What is the OTUk_TT_Sk Function?

This blog post briefly describes the OTUk_TT_Sk (OTUk Trace Termination Sink) Atomic function.

What is the OTUk_TT_Sk Atomic Function?

We formally call the OTUk_TT_Sk Atomic Function the OTUk Trail Termination Sink function.

Introduction

The OTUk_TT_Sk function is any circuit that accepts an OTUk data-stream from the upstream OTSi/OTUk_A_Sk function (for OTU1 and OTU2 applications) or the upstream OTSiG/OTUk_A_Sk function (for OTU3 or OTU4 applications) and extracts and processes the data within the OTUk Section Monitoring Overhead (OTUk-SMOH) from the incoming OTUk signal.

The OTUk_TT_Sk function will evaluate this data to check for various types of defects and errors.

NOTE:  I offer an extensive discussion of the OTUk_TT_Sk Atomic Function within Lesson 9 of THE BEST DARN OTN TRAINING PRESENTATION….PERIOD!!!

So What Does this Atomic Function Do?

If you recall, from our discussion of the OTUk/ODUk_A_So and OTUk_TT_So functions, those two particular functions will take an ODUk signal and will work together to create an OTUk data-stream with some newly computed OTUk-SMOH.

The OTUk_TT_So function will then route this OTUk data-stream to the OTSi/OTUk-a_A_So (for OTU1/2 applications) or the OTSiG/OTUk-a_A_So functions (for OTU3/4 applications).

These functions will condition the OTUk signal for transport.  Next, one of these functions will route this OTUk signal through other circuitry that will convert this OTUk data-stream into the optical format and transport this data-stream over optical fiber.

A receiving Network Element will receive this optical signal and convert this data back into the electrical format.  This electrical signal will pass through the OTSi/OTUk-a_A_Sk atomic function (for OTU1/2 applications) or the OTSiG/OTUk-a_A_Sk atomic function (for OTU3/4 applications) before it finally reaches the OTUk_TT_Sk function.

I show an illustration of where the OTUk_TT_Sk function “fits in the big picture” below in Figure 1.

OTUk_TT_Sk Function Highlighted in Unidirectional OTUk End-to-End Connection

Figure 1, Illustration of Unidirectional Connection between a Source STE and a Sink STE with the OTUk_TT_Sk function highlighted.

Once this OTUk data arrives at the OTUk_TT_Sk function, it will perform the following tasks on this data-stream.

Extracts and Processes the OTUk-SMOH within the incoming OTUk Data-Stream

The OTUk_TT_Sk function will accept this OTUk data-stream and will extract out and process the OTUk-SMOH data from the incoming OTUk signal.  The OTUk_TT_Sk function will evaluate this data to check for various types of defects and errors.

In other words, the OTUk_TT_Sk function will evaluate the OTUk_SMOH (that the OTUk_TT_So function, at the remote STE) created.  The OTUk_TT_Sk function will evaluate the OTUk-SMOH to check and see if it should declare certain types of defect conditions, or determine if certain kinds of errors have occurred within this OTUk signal, during transmission over optical fiber, as we describe below.

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Detect and Flag Defects and Errors within the Incoming OTUk Data-Stream

More specifically, the OTUk_TT_So function will check for (and declare or clear) the following defect conditions.

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

Additionally, the OTUk_TT_Sk function will also detect and flag the following errors (within this OTUk data-stream):

Some Details about the OTUk_TT_Sk Function

Figure 2 presents a simple illustration of the OTUk_TT_Sk function.

OTUk_TT_Sk Function - Trail Trace Atomic Function

Figure 2, Simple Illustration of the OTUk_TT_Sk Atomic Function

The Interfaces within the OTUk_TT_Sk Atomic Function

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

  • OTUk_TCP – The OTUk Termination Connection Point:  This is where the function user supplies data (which most likely came from an upstream OTSi/OTUk-a_A_Sk or OTSiG/OTUk-a_A_Sk function) to the OTUk_TT_Sk function.  This data will typically consist of the entire OTUk data-stream (but without the FEC, which was already decoded by the upstream OTSi/OTUk-a_A_Sk or OTSiG/OTUk-a_A_Sk function).
  • OTUk_AP – The OTUk Access Point:  This is where the function outputs OTUk data, clock, frame, and multi-frame signals (of the incoming OTUk data-stream) to down-stream circuitry (towards the OTUk/ODUk_A_Sk function).
  • OTUk_TT_Sk_MP – The Function Management Point:  This interface permits the function-user to exercise control and monitoring of the activity within the OTUk_TT_Sk function.  Some of the information that the user can obtain from the Management Point includes Performance Monitoring and Correlated Defect Identification.
  • OTUk_TT_RP – The Function Remote Point:  This interface permits the function-user to output some information to a collocated OTUk_TT_So function.  This information includes the BDI, BEI, and BIAE indicators.  The collocated OTUk_TT_So function will respond to this signaling (from the OTUk_TT_Sk function – via the RP port) by transmitting the BEI values, BDI and BIAE indicators, back out to the Remote STE, as appropriate.

A Closer Look at the Interfaces within the OTUk_TT_Sk Function.

We will now take a closer look at these interfaces below.

The OTUk_TCP (Termination Connection Point) Interface

The OTUk_TT_Sk function accepts an OTUk data-stream from either the upstream OTSi/OTUk-a_A_Sk or OTSiG/OTUk-a_A_Sk function via the OTUk_TCP Interface.

The data that either the OTSi/OTUk-a_A_Sk or the OTSiG/OTUk-a_A_Sk function outputs are a full-blown OTUk frame (that has been descrambled) by those functions.

Figure 3 presents a functional block of the OTUk_TT_Sk function.

OTUk_TT_Sk Functional Block Diagram

Figure 3, Functional Block Diagram of the OTUk_TT_Sk Function

Note that Figure 3 shows that the equipment that we connect to the OTUk_TCP (of the OTUk_TT_Sk function) will supply the following signals to this function.

  • CI_D
  • CI_CK
  • CI_FS
  • CI_MFS

The OTUk_TT_Sk function will then perform the following operations on each OTUk frame within this signal.

  • OTUk-SMOH (Section Monitoring Overhead) Extraction
  • Compute and Verify the BIP-8 Value
  • Receive and Process TTI (Trail-Trace Identifier) Messages
  • Declares and clear the following defects (as appropriate)
    • dIAE – Will also be forward to the RI_BIAE output in the form of the BIAE indicator.
    • dTIM  – Will be reported via the RI_BDI output by way of the BDI signal, and will also be reported via the AI_TSF output.
    • dDEG – will also be reported via the AI_TSD output
    • dBDI
    • dBIAE

The OTUk_TT_Sk_MP (Management Point) Interface

As the OTUk_TT_Sk function performs all of the actions mentioned above on the data (that it receives via the OTUk_TCP Interface), it will tally and report all of the following performance monitoring parameters to System Management (via the Management Interface).

  • Report and Tally the following errors
    • BIP-8 Errors– reported as nBIPV (to the RI_REI output) and as nN_B in performance monitoring.
    • BEI Count – reported as nF_B in Performance Monitoring
  • To provide Performance Monitoring reports on the following parameters to System Management

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The OTUk_TT_Sk_RP (Remote Point) Interface

The OTUk_TT_Sk_RP Interface contains the following three (3) output ports that the System Designer should connect to the collocated OTUk_TT_So Atomic Function.

Whenever the user connects these three (3) output pins to similarly named pins at the collocated OTUk_TT_So function, these two functions will work together to transmit backward alarm and error information to the remote STE (the source of the OTUk data-stream that this OTUk_TT_Sk function is receiving).

Please click on the appropriate links to learn more about these backward (or far-end) indicators as well as how the OTUk_TT_Sk function accomplishes these forms of signaling with its collocated OTUk_TT_So function.

