What is the Multiplex Structure Identifier

This post briefly defines the term Multiplex Structure Identifier (MSI) for OTN Applications.


What is the Multiplex Structure Identifier (MSI) within the PSI Message?

The purpose of this post is to define the term:  Multiplex Structure Identifier.

Introduction

In another post, we spoke about the PSI (Payload Structure Identifier) Message.

That post states a few things that are of interest to this post.

  • The PSI Message is a 256-byte Message that a given Source PTE will repeatedly transmit to the Sink PTE.
  • The Source PTE will repeatedly transmit this PSI Message via the PSI byte (within each ODUk/OPUk frame).
  • The purpose of this PSI Message is to permit the Source PTE to inform the Sink PTE of the type of traffic that this particular ODUk/OPUk server signal is transporting.
  • The first byte (Byte 0 – within the PSI Message) will be the PT (or Payload Type) byte.
  • This means that there are still 255 other bytes that are available to transport information within each PSI Message.
    • The PSI post also states that there are two different types of PSI Messages.
    • The Non-Multiplexed Traffic Type of PSI Message, and
    • The Multiplexed Traffic Type of PSI Message.  

If we’re discussing the MSI (Multiplex Structure Identifier), which involves OPU/ODU server signals that are transporting numerous lower-speed ODUj tributary signals, then we will be dealing with the Multiplexed Traffic Type of PSI Message.  

I show an illustration of the PSI byte-field (within an OPU frame) and a blow-up of the  Multiplexed-Traffic Type of PSI Message below in Figure 1.

OPU Frame with PSI Byte-Field Highlighted and a Breakout of the Multiplexed Structure PSI Message

Figure 1, Illustration of the PSI byte-field and a Multiplexed-Traffic Type of PSI Message

Please note that the PSI Message, within Figure 1, does not contain a CSF (Client Signal Fail) bit-field.  Hence, you should be able to identify this PSI Message as being the Multiplexed Traffic type of PSI Message.  

A Multiplex Structure ODUk

If the Source PTE (that is transmitting an ODUk signal to the remote Sink PTE) has set the PT byte value (within each PSI Message) to either 0x20 or 0x21, then this means that this ODUk signal is a Multiplex Structure ODUk signal.

If a given ODUk signal is a Multiplex Structure ODUk signal, then this means that it is transporting at least one lower-speed ODUj tributary signal within its payload (where k > j).

NOTE:  We will talk about PT = 0x22 and ODUCn signals in another post.

In this case, the Source PTE (or upstream circuitry) has mapped and multiplexed some number of lower-speed ODUj tributary signals into this particular higher-speed ODUk server signal.

For the OTN to work correctly, the Source PTE needs to send sufficient information to Sink PTE, about the type of traffic/data that a given ODUk signal is carrying.

Hence the purpose of the PSI Message.

The Sink PTE needs more information than the PT byte value

So if the Source PTE sets the PT Byte value (within each outbound PSI Message) to 0x20 or 0x21, then it is telling the remote Sink PTE that this ODUk signal is a Multiplex Structure signal that is transporting some number of Lower-Speed ODUj tributary signals.

However, the Sink PTE needs more information for it to be able to identify and handle this ODUk data-stream accurately.

In particular, the Sink PTE needs to “know” how many, and what type of lower-speed ODUj tributary signals that this ODUk/OPUk server signal is transporting.  

We can think of the remaining bytes (within the PSI Message, following the PSI byte) as being a passenger manifest for each of the Lower-Speed ODUj Tributary signals that we are transporting within this OPUk/ODUk server.  

Depending upon the PT value and the type of OPUk/ODUk server signal, that we are working with, the number of MSI bytes (within the PSI Messages for that particular server signal) will vary, as I show below.

For PT = 0x20

  • If we’re working with an OPU1/ODU1 server signal, then the MSI will consist of 2 bytes.
  • If we’re working with an OPU2/ODU2 server signal, then the MSI will consist of 4 bytes.
  • An OPU3/ODU3 server signal will use 16 bytes for its MSI.  

For PT = 0x21

  • If we’re working an OPU2/ODU2 server signal, then the MSI will consist of 8 bytes.
  • An OPU3/ODU3 server signal will use 32 bytes for its MSI, and
  • An OPU4/ODU4 server signal will use 80 bytes for its MSI.  

