal TRUE coincident to whenever it is supplying the very first bit or byte (of a given ODUk/OTUk Superframe) to the CI_D input. The ODUk-client is expected to assert this signal once for each OTUk/ODUk superframe period, or once every 256 ODUk frame periods.
CI_APS	Input	ODUk Characteristic Information - APS Channel Data: The system-side equipment is expected to apply the APS Channel to this input. The function user must set the MI_APS_En input to TRUE and must place a valid value (for APS Level) at the MI_APS_LVL input pins, or the OTUk/ODUk_A_So function will ignore the data at this input. The OTUk/ODUk_A_So function will map this data into the APS/PCC channel within the ODUk data-stream. Please see the blog post about the APS/PCC channel for more information.
OTUk_AP Interface
AI_D	Output	OTUk Adapted Information - OTUk Data Output: The OTUk/ODUk_A_So function will take all of the data (that the ODUk-client applies to both the CI_D and CI_APS input pin) and will combine this data together to form a bare-bones OTUk data-stream. NOTE: This OTUk data will contain the following fields. - Default OTUk SMOH data, - The contents of the APS/PCC channel and - The rest of the OTUk frame. This OTUk data-stream will not include the FAS, MFAS or FEC fields. Additionally, the downstream OTUk_TT_So function will compute and generate the correct values for the OTUk-SMOH.
AI_CK	Output	OTUk Adapted Information - Clock Output: As the OTUk_AP Interface outputs data via the AI_D, AI_FS, AI_MFS and AI_IAE outputs; it will updata all of this data on one of the edges of this clock output signal.
AI_FS	Output	OTUk Adapted Information - Frame Start Output: The OTUk_AP Interface will pulse this output signal HIGH whenever the OTUk_AP Interface outputs the very first bit (or byte) of a new OTUk frame, via the AI_D output. The OTUk_AP Interface will pulse this output HIGH once for each outbound OTUk frame.
AI_MFS	Output	OTUk Adapted Information - Multiframe Start Output: The OTUk_AP Interface will pulse this output signal HIGH whenever the OTUk_AP Interface outputs the very first bit (or byte) of a new OTUk superframe, via the AI_D output. The OTUk_AP Interface will pulse this output HIGH once for each OTUk Superframe (or once each 256 OTUk frames).
AI_IAE	Output	OTUk Adapted Information - Input Alignment Error Output: The OTUk_AP Interface will drive this output signal HIGH whenever the OTUk/ODUk_A_So function detects a frame slip within the ODUk_CP Interface. More specifically, if the OTUk/ODUk_A_So determines that the upstream equipment has pulses the CI_FS input at an unexpected CI_CK period, then this function will drive this output HIGH. This function will keep this output signal HIGH until the OTUk/ODUk_A_So function starts to receive pulses at the CI_FS during the "expected" CI_CK periods again. Once the OTUk/ODUk_A_So function starts to receive pulses at the CI_FS input (during the "expected" CI_CK period) then it will drive this output pin LOW.
OTUk/ODUk_A_So_MP Interface
MI_AdminState	Input	Management Interface - AdminState Input: This input pin permits the user to configure the OTUk/ODUk_A_So function to operate in either the LOCKED State or the NORMAL state. If the user configures this function to operate in the NORMAL state, then it will map NORMAL ODUk traffic (e.g., ODUk traffic that is carrying client-data) into an OTUk frame as it passes through this function. Conversely, if the user configures this function to operate in the LOCKED state, then the function will generate and map the ODUk-LCK Maintenance signal into the outbound OTUk data-stream.
MI_APS_En	Input	Management Interface - APS Channel Enable Input: This input pin permits the user to either enable or disable the OTUk/ODUk_A_So function to/from accessing the APS/PCC channel within the ODUk overhead. Setting this input HIGH permits the OTUk/ODUk_A_So function to access (and send APS messages via) the APS/PCC channel. Setting this input LOW prevents the OTUk/ODUk_A_So function from accessing (and sending APS messages) via the APS/PCC channel.
MI_APS_LVL	Input	Management Interface - APS Level: This input permits the user to specify the APS Level, that this OTUk/ODUk_A_So function can use when it accesses the APS/PCC channel. NOTES: 1. This input is ignored if MI_APS_En = FALSE. 2. There are 8 possible valid inputs to this port. Please see the blog post on the APS/PCC channel for more information about this topic.

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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:

Which atomic functions apply to your system (or chip) design, and
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.

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.

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 an STE for OTN Applications?

This post defines and describes both a Section and Section Terminating Equipment for OTN applications. This post also defines the term: OTUk-SMOH (Section Monitoring Overhead).

What is Section Terminating Equipment (STE) for OTN Applications?

Whenever we discuss the OTN Digital Layers (e.g., the OPUk, ODUk, and OTUk layers), we can group Networking Circuits and Equipment into one of two broad categories.

STE – Section Terminating Equipment and
PTE – Path Terminating Equipment

I will be using these terms throughout various OTN-related posts within this blog. So, we must have a strong understanding of these terms.

I have devoted this blog post to STE (Section Terminating Equipment).

I have devoted another post to PTE (Path Terminating Equipment).

NOTE: I discuss STEs and PTEs extensively in Lesson 3 within THE BEST DARN OTN TRAINING PRESENTATION….PERIOD!!! I also discuss the differences between STEs and PTEs as well.

What is a Section?

Before we define the term Section Terminating Equipment (or STE), we must first define the word Section as it pertains to an Optical Transport Network (OTN).

For OTN applications, a Section is a single optical link (or span) between two adjacent pieces of networking equipment.

NOTE: For lower speed applications, one can realize a Section via a Copper Medium (such as CAT5 or CAT6 Cable).

Figure 1 presents a simple illustration of an Optical Transport Network with some boxes labeled PTE and others labeled STE.

Figure 1 illustrates STE (Section Terminating Equipment) and PTE (Path Terminating Equipment). Note: Figure 1 shows a total of five (5) different boxes.

Two of these boxes are labeled PTE, and three of these boxes are labeled STE.

However, in reality, all 5 of these boxes are STEs.

From a system standpoint, many PTEs are STEs. However, not all STEs are PTEs.

We can also define a Section as any optical connections connecting these boxes (in Figure 1).

Now, we will define the term Section Terminating Equipment.

What is an STE (Section Terminating Equipment)?

For OTN applications, the basic definition of a Section Terminating Equipment is any equipment that (1) transmits data into or receives data from the Section and (2) also monitors and manages the data transmission over this Section (e.g., the optical fiber link that exists between the Near-End and the adjacent Far-End Network Equipment).

For OTN applications, the OTUk Layer is the protocol layer responsible for managing and monitoring the transmission/reception of data across a Section.

More specifically, an OTN Source (or Transmitting) STE is any equipment that performs ALL the following functions.

The Source STE Operation In the Transmit Direction

It will accept data from upstream circuitry (typically in the form of ODUk frames).
It electrically preconditions all data (that it is about to transmit to the remote Sink STE via an optical connection) by computing and attaching the OTUk (or OTUkV) overhead to this data stream. This data will typically (but not always) include the FEC.
Once the Source STE has finished preconditioning this data, it will convert this electrical data into the optical format and transmit it over optical fiber to the remote Sink STE.

Sink STE Operation In the Receive Direction

The Sink (Receiving) STE performs all of the following operations.

