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

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

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

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

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

Check Out the Video Below

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

OTN – Lesson 12 – Detailed Discussion of CL-SNCG/I Monitoring (Protection Switching)

This blog post presents a video that describes (in detail) CL-SNCG/I (Compound Links – Subnetwork Circuit Group – Inherent) Monitoring for Protection Switching.

Lesson 12 – Video 5 – Detailed Discussion of CL-SNCG/I (Compound Links – Subnetwork Circuit Group – Inherent) Monitoring for Protection Switching

This blog post contains a video that presents a detailed discussion of CL-SNCG/I Monitoring ], for Protection Switching purposes, at the ODU layer.

In particular, this video will discuss the following topics:

  • A Quick Review of the SNC/I Monitoring at the ODU Layer
    • A Single ODUj Tributary is the Normal Traffic Signal
    • How CI_SSF and CI_SSD initiate Protection Switching
  • How to perform CL-SNCG/I Monitoring at the ODU Layer
    • What Circuitry (Atomic Functions) that we should use
    • What defects to monitor
    • Which is the Normal Traffic Signal when doing CL-SNCG/I Monitoring at the ODU Layer?
    • What happens when we declare an ODUk Server-Layer service-affecting defects (such as dAIS, dOCI, dLCK, dTIM)?
    • What happens when we declare the PM-dDEG (ODU-Layer Signal Degrade) defect?
    • How does protection-switching work?
  • How does CL-SNCG/I Monitoring (for Protection-Switching) differ from SNC/I Monitoring for Protection-Switching?
    • PI-TSF/PI-TSD versus CI_SSF[n]/CI_SSD[n]
    • Multiple ODUj Tributary Signals are the Normal Traffic Signal
    • dPLM, dLOOMFI, dMSIM[n], and dLOFLOM[n] do not cause Protection-Switching when CL-SNCG/I Monitoring.

Check Out the Video Below

Continue reading “OTN – Lesson 12 – Detailed Discussion of CL-SNCG/I Monitoring (Protection Switching)”

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 tributary signals into the ODUk, or
  • Use the PT = 21 (or 0x21) Method for Mapping/Multiplexing the ODUj tributary 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 use the PT = 21 Method, we will set 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 use 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 methods 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 BEST DARN OTN TRAINING PRESENTATION…PERIOD!!  program to see this link.

In Conclusion

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

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

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

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What is the PTE for OTN Applications?

This post defines and describes the Path and Path Terminating Equipment for OTN Applications.

What is Path Terminating Equipment (PTE) for OTN Applications?

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

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

I have devoted this blog post to discussing PTE (Path Terminating Equipment).

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

You can also find a detailed discussion of PTEs and STEs within Lesson 3 of THE BEST DARN OTN TRAINING PRESENTATION…PERIOD!!!  This discussion also describes the differences between PTEs and STEs.

What is the Path?

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

For OTN applications, there are two different types of Paths.

  • A Non-OTN Client Signal Path (for Non-Multiplexed ODU traffic) and
  • An ODUk Server Signal Path (for Multiplexed ODU traffic)

We will define each of these types of Paths below.

Non-OTN Client Signal Path

When transporting a single non-OTN client signal (such as 100GBASE-R) over OTN (e.g., an ODU4/OTU4 signal in this case), the Path begins where the circuitry maps the 100GBASE-R signal into an OPU4 signal.

We can say that the 100GBASE-R signal officially enters the OTN at this point.

This Path ends at the location where the circuitry de-maps the 100GBASE-R signal from the OPU4 signal (and exits the OTN) at the other end of the network.

Figure 1 presents a simple illustration of an OTN that contains some Path Terminating Equipment and some STEs.

Difference between Section Termination Equipment and Path Terminating Equipment

Figure 1, Illustration of both PTE (Path Terminating Equipment) and STE (Section Terminating Equipment) within an Optical Transport Network

In Figure 1, we show that a Source PTE is mapping a 100GBASE-R signal into an OTU4 signal on the left-hand side of Figure 1.

The OTU4 signal transports this 100GBASE-R signal throughout this OTN and through various Section Terminating Equipment blocks labeled STE#1, STE#2, and STE#3.

Afterward, the OTU4 signal finally arrives at the Sink PTE on the right-hand side of Figure 1.

The Sink PTE then de-maps the 100GBASE-R signal from this OTU4 signal.

In the case of Figure 1, the Path (for the 100GBASE-R signal) is that portion of the OTN that exists between the Source PTE (on the left-hand side of Figure 1) and the Sink PTE (on the right-hand side of the same figure).

As this 100GBASE-R signal travels from the Source PTE to the Sink PTE, it will pass through multiple Sections and STEs (we describe in another post).  The Path is the route the 100GBASE-R signal takes (through the OTN, via the OTU4 signal).

A Closer Look at the Non-OTN Client SIGNAL Path

Now that we have a basic understanding of what a Path is, let’s take a much closer look at the Path.

Figure 2 presents a more detailed illustration of the Non-OTN Client Signal path within an OTN.  This figure also indicates where this Path begins and ends within the OTN.

100GbE/OTU4 Path - Path Terminating Equipment

Figure 2, A Closer Look at the Non-OTN Client Signal Path

Once again, Figure 2 shows that the Non-OTN Client Signal Path begins when we map the client signal into an OPU4 signal (and then an ODU4 and OTU4 signal).

In this case, we are mapping a 100GBASE-R client signal into an OPU4 signal at the OPU4 Mapper block.

This figure also shows that this same Path ends where we de-map that same client signal from the OPU4 signal (at the OPU4 De-Mapper block on the lower-right-hand side of Figure 2).

Please note that the diagram in Figure 2 is functionally equivalent to that in Figure 1.  In Figure 1, we referred to each signal (between the STE and PTE boxes) as OTU signals.  We did not discuss these signals at the OPU4 or ODU4 layers, as shown in Figure 2.

For more details on how we map a 100GBASE-R signal into an OPU4 (and ODU4) server signal, please see Lesson 4 within THE BEST DARN OTN TRAINING PERIOD!!

Let’s now move on to the other type of Path.

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The ODUk Server Signal Path (for Multiplexed ODU Signals)

Another type of OTN Path is the ODUk Server Signal Path.

In the ODUk Server Signal Path, we can map and multiplex multiple lower-speed ODUj tributary signals into a Higher-Speed ODUk server signal (where k > j).

We describe the exact procedure for mapping/multiplexing lower-speed ODUj signals into a higher-speed ODUk signal in other posts.

Figure 3 illustrates a Unidirectional Network that contains both a Non-OTN Client Signal and