Let’s Take a Look at an ODU4/OPU4 Signal

For example, if we are dealing with an ODU4 signal, and if the PT byte is set to 0x21, then the PSI Message (that this ODU4/OPU4 signal transports) would have the format that we show below in Figure 2.

Multiplex Structure Identifier for 80 ODU0 Signals within an OPU4 Signal

Figure 2, Illustration of the PSI Message for an ODU4/OPU4 that is transporting 80 ODU0 signals

Figure 2 shows the PSI Message that a Source PTE would carry (within an ODU4 signal) if that ODU4 signal were transporting 80 ODU0 signals (that it has mapped and multiplexed into this ODU4).

Please note that ODU4/OPU4 signals can transport other types of multiplexed traffic.  For example, it can carry any of the following types of multiplexed traffic.

  • 80 ODU0 signals.
  • 40 ODU1 signals
  • 10 ODU2 or ODU2e signals
  • 2 ODU3 signal
  • Some number of ODUflex signals (provided that the total bandwidth of all of these signals does not exceed 80 time-slots or the OPU4 payload carrying capacity of 104.35597533 Gbps).
  • Various combinations of each of the above signals (again, provided that the total bandwidth of all of these signals does not exceed 80 time-slots

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How to Read/Decipher these Multiplex Structure Identifier fields

Figure 2 shows that each PSI Message (starting at Byte 2) for an OPU4/ODU4 server signal, has 80 consecutive bytes of data. 

These 80 bytes (of data) are the Multiplex Structure Identifier (MSI) for this OPU4/ODU4 serval signal.  In this case, each byte of data (within the MSI) represents a bandwidth of approximately 1.25Gbps.

If we’re working with an OPU4/ODU4 server signal, then:

80 bytes x 1.25Gbps = 100Gbps.

And that makes sense because 100Gbps is the approximate bandwidth of an OPU4/ODU4 signal.  

The MSI will alert the Sink PTE of the type of Lower-Speed ODUj Tributary Signals we are transporting within this OPU4/ODU4 server signal. 

Is the Time-Slot Allocated?

The first bit-field (within each MSI byte) will indicate whether this 1.25Gbps time-slot (within this OPU4/ODU4 server signal) has been allocated or not-allocated, as I show below in Figure 3.  

If this bit-field is set to “1”, then that particular time-slot (or bandwidth) within the OPU4/ODU4 signal is allocated.  

Conversely, if this bit-field is set to “0”, then this particular time-slot (or bandwidth) within the OPU4/ODU4 server signal is NOT allocated (or not being used to transport a lower-speed ODUj tributary signal).  

NOTE:  In the PT = 0x21 post, we mention that each time-slot (for PT = 0x21 applications) represents approximately 1.25Gbps of bandwidth.

I have also included Figure 3, which will help you better understand these Multiplex Structure Identifier fields.

Mutliplex Structure Identifier Definition for OPU4 Applications

Figure 3, Multiplex Structure Identifier – Bit Definitions for ODU4/OPU4 Applications.  

The Port ID Number

The remaining 7-bits, within each MSI byte, are the Tributary Port Number (or Port ID Number.  

The Port ID Number identifies which lower-speed ODUj Tributary signal that we are transporting within this OPU4/ODU4 server signal.  

Now, since each byte (within the MSI) represents a bandwidth of 1.25Gbps, then the number of times that we see a particular Port ID Number, appearing within our 80 bytes of MSI, indicates the bandwidth (and in-turn) the type ODUj Tributary signal that we are working with.

For example, if we only see that Port ID Number = 0x00, only appears once within this set of 80 bytes, then we know that this particular ODUj Tributary signal (that corresponds with Port ID Number = 0x00) has a bandwidth of:

1 byte x 1.25Gbps = 1.25Gbps

And is most likely an ODU0 signal.  

In the case, where we see that Port ID Number = 0x00, appears twice, within this set of 80 bytes, then we know that this particular ODUj Tributary signal has a bandwidth of:

2 bytes x 1.25Gbps = 2.50Gbps

And is most likely an ODU1 signal.  

And so on.  

Up in Figure 2, I show that the MSI for this OPU4/ODU4 server signal consists of 80 bytes, in which the Port ID Numbers range from 0x00, all the way to 0x4F (or 79 in decimal format). 