It receives data (from a remote Source STE) in the optical format.
The Sink STE then converts this optical data into the electrical format, where it can check and process these newly received OTUk/OTUkV frames.
As the Sink STE checks and processes this data, it will check for the following items.
- FEC errors (correctable and uncorrectable)
- Defects or Failures (e.g., dLOF, dLOM, dTIM, dAIS, dIAE, dBIAE, dDEG, dLOL, dLOFLANE[j], dLOS-P and SM-BDI)
- Other errors (e.g., SM-BIP-8, SM-BEI)
It will then pass this data to the downstream circuitry as an ODUk data stream (for further processing at the ODUk-layer).

Therefore, if we were to combine our simple definition of the word Section with the description of a Section Terminating Equipment, we can say the following.

Summarizing our Definitions of Section and STE

An STE begins at the point where the Network Equipment (or the Source STE) will precondition and process electrical data in preparation for transmission over an Optical link.

Afterward, the Source STE will convert this signal into the Optical Format, transmitting this optical signal to the remote Sink (or Receiving) STE.

A Section ends (or is terminated) at the point where the Sink STE (that receives this optical signal) converts it back into the electrical format, processes this data, and sends it to downstream equipment.

How the STE Operates in the Optical Transport Network (OTN)

A Source STE will manage and monitor the transmission of this data (across a Section) by encapsulating this data into OTUk/OTUkV frames.

This Source STE will encapsulate this (ODUk) data by generating and inserting some overhead data (that we call the OTUk-SMOH [Section Monitoring Overhead]) into these OTUk/OTUkV frames.

NOTE: In some of my other posts, I refer to this Source (or Transmitting) STE as the OTUk/ODUk_A_So, OTUk_TT_So, and OTSi/OTUk_A_S0 or OTSiG/OTUk_A_So atomic functions.

The Sink (or Receiving) STE will use this OTUk-SMOH to manage data reception across the Section.

NOTE: In my other posts, I also refer to this Sink (or Receiving) STE as the OTUk/ODUk_A_Sk, OTUk_TT_Sk, and OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk atomic functions.

The STE STE will manage the reception of data across the Section by using this OTUk-SMOH to check for data transmission errors and service-affecting defects.

What is the OTUk-SMOH (Section Monitoring Overhead)?

But when we say “OTUk-SMOH,” what exactly do we mean?

Figure 2 illustrates the OTUk Overhead data (within an OTUk frame) that the Section Terminating Equipment will process and terminate as it manages data transmission across a Section.

This figure also highlights a particular field (regarding Section Monitoring). This figure highlights the Section Monitoring field.

Figure 2, Illustration of an OTUk Frame with the OTUk SMOH Fields highlighted

I highlight the SM (or Section Monitoring) field because the actual OTUk-SMOH (that the Sink STE will use to check for the presence of defects or errors) resides within the Section Monitoring (or SM) field (within the OTUk Overhead).

In Figure 3, I focus on the Section Monitoring field and illustrate the byte format of this 3-byte field.

Figure 3, Illustration of the Byte-Format of the Section Monitoring field.

Figure 3 shows that the Section Monitoring field contains the following three byte-fields.

The BIP-8 Byte
The TTI Byte and
The Section Monitoring (or SM) Byte

In Figure 4, I further focus on the SM Byte and show the bit format of that particular byte field.

Figure 4, Bit-Format of the SM (Section Monitoring) Byte – within the Section Monitoring field

If you have seen the OTUk Frame post, Figures 2 through 4 should look familiar.

All of the overheads fields that the Sink STE will need to check for OTUk-related defects and errors (not including FEC) reside within the SM field.

Hence, the OTUk-SMOH is the Section Monitoring field within the OTUk Overhead.

NOTE: For “nuts and bolts” details on the Source and Sink STEs handling and processing the OTUk-SMOH, check out the posts on the following Atomic Functions.

For the Source STE
- OTUk/ODUk_A_So – OTUk to ODUk Adaptation Source Function
- OTUk_TT_So – OTUk Trace Termination Source Function
- OTSi/OTUk_A_So – OTSi to OTUk Adaptation Source Function (Single-Lane Applications)
- OTSiG/OTUk_A_So – OTSiG to OTUk Adaptation Source Function (Multi-Lane OTU3/OTU4 Applications)
For the Sink STE
- OTUk_TT_Sk – OTUk Trace Terminating Sink Function
- OTUk/ODUk_A_Sk – OTUk to ODUk Adaptation Sink Function
- OTSi/OTUk_A_Sk – OTSi to OTUk Adaptation Sink Function (Single-Lane Applications)
- OTSiG/OTUk_A_Sk – OTSiG to OTUk Adaptation Sink Function (Multi-Lane OTU3/OTU4 Applications)

Now let’s proceed to show an example of STE and its Section.

AN EXAMPLE OF AN STE AND ITS SECTION

Figure 5 illustrates an STE and Section within a typical OTN network connection.

Figure 5, Illustration of the STE and Section (from End to End) in a Typical OTN System

Finally, Figure 5 shows that the Section and STE begin (and end) before and after the OTUk Framer Block.

Please note that the STE also includes the OTUk Framer blocks in this Figure.

The OTUk Framer Blocks (and, in some cases, the OTUk Transceiver Blocks) are responsible for generating and inserting the OTUk-SMOH into the outbound OTUk data stream.

These same functional blocks are also responsible for processing and terminating the OTUk-SMOH within the incoming OTUk data stream.

Throughout numerous blog posts, we discuss the generation and processing of the OTUk-SMOH in detail.

Examples of STE

The following is a list of examples of the various types of OTN STE that are being deployed into the network infrastructure today.

Any 3R type of repeater.
Any network element that takes electrical data and maps it into an OTUk signal for transport to another terminal over an optical (or copper) connection (e.g., equipment that transmits data through sub-marine links, etc.).
CFP Optical Modules that also contains the DSP Transceiver.
Line Cards that include CFP2/CFP4 Optical Modules and OTN Framers.

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What is OTUk-BIP-8 or SM-BIP-8?

This post describes the OTUk-BIP-8 (or Section Monitoring BIP-8) value for OTN applications. This post also describes how Networking Equipment both computes and transports this data over a fiber optic connection, as well as how Networking Equipment checks and identifies data transmission errors through the SM-BIP-8 parameter.

What is the OTUk-BIP-8 or Section Monitor (SM-BIP-8) Parameter, and How Do We Compute and Verify it?

This post will define and describe the SM-BIP-8 (Section Monitoring – Bit Interleaved Parity – 8 bit) parameter.

In particular, we will describe how the OTN uses this parameter to perform error detection at the OTUk layer.
Secondly, we will describe how a Transmitting OTUk Network Element (or a Source Section Terminating Equipment) computes and inserts the SM-BIP-8 Value into the OTUk data stream.
Third, we will describe how a Receiving OTUk Network Element (or a Sink Section Terminating Equipment) computes and verifies the SM-BIP-8 Value to check for data transmission errors.
Finally, we will discuss the results that a Receiving OTUk Network Element will come up with whenever it does compute and verify the SM-BIP-8 byte value.

NOTES:

From this point on, I will refer to the Transmitting OTUk Network Element as the Source STE (or Section Terminating Equipment). I will also refer to the Receiving OTUk Network Element as the Sink STE.
We discuss the SM-BIP-8 field extensively in Lesson 9 within THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

Introduction

For OTN applications, the OTUk layer supports Error Detection and Correction through two means.

FEC – Forward Error Correction and
BIP-8 – Bit Interleaved Parity – 8 bits

FEC is an Error Detection and Error-Correction scheme discussed in another post.

BIP-8 is purely an error-detection scheme. It does not support any error correction capabilities.

The OTUk, ODUk, and Tandem Connection Monitoring layers use the BIP-8 error detection scheme.