The OTUk_AP (Access Point) Interface (Output)

The OTUk_TT_Sk function will output the following signals, via the OTUk_AP Interface.

  • AI_D – OTUk Adapted Information – Data Output
  • AI_CK – OTUk Adapted Information – Clock Output
  • AI_FS – OTUk Adapted Information – Frame Start Output
  • AI_MFS – OTUk Adapted Information – Multi-Frame Start Output
  • AI_TSF – OTUk Adapted Information – Trail Signal Fail (TSF) Indicator Output
  • AI_TSD – OTUk Adapted Information – Trail Signal Degrade (TSD) Indicator Output.

In most cases, the System Designer would route these output signals to the downstream OTUk/ODUk_A_Sk function for further processing.

AI_D, AI_CK, AI_FS, and AI_MFS will contain the remaining OTUk data-stream, clock, frame-start, and multi-frame start indicators for the OTUk/ODUk_A_Sk function.

Defect Notification – Downstream

The OTUk_TT_Sk function will assert the AI_TSF output pin anytime it declares a service-affecting defect (dTIM) itself, or if the upstream circuitry (e.g., the OTSiG/OTUk-a_A_Sk or the OTSi/OTUk-a_A_Sk functions) are declaring service-affecting defects and asserting the CI_SSF input to this function.

Likewise, the OTUk_TT_Sk function will assert the AI_TSD output pin anytime it declares the dDEG (Signal Degrade) defect condition.

Consequent Actions

Consequent Action Equations specify what actions an Atomic Function should take any time (and for the duration) that it declares a certain defect.  ITU-T G.798 presents the following equations for consequent actions, within the OTUk_TT_Sk function.

  • aTSF <- CI_SSF or [dTIM and (NOT TIMActDis)]
  • aBDI <- CI_SSF or dTIM
  • aBEI <- nBIPV
  • aBIAE <- dIAE
  • aTSD <- dDEG

I will discuss each of these consequent action equations below.

aTSF <- CI_SSF or [dTIM and (NOT TIMActDis)]

Where:  

aTSF is the Trail Signal Fail parameter that the OTUk_TT_Sk function will set LOW or HIGH to send current defect-state information towards downstream circuitry.

If aTSF = TRUE, then the OTUk_TT_Sk function will set its AI_TSF output HIGH.  Conversely, if aTSF = FALSE, then the OTUk_TT_Sk function will set its AI_TSF output LOW.

CI_SSF is the current state of the CI_SSF (Server Signal Fail Indicator) input from the upstream OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk atomic functions.  The OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk function will assert this signal anytime it is declaring a service-affecting defect.

dTIM is the current state of the dTIM defect condition.

TIMActDis is a parameter that the user can set to configure the dTIM to (optionally) drive the aTSF parameter.

This equation means that the OTUk_TT_Sk function will assert an internal signal (we call aTSF) if either of the following conditions is true.

  • The upstream circuitry (e.g., the OTSiG/OTUk-a_A_Sk or the OTSi/OTUk-a_A_Sk function) is asserting the CI_SSF input to this function, or
  • The OTUk_TT_Sk function is declaring the dTIM defect condition.

NOTES:

  1. If the OTUk_TT_Sk function asserts the aTSF signal, then it will indicate so by asserting the AI_TSF output pin towards downstream circuitry (e.g., the OTUk/ODUk_A_Sk function).
  2. The AI_TSF output signal is a crucial signal for Automatic Protection Switching purposes.
  3. Please see the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk posts, for information on what causes these two functions to drive the CI_SSF signal HIGH.

aBDI <- CI_SSF or dTIM

This equation means that the OTUk_TT_Sk function will assert another internal signal (that we call the aBDI signal) if either of the following conditions is true.

  • The upstream circuitry (e.g., the OTSiG/OTUk-a_A_Sk or the OTSi/OTUk-a_A_Sk function) is asserting the CI_SSF input to this function, or
  • The OTUk_TT_Sk function is declaring the dTIM defect condition.

NOTES:

  1. If the OTUk_TT_Sk function is asserting the aBDI signal, then it will indicate so by asserting the RI_BDI output pin (via the Remote Point Interface).  This signaling will command the collocated OTUk_TT_So function to set its BDI bit-field to TRUE, within its next outbound OTUk frame.
  2. The OTUk_TT_Sk function will assert the RI_BDI and AI_TSF output pins under the same conditions.
  3. Please see the OTSi/OTUk_A_Sk or OTSiG/OTUk_A_Sk posts, for information on what causes these two functions to drive the CI_SSF signal HIGH.

aBEI <- nBIPV

This equation means that the OTUk_TT_Sk function will automatically set the internal signal aBEI to the total number of BIP-8 errors, that it has detected within a given OTUk frame.  This means that the OTUk_TT_Sk function can set aBEI to a value anywhere between 0 and 8, within each OTUk frame.

NOTE:  If the OTUk_TT_Sk function sets aBEI to a particular value, it will set the RI_BEI output pin (via the Remote Point Interface) to this same value.  This signaling will command the collocated OTUk_TT_So function to set its BEI nibble-field to this same value (aBEI), within its next outbound OTUk frame, provided that RI_BIAE is set FALSE.

aBIAE <- dIAE

This equation means that the OTUk_TT_Sk function will assert the internal signal, aBIAE, if it is declaring the dIAE (Input Alignment Error) defect condition.

NOTES:

  1. If the OTUk_TT_Sk function is asserting the aBIAE signal, then it will indicate so by asserting the RI_BIAE output pin (via the Remote Point Interface).  This signaling will command the collocated OTUk_TT_So function to set the BEI/BIAE nibble-field to reflect the BIAE condition, within its next outbound OTUk frame.
  2. The OTUk_TT_Sk function will NOT assert the AI_TSF or RI_BDI output signals due to it declaring the dIAE defect condition.

aTSD <- dDEG

This equation means that the OTUk_TT_Sk function will assert the internal signal aTSD anytime it is declaring the OTUk-dDEG (Signal Degrade) defect condition.

NOTES:

  1.   If the OTUk_TT_Sk function is asserting the aTSD condition, then it will indicate so by asserting the AI_TSD output signal towards the downstream circuitry (e.g., the OTUk/ODUk_A_Sk function in this case).
  2. The OTUk_TT_Sk function will NOT assert the RI_BDI output signal due to it declaring the dDEG defect condition.

The AI_TSD output signal is an essential signal for Automatic Protection Switching purposes.

The OTUk_TT_Sk Function Pin Description

Table 1 presents a Description for each of the Input and Output pins of the OTUk_TT_Sk function.

Table 1, Pin Description of the OTUk_TT_Sk Atomic Function

Signal NameTypeDescription
OTUk_TCP Interface
CI_DInputOTUk Characteristic Information - Data Input:
The OTUk_TT_Sk function will accept this data from either the upstream OTSi/OTUk-a_A_Sk or OTSiG/OTUk-a_A_Sk function via this input pin. The OTUk_TT_Sk function will then perform the following actions on this data.
- It will extract out and process the SMOH (Section Monitoring Overhead) and
-- Compute and Verify the BIP-8 data and it will detect and flag any BIP-8 errors within each OTUk frame.
-- It will extract out the Section Monitoring Byte and check the state of the BDI and IAE bit-fields.
-- It will read in the value of the BEI/BIAE nibble field and check for the BIAE indicator.
-- It will also read in and tally all non-zero (and non-BIAE) BEI values and BIP-8 errors.
-- It will extract out the TTI message and compare this read-out value with that of the expected TTI Message.