This means that each of the 80 MSI bytes contains a unique Port ID value.  In other words, no two MSI bytes contain the same Port ID value.  

This set of MSI bytes indicates that this OPU4/ODU4 server signal is transporting 80 ODU0 tributary signals or 80 sets of signals with a bandwidth of 1.25Gbps.  

Other Examples of Multiplex Structure Identifiers

  • PT = 0x21 Applications
    • ODU2/OPU2 Server Applications
    • ODU3/OPU3 Server Applications
    • ODU4/OPU4 Server Applications
  • PT = 0x20 Applications
    • ODU1/OPU1 Server Applications
    • ODU2/OPU2 Server Applications
    • ODU3/OPU3 Server Applications

NOTE: We cover Multiplexed Traffic and their resulting MSIs extensively within Lesson 5 of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!

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What is PT = 0x21 for OTN Applications?

This post discusses and describes the PT = 21 Method for Mapping and Multiplexing Lower-Speed ODUj signals into a Higher-Speed ODUk Signal.


What is PT (Payload Type) = 0x21 for OTN Applications, and what does it Mean?

Whenever we are mapping/multiplexing lower-speed ODUj signals into a higher-speed ODUk signal, for up to the ODU3 rate, we have the following two options:

  • Use the PT = 20 (or 0x20) Method for Mapping/Multiplexing the ODUj signals into the ODUk, or
  • Use the PT = 21 (or 0x21) Method for Mapping/Multiplexing the ODUj signals into the ODUk.

If you wish to map/multiplex some lower-speed ODUj signals into an ODU4 signal, then you MUST use the PT  = 21 (ox21) approach.

NOTE:  We discuss the PT = 21 Approach (for mapping/multiplexing) some lower-speed ODUj tributary signals into an ODU4 in Lesson 5/ODU4 within THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

What is the PT = 21 Method?

Whenever we are using the PT = 21 Method, this means that we will be setting the PT byte (within the PSI Message) to the value 0x21, within this OPUk/ODUk signal.

The PT = 21 Method, for Mapping/Multiplexing of ODUj signals into an ODUk signal has the following characteristics.

  • We do Mapping/Multiplexing with 1.25Gbps time-slots (instead of the 2.5Gbps time-slots for PT = 20).
  • In most cases, we are using GMP to map the ODUj signal into the ODTUk.ts or ODTUjk structures.
  • However, we do use AMP as the mapping procedure in some cases.

Is the PT = 21 Method better than PT = 20 Method?

The PT = 21 Method is the newer standard and is (therefore) the preferred approach.

For example, for 2-Fibre/2-Lambda Shared-Ring Protection-Switching applications, ITU-T G.873.2 strongly recommends that the System Designer use the PT = 21 method for combining the Working and Protection time-slots into a single ODUk signal.

Please see the 2-Fibre/2-Lambda Shared-Ring Protection-Switching post for more information on this topic.

What Mapping/Multiplexing Schemes can one use for the PT = 21 Method for Mapping/Multiplexing ODUj Signals into an ODUk Signal?

I summarize the Mapping/Multiplexing scheme information for each of the PT = 21 Cases (for Mapping/Multiplexing Numerous Lower-Speed ODUj signals into a Higher-Speed ODUk signal) in Table 1 below.

Table 1, Summary of Schemes for Mapping/Multiplexing Multiple Lower-Speed ODUj Signals into a Higher-Speed ODUk Signal, PT = 0x21

ODUj SignalMapping StructureMapping MethodNumber of ODUj SignalsIntermediate StructureODUk/OPUk Signal
ODU0ODTU2.1GMP8ODTUG2ODU2/OPU2
ODUflexODTU2.tsGMP1 to 8ODTUG2ODU2/OPU2
ODU1ODTU12AMP4ODTUG2ODU2/OPU2
ODU0ODTU3.1GMP32ODTUG3ODU3/OPU3
ODUflexODTU3.tsGMP1 to 32ODTUG3ODU3/OPU3
ODU1ODTU13AMP16ODTUG3ODU3/OPU3
ODU2ODTU23AMP4ODTUG3ODU3/OPU3
ODU2eODTU3.9GMP3ODTUG3ODU3/OPU3
ODU0ODTU4.1GMP80ODTUG4ODU4/OPU4
ODUflexODTU4.tsGMP1 to 80ODTUG4ODU4/OPU4
ODU1ODTU4.2GMP40ODTUG4ODU4/OPU4
ODU2ODTU4.8GMP10ODTUG4ODU4/OPU4
ODU2eODTU4.8GMP10ODTUG4ODU4/OPU4
ODU3ODTU4.31GMP2ODTUG4ODU4/OPU4

I have also drawn out these cases below as well.