In this post, we will discuss (what we call) the SM-BIP-8 (Section Monitoring – Bit Interleaved Parity – 8 bits) scheme for the OTUk layer.

NOTE: We refer to this error detection scheme as SM-BIP-8 (Section Monitoring – Bit Interleaved Parity – 8 bits) because this is the detection scheme that OTN Equipment would employ over a Section via STE (or Section Terminating Equipment).

Please see the post on Section Terminating Equipment for more information on this.

In another post, we discuss the PM-BIP-8 (Path Monitoring – Bit Interleaved Parity – 8 bits) scheme for the ODUk layer.

NOTE: In this post, we will interchangeably use the terms BIP-8, OTUk-BIP-8, and SM-BIP-8.

So How does the OTN use the SM-BIP-8 scheme?

In every connection between any two adjacent pieces of Networking Equipment, there is an entity that transmits data (e.g., the Source STE), and there is also an entity that receives that data (e.g., the Sink STE).

In most cases, two adjacent pieces of Networking Equipment will also be communicating with each other in a bi-directional manner.

This means that every piece of Network Equipment will transmit and receive data. This also means that every piece of Network Equipment will contain both a Source STE and a Sink STE.

For OTN application, any time a Source STE transports data to another Network Element via optical fiber or a copper medium, it must encapsulate this data into a series of back-to-back OTUk frames.

Please see the post on OTUk frames to learn more about the OTUk frame structure.

Brief Overview – How the Source STE creates and transports the SM-BIP-8 Byte Value

As the Source STE encapsulates its outbound (client and ODUk) data into a series of OTUk frames, it will perform various functions.

It will compute and append the FEC field to the back-end of each outbound OTUk frame.
It will compute and insert the SMOH (Section Monitoring Overhead) into each outbound OTUk frame. In particular, the Source STE will
- Insert the Trail Trace Message bytes into the TTI byte-field
- Set the BDI (Backward Defect Indicator) and IAE (Input Alignment Error) bit-fields to the appropriate values (depending upon Network Conditions)
- Set the BEI/BIAE nibble-field to the appropriate Value (depending upon Network Conditions).

Finally, the Source STE will compute an SM-BIP-8 value for each outbound OTUk frame.

Whenever the Source STE computes the SM-BIP-8 byte value, it will do so by performing a specific type of parity calculation over much of the data within the OTUk frame.

Afterward, the Source STE will insert this SM-BIP-8 byte value into the SMOH (Section Monitoring Overhead) within each outbound OTUk frame.

The Source STE will transport this data (e.g., the OTUk frame data and the SM-BIP-8 Value) over optical fiber to the remote Sink STE.

Brief Overview – How the Sink STE Receives and Processes the SM-BIP-8 byte Values

The Sink STE will accept and process this continuous stream of incoming OTUk frames that it is receiving from the remote Source STE.

As it processes this OTUk data stream, it will verify the SM-BIP-8 byte value within each OTUk frame it receives from the (Remote) Source STE.

The Sink STE verifies this data to check for any transmission errors that might have occurred as these OTUk frames travel from the (Remote) Source STE to the (Near-End) Sink STE.

As the Sink STE verifies this data, it will perform the same parity calculations on the data within the OTUk frames as the (remote) Source STE.

Afterward, the Sink STE will compare its “Locally-Computed” SM-BIP-8 byte value with that computed by the (remote) Source STE.

If the two values for the SM-BIP-8 byte match, then we can state that the Sink STE received the corresponding OTUk frame error-free.

On the other hand, if the two values for SM-BIP-8 do not match, then we know that the Sink STE has detected at least a one-bit error within this particular OTUk frame.

The Details – How does the Source STE generate the SM-BIP-8 Value?

Now that we have the Brief Introductory material out of the way, let’s discuss this in greater detail.

In this section, we will describe the following:

Exactly how the Source STE computes the SM-BIP-8 byte value, and
How it inserts this SM-BIP-8 byte into the OTUk data-stream, as it transmits this data to the remote Sink STE.

The Source STE and Introduction to the OTUk_TT_So Atomic Function

ITU-T G.798 refers to the Source STE, which is responsible for (among other things) computing and inserting the SM-BIP-8 Value into the OTUk SMOH as the OTUk_TT_So (OTUk Trail Termination Source) atomic function.

Please see the post on the OTUk_TT_So function to learn more about this atomic function.

NOTE: We will use the terms Source STE and the OTUk_TT_So function interchangeably throughout this post.

How do we perform a BIP-8 (Bit Interleaved Parity – 8 Bit) Calculation?

The OTUk_TT_So function will compute the SM-BIP-8 Value (for a given OTUk frame) over the data that resides within the OPU portion of that outgoing OTUk frame (e.g., byte-columns 15 through 3824).

Figure 1 presents an illustration that identifies that portion of the OTUk frame that the OTUk_TT_So function will use to perform the BIP-8 Calculations.

Figure 1, Illustration of that portion of the OTUk frame, which the OTUk_TT_So function will use for the Section Monitoring BIP-8 Calculation

NOTE: The OTUk_TT_So function will also include the OPU Overhead within these BIP-8 calculations.

This also means that the OTUk_TT_So function will compute the BIP-8 Value (4 x 3,810 =) 15,240 bytes within each outbound OTUk frame.

The OTUk_TT_So function will compute the BIP-8 Value over this 15,240-byte structure by effectively stacking all 15,240 bytes in a single byte-wide column, similar to what we show below in Figure 2.

Figure 2, Illustration of How the OTUk_TT_So function computes the BIP-8 Value

Figure 2 shows that the OTUk_TT_So function has (effectively) created a 15,240 row by an 8-bit column data structure.

The OTUk_TT_So function will then parse through each of the 8-bit columns within this data structure and compute the EVEN parity value for each of these bit-columns (over 15,240 bits).

Since there are 8-bit columns, the OTUk_TT_So function will compute eight individual EVEN parity bits (one for each bit-column).

This resulting set of the 8 EVEN parity bits is the SM-BIP-8 byte value for this particular OTUk frame.

This procedure describes how we perform a BIP-8 calculation over a block of data (such as the OPUk-portion of an OTUk frame).

How does one Source STE transport the SM-BIP-8 to another Network Element?

The OTUk_TT_So function will then take this BIP-8 byte value and insert it into the SM-BIP-8 byte field within the Section Monitoring field of the outbound OTUk frame, two frame periods later, as we show below in Figure 3.

Figure 3, Illustration of How the OTUk_TT_So function inserts the SM-BIP-8 byte values into the OTUk data-stream

The OTUk_TT_So function adds this 2-frame delay to give the Sink STE (at the remote terminal) enough time to compute and verify the SM-BIP-8 byte value (at its end).

Figures 4 and 5 together present the exact location of the SM-BIP-8 byte-field within each outbound OTUk frame.

Figure 4 illustrates the OTUk frame format, with the Section Monitoring (SM) field highlighted.

Figure 4, Illustration of the OTUk Frame with the Section Monitoring (SM) field highlighted

And Figure 5 presents an illustration of the Section Monitoring (SM) field with the SM-BIP-8 byte-field highlighted.

Figure 5, Illustration of the Section Monitoring (SM) field, with the BIP-8 byte-field highlighted

The OTUk_TT_So function will transmit this OTUk data stream (along with the locally-computed SM-BIP-8 byte value) to the remote terminal equipment.

We will discuss below how the Remote Sink STE receives and processes these OTUk frames and their SM-BIP-8 values.

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What does the Sink STE do with the SM-BIP-8 Value?

The Sink STE performs the exact opposite role, as does the Source STE.