As the OTUk_TT_Sk performs all of these tasks it will declare or clear the following defect conditions (as warranted).
- dBDI
- dTIM
- dIAE
- dBIAE
- dDEG

It will tally the following events for Performance Monitoring purposes.
- pIAE - Number of seconds in which the OTUk_TT_Sk function declared the dIAE defect.
- pN_BIAE - Number of seconds in which the OTUk_TT_Sk function declared the dBIAE defect.
- pN_EBC - Number of Near-End Errored Block Counts (BIP-8 Errors).
- pN_DS - Number of Defect Seconds (seconds in which the OTUk_TT_Sk (or upstream circuitry) declared certain near-end defect conditions.
- pF_EBC - Number of Far-End Errored Block Counts (BEI Count)
- pF_DS - Number of Far-End Defect Seconds (seconds in which the OTUk_TT_Sk function is declaring the dBDI defect condition).

The OTUk_TT_Sk function will sample this data on one of the edges of the CI_CK input clock signal.
CI_CKInputOTUk Characteristic Information - Clock Input:
The OTUk_TCP Interface will use this clock input signal to sample all of the following input signals.
- CI_D
- CI_FS
- CI_MFS
- CI_SSF

This clock signal also functions as the timing source of the OTUk_TT_Sk function.
CI_FSInputOTUk Characteristic Information - Frame Start Input:
The upstream circuitry should drive this input signal HIGH whenever it is applying the very first bit/byte of a new OTUk frame to the CI_D input.

The upstream circuitry should drive this input signal HIGH once for each incoming OTUk frame.
CI_MFSInputOTUk Characteristic Information - Multi-Frame Start Input:
The upstream circuitry should drive this input signal HIGH whenever it is applying the very frist bit/byte of a new OTUk superframe to the CI_D input.

The upstream circuitry should drive this input signal HIGH once for each incoming OTUk superframe (or once every 256 OTUk frames).
CI_SSFInputOTUk Characteristic Information - Server Signal Failure Indicator Input:
This input pin indicates whether or not the upstream circuitry is declaring a service-affecting defect with the OTUk data-stream (that it is applying to the CI_D input). These service-affecting defects include:
- dLOF
- dLOM
- dAIS (for OTU1 or OTU2 applications only).

This signal is functionally equivalent to the AIS indicator.

LOW - Indicates that the upstream circuitry is NOT declaring a service-affecting defect with the OTUk signal (being applied to the CI_D input).

HIGH - Indicates that the upstream circuitry IS declaring a service-affecting defect with the OTUk signal (being applied to the CI_D input).
OTUk_AP Interface
AI_DOutputOTUk Adapted Information - Data Output:
The OTUk_TT_Sk function will output the OTUk data, after it has passed through and been processed by this function. This data will typicallly be routed to the OTUk/ODUk_A_Sk function for further processing.

This data will be updated (and output) synchronously with the AI_CK clock output signal.
AI_CK OutputOTUk Adapted Information - Clock Output:
The OTUk_TT_Sk function will update/output signals via the OTUk_AP Interface on one of the edges of this clock output signal.
- AI_D
- AI_FS
- AI_MFS
- AI_TSF
- AI_TSD
AI_FSOutputOTUk Adapted Information - Frame Start Output:
The OTUk_AP Interface will drive this output signal HIGH whenever it is also driving the very first bit/byte of a new OTUk frame via this AI_D output.

The OTUk_AP Interface will drive this output HIGH once for each outbound OTUk frame.
AI_MFSOutputOTUk Adapted Information - Multiframe Start Output:
The OTUk_AP Interface will drive this output signal HIGH whenever it is also driving the very first bit/byte of a new OTUk superframe via the AI_D output.

The OTUk_AP Interface will drive this output HIGH once for each oubound OTUk superframe.
AI_TSF OutputOTUk Adapted Information - Trail Signal Fail Output Indicator Output:
The OTUk_TT_Sk function will indicate whether or not it is declaring the Trail-Signal Fail (TSF) condition. The OTUk_TT_Sk function will declare the TSF condition, if it also declares any of the following defect conditions.
- dTIM
- SSF (if the CI_SSF input was driven HIGH due to any of the following defects within the upstream circuitry).
-- dLOF
-- dLOM
-- dAIS (OTU1/OTU2 applications only).

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the TSF indicator.

HIGH- Indicates that the OTUk_TT_Sk function is currently declaring the TSF indicator.
AI_TSDOutputOTUk Adapted Information - Trail Signal Declared Indicator Output:
The OTUk_TT_Sk function will use this output signal to indicate if it is declaring the Trail-Signal Defect (TSD) Condition. The OTUk_TT_Sk function will declare the TSD condition if it also declares the dDEG (Signal Degrade) defect condition.

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the TSD indicator.

HIGH - Indicates that the OTUk_TT_Sk function is currently declaring the TSD indicator.
OTUk_RP Interface
RI_BEIOutputOTUk Remote Point Information - Backward Error Indicator:
As the OTUk_TT_Sk function computes and verifies the BIP-8 values (within the OTUk signal that it is receiving via the CI_D input), it will output date through this output to reflect the number of BIP-8 errors that it is declaring within each incoming OTUk frame. This output signal will be connected to the RP input of its collocated OTUk_TT_So function.

If the OTUk_TT_Sk detects ZERO BIP-8 errors within the most recently received OTUk frame, then it will set RI_BEI = 0 for that OTUk frame period.

Likewise, if the OTUk_TT_Sk function detects five (5) BIP-8 errors within the most recenlty received OTUk frame, then it will set RI_BEI = 5 for that OTUk frame period.
RI_BIAEOutputOTUk Remote Point Information - Backward Input Alignment Error Indicator:
If the OTUk_TT_Sk function declares the dIAE defect condition, then it will set the RI_BIAE indicator true. This output signal will be connected to the corresponding RP Input of the collocated OTUk_TT_So function.

The collocated OTUk_TT_So function is expected to overwrite the BEI nibble-field (within the next outbound OTUk frame).

Please see the OTUk_TT_So function post for more details on this topic).
RI_BDIOutputOTUk Remote Point Information - Backward Defect Indicator:
If the OTUk_TT_Sk function declares any of the following defect conditions, then it will set this output pin TRUE.
- dTIM
- CI_SSF

The user should connect this output signal to the RI_BDI input of the collocated OTUk_TT_So function.

The collocated OTUk_TT_So function is expected to set the BDI bit-field (within the Section Monitoring byte of the SMOH) to "1" within the next outbound OTUk frame, if this output pin is TRUE.

Otherwise, the OTUk_TT_So function should set the BDI bit-field to "0" within the very next outbound OTUk frame.
OTUk_TT_So_MP Interface
MI_AcTIOutputManagement Interface - Accepted Trail Trace identifier Message Output:
The OTUk_TT_Sk function will output the contents of the Accepted Trail Trace Identifier Message via this output signal.

The OTUk_TT_Sk function will output the accepted TTI Message via this output, whenever the user issues a command requesting this data via the MI_GetAcTI input.
MI_ExSAPIInputManagement Interface - Expected SAPI (Source Access Point Identifier) Input:

The OTUk_TT_Sk function will compare the SAPI-portion of the "Accepted Trail-Trace Identification" Message (that it receives from the SMOH (within the OTUk signal) with that which the user supplies to this input.

If the two values do not match, then the OTUk_TT_Sk function will declare the dTIM defect condition.
MI_ExDAPIInputManagement Interface - Expected DAPI (Destination Access Point Identifier) Input:
The function user is expected to apply the Expected Value of the DAPI portion of the Trail-Trace Identification Message.

The OTUk_TT_Sk function will compare the DAPI portion of the "Accepted Trail-Trace Identification" Message (that it received from the SMOH (within the OTUk signal) with that which the user supplies to this input.