  • ODU0 ⇒ ODTU2.1 ⇒ ×8 ⇒ ODTUG2 ⇒ OPU2 ⇒ ODU2

This scheme will map/multiplex as many as 8 ODU0 signals into an ODU2 signal.

ODU0 to ODU2 - Using PT = 21 Method

Figure 1, Simple Illustration of the ODU0 -> ODU2 Multiplexing/Mapping scheme

Click on the figure above to learn more about this Mapping/Multiplexing scheme. (COMING SOON).

  • ODU1 ⇒ ODTU12 ⇒ ×4 ⇒ ODTUG2 ⇒ OPU2 ⇒ ODU2

This scheme will allow one to map/multiplex as many as 4 ODU1 signals into an ODU2 signal.

ODUflex to ODU4 - Using PT = 21 Method

Figure 2, Simple Illustration of the ODU1 -> ODU2 Multiplexing/Mapping scheme

Click on the figure above to learn more about this Mapping/Multiplexing scheme. (COMING SOON).

  • ODUflex ⇒ ODTU2.ts ⇒ ×8/ts ⇒ ODTU2G ⇒ OPU2 ⇒ ODU2

This scheme will allow one to map/multiplex anywhere from 1 to 8 ODUflex signals into an ODU2 signal.

ODUflex to ODU2 - Using PT = 21 Method

Figure 3, Simple Illustration of the ODUflex ⇒ ODU2 Multiplexing/Mapping scheme.

Click on the figure above to learn more about this Mapping/Multiplexing scheme. (COMING SOON).

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  • ODU0 ⇒ ODTU3.1 ⇒ ×32 ⇒ ODTUG3 ⇒ OPU3 ⇒ ODU3

This scheme will allow one to map/multiplex as many as 32 ODU0 signals into an ODU3 signal.

ODU0 to ODU3 - Using PT = 21 Method

Figure 4, Simple Illustration of the ODU0 ⇒ ODU3 Mapping/Multiplexing scheme

Click on the figure above to learn more about this Mapping/Multiplexing scheme. (COMING SOON).

  • ODU1 ⇒ ODTU13 ⇒ ×16 ⇒ ODTUG3 ⇒ OPU3 ⇒ ODU3

This scheme will allow one to map/multiplex as many as 16 ODU1 signals into an ODU3 signal.

ODU1 to ODU3 - Using PT = 21 Method

Figure 5, Simple Illustration of the ODU1 ⇒ ODU3 Mapping/Multiplexing scheme.

Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (COMING SOON).

  • ODU2 ⇒ ODTU23 ⇒ ×4 ⇒ ODTUG3 ⇒ OPU3 ⇒ ODU3

This scheme will allow one to map/multiplex as many as 4 ODU2 signals into an ODU3 signal.

ODU2 to ODU3 - Using PT = 21 Method

Figure 6, Simple Illustration of the ODU2 ⇒ ODU3 Mapping/Multiplexing scheme.

Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (COMING SOON).

  • ODU2e ⇒ ODTU3.9 ⇒ ×3 ⇒ ODTUG3 ⇒ OPU3 ⇒ ODU3

This scheme will allow one to map/multiplex as many as 3 ODU2e signals into an ODU3 signal.

ODU2e to ODU3 - Using PT = 21 Method

Figure 7, Simple Illustration of the ODU2e ⇒ ODU3 Mapping/Multiplexing scheme. 

Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (COMING SOON).

  • ODUflex ⇒ ODTU3.ts ⇒ ×32/ts ⇒ ODTUG3 ⇒ OPU3 ⇒ ODU3

This scheme will allow one to map/multiplex anywhere from 1 to 32 ODUflex signals into an ODU3 signal.

ODUflex to ODU3 - Using PT = 21 Method

Figure 8, Simple Illustration of the ODUflex ⇒ ODU3 Mapping/Multiplexing scheme.  

Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (COMING SOON).

  • ODU0 ⇒ ODTU4.1 ⇒ ×80 ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex as many 80 ODU0 signals into an ODU4 signal.

ODU0 to ODU4 - Using PT = 21 Method

Figure 9, Simple Illustration of the ODU0 ⇒ ODU4 Mapping/Multiplexing scheme.  

Click HERE or click on the figure above to learn more about this Mapping/Multiplexing scheme.

  • ODU1 ⇒ ODTU4.2 ⇒ ×40 ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex as many as 40 ODU1 signals into an ODU4 signal.

ODU1 to ODU4 - Using PT = 21 Method

Figure 10, Simple Illustration of the ODU1 ⇒ ODU4 Mapping/Multiplexing scheme.

Click HERE or Click  on the figure above to learn more about this Mapping/Multiplexing scheme. (*).

  • ODU2 ⇒ ODTU4.8 ⇒ ×10 ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex as many as 10 ODU2 signals into an ODU4 signal.

ODU2 to ODU4 - Using PT = 21 Method

Figure 11, Simple Illustration of the ODU2 ⇒ ODU4 Mapping/Multiplexing scheme.

Click HERE or Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (*).

  • ODU2e ⇒ ODTU4.8 ⇒ ×10 ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex as many as 10 ODU2e signals into an ODU4 signal.

ODU2e to ODU4 - Using PT = 21 Method

Figure 12, Simple Illustration of the ODU2e ⇒ ODU4 Mapping/Multiplexing scheme.  

Click HERE or Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (*).

  • ODU3 ⇒ ODTU4.31 ⇒ ×2 ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex as many as 2 ODU3 signals into an ODU4 signal.

ODU3 to ODU4 - Using PT = 21 Method

Figure 13, Simple Illustration of the ODU3 ⇒ ODU4 Mapping/Multiplexing scheme.

Click HERE or Click on the figure above to learn more about this Mapping/Multiplexing scheme.  (*).

  • ODUflex ⇒ ODTU4.ts ⇒ ×80/ts ⇒ ODTUG4 ⇒ OPU4 ⇒ ODU4

This scheme will allow one to map/multiplex anywhere from 1 to 80 ODUflex signals into an ODU4 signal.

ODUflex to ODU4 - Using PT = 21 Method

Figure 14, Simple Illustration of the ODUflex ⇒ ODU4 Mapping/Multiplexing scheme.  

Click HERE or Click on the figure above to learn more about this Mapping/ Multiplexing scheme.  (*).

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

In Conclusion

In this posting, we briefly listed out the characteristic of a PT = 21 scheme for Mapping/Multiplexing numerous lower-speed ODUj signals into a higher-speed ODUk signal.

We have also listed out each of the 14 PT = 21 schemes for Mapping/Multiplexing numerous lower-speed ODUj signals into a higher-speed ODUk signal.

Please check out the appropriate post for similar information on PT = 20 schemes on Mapping/Multiplexing numerous lower-speed ODUj signals into a higher-speed ODUk signal.

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What is the ODUk-AIS Signal?

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


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

What is the ODUk-AIS Maintenance signal?

AIS is an acronym for Alarm Indication Signal.

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

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

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

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

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

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

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

ODUk-AIS Pattern

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

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

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

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

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

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

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

OTUk Bit Rate

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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What is an ODTU4.1 Structure?

This post defines the ODTU4.1 (Optical Tributary Data Unit 4.1). This post also describes how we use the ODTU4.1 structure/frame whenever we are mapping/multiplexing ODU0 signals into an OPU4 signal.


What is the ODTU4.1 Frame/Structure? And When do We use it?

Introduction

The term, ODTU4.1, is an acronym for Optical Data Tributary Unit 4.1.

A Mapper circuit will use this structure whenever it is mapping and multiplexing anywhere between 1 and 80 ODU0 tributary signals into an OPU4 server signal.

We will discuss the following topics within this blog post.

  • What does the term ODTU4.1 mean?
  • A description/definition of the ODTU4.1 frame/structure.
  • How do we use the ODTU4.1 structure when mapping/multiplexing numerous lower-speed ODU0 tributary signals into an OPU4 server signal.
    • What is the timing/frequency relationship between each ODTU4.1 signal, and
    • What is the timing/frequency relationship between each ODTU4.1 signal, and the outbound OPU4 frame data?