The Sink STE and Introduction to the OTUk_TT_Sk atomic function

ITU-T G.798 refers to the entity that (among other things) computes and verifies the SM-BIP-8 byte values (for each OTUk frame) as the OTUk_TT_Sk (OTUk Trail Termination Sink) atomic function.

Please see the post on the OTUk_TT_Sk function to learn more about this atomic function.

NOTE: We will use the terms Sink STE and OTUk_TT_Sk function interchangeably throughout the remainder of this post.

I stated earlier that the OTUk_TT_Sk function has the exact opposite role, as does the OTUk_TT_So function.

The OTUk_TT_Sk function verifies the SM-BIP-8 byte value for each OTUk frame it receives from the remote Source STE (OTUk_TT_So Function).

Once again, the purpose of having the OTUk_TT_Sk function check and verify the SM-BIP-8 byte values is to check for the occurrence of bit errors within the OTUk data stream as it travels from the OTUk_TT_So function (within the Source STE), across optical fiber, to the OTUk_TT_Sk function (within the Sink STE).

Figure 6 presents a simple illustration of an OTUk_TT_So function transporting this OTUk data stream to the OTUk_TT_Sk function at the remote terminal.

Figure 6, Illustration of the OTUk_TT_So function transporting an OTUk data-stream to the OTUk_TT_Sk function (at the remote terminal)

For your reference, the circuitry (that I show above) in Figure 6 is functionally equivalent to the Network Element connections I show below in Figure 7.

Figure 7, Illustration of the Equivalent Circuitry (in Figure 6), expressed at the Network Element Layer.

We will describe how the OTUk_TT_Sk function computes and verifies the SM-BIP-8 byte value within each incoming OTUk frame.

The OTUk_TT_Sk function computes and verifies these SM-BIP-8 byte values by executing the following two steps to process each OTUk frame it receives.

Step 1 – The OTUk_TT_Sk function will locally compute its SM-BIP-8 byte value for an incoming OTUk frame, and
Step 2 – The OTUk_TT_Sk function will then compare its locally-computed BIP-8 byte value with that which the OTUk_TT_So function (at the Remote STE) inserted into the SM-BIP-8 byte field within the incoming OTUk data-stream.

We will discuss each of these steps below.

STEP 1 – The OTUk_TT_Sk function will locally compute Its sm-BIP-8 byte value for an incoming OTUk frame.

The OTUk_TT_Sk function will locally compute its SM-BIP-8 byte value for an incoming OTUk frame by performing the same procedure that the OTUk_TT_So function did at the remote terminal (Source STE).

The OTUk_TT_Sk function will take the 15,240 bytes of data (that resides within the OPU portion of the OTUk frame), and it will (effectively) stack this data into a 15,240-row x 8-bit column structure.

Figure 8 (once again) presents a simple illustration of an OTUk frame, with the OPU portion (e.g., that portion of the OTUk frame that we use to compute the BIP-8 Value) highlighted.

Figure 8, A Simple Illustration of the OTUk Frame, with the OPU-Portion of the Frame, Highlighted.

And if we were to look at this data differently, Figure 9 presents an illustration of the 15,240 Row by 8-bit column structure that the OTUk_TT_Sk function effectively creates from the OPU portion of each incoming OTUk frame.

Figure 9, Illustration of How the OTUk_TT_Sk Computes the SM-BIP-8 byte value for each incoming OTUk frame

The OTUk_TT_Sk function will then parse through each 8-bit column (shown above in Figure 9) individually and compute the EVEN parity of the contents within each bit-column.

Note that it will perform parity calculations over 15,240 bits of data.

Once the OTUk_TT_Sk function has completed this process over each of the eight bit-columns, it will have an 8-bit expression.

This 8-bit expression is (once again) the SM-BIP-8 byte value for this particular OTUk frame.

After the OTUk_TT_Sk function computes its version of the SM-BIP-8 byte value, it needs to perform STEP 2 (of this BIP-8 Verification Process).

STEP 2 – The OTUk_TT_Sk function will compare its Locally-Computed BIP-8 Value with that inserted into the BIP-8 field (by the OTUk_TT_So function at the remote STE).

Once the OTUk_TT_Sk function reads in the contents of an OTUk frame and locally computes its SM-BIP-8 byte value (for that OTUk frame), it then needs to obtain the Value of the remotely-computed SM-BIP-8 byte-field.

If you recall, earlier in this post, I mentioned that the OTUk_TT_So function (at the remote terminal) would compute the SM-BIP-8 byte value for a given OTUk frame, and then it will insert this BIP-8 Value into the SM-BIP-8 byte-field, two OTUk frames later.

I show this relationship between the OTUk frame (that the OTUk_TT_So function computed the SM-BIP-8 byte value for) and its placement within the OTUk data stream above in Figure 3.

Therefore, the OTUk_TT_Sk function will find this remotely-computed SM-BIP-8 byte value for a given OTUk frame, two (2) OTUk frames later, within the SM-BIP-8 byte-field position.

Once the OTUk_TT_Sk function has obtained these two versions of the SM-BIP-8 byte values, it will then need to compare those two values with each other.

If the two BIP-8 byte-values are equal, then this means that this particular OTUk frame incurred no bit errors during transmission over the optical fiber.

On the other hand, if these two BIP-8 byte values are NOT the same, this particular OTUk frame DID incur bit errors during transmission over optical fiber to the Sink STE.

In this case, the OTUk_TT_Sk function must determine how many bits (between these two versions of the SM-BIP-8 byte values) are different from each other.

Stated differently, the OTUk_TT_Sk function compares its locally computed SM-BIP-8 byte value and that it reads in from the SM-BIP-8 byte-field within the incoming OTUk data-stream and will perform a bit-by-bit XOR operation with each of these byte values.

The OTUk_TT_Sk function must then count the number of “1s” that occurs during that bit-wise XOR calculation (for each incoming OTUk frame).

The OTUk_TT_Sk function will come up with any one of the following nine (9) possible results.

0 bits in Error – Error-Free Transmission
1 bit in Error
2 bits in Error
3 bits in Error
4 bits in Error
5 bits in Error
6 bits in Error
7 bits in Error
8 (or all) bits in Error

Figure 10 presents a simple illustration of the Bit-Wise XOR Operation that the OTUk_TT_Sk function performs with both the locally-computed and remotely-computed SM-BIP-8 byte values.

Figure 10, Illustration of the Bit-Wise XOR Process for Verifying and Comparing the Locally-Computed SM-BIP-8 Byte Value with the Extracted (Remotely Computed) SM-BIP-8 Byte value for a given OTUk frame

The OTUk_TT_Sk function will then need to use the results of these BIP-8 comparisons for the following purposes.

To send out the results of these comparisons to the remote terminal in the form of the SM-BEI (Section Monitor – Backward Error Indicator) Value. Please see the post on SM-BEI to learn more about this topic.
It will use these results to determine if the OTUk_TT_Sk function should declare or clear the dDEG (Signal Degrade) defect condition. (*)
To use for Performance Monitoring Purposes (e.g., to compute the pN_EBC parameter in this case). Please see the post on the pN_EBC (Near-Error Block Count) Performance Monitor parameter to learn more about this topic.

Will the OTN Network Element ever declare any defects due to excessive SM-BIP-8 errors?

Yes, if the Sink STE were to detect a large number of SM-BIP-8 byte errors over a long period (e.g., typically on the order of seconds), then the Sink STE (or OTUk_TT_Sk Function) can declare the dDEG (Signal Degrade) defect condition.