If the two values do not match, then the OTUk_TT_Sk function will declare the dTIM defect condition.
MI_GetAcTIInputMangement Interface - Get Accepted Message Command Input:
This input permits the user to request that the OTUk_TT_Sk function provide the user with the currently "accepted" TTI Message. Whenever the user invokes this command, the OTUk_TT_Sk function will output the contents of the currently "accepted" TTI Message via the MI_ActTI output.
MI_TIMDetMoInputManagement Interface - TIM (Trace Identifier Mismatch) Detection Mode:
This input permits the user to specify which portion of the TTI Message that the OTUk_TT_Sk function should check and verify when checking for the dTIM defect condition. Please see the dTIM blog post for more details.
MI_cTIMOutputManagement Interface - Correlated TIM (Trail-Trace Identifier Mismatch) Defect:
This output signal indicates if the OTUk_TT_Sk function is declaring the dTIM defect condition.

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the dTIM defect condition.

HIGH - Indicates that the OTUk_TT_Sk function is currently declaring the dTIM defect condition.
MI_cDEGOutputManagement Interface - Correlated DEG (Signal Degrade) Defect:
This output signal indicates if the OTUk_TT_Sk function is declaring the dDEG defect condition.

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the dDEG defect condition.

HIGH - Indicates that the OTUk_TT_Sk function is currently declaring the dDEG defect condition.
MI_cBDIOutputManagement Interface - Correlated BDI (Backward Defect Indicator) Defect:
This output signal indicates if the OTUk_TT_Sk function is declaring the dBDI defect condition.

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the dBDI defect condition.

HIGH - Indicates that the OTUk_TT_Sk function is currently declaring the dBDI defect condition.
MI_cSSFOutputManagement Interface - Correlated SSF (Server Signal Fail) Defect:
This output signal indicates if the OTUk_TT_Sk function is declaring the SSF defect condition.

LOW - Indicates that the OTUk_TT_Sk function is NOT currently declaring the SSF defect condition. This also means that the upstream circuitry is currently drving the CI_SSF input pin LOW.

HIGH - Indicates that the OTUk_TT_Sk function is currently declaring the SSF defect condition. This also means that upstream circuitry is currently driving the CI_SSF input pin HIGH.
MI_pIAEOutputManagement Interface - IAE Performance Monitor Parameter:
The OTUk_TT_Sk function will drive this output pin HIGH, for one full second, if it has declared the dIAE defect for any portion of the previouis one-second period.

Conversely, the function will keep this output pin LOW, for one full second, if it has NEVER declared the dIAE defect, during the previous one-second period.

This one second period will be dictated by the 1-Second Clock signal that the user supplies to the MI_1Second input to this function.
MI_pBIAEOutputManagement Interface - BIAE Performance Monitor Parameter:
The OTUk_TT_Sk function will drive this output pin HIGH for one full second, if it has declared the dBIAE defect for any portion of the previous one second period.

Conversely, the function will keep tis output pin LOW for one full second, if it has NEVER declared the dBIAE defect, during the previous one second period.

This one second period will be dictated by the 1 Second Clock signal that the user supplies to the MI_1Second input to this function.
MI_pN_EBCOutputManagement Interface - Number of Near-End Errored Block Count (BIP-8 Errors) - One Second Performance Monitoring Parameter:
The OTUk_TT_Sk function will tally and report the total number of BIP-8 errors, that it has detected and flagged (within the incoming OTUk data-stream), during the previous 1 second period.
MI_pN_DSOutputManagement Interface - Near-End Defect - One Second Performance Monitoring Parameter:
The OTUk_TT_Sk fuinction will drive this output pin HIGH for one full second, if it has declared at least one of the following defects for any portion of the previous one-second period.
- CI_SSF or
- dTIM

Conversely, the function will keep this output pin LOW, for one-full second, if it has NEVER declared any of these defect during the previous one-second period.

This one-second period will be dictated by the 1 Second Clock signal that the user supplies to the MI_1Second input to this function.
MI_pF_EBCOutputManagement Interface - Number of Far-End Errored Block Count (BEI Errors) - One Second Performance Monitoring Parameter:
The OTUk_TT_Sk function will tally and report the total number of BEI counts that it has read and captured (within the incoming OTUk data-stream) during the previous one-second period.
MI_pF_DSOutputManagement Interface - Far-End Defect - One Second Performance Monitoring Parameter:
The OTUk_TT_Sk function will drive this output pin HIGH, for one full second, if it has declared the dBDI defect for any portion of the previous one-second period.

Conversely, this function will keep this output pin LOW, for one-full second, if it has NEVER declared the dBDI defect, during the previous one-second period.
MI_1SecondInputManagement Interface - One Second Clock Input:
The user is expected to supply a clock signal, which has a frequency of 1Hz, to this input.

The Performance Monitoring portino of the OTUk_TT_Sk function will use this clock signal as its timing reference for tallying and reporting the various one-second Performance Monitoring parameters.
MI_DEGThrInputManagement Interface - The dDEG BIP-8 Error Threshold for a Bad One-Second Interval:
The user can specify the BIP-8 error threshold for which the OTUk_TT_Sk function should count a given one second period as a "Bad One-Second" period, for the sake of dDEG declaration.

If the OTUk_TT_Sk function detects DEGThr or more BIP-8 errors, during a one-second interval, then the OTUk_TT_Sk function will count that one-second interval as a "Bad" interval.

If the OTUk_TT_Sk function detects less than DEGThr BIP-8 errors, during a one-second interval, then the OTUk_TT_Sk function will NOT count that one-second as a "Bad" interval.
MI_DEGMInputManagement Interface - Number of "Bad One-Second" Intervals for dDEG Declaration:
The user can specify the minimum number of consecutive "Bad One Second" intervals that the OTUk_TT_Sk function must detect before declaring the dDEG defect condition.

If the OTUk_TT_Sk function detects and flags DEGM consecutive "Bad One-Second" Intervals, then the OTUk_TT_Sk function will declare the dDEG defect condition.

NOTE: DEGThr defines the threshold for a "Bad One-Second" interval.

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What is the OTUk_TT_So Atomic Function?

This blog post briefly defines the OTUk_TT_So (OTUk Trail Termination Source) Atomic Function.


What is the OTUk_TT_So Atomic Function?

We formally call the OTUk_TT_So Atomic Function the OTUk Trail Termination Source Function.

Introduction

The OTUk_TT_So function is any function that accepts data from upstream circuitry (usually the OTUk/ODUk_A_So function).  It uses the data (within this data-stream) along with signals from a collocated OTUk_TT_Sk function to compute/generate and insert the OTUk Section Monitoring Overhead (SMOH) into the OTUk signal.

We have an extensive discussion of the OTUk_TT_So Atomic Function in Lesson 9, within THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

I show how we can connect these atomic functions below in Figure 1.

OTUk_TT_So_Function_with_OTUk/ODUk_A_So and Collocated OTUk-TT_Sk functions highlighted

Figure 1, Drawing of a Bidirectional Network (consisting of various Atomic Functions) with the OTUk/ODUk_A_So, the OTUk_TT_So, and its collocated OTUk_TT_Sk functions highlighted 

So What Does this Atomic Function Do?

If you recall, from our discussion of the OTUk/ODUk_A_So function, that function will only generate default values for the OTUk-SMOH, within the OTUk signal that it transmits.  The OTUk/ODUk_A_So function simply creates this default SMOH as a place-holder for a future (and real) SMOH.

Computes and Inserts the Real SMOH Values into the Outbound OTUk Frames

Well, the purpose of the OTUk_TT_So function is to calculate and replace these default SMOH values, with real SMOH values.

More specifically, this function will compute and replace the following SMOH fields with real Overhead data.

  • SM-BIP-8 field, within the Section Monitoring field
  • SM-BEI/BIAE nibble field within the Section Monitoring Byte
  • SM-BDI bit-field within the Section Monitoring Byte
  • IAE bit-field within the Section Monitoring Byte
  • SM-TTI (Trail Trace Identification) byte within the Section Monitoring field.