What is the meaning of the term ODTU4.1?

The numeral 4 (within the expression ODTU4.1) reflects that we use this structure to map data into an OPU4 signal.

The numeral 1 (again, within the expression ODTU4.1) reflects that this structure transports a single ODU0 signal (which contains only 1 (one) 1.25Gbps-unit  of bandwidth).

Therefore, the ODTU4.1 structure only transports 1 (one) 1.25Gbps-unit (or tributary-slot) of bandwidth as we map/multiplex this data into an OPU4 signal.

NOTE:  I have provided an extensive discussion of how we map 80 ODU0 tributary signals into an ODU4 server signal, within Lesson 5/ODU4 of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!

There are other similar structures, such as the ODTU4.2, ODTU4.8, ODTU4.31 and ODTU4.ts frames, that we will use to map an ODU1 (2 time-slots), ODU2/2e (8 time-slots), ODU3 (31 time-slots) and ODUflex (ts time-slots) into an OPU4 signal, respectively.

We will discuss each of these structures in other posts.

When do we use the ODTU4.1 structure?

We use these structures anytime we are mapping and multiplexing anywhere from 1 to 80 lower-speed ODU0 tributary signals into an OPU4 server signal.

ITU-T G.709 states that whenever we map/multiplex some ODU0s into an OPU4 signal, then we need to do this by executing the following four-step process.

  • Convert each ODU0 signal into an Extended ODU0 signal.
  • GMP map each ODU0 signal into its own ODTU4.1 structure/signal, and
  • Byte-Wise Multiplex as many as 80 ODTU4.1 signals together and then
  • Load this data into the OPU4 Payload area.

ITU-T G.709 presents a series of figures on how to map/multiplex lower-speed ODUj tributary signals into a higher-speed OPUk server signal (e.g., k > j).

The standard presents the following figure on how to map/multiplex ODU0 signals into an OPU4.

ITU-T G.709 using ODTU4.1 to map ODU0s into an OPU4

Figure 1, Illustration of the ITU-T G.709 Drawing on how to Map/Multiplex up to 80 ODU0s signals into an OPU4 signal.  

I (more or less) copied Figure 1 straight out of ITU-T G.709.

I did also add some text to further explain this figure and ITU-T G.709’s instructions.

Figure 1 states that we must first map a single “Extended ODU0 signal” into a single ODTU4.1 signal, using GMP (Generic Mapping Procedure).

What Do We Mean by an Extended ODU0 Signal?

Before we can begin the process of mapping/multiplexing any ODU0 signals into an OPU4 signal, then we must first convert each of these ODU0 signals into an Extended ODU0 signal.

This means that we need to take an ODU0 frame and then “extend it” by attaching both the FAS and MFAS fields to this frame, as we show below in Figure 2.

Extended ODUk Framing Format

Figure 2, Illustration of the Extended ODU0 Framing Format

The reason that we attach the FAS and MFAS fields to each of these ODU0 frames is so that the Sink PTE circuitry (at the remote end of the fiber link) will be able to locate the boundaries of ODU0 frames, as it de-maps this data from the ODTU4.1 structures.

Please see the OTU Post for more information on the FAS and MFAS fields.

Please also note that (as we include the FAS and MFAS fields within the ODU0), we fill in the rest of the OTUk Overhead to an all-zeroes pattern, and we don’t append the FEC to the back-end of the ODU0 frame.

Mapping the Extended ODU0 signals into the ODTU4.1 Signal/Structure

Once we have converted each of the ODU0 signals into Extended ODU0 signals, we will then proceed to GMP map this data into the ODTU4.1 signal/structure.

After we have performed this mapping step, then we will (from here on) be working with ODTU4.1 signals (instead of ODU0 signals) as we load this data into an OPU4 frame structure and transport it across an optical link.

These ODU0s will remain embedded within this ODTU4.1 data-stream until some “ODTU4.1 to ODU0 De-Mapper” circuit de-maps/extracts the ODU0 signals out from the ODTU4.1 signals.

If we are mapping/multiplexing 80 ODU0 signals into an OPU4 signal, then we will map 80 ODU0 signals into each of their own 80 ODTU4.1 signals in parallel.