I describe how the OTUk_TT_Sk atomic function declares and clears the OTUk-dDEG (Signal Degrade) defect condition within Lesson 9 of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!

Summary

This post describes the SM-BIP-8 (Section Monitoring – Bit Interleaved Parity – 8 bit) parameter.

At a high level, we have described how the OTN uses this parameter to perform error detection at the OTUk layer.

We have also specifically described how a Source STE computes and inserts the SM-BIP-8 byte value into the OTUk data stream.

We have also described how a Sink STE computes and verifies the SM-BIP-8 byte value (within each incoming OTUk frame) to check for the occurrence of data transmission errors.

Finally, we have identified the results that a Sink STE will come up with whenever it does compute and verify the SM-BIP-8 byte value. We also mentioned that the Sink STE would use these results to:

Determine if the Sink STE should declare or clear the dDEG (Signal Degrade) defect condition.
Support the generation of Performance Monitor reports for the pN_EBC (Near-End Error Block Count) parameter to System-Level Management.
Support the generation and transmission of the SM-BEI (Section Monitoring – Backward Error Indicator) parameter within the OTUk data stream.

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OTUk-Backward Defect Indicator

This post defines and describes the Backward Defect Indicator (dBDI) defect for the OTUk Layer

What is the dBDI (Backward Defect Indicator) defect at the OTUk Layer?

In short, the dBDI (or Backward Defect Indicator) signal is functionally equivalent to the RDI (Remote Defect Indicator) for OTN applications.

In OTN applications, Network Equipment can declare the dBDI defect at either the OTUk Layer or the ODUk Layer.

This post will discuss the dBDI defect for the OTUk Layer, which we can call the OTUk-BDI defect condition.

We address the dBDI defect for the ODUk Layer in another post.

In another post, I’ve also described the RDI (Remote Defect Indicator) signal or defect in generic terms.

In this post, we are going to describe the following items.

What conditions will cause an OTUk Network Element to transmit the dBDI indicator to the remote Network Element?
How does the OTUk Network Element transmit the dBDI indicator to the remote Network Equipment?
How does the OTUk Network Element receiving the dBDI signal detect and declare the dBDI defect condition?
And, how does the OTUk Network Element clear the dBDI defect condition?

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What conditions will cause an OTUk Network Element to transmit the dBDI indicator?

In Figure 1, we illustrate two Network Elements (consisting of OTUk Framers and OTUk Transceivers) exchanging OTUk traffic over Optical Fiber.

We will call one of these Network Elements NETWORK ELEMENT WEST and the other Network Element, NETWORK ELEMENT EAST.

NETWORK ELEMENT WEST contains the following pieces of hardware

OTUk Framer West
OTUk Transceiver East and
Optical I/F Circuitry (O->E)/(E->O)

Likewise, NETWORK ELEMENT EAST contains the following pieces of hardware.

OTUk Framer East
OTUk Transceiver East and
Optical I/F Circuitry (O -> E)/(E -> O)

Figure 1, Illustration of two Network Elements that are connected over Optical Fiber

A Defect Condition

Now, let us imagine that some impairment occurs in the span of Optical Fiber carrying OTUk traffic from NETWORK ELEMENT WEST to NETWORK ELEMENT EAST.

This impairment will then cause NETWORK ELEMENT EAST to declare a service-affecting defect, as shown in Figure 2.

Figure 2, Illustration of NETWORK ELEMENT EAST declaring a Service-Affecting Defect due to an impairment in Optical Fiber

NETWORK ELEMENT EAST might respond to this defect condition in several ways. It might transmit the ODUk-AIS indicator towards downstream equipment (as a replacement signal).

NETWORK ELEMENT EAST might also invoke Protection Switching (if supported).

Sending the OTUk-BDI Indicator in Response

Finally, NETWORK ELEMENT EAST will also respond to this defect by transmitting the dBDI (or OTUk-BDI) indicator back towards the upstream Network Element (NETWORK ELEMENT WEST, in this case).

Figure 3 shows an illustration of NETWORK ELEMENT EAST, transmitting the OTUk-BDI indicator (back towards NETWORK ELEMENT WEST) in response to it declaring this service-affecting defect.

Figure 3, Illustration of NETWORK ELEMENT EAST responding to the Defect Condition by sending the OTUk-BDI indicator back towards NETWORK ELEMENT WEST

NETWORK ELEMENT EAST sends the OTUk-BDI indicator (back to NETWORK ELEMENT WEST) to alert it of this defect condition (between the two Network Elements).

In other words, NETWORK ELEMENT EAST is saying, “Hey, NETWORK ELEMENT WEST, I’m having problems with the data that you are sending me. I’d just thought that I’d let you know”.

There are many reasons why all of these notifications are useful.

This notification gives the Overall Network a clearer picture of exactly where the problem (or impairment) is.

It can also notify maintenance personnel of these problems and provide them with helpful information before they “roll trucks.”

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So What EXACTLY are those Defects that will cause a Network Element to transmit the OTUk-BDI indicator?

The Network Element will transmit the OTUk-BDI indicator anytime it declares any service-affecting defect conditions.

dTIM – Trail Trace Identification Mismatch Defect(*)
dAIS – OTUk-AIS Defect
dLOF – Loss of Frame Defect
dLOM – Loss of Multiframe Alignment Defect
dLOS-P/dLOS-P[i] – Loss of Signal – Payload Defect
dLOFLANE[j] – Loss of Frame – Lane Signal Defect (OTL3.4 and OTL4.4 Applications)(*)
dLOL – Loss of Lane Alignment (OTL3.4 and OTL4.4 Applications)(*)

(*) – Must be a member of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!! to see this material.

The Network Element will continue to transmit the OTUk-BDI indicator for the duration it declares any of these defects.

Once the Network Element no longer declares these defect conditions, it will stop transmitting the OTUk-BDI indicator.

NOTE: ITU-T G.798 is the standards document that specifies the conditions and set of defects that will cause the Network Element to transmit the OTUk-BDI indicator to the remote terminal.

If you wish to see a detailed analysis of how ITU-T G.798 specifies these requirements, please look at the standards document itself or check out the OTUk-BDI – ITU-T G.798 Analysis post.

How does the OTUk Network Element transmit the dBDI indicator?

The Network Element will send the OTUk-BDI indicator by setting the BDI bit-field (Bit 5) within the SM (Section Monitoring) Byte, to 1, within each outbound OTUk frame.

The SM byte resides within the 3-byte SM (Section Monitoring) field of the OTUk Overhead.

Figures 4a, 4b, and 4c present the location of the BDI field.
Figure 4a presents an illustration of the SM-field within the OTUk Overhead.

Figure 4a, The SM Field within the OTUk Overhead

Further, Figure 4b illustrates the SM byte’s location within the 3-byte SM Field (within the OTUk Overhead).

Figure 4b, The SM-Byte within the SM Field

Finally, Figure 4c shows the location of the BDI-field within the SM-byte (within the SM-field of the OTUk Overhead).

Figure 4c, The Location of the BDI bit-field within the SM Byte, within the SM Field, within the OTUk Overhead

Likewise, the Network Element will end its transmission of the OTUk-BDI indicator by setting the BDI bit-field back to “0” within each outbound OTUk frame.

How does the OTUk Network Element detect and declare the dBDI indicator?

In the scenario that we described above (via Figure 3), NETWORK ELEMENT EAST will continue to transmit the OTUk-BDI signal to NETWORK ELEMENT WEST as long as it (NETWORK ELEMENT EAST) declares the service-affecting defect within its Ingress (Receive) signal.

If NETWORK ELEMENT WEST receives the OTUk-BDI indicator within at least five (5) consecutive OTUk frames, it will declare the dBDI defect condition.