Afterward, the OTUk_TT_So function will transmit this OTUk data-stream to either the OTSi/OTUk-a_A_S0 function (for OTU1/2 applications) or the OTSiG/OTUk-a_A_S0 function (for OTU3/4 applications). 

These functions will condition the OTUk data-stream for transmission over Optical Fiber.

Why Do We Care about the SMOH from the OTUk_TT_So Function?

The SMOH that the OTUk_TT_So function computes and inserts into the OTUk data-stream serves as the basis of comparison for the OTUk_TT_Sk function (at the remote Network Element).

The OTUk_TT_Sk function (at the remote end of our OTUk connection) will use this SMOH data to determine:

  • if it should declare any defect conditions, or
  • if errors have occurred during transmission between the near-end OTUk_TT_So and the remote OTUk_TT_Sk functions.

I show an illustration where both the OTUk_TT_So and OTUk_TT_Sk functions “fit into the big picture” below in Figure 2.

Roles of the SMOH within the OTUk_TT_So function

Figure 2, Drawing of Unidirectional Connection between a Source STE and a Sink STE with the OTUk_TT_So and OTUk_TT_Sk functions highlighted.  

Some Details about the OTUk_TT_So Function

Figure 3 presents a drawing of the ITU-T G.798 symbol for the OTUk_TT_So function.

OTUk_TT_So Simple Block Diagram - ITU-T G.798 Symbol

Figure 3, Simple Drawing of the OTUk_TT_So function

The OTUk_TT_So function accepts a basic OTUk data-stream from the upstream OTUk/ODUk_A_So function via the OTUk_AP Interface.

The data that is output from the OTUk/ODUk_A_So function includes the Clock Signal (AI_CK), Frame Synchronization Signal (AI_FS), the Multi-Frame Synchronization Signal (AI_MFS), the OTUk data-stream (AI_D) and the IAE (Input Alignment Error) indicator (via the AI_IAE signal).

The OTUk_TT_So function has the responsibility for accepting data from its various interfaces and then compute and insert the correct SMOH data into the OTUk data-stream.

Figure 2 shows that this function consists of the following four different interfaces.

  • OTUk_AP
  • OTUk_CP
  • OTUk_RP and
  • OTUk_TT_So_MP

We will discuss each of these interfaces below.

Figure 4 presents a functional block diagram of the OTUk_TT_So function.

OTUk_TT_So Atomic Functional Block Diagram

Figure 4 Functional Block Diagram of the OTUk_TT_So function

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The OTUk_AP (OTUk Access Point) Interface

Figure 4 shows that the circuitry that is connected to (and driving) the OTUk_AP Interface (e.g., the OTUk/ODUk_A_So function) will supply the following signals to this interface.

  • AI_D – Bare-bones OTUk data (with the default SMOH)
  • AI_CK – The OTUk clock input signal
  • AI_FS – The OTUk Frame Start Input
  • AI_MFS – the OTUk Multi-Frame Start Input
  • AI_IAE – The OTUk Input Alignment Error Indicator Signal

The OTUk_TT_So function will then perform the following operations on these signals.

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

Let’s move on to another port within this atomic function.

The OTUk_TT_So_RP (Remote Port) Interface

The OTUk_TT_So function will also accept data via the OTUk_TT_So_RP interface.  This interface consists of the following inputs.

  • RI_BEI – Remote Interface – Backward Error Indicator
  • RI_BIAE – Remote Interface – Backward Input Alignment Error Indicator
  • RI_BDI – Remote Interface – Backward Defect Indicator

The OTUk_TT_So function will operate in conjunction with a collocated Near-End OTUk_TT_Sk function and will perform the following operations on these signals.

  • BDI Insertion (into the OTUk-SMOH) – The OTUk_TT_So function will accept the BDI information from the Near-End Collocated OTUk_TT_Sk function, via the RI_BDI input and insert this data into the SM-BDI bit-field (within the SMOH) of the very next outbound OTUk frame.
  • BEI Insertion (into the OTUk-SMOH) – The OTUk_TT_So function will take the BEI information from the Near-End Collocated OTUk_TT_Sk function, via the RI_BEI input and insert this data into the SM-BEI/BIAE nibble-field (within SMOH) of the very next outbound OTUk frame.
  • BIAE Insertion (into the OTUk-SMOH) – The OTUk_TT_So function will accept the BIAE information from the Near-End Collocated OTUk_TT_Sk function, via the RI_BIAE input and (if appropriate) will insert this information into the SM-BEI/BIAE nibble-field (within the SMOH) of the very next outbound OTUk frame.

I show a drawing of our OTUk_TT_So function, that is electrically connected to its collocated, Near-End OTUk_TT_Sk function, via the Remote Port, below in Figure 5.

OTUk_TT_So Atomic Function connected to its Collocated OTUk_TT_Sk function

Figure 5, Illustration of our OTUk_TT_So Function, along with its collocated, Near-End OTUk_TT_Sk function

We discuss the operations through the RP Interface in another post.

Next, let’s move on and discuss the Management Port of this atomic function.

The OTUk_TT_So_MP (Management Port) Interface

Finally, the OTUk_TT_So function accepts data from the OTUk_TT_So_MP Interface.  This particular interface consists of the following input pin.

  • MI_TxTI – Trail Trace Identifier Input

The function-user is expected to load the contents of the outbound Trail Trace Identifier Message (64 bytes) to this input port.

The OTUk_TT_So function will then take this message data, and it will proceed to use the TTI byte-field within the OTUk-SMOH to transmit the contents of this message, one byte at a time, to the OTUk_TT_Sk function within the remote Network Element, via the OTUk data-stream.  Since the TTI Message is 64-bytes longs, the OTUk_TT_So function will require 64 OTUk frames for it to transmit the complete TTI Message.

We will discuss these processes in greater detail in the Trail Trace Identifier post.

How the OTUk_TT_So function sources each of the various Overhead Fields within the SMOH

As we mentioned earlier, the main responsibility of the OTUk_TT_So function is to compute/source the correct values for multiple fields within the SMOH and insert those values into the SMOH within each outbound OTUk frame.

Table 1 presents a list of Overhead-fields that the OTUk_TT_So function computes and sources.  This table also shows where this function gets its data for these Overhead fields.

Table 1, A List of the SMOH Overhead-fields that the OTUk_TT_So function computes/sources and how/where this function gets/derives this data

Overhead FieldLocation within OTUk-SMOHSource of Data/How Derived?
BIP-8 ByteBIP-8 Byte within the Section Monitoring FieldThe OTUk_TT_So function locally computes the BIP-8 value based upon the contents within the OPUk portion of the OTUk frame.
IAE Bit-FieldThe IAE Bit-field within the Section Monitoring ByteBased upon the AI_IAE input to the function (at the OTUk_AP Interface)
BDI Bit-FieldThe BDI bit-field within the Section Monitoring byteBased upon the RI_BDI input to this function (at the Remote Port Interface).
BEI Nibble-FieldThe BEI/BIAE Nibble-field within the Section Monitoring ByteBased upon the RI_BEI and RI_BIAE inputs to this function (at the Remote Port Interface).
BIAE Nibble-FieldThe BEI/BIAE bit-fields within the Section Monitoring byte.Based upon the RI_BIAE and RI_BEI inputs to this function (at the Remote Port Interface).
TTI Byte-FieldTTI Byte within the Section Monitoring Field.The user is expected to load in the contents of the 64-byte Trace Identifier Message (TIM) into a buffer via the MI_TxTI input to this function.

The function will proceed to transmit the contents of this TIM, one byte at a time, via the TTI byte-field within each outbound OTUk Frame.

The OTUk_TT_So function will transport the entire TIM over 64 consecutive OTUk frames.

List of Input and Output Signals for the OTUk_TT_So Atomic Function

Table 2 presents a Pin Description for each of the Input/Output signals of the OTUk_TT_So Atomic Function.