And we will then have 80 separate ODTU4.1 signals to process and manipulate.

Figure 4 (further down in this post) presents an illustration of some “Mapping circuitry” that maps 80 ODU0 signals into 80 ODTU4.1 signals, in parallel.

Byte-Wise Multiplexing the ODTU4.1 Data into the ODTUG4 Structure

Next, Figure 1 then states that we must byte-wise multiplex each of the 80 ODTU4.1 signals together into a single ODTUG4 data stream.

And finally, we should then map (or insert) this ODTUG4 data stream into the OPU4 payload.

What does the ODTU4.1 Structure Look Like?

Figure 3 presents an illustration of the ODTU4.1 Framing Format.

ODTU4.1 Frame Format

Figure 3, Illustration of the ODTU4.1 Frame Format

This figure shows that the ODTU4.1 Frame consists of two different sections.

  • The ODTU4.1 payload area and
  • The ODTU4.1 overhead area

Figure 3 also shows that the ODTU4.1 payload is 160 Row x 95 Byte Column structure.  Additionally, this figure also shows that the ODTU4.1 frame consists of 6 bytes of overhead.

Please note that 160 Rows x 95 Byte Columns = 15,200 Bytes.

This means that the payload portion of each ODTU4.1 frame will carry 15,200 bytes (which is the exact number of payload bytes that each OPU4 frame carries).

What kind of data resides within the ODTU4.1 Payload?

In short, the ODTU4.1 Payload will contain the contents of its respective Extended ODU0 signal.

Whenever we are GMP mapping an Extended ODU0 signal into an ODTU4.1 signal, then we will load the entire Extended ODU0 data stream (e.g., ODU0 overhead, FAS field, and payload data) into the ODTU4.1 payload.

We will load this data into the ODTU4.1 payload in the normal transmission order.

What kind of data resides within the ODTU4.1 Overhead?

When the Mapper circuitry GMP maps the Extended ODU0 signal into the ODTU4.1 structure, it will then compute and generate some GMP parameters (for this particular mapping operation).

The Mapper circuitry will compute these GMP parameters based upon the exact bit-rates of the Extended ODU0 signal and that on the ODTU4.1 (Server) signal.

The Mapper circuitry will then load this GMP mapping data into the JC1 through JC6 fields (within the ODTU4.1 overhead), just as a GMP mapper would do for any client-signal.

This set of JC1 through JC6 fields serve the exact same roles as do the JC1 through JC6 fields (within an OPUk structure) whenever we are using GMP mapping.

How do we transport the ODTU4.1 Overhead and Payload data across the Optical Link (within an OTN)?

Please see the OMFI Post for details.

Are all the ODTU4.1 signals both frame and byte-synchronous with each other whenever we map this data into the OPU4 payload?

In short, the answer is “Yes.”

The ODTU4.1 frames and signals must have the following timing/synchronization characteristics.

  • Each of the 80 ODTU4.1 signals must be bit-synchronous with each other.
  • These ODTU4.1 signals must also be bit-synchronous with the outbound OPU4 data-stream.
  • Each of the 80 ODTU4.1 signals must be frame-synchronous with each other, and
  • All 80 of the ODTU4.1 signals must be frame synchronous with the 80 OPU4 Frame Superframe, that they will eventually be multiplexed into.

We will discuss each of these characteristics (of the ODTU4.1 signals) below.

BUT FIRST – What about the timing and requirements of the ODU0 signals?

Each of the ODU0 signals (that we are mapping into an OPU4 signal) can be completely asynchronous with respect to each other.

Additionally, the only real timing requirements for the ODU0 signals is that they have to comply with the Frequency Tolerance requirements per ITU-T G.709.

There is also no requirement that these 80 ODU0 signals be frame-aligned with each other either.

However, once the ODU0 signals are each GMP mapped into their ODTU4.1 signal, then each of the ODTU4.1 signals MUST be both byte- and frame-synchronous with respect to each other.

Each of these ODTU4.1 signals must also be bit-synchronous with the outbound OPU4 signal.

Additionally, each of these ODTU4.1 frames must also be framed aligned with the 80 OPU4 frame Superframe (that they will eventually be a part of).