In other words, if NETWORK ELEMENT WEST (or any Network Element) were to receive at least five (5) consecutive OTUk frames, in which the BDI bit-field is set to “1”, then it will declare the dBDI defect.

Figure 5 illustrates NETWORK ELEMENT WEST declaring the dBDI defect after receiving five consecutive OTUk Frames with the SM-BDI field set to “1”.

Figure 5, Illustration of NETWORK ELEMENT WEST declaring the dBDI defect condition

How does the OTUk Network Element clear the dBDI defect condition?

Whenever NETWORK ELEMENT EAST has determined that the service-affecting defect (which caused it to transmit the dBDI signal in the first place) is cleared, it will stop sending the dBDI signal back out to NETWORK ELEMENT WEST.

NETWORK ELEMENT EAST will stop sending the dBDI signal by setting the BDI bit-field (within the SM field) to “0” within each outbound OTUk frame.

If NETWORK ELEMENT WEST (which is currently declaring the dBDI defect condition) were to receive at least five (5) consecutive OTUk frames, in which the BDI bit-field is set to “0”, then it will clear the dBDI defect.

Figure 6 illustrates NETWORK ELEMENT WEST clearing the dBDI defect after receiving five consecutive OTUk Frames with the SM-BDI field set to “0”.

Figure 6, Illustration of NETWORK ELEMENT WEST clearing the dBDI defect condition

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What is the RDI (Remote Defect Indicator)?

This post presents a generic definition of the term: RDI (Remote Defect Indicator) signal. It also describes how and when Network Equipment will transmit this type of signal.

What is the RDI (Remote Defect Indicator) Signal?

What does RDI Mean?

RDI is an acronym for Remote Defect Indicator.

Where is the RDI Signal Used?

RDI is a particular type of alarm signal that a Network Element (within a Telecom/Datacom application) will generate and transmit (back towards upstream Network Equipment) anytime it detects a servicing-affect defect within the signal from that same upstream Network Equipment.

Stated differently, the Network Element (NE) will transmit the RDI indicator (upstream) at the same time (and under the same conditions) that it will send the AIS signal downstream.

For example: If an NE were to declare the LOS (Loss of Signal) or the LOF (Loss of Frame) defect within its incoming telecom/datacom signal, then it will respond to this defect condition by transmitting the RDI signal (back) upstream towards the source of the defective signal.

Whenever the Network Element transmits this RDI signal upstream, it notifies the upstream NE that there are problems with its data.

What EXACTLY is an RDI Signal?

The method we use to transmit the RDI signal depends upon the telecom/datacom standard and network layer we use.

However, in most cases, the Network Element will transmit the RDI signal by setting a certain overhead bit-field (within the signal it is transmitting back to the remote or upstream NE) to “1”.

The Network Element will continue to set this bit-field to “1” within each data frame (transmitting back to the remote NE) for as long as it declares the defect within its incoming data stream.

Likewise, once the Network Element clears the service-affecting defect, it will stop sending the RDI signal by clearing that same overhead bit-field to “0”.

For OTN applications, we call the RDI signal the BDI (or Backward Defect Indicator) signal.

I have included posts that describe the BDI signal for both the OTUk and ODUk frames.

For example, SONET Line-Terminating Equipment will transmit the RDI-L indicator, and SONET Path-Terminating Equipment will send the RDI-P indicator.

In the case of PDH signals (e.g., T1/E1 or T3/E3), we call the RDI signal by other synonymous names such as FERF (Far-End Receive Failure) or the “Yellow Alarm.“

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When do we transmit the RDI Signal?

We will use a couple of examples to illustrate how and when we transmit the RDI signal.

Example # 1 – The Unerred/Normal Condition

Figure 1 presents a simple illustration of a portion of a 3R Repeater/Regenerator, which consists of the following components:

Two (2) Receive Line Interface blocks (one block is labeled W for West, and the other block is labeled E for East)
Two (2) Receive Framer blocks (W – West and E – East)
Two (2) Transmit Line Interface blocks (W – West and E – East)
Two (2) Transmit Framer blocks (W – West and E – East)
CS (Clock Smoothing/Jitter Attenuation) PLL (Phase-Locked Loop)
AIS OSC (Stand-Alone Oscillator)
FIFO/Buffer
Two (2) Defect Decoder blocks (W – West and E – East)

In this figure, our 3R Repeater/Regenerator receives a good (error-free) signal from the West Terminal.

The 3R Repeater/Regenerator will first receive this signal through its Receive Line Interface (W) block.

Afterward, this signal passes through to the Receive Framer (W) block.

If the Receive Line Interface (W) and Receive Framer (W) blocks were to declare no problems within this signal. The 3R Repeater/Regenerator would allow this signal to pass through both the Transmit Framer (E) and Transmit Line Interface (E) blocks as is.

The Receive Line Interface (W) and the Receive Framer (W) blocks would also do nothing to alter the data that the Near-End Transmitter circuitry (e.g., the Transmit Line Interface (W) and Transmit Framer (W) blocks) is transmitting back out to the West Terminal.

Figure 1 presents an illustration of this Normal (No Defect) Condition.

Figure 1, Illustration of the 3R Repeater/Regenerator – during Good/Normal Conditions.

Please note that I have grayed out the non-relevant portions of Figure 1 to focus our discussion on this Defect Declaration to the RDI Generation mechanism on the West-side of the 3R Repeater/Regenerator circuit.

Let’s discuss the case where we will transmit the RDI indicator.

Example # 2 – The dLOS/Abnormal Condition

Figure 2 presents another simple illustration of a 3R Repeater/Regenerator.

However, in this figure, there is an impairment in the signal that originates from the West Terminal such that our Network Element is now declaring the dLOS (Loss of Signal) defect with this signal.

It is possible that a backhoe or some other mishap severed this signal.

Nonetheless, this means that our 3R Repeater/Regenerator is no longer receiving its signal from the West Terminal.

In this case, the 3R Repeater/Regenerator will respond by doing all the following:

The Receive Line Interface (W) or the Receive Framer (W) blocks will declare the dLOS (Loss of Signal) defect with the signal that it is receiving from the West Terminal.
The Transmit Framer (E) and the Transmit Line Interface (E) (which sit directly behind the Receive Line Interface and Framer blocks – that are declaring the dLOS condition) will now transmit the AIS indicator (to the East Terminal) as we discussed in the AIS post of this blog.
Additionally, the Receive Line Interface (W) and/or the Receiver Framer (W) blocks will also command its “near-end” transmitting circuitry [e.g., the Transmit Framer (W) and Transmit Line Interface (W) blocks] to start sending the RDI signal, back out to the West Terminal.

Figure 2 illustrates the dLOS/RDI Transmission Condition for our 3R Regenerator/Repeater.

Figure 2, Illustration of the 3R Repeater/Regenerator – during the dLOS/Abnormal Condition

The Transmit Framer (W) and Transmit Line Interface (W) blocks will send the RDI indicator to the West Terminal for as long as the Receive Line Interface (W) and the Receive Framer (W) blocks declare the dLOS defect within the signal they are receiving from the West Terminal.

The Transmit Framer (W) and Transmit Line Interface (W) blocks will stop sending the RDI indicator once the Receive Line Interface (W) and the Receive Framer (W) blocks clear the dLOS defect and starts to receive good/normal data from the West Terminal.