Table 2, Input/Output Pin Description of the OTUk_TT_So Atomic Function

Signal NameTypeDescription
OTUk_AP Interface
AI_DInputOTUk Adapted Interface - OTUk Data Input:
The function user is expected to apply a bare-bones OTUk signal (which is output from the AI_D output of the OTUk/ODUk_A_So function) to this input pin.

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 field. This function will compute, generate and insert the appropriate OTUk-SMOH into this OTUk data-stream

The OTUk_TT_So function will sample this input signal on one of the edges of the AI_CK input clock signal.
AI_CKInputOTUk Adapted Interface - Clock Input:
The OTUk_TT_So function will sample all data and signals (that the user applies to the OTUk_AP Interface) upon one of the edges of this input clock signal. This statement applies to the following signals: AI_D, AI_FS, AI_MFS and AI_IAE.

This clock signal will also function as the timing source for this function as well.
AI_FSInputOTUk Adapted Information - Frame Start Input:
The upstream OTUk/ODUk_A_So function should pulse this input signal HIGH whenever the OTUk_AP Interface accepts the very first bit (or byte) of a new OTUk frame, via the AI_D inputs.

The upstream OTUk/ODUk_A_So function should drive this input HIGH once for each OTUk frame.
AI_MFSInputOTUk Adapted Information - Multiframe Start Output:
The upstream OTUk/ODUk_A_So function should pulse this input signal HIGH whenever the OTUk_AP interface accepts the very first bit (or byte) of a new OTUk superframe, via the AI_D input.

The upstream OTUk/ODUk_A_So function should drive this input HIGH once for each OTUk superframe.
AI_IAEInputOTUk Adapted Information - Input Alignment Error Input:
the OTUk/ODUk_A_So function (upstream from this function) will drive this input pin HIGH whenever it detects a frame-slip (or IAE event).

Anytime the OTUk_TT_So function detects this input pin, going from LOW to HIGH, then it should respond by setting the IAE bit-field to "1" for 16 consecutive Superframes (or 4096 consecutive OTUk frames).

Please see the blog on IAE for more information on this feature.
OTUk_CP Interface
CI_DOutputOTUk Characteristic Information - OTUk Data Output:
The OTUk_TT_So function will compute, generate and insert the SMOH (Section Monitoring Overhead) into the outbound OTUk data-stream. It will then output this OTUk data-stream via this output signal.

NOTE: This OTUk data will contain the following fields.
- The newly computed, inserted BIP-8 value
- The newly received and inserted BEI-nibble value or BIAE indicator.
- The newly received and inserted BDI bit-value.
- the newly received and inserted IAE value.
- 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 field.

The OTUk_TT_So function will update this output signal on one of the edges of the CI_CK output clock signal.
CI_CKOutputOTUk Adapted Information - Clock Output:
The OTUk_TT_So function will output all data and signals (via the OTUk_CP interface) upon one of the edges of this output clock signal. This statement applies to the following signals: CI_D, CI_FS and CI_MFS.
CI_FSOutputOTUk Characteristic Information - Frame Start Output:
This function will drive this output pin HIGH whenever the OTUk_CP interface outputs the very first bit (or byte) of a new OTUk frame, via the CI_D output.

The OTUk_TT_So function should only pulse this output pin HIGH once for each outbound OTUk frame.
CI_MFSOutputOTUk Characteristic Information - Multiframe Start Output:
This function will drive this output pin HIGH whenever the OTUk _CP Interface outputs the very first bit (or byte) of a new OTUk Superframe via the CI_D.

The OTUk_TT_So function will drive this output pin HIGH once for each OTUk Superframe.
OTUk_TT_So_RP Interface
REI_BEIInputRemote Port Interface - BEI (Backward Error Indicator) Input:
The OTUk_TT_So function will accept one nibble of data (for each outbound OTUk frame) via this input signal and it will insert this data into the BEI/BIAE nibble-field within the Section Monitor field within each outbound OTUk frame.

The BEI value will reflect the number of BIP-8 errors that the collocated OTUk_TT_Sk function has detected and flagged within its most recently recevied and verified OTUk frame.

NOTE: If the OTUk_TT_So function receives a BIAE = 1 (via the RI_BIAE input) then it will overwrite the BEI/BIAE nibble-field with the value "1011" to denote a BIAE event.

Please see the BEI post for more information about Backward Error Indication.
RI_BIAEInputRemote Port Interface - BIAE (Backward Input Alignment Error) Input:
The OTUk_TT_So function will accept one bit of data (for each outbound OTUk frame) via this input signal and it will do either of the following, depending on the value of this single bit-field.

If BIAE = 0
Then the OTUk_TT_So function will write the BEI value that it has received via the RI_BEI input, into the BEI nibble-field within the Section Monitor byte of the next outbound OTUk frame.

If BIAE = 1
Then the OTUk_TT_So function will not write the BEI value (that it has received from the collocated OTUk_TT_Sk function). It will instead, write the value "1011" into the BEI/BIAE nibble-field, within the Section Monitor byte of the next outbound OTUk frame.
RI_BDIInputRemote Port Interface - Backward Defect Indicator Input:
The OTUk_TT_So function will accept one bit of data (for each outbound OTUk frame) via this input pin and it will write the contents of this value into the RDI bit-field (within the Section Monitor byte) of the next outbound OTUk frame.

If RI_BDI = 0
The the OTUk_TT_So function will set the BDI bit-field to "0" within the next outbound OTUk frame.

If RI_BDI = 1
Then the OTUk_TT_So function will set the BDI-bit-field to "1" within the next outbound OTUk frame.
OTUk_TT_So_MP Interface
MI_TxTIInputManagement Interface - Trail Trace Identifier Input:
The function user is expected to load in the 64-byte TTI Message into the OTUk_TT_So circuitry via this input. The OTUk_TT_So function will then transmit the message to the remote Network Element, one byte-at-a-time, over 64 consecutive outbound OTUk frames.

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

More specifically, this function will:

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

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

OTUk/ODUk_A_Sk Function - Adaptation Atomic Function

Figure 1, Simple Illustration of the OTUk/ODUk_A_Sk Function

As the OTUk/ODUk_A_Sk function converts an OTUk signal into an ODUk signal, it will terminate, process, and remove the OTUk-SMOH from this incoming OTUk data-stream.  It will also extract out 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 monitoring of 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) as well.

Functional Block Diagram

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

OTUk/ODUk_A_Sk Atomic Functional Block Diagram

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

This figure shows that 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 then 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 out 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 then 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.

  • That the function will NOT declare the SSF (Server Signal Failure) condition if the user has configured 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, then it will indicate so by asserting the CI_SSF output pin towards downstream circuitry.

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

aAIS <- AI_TSF and (NOT MI_AdminState = LOCKED)

This equation means two things.

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

This equation also means that if 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.

  • That this function will not declare the SSD (Server Signal Degrade) condition if the user has configured 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, then 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) are dependent upon the state of the AI_TSF and MI_AdminState Inputs, as we show in Table 1 below.

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

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

Defect Correlations

None for this function.

Performance Monitoring

None

Pin Description

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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What is 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 next 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, then 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 considerable 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.

OTUk/ODUk_A_So Simple Block Diagram - ITU-T G.798 Symbol

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 be inserting 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.

OTUk/ODUk_A_So Functional Block Diagram

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 down-stream 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 (that we’ve 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 then 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 internally generate the ODUk-LCK maintenance signal upon command.

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 traffic that is carrying user/client data will be replaced with the ODUk-LCK maintenance signal.