GMP mapping addresses the timing differences between each of the individual ODU0 signals, as they transition from the “ODU0 time-domains” to the “ODTU4.1/OPU4 Time Domain”.

All of this means that the ODU0 to OPU4 Mapper Circuit must ensure that “Byte 1” (the very first payload byte) within each of the 80 ODTU4.1 frames are all being applied to the “ODTU4.1 Byte MUX” simultaneously.

Let’s focus on these points in greater detail.

ODTU4.1 Signals being Bit-Synchronous with each other

Figure 4 presents an illustration of an ODU0 to OPU4 Mapper circuit.

This figure presents 80 sets of “ODU0 Frame Extender/ODU0 to ODTU4.1 Mapper” blocks.

Each of these blocks is responsible for GMP mapping their own ODU0 signal into an ODTU4.1 Data Signal.

ODU0 to OPU4 Mapper Circuit

Figure 4, Illustration of an ODU0 to OPU4 Mapper Circuit

Figure 4 also shows that a single clock source (e.g., ODTU4.1 and OPU4 Clock Source) will function as the timing source for each of the 80 ODU0 Frame Extender/ODU0 to ODTU4.1 Mapper blocks.

This means that each of the resulting ODTU4.1 signals will be generated based on and synchronized with a common clock source (e.g., the ODTU4.1 and OPU4 Clock Source, in this case).

The OPU4 Output signal will also use the ODTU4.1 and OPU4 Clock Source as is timing source as well.

ODTU4.1 Signals are Byte-Aligned with Each Other

Figure 5 presents an illustration of an abbreviated byte-stream for each of the 80 ODTU4.1 payload signals.

80 ODTU4.1 Byte Data Streams

Figure 5, Illustration of the Byte Streams for each of the 80 ODTU4.1 Signals (output from the ODU0 Frame Extender/ODU0 to ODTU4.1 Mapper block in Figure 4).

This figure shows that each of the ODU0 Frame Extenders/ODU0 to ODTU4.1 Mapper circuits must all generate and transmit the very first payload byte of their ODTU4.1 frame, simultaneously.

Likewise, each of these ODU0 Frame Extender/ODU0 to ODTU4.1 Mapper circuits must all generate and transmit the very second payload byte of their ODTU4.1 frame, simultaneously, and so on.

All 80 of these byte streams will then be routed to downstream circuitry, which will byte-multiplex and map this data into the OPU4 payload, as I show below in Figure 6.

Byte Wise Multiplexing 80 ODTU4.1 Signals into the OPU4 Payload

Figure 6, Simple Illustration of Circuitry Byte-Wise Multiplexing Each (of 80) ODTU4.1 Signals into an OPU4 Payload.  

ODTU4.1 Signals MUST be Frame Aligned to the 80 OPU4 Frame Superframe

In the OMFI post, we mentioned that we will ultimately map and multiplex each of the ODTU4.1 signals into an 80 OPU4 Frame Superframe.

Figure 7 presents an illustration of an 80 OPU4 frame Superframe that we created by byte-wise multiplexing these 80 ODTU4.1 data streams together.

Full OPU4 Superframe

Figure 7, Illustration of an 80 OPU4 frame Superframe.

If you look at Row 1, Byte-Column 17 within OPU4 Frame # 1, you will see that we have designated this byte-field as “1-1“.

This designation means that this byte originated from ODTU4.1 Signal # 1 and that it is the very first byte (e.g., byte # 1) within that particular ODTU4.1 frame.

Likewise, we designated the very next byte-field (to the right) as “2-1“.

This means that this byte originated from ODTU4.1 Signal # 2 and that it is the very first byte within that particular ODTU4.1 frame, and so on.

Figure 6 also shows that the very first payload byte (within the 80 OPU4 frame Superframe) is the very first payload byte (within an ODTU4.1 frame) that originates from ODTU4.1 Signal # 1 (e.g., byte-field “1-1“).

This figure also shows that the next 79 bytes (within this OPU4 frame) are also the very first bytes (within each of their ODTU4.1 frames) that originate from ODTU4.1 Signal # 2 through ODTU4.1 # 80.

We have designated the next 79 bytes as “2-1“, “3-1“, and so on, all the way to “80-1“.

This figure reinforces the fact that each of the ODTU4.1 streams must also be frame-aligned with each outbound 80 OPU4 frame Superframe.

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