In addition to the dLOS defect, the Network Element will transmit the RDI Indicator (upstream) in response to any other service-affecting defects, such as:

OTN Applications (Sending the SM-BDI or PM-BDI Indicator)
- dLOF – Loss of Frame defect
- dLOM – Loss of Multi-Frame defect
- dLOFLANE – Loss of Frame defect for Logical Lane (for OTL3.4 or OTL4.4 applications)
- dLOL – Loss of Lane Alignment defect (for OTL3.4 or OTL4.4 applications)
- dLOFLOM – Loss of Frame and Multi-Frame defect (for Multiplexed Applications)
- dLOOMFI – Loss of OMFI defect (for Multiplexed Applications using an ODU4 server signal)
- dPLM – Payload Type Mismatch (for Multiplexed Applications)
- dTIM – Trail Trace Identifier Mismatch defect

Please check out the appropriate blog posts to learn more about the SM-BDI or PM-BDI indicators for OTN applications.

Why do we bother to transmit the RDI Signal?

The main reason we send the RDI signal (back to upstream equipment) in response to service-affecting defects is to alert that NE that there is a service-affecting defect within its output signal between its location and that of the next downstream NE.

This notification aids in troubleshooting and system debugging of fault conditions in the network.

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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.

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.

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.

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.

dLOS-P/dLOS-P[i] (Loss of Signal Defect)
dLOFLANE[j] – Loss of Frame of Logical Lane – Logical Lane j
dLOL – Loss of Lane Alignment
dAIS (OTUk-AIS) Defect
dLOF (Loss of Frame Defect)
dLOM (Loss of Multframe Defect)
dTIM (Trace Identifier Mismatch Defect)

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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What is the OTUk-AIS Indicator?

This post defines and describes the OTUk-AIS signal for OTN applications.

What is the OTUk-AIS Maintenance Signal?

What exactly is an OTUk-AIS signal?

AIS is an acronym for Alarm Indication Signal.

Another post describes the role/function of AIS.

Whenever an OTN Network Equipment (NE) transmits an OTUk-AIS signal, it generates and transmits an Unframed PN-11 (e.g., PRBS11) Pattern.

More specifically, ITU-T G.709 defines this PN-11 sequence by the generating polynomial: 1 + x⁹ + x¹¹.

Since this is an Unframed signal, then this means that all of the OTUk, ODUk, and OPUk overhead fields (within the OTUk signal) will be overwritten with this PN-11 pattern.

Figure 1 presents a simple illustration of an OTUk-AIS signal.

Figure 1, Simple Illustration of an OTUk-AIS signal.

What are the timing/frequency requirements for an OTUk-AIS signal?

The OTN NE will need to transmit this signal at the same nominal bit rate as an ordinary OTUk signal.

Like any ordinary OTUk signal, the OTN STE 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-AIS signal) for each value of k.

Table 1, Required Bit Rates for the OTUk-AIS signal.

Does the OTN NE need to align the PN-11 pattern sequence with the OTUk frame?

In short, the answer is No.

The length of the PN-11 sequence is 2047 bits (e.g., 2¹¹ – 1). And the capacity of a given OTUk frame is 130,560 bits.

Since the numeral 130,560 is NOT an integral multiple of 2047, the PN-11 sequence will cross OTUk frame boundaries.

When would OTN Network Equipment transmit/generate an OTUk-AIS signal?

For the time being, ITU-T G.709 has not defined a set of conditions (or defects) upon which the OTN STE would transmit the OTUk-AIS signal.

ITU-T G.709 has reserved this type of signal as a placeholder for future use.

The standards committee may (at a later time) specify a set of conditions upon which an OTN STE would transmit the OTUk-AIS signal.

Additionally, ITU-T G.709 is NOT requiring that OTN Equipment or Chip Vendors design their products to be capable of generating/transmitting the OTUk-AIS signal.

However, ITU-T G.709 mandates that OTN Equipment and Chip Vendors be capable of receiving, detecting, and flagging the OTUk-AIS pattern.

Click HERE for Information on How an STE does declare and clear the dAIS (OTUk-AIS) defect condition.

Why are we even talking about an OTUk-AIS Signal if we are NOT currently required to generate it?

Once again, the Standards Committee has reserved this signal for FUTURE USE.

They envision defining conditions for which an OTN Section Terminating Equipment (STE) would generate and transmit the OTUk-AIS signal in a system application.

Is there another type of AIS signal that OTN APPLICATIONS ARE ACTIVELY USING?

Yes, ITU-T G.709 also recommends the use of ODUk-AIS. OTN Path Terminating Equipment is actively using the ODUk-AIS indicator.

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What is AIS (Alarm Indication Signal)?

This post defines and describes the AIS (Alarm Indication Signal). It also describes how and when Network Equipment will transmit this type of signal.

What is an AIS (Alarm Indication Signal)?

What does the term AIS Mean?

AIS is an acronym for Alarm Indication Signal.

Where is the AIS Signal Used?

The AIS signal is a particular type of alarm (or maintenance) signal that a Network Element (within a Telecom/Datacom application) will generate and transmit (in its downstream path) anytime it detects some service-affecting defect upstream.

For example:

Suppose a Network Element (NE) was to declare the LOS (Loss of Signal) or the LOF (Loss of Frame) defect within its incoming telecom/datacom signal. In that case, it will respond to this defect condition by transmitting the AIS signal downstream.

Whenever the Network Element transmits this AIS signal downstream, it is (in effect) replacing its defective incoming signal with the AIS signal.

What EXACTLY is an AIS signal?

The exact pattern/signature of an AIS signal depends upon the telecom/datacom standard and network layer we use.

For some datacom/telecom standards, the AIS signal is transmitted (and received) as an Unframed All One’s pattern.

In other standards, we will transmit the AIS indicator as a Framed All One’s pattern (e.g., where the framing alignment fields still use typical values, but the payload fields are filled with an All One’s pattern).

Finally, the OTUk AIS pattern is an Unframed PN-11 (PRBS11) pattern.

In all cases, the NE will generate and transmit the AIS signal at the nominal line rate (of the customarily transmitted signal).

The frequency accuracy requirements for this AIS signal also depend on the governing standards for the Telecom/Datacom system.

I have included posts that define the AIS patterns for OTUk and ODUk types of signals (for OTN applications).

When do we transmit the AIS pattern?

We will go through a couple of examples to illustrate how and when we will transmit the AIS signal.

Example # 1 – The Unerred/Normal Condition

Figure 1 presents a straightforward illustration of a portion of a 3R Repeater/Regenerator, which consists of the following components:

Two (2) Receive Line Interface blocks (one block is labeled W for West, and the other block is labeled E for East)
Two (2) Receive Framer blocks (W – West and E – East)
Two (2) Transmit Line Interface blocks (W – West and E – East)
Two (2) Transmit Framer blocks (W – West and E – East)
CS (Clock Smoothing/Jitter Attenuation) PLL (Phase-Locked Loop)
AIS OSC (Stand-Alone Oscillator).
FIFO/Buffer
Two (2) Defect Decoder blocks (W – West and E – East)

In this figure, our 3R Repeater/Regenerator receives a good (error-free) signal from the “West Terminal.”

The 3R Repeater/Regenerator will first receive this signal through its Receive Line Interface (W) block.

Afterward, this signal passes through to the Receive Framer (W) block.

Suppose the Receive Line Interface (W) and the Receive Framer (W) blocks were to detect no problems within this signal. In that case, the 3R Repeater/Regenerator will allow this signal to pass through the Transmit Framer (E) and Transmit Line Interface (E) blocks as is.

Our 3R Repeater/Regenerator will transmit this same data to the East Terminal.

Additionally, the Transmit Framer (E) and Transmit Line Interface (E) blocks would transmit the outbound data (towards the East Terminal) based upon the Recovered Clock signal (which originated from the West Terminal and has been routed through the Clock Smoothing PLL for Jitter Attenuation purposes).

Figure 1 presents an illustration of this Normal (No Defect) Condition.

Figure 1, Illustration of the 3R Repeater/Regenerator – during Good/Normal Conditions.

Please note that I have grayed out the non-relevant portions of Figure 1 so we can focus our discussion on this Defect Declaration to AIS Generation mechanism in the West-to-East Terminal Path.

Now we will illustrate the case where we will transmit the AIS indicator.

Example # 2 – The dLOS/Abnormal Condition

Figure 2 presents another straightforward illustration of a 3R Repeater/Regenerator.

However, in this figure, there is an impairment in the signal that originates from the West Terminal such that our Network Element is now declaring the dLOS (Loss of Signal) defect with this signal.

It is possible that a backhoe or some other mishap severed this signal.

Nonetheless, our 3R Repeater/Regenerator is no longer receiving its signal from the West Terminal.

This also means that our 3R Repeater/Regenerator has no data to send to the East Terminal.

In this situation, our 3R Repeater/Regenerator will respond by doing the following things.

The Receive Line Interface (W) or the Receive Framer (W) blocks will declare the dLOS (Loss of Signal) defect with the signal that it is receiving from the West Terminal.

The Transmit Framer (E) and Transmit Line Interface (E) (which resides directly behind the Receiving Line Interface and Framer blocks – that are declaring the dLOS condition) will proceed to transmit the AIS indicator (to the East Terminal) as a replacement signal for the signal that we are no longer receiving from the West Terminal.

Additionally, the Transmit Framer (E) and Transmit Line Interface (E) blocks would transmit the AIS pattern (towards the East Terminal) based upon the output frequency of the AIS Oscillator (which is a stand-alone oscillator – that operates at the specified line-rate/clock frequency).

Figure 2 illustrates the dLOS/AIS Transmission Condition for our 3R Regenerator/Repeater.

Figure 2, Illustration of the 3R Repeater/Regenerator – during the dLOS/Abnormal Condition.

The Transmit Framer (E) and Transmit Line Interface (E) blocks will continue to transmit the AIS indicator to the East Terminal for the duration that the Receive Line Interface (W) and the Receive Framer (W) blocks are declaring the dLOS defect with the signal that they are receiving from the West Terminal.

The Transmit Framer (E) and Transmit Line Interface (E) blocks will cease to transmit the AIS indicator once the Receive Line Interface (W) and the Receive Framer (W) blocks clear the dLOS defect and start to receive good/normal data from the West Terminal.

At this point, the Transmit Framer (E) and Transmit Line Interface (E) blocks will transmit good/normal data to the East Terminal.

In addition to the dLOS defect, the Network Element will typically transmit the AIS indicator (downstream) in response to the following other defects.

dLOF (Loss of Frame Defect)
dLOM (Loss of Multi-Frame Defect)
dLOFLANE (Loss of Frame of Logical Lane) – for OTL3.4 or OTL4.4 applications (*)
dLOL (Loss of Lane Alignment) – for OTL3.4 or OTL4.4 applications (*)
dTIM (Trail Trace Identifier Mismatch)

(*) – Need to be a member of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!! to access these links.

Why do we bother to transmit the AIS signal as a replacement signal?

We transmit the AIS indicator downstream in response to service-affecting defects for several reasons.

I will list some of those reasons below.

Alerts downstream equipment that we have detected and declared a service-affect defect upstream.
To suppress (or prevent) the downstream equipment from declaring their service-affecting defect.
Aids in troubleshooting and system debugging. It is easier to isolate the causes of defect conditions if we know exactly which NE is declaring the defect and not the whole chain of NEs downstream.
The downstream Receive Circuitry provides a much-needed clock signal at the correct bit rate. Clock Recovery PLLs (Phase-Locked-Loops) and Bias Controllers (for Optical Receive circuitry) all need upstream NEs to provide them with a line signal with the appropriate timing (bit-rate).

The AIS signal accomplishes these goals.

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Introduction

The Interfaces within the OTUk/ODUk_A_Sk Function

Functional Block Diagram

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So What All Does this Atomic Function Do?

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.

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

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

Function Defects

Consequent Actions

aSSF <- AI_TSF and (NOT MI_AdminState = LOCKED)

aAIS <- AI_TSF and (NOT MI_AdminState = LOCKED)

aSSD <- AI_TSD and (NOT MI_AdminState = LOCKED)

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

Defect Correlations

Performance Monitoring

Pin Description

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Introduction

Functional Block Diagram for the OTUk/ODUk_A_So Function

Interfaces within the OTUk/ODUk_A_So Function

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So What Does This Function Do?

Optionally Generates the ODUk-LCK Maintenance Signal

Allows User to Insert APS (Automatic Protection Switching) Commands into the APS Channel (within the ODUk-PMOH).

Generates OTUk Clock, FS (Frame Start), and MFS (Multi-Frame Start) Signals via the OTUk_AP Interface

Generates the IAE (Input Alignment Error) Indicator for the downstream OTUk_TT_So function

Generate and Route the OTUk Data-Stream to downstream circuitry

List of Input and Output Signals for the OTUk/ODUk_A_So Function

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OK, So What are these Atomic Functions?

OK, So Why bother with these Atomic Functions?

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

Adaptation Functions

Another Way to Identify an Adaptation Function?

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Trail-Termination Functions

Another way to Identify a Trail-Termination Function?

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What is Section Terminating Equipment (STE) for OTN Applications?

What is a Section?

What is an STE (Section Terminating Equipment)?

The Source STE Operation In the Transmit Direction

Sink STE Operation In the Receive Direction

Summarizing our Definitions of Section and STE

How the STE Operates in the Optical Transport Network (OTN)

What is the OTUk-SMOH (Section Monitoring Overhead)?

AN EXAMPLE OF AN STE AND ITS SECTION

Examples of STE

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Introduction

So How does the OTN use the SM-BIP-8 scheme?

Brief Overview – How the Source STE creates and transports the SM-BIP-8 Byte Value

Brief Overview – How the Sink STE Receives and Processes the SM-BIP-8 byte Values

The Details – How does the Source STE generate the SM-BIP-8 Value?

The Source STE and Introduction to the OTUk_TT_So Atomic Function

How do we perform a BIP-8 (Bit Interleaved Parity – 8 Bit) Calculation?

How does one Source STE transport the SM-BIP-8 to another Network Element?

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What does the Sink STE do with the SM-BIP-8 Value?

The Sink STE and Introduction to the OTUk_TT_Sk atomic function

STEP 1 – The OTUk_TT_Sk function will locally compute Its sm-BIP-8 byte value for an incoming OTUk frame.

STEP 2 – The OTUk_TT_Sk function will compare its Locally-Computed BIP-8 Value with that inserted into the BIP-8 field (by the OTUk_TT_So function at the remote STE).

Will the OTN Network Element ever declare any defects due to excessive SM-BIP-8 errors?

What is the OTUk/ODUk_A_Sk Atomic Function?

What is the OTUk/ODUk_A_So Atomic Function?

What is an Atomic Function for OTN Applications?

What is the OTUk-BIP-8 or Section Monitor (SM-BIP-8) Parameter, and How Do We Compute and Verify it?

What is the dBDI (Backward Defect Indicator) defect at the OTUk Layer?

What is the RDI (Remote Defect Indicator) Signal?

What is the OTUk-AIS Maintenance Signal?

What is an AIS (Alarm Indication Signal)?