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 have access to 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 either enable or disable the APS Channel and to configure this particular function to operate at a specific APS Level, through both the MI_APS_En andMI_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 is signaling 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 some additional 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, that I will call a partial OTUk data-stream

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

It will just include the ODUk-portion of the OTUk frame, along with 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 of the 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 NameTypeDescription
ODUk_CP Interface
CI_DInputODUk 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_CKInputODUk 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_FSInputODUk 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_MFSInputODUk 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_APSInputODUk 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_DOutputOTUk 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_CKOutputOTUk 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_FSOutputOTUk 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_MFSOutputOTUk 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_IAEOutputOTUk 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_AdminStateInputManagement 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_EnInputManagement 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_LVLInputManagement 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 Full-Duplex Communication?

This post briefly defines Full-Duplex Communication. It also highlights differences between Full-Duplex and Half-Duplex Communication.


What is Full-Duplex Communication?

We define Full-Duplex Communication as communication occurring in both directions, simultaneously.

Some Communications Literature will use the abbreviation FDX to denote Full-Duplex Communication.

A couple of examples of Full-Duplex Communications would be Cellular Phones and much of modern internet-based communication services (e.g., Video Communication via Skype, Face-Time, etc.).

Two women demonstrating Full-Duplex communications via cell phones.
Isolated portrait of two teenage girls with cell phones

In all of these technologies, we have bandwidth (or a communications channel) available in both directions.

Unlike for Half-Duplex Communication, there is no means (or need) to control access to a single communications channel.

Each direction has their own communications channel and can communicate freely, at will, or whenever data is available.

An Analogy for Full-Duplex Communications

We can think of Full-Duplex Communications as being just like a two-way street, on the roadways.

A Freeway is a good analogy to Full-Duplex Communications

Most modern forms of communication that we use today (e.g., cell phones or tablets engaging in video conferencing, or just communicating with websites – for gaming, social media, etc.) all use Full-Duplex Communications.

In the old-days, Ethernet started out using Half-Duplex communications (for 10BASE-T, etc.)  However, once Ethernet moved on to faster speeds and started to use switching technology, then it started supporting Full-Duplex communications as well.

Other forms of Communication types include:

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What is Half-Duplex Communication?

This post briefly defines the term: Half-Duplex Communication.


What is Half-Duplex Communication?

We define Half-Duplex Communication as communication occurring in both directions, but in only one direction at a time.

Some Communications Literature will use the abbreviation HDX to denote Half-Duplex Communication.

A couple of examples of Half-Duplex Communications systems would be Speakerphones or Walkie Talkies.

A speakerphone is an example of Half-Duplex Communication

In both of these examples, legible communication can only flow if only one side is talking, and the other direction (or side) is silent.

Controlling the Communication

In Half-Duplex Communication systems, there must be some control (or protocol) that decides which side (or direction) gets to transmit their information or data at a given time.

In the case of speakerphones or walkie-talkies, there needs to be some sort of agreement (or understanding) among human beings (on both ends of the connection) on who gets to speak and when.

For electronic or automatic half-duplex systems, electronic circuitry controls which side gets to communicate or use the “channel”, when and for how long.

We will typically use Half-Duplex Communication to:

  • Support bi-directional communication, and
  • Conserve bandwidth (both directions use the same channel or bandwidth).

What are Differences between Simplex and Half-Duplex Communication?

Half-Duplex communication is similar to Simplex Communication in that communication can only occur in one direction, at a time.

However, Half-Duplex communication is different from Simplex Communication, in that it does support communication in the other direction as well.

It just doesn’t support bi-directional communication simultaneously.  That would be Full-Duplex Communication.

Another Example?

A good analogy for Half-Duplex Communication would be with a road construction scenario.  Consider the case where there is only one lane available to two-way traffic (over a bridge – for example).

Road Construction is an example of Half-Duplex Communication

In this case, traffic controller personnel (with signs) would be deciding and controlling which direction gets to use the available lane.  In the meantime, traffic in the other direction has to wait until they get the “go ahead” from the traffic controllers.

Other forms of Communication types include:

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What is Simplex Communication?

This post briefly defines the term: Simplex Communication.


What is Simplex Communication?

We define simplex communication as communication that only operates in one direction.

Simplex is One Way or One Direction Communication

A couple of obvious examples of Simplex Communication would be Radio or Television Broadcasting.

Satellite Dish receives One-Way Communication (or Broadcasts) from Radio/TV Stations
Satellite dish on the modern building roof corner with blue sky in the background.

Unless you count being able to place a phone call to your Radio or TV Station, you don’t usually have the ability to send traffic back to the Radio or TV Station transmitter.

ITU (International Telecommunication Union) does define Simplex Communication as a communication channel that operates in one direction at a time, but that may be reversible (communication can occur in the opposite direction).

I would argue that ITU’s definition is that for Half-Duplex Communication.

Other basic terms for communications includes:

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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 ever read through many of the ITU standards, particularly those documents that discuss the declaration and clearance of defect conditions, then 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 all of this, I will dedicate numerous blog postings to explaining and defining 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 also specify a functional architecture and behavior each of these functions.

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 actual 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 any chips that have the same I/O (for Traffic Data, System Management, etc.).

However, if you were to design and build networking equipment that handles OTN traffic, then you are required to perform the functions that ITU has 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 functionality that ITU has defined for those functional blocks.

Therefore, it is crucial that you understand the following:

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

If you understand both of these items, then 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 are reading about atomic functions (in ITU-T G.798), then 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

Another Way to Identify an Adaptation Function?

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

OTUk/ODUk_A_Sk Function - Adaptation Atomic Function

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

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

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Trail-Termination Functions

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

Whenever you are reading about atomic functions (in ITU-T G.798), then 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 make it possible for us to declare/clear defects and to flag/count bit-errors.

I’ve listed some of the Atomic Trail-Termination Functions, that we will be discussing with 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?

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

OTUk_TT_Sk Function - Trail Trace Atomic Function

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

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

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What is Ring Switching?

This post briefly describes and defined Ring-Switching within a Shared-Ring Protection-Switching system.


What is Ring-Switching within a Shared-Ring Protection-Switching System?

COMMENT:  Throughout this post, I will be using the terms, Ring-Switching and Ring Protection-Switching interchangeably.

A Shared-Ring Protection-Switching system, whether it is a 2-Fibre/2-Lambda or a 4-Fibre/4-Lambda system, will support Ring Switching.

NOTE:  A 4-Fibre/4-Lambda Shared-Ring Protection-Switching system will also support Span Switching.  However, the 2-Fibre/2-Lambda Protection-Switching System does not support Span-Switching.

Ring-Switching is a Protection-Switching scheme that involves the entire Ring.

Example of Ring-Switching

Just like what I said in the Span-Switching post, the best way to describe Ring-Switching is to show an example of how it works.

Let’s suppose that we are using a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system.  I present an illustration of a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system below in Figure 1.

4-Fibre/4-Lambda Shared-Ring Protection-Switching System

Figure 1, Illustration of a 4-Fibre/4-Lambda Shared-Ring Protection-Switching

This 4-Fibre/4-Lambda Shared-Ring Protection-Switching system consists of a total of four optical rings (or loops).

  • One Optical Loop is a Working Transport entity, in which the data flows in the Clockwise direction.  (e.g., the Blue-Shaded Loop, that I’ve labeled W(a)).
  • Another Optical Loop is a Protection Transport entity, in which the data also flows in the Clockwise Direction (e.g., the Pink-Shaded Loop, that I’ve labeled P(b)).
  • A 3rd Optical Loop is a Protection Transport entity, in which the data is flowing in the Counter-Clockwise Direction. (e.g., the Pink-Shaded Loop, that I’ve labeled P(a)).
  • And finally, the fourth Optical Loop is a Working Transport entity, in which the data is also flowing in the Counter-Clockwise Direction (e.g., the Blue-Shaded Loop, that I’ve labeled W(b)).

Now that we’ve introduced our 4-Fibre/4-Lambda Shared-Ring Protection-Switching system let’s move on to Ring Protection-Switching.

Defects in the Fiber

Let’s assume that we are experiencing service-affecting defects within both of the Clockwise-Direction fibers (Working and Protection), between Nodes B and C, as I show below in Figure 2.

Defects in Both Working and Protection Transport Entity - Ring Protection Switching

Figure 2, Illustration of Service-Affecting Defects within both the Working and Protection Transport fibers, that were carrying data from Node B to Node C

Whenever this event occurs, then Node C will declare the SF defect for both the Working Transport entity (SF-W) and the Protection Transport entity (SF-P).  Anytime the Tail-End circuitry (within Node C) declares both the SF-W and the SF-P defect simultaneously, then it will also declare the SF-R (Signal Fail-Ring) defect.

Whenever Node C declares the SF-R condition, then it will respond to this event by issuing a Ring-Switching request between it and Node B.

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Implementing Ring-Switching

Nodes B and C will exchange APS command information with each other, through a protocol (that we call the Shared-Ring Protection-Switching system APS/PCC protocol).

Since the defects (within this example) affect both the Working and Protection Transport entities (in the Span, going from Nodes B and C), then these nodes will have to communicate with each other via both Short- and Long-Paths.

If Nodes B and C only respond and perform Ring Protection-Switching, directly in response to the SF-R defect condition (that Node C has declared), then we get the Ring Protection-Switching results that we show below.

Ring-Switching in the Defect Direction

Figure 3, Illustration of Ring Protection-Switching Results (in the Defect Direction)

If you were to study Figure 3, you would see that Ring-Switching works by routing all of the traffic, such that the following is true.

  • That we are routing traffic away from the locations of the defects, and
  • We are still routing traffic through each of the nodes within the Ring.

However, we are not done yet.

ITU-T G.808.2 states that all protection-switching on a Shared-Ring Protection-Switching system must be bidirectional.   Therefore, we must also implement Ring Protection-Switching in the Opposite Direction as well.  I show this “Opposite-Direction” Ring Protection-Switching below in Figure 4.

Ring-Switching in the Opposite Direction - Opposite from Defect-Direction

Figure 4, Opposite-Direction Ring Protection-Switching

If I were to combine the Ring Protection-Switching Paths of both the Defect-Direction and the Opposite Direction, into a single figure; then I get the drawing that I present below in Figure 5.

Ring-Switching in Both Directions

Figure 5, Bidirectional Ring Protection-Switching

Can the User Implement Ring-Switching at other locations in the Shared-Ring Protection-Switching System?

In general, the answer is No.

In our example, Nodes B and C are using the Protection-Transport entity resources within much of the Shared-Ring Protection-Switching system.  This fact makes supporting an additional Ring-Switching path very difficult.

That being said, there might be strange scenarios that one can dream up that (temporarily) creates two separate ring protection loops.

Why can’t we use Span-Switching whenever we have defects in both the Working and Protection Transport entity, within a Span?

In the Span-Switching post, we considered a single defect that is occurring only in the Working-Transport entity (in the span, going from Node B to Node C).  As a consequence, Node C declared the SF-W (and, in-turn) the SF-S (Signal Fail – Span) condition.

In this case, we were able to use Span-Switching, because we still had a Protection-Transport entity fiber (that was transmitting data in the same direction as the broken Working Transport entity fiber).  Therefore, we were able to simply by-pass the single defect by using Span-Switching.

In this post, we have defects in both the Working and Transport entity fibers (in the span going from Node B and Node C).  Since we now have a defect within the Protection-Transport entity, that path (of by-passing the defect in the Working Transport entity) is not available to us, in this scenario.

Therefore, we have to use a different protection-switching approach.

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What is Span-Switching?

This post defines and describes the term: Span-Switching


What is Span-Switching within a Shared-Ring Protection-Switching System?

A 4-Fibre/4-Lambda Shared-Ring Protection-Switching system will support the two-types of Protection-Switching.

NOTE:  A 2-Fibre/2-Lambda Shared-Ring Protection-Switching system will NOT support Span-Switching.  It will only support Ring-Switching.

Span-Switching is a Protection-Switching scheme that only involves a single-Span.

Example of Span-Switching

The best way to describe Span-Switching is to show an example of how it works.

Let’s suppose that we are using a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system.  Additionally, in this case, I will be focusing on the Span between Nodes B and C.

Therefore, in Figure 1, I show an illustration of a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system with the span between Nodes B and C, highlighted.

Span between Nodes B and C

Figure 1, Illustration of a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system, with the span (between Nodes B and C) highlighted.

If you take a close look at the span between Nodes B and C, you will notice that this span contains the following four optical signals.

  • The Clockwise Optical Signal – Working Transport entity (the blue-shaded fiber – with the signal passing through it in the clockwise direction),
  • The Clockwise Optical Signal – Protection Transport entity (the pink-shaded fiber – with the signal moving through it in the clockwise direction),
  • The Counter-Clockwise Optical Signal – Working Transport entity (the blue-shaded fiber – with the signal passing through it in the counter-clockwise direction),
  • The Counter-Clockwise Optical Signal – Protection Transport entity (the pink shaded fiber – with the signal passing through it in the counter-clockwise direction).

Now that we’ve introduced our 4-Fibre/4-Lambda Shared-Ring Protection-Switching system let’s see some protection-switching.

A Defect in the Fiber

Let’s further assume that we are experiencing a service-affecting defect within the Clockwise-Direction Working Transport entity fiber, as I show below in Figure 2.

SF-S Defect in Span between Nodes B and C - Span Switching

Figure 2, Illustration of a Service-Affecting Defect within the Clockwise Direction Working Transport entity fiber (between Nodes B and C)

Whenever this particular service-affecting defect occurs (within the Span between Nodes B and C), then Node C will declare the SF-S (Signal Fail – Span) defect condition.  Node C will then respond to this SF-S defect condition by issuing a Span-Switching request between it and Node B.

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Implementing Span-Switching

Nodes B and C will exchange information with each other via a communications protocol (that we called the Shared-Ring Protection-Switching system APS/PCC protocol).

After Nodes B and C have completed this exchange of information (via the APS/PCC protocol), each of these nodes will have executed some protection-switching, such that both Nodes will now be exchanging regular ODUk traffic via the Protection Transport entities (in both directions), rather than using the Defective Working Transport entity (in the Clockwise Direction).

I show the results of this Protection-Switching effort, below in Figure 3.

Span-Switching between Nodes B and C

Figure 3, Illustration of Span-Switching, between Nodes B and C

Span-Switching works (in this scenario) because we can use the Protection-Transport entity fiber.  This Protection Transport entity fiber carries traffic in the same direction as does the broken Working Transport entity (within the Span, going from Nodes B to C).

Therefore, we can use it to bypass the defect within the Working Transport entity fiber.

NOTE:  All Shared-Ring Protection-Switching will use a 1:1 Protection-Switching Architecture.

Why is this Span-Switching Bidirectional?

Question:

Our 4-Fibre/4-Lambda Shared-Ring Protection-Switching system experienced a single Service-Affecting Defect (within the Working Transport entity of the Clockwise Optical Loop).

Why did we perform Span-Switching in both directions (even for the Counter-Clockwise Optical Loops)?

Answer:

ITU-T G.808.2 states that all Shared-Ring Protection-Switching MUST be Bidirectional.

Therefore, if we are required to perform protection-switching in one direction (to avert a defect condition), we must also complete a similar protection-switch in the opposite direction – to make it bidirectional.

Can the User Implement Span-Switching at other locations in the Shared-Ring Protection-Switching System?

In a word, Yes.

In our example, Nodes B and C are only using the Protection-Transport entity resources between these two nodes.  We are not taken up any other Protection-Transport entity resources along any of the remaining spans within the ring.

Therefore, the user can have multiple instances of Span-Switching within a Single Ring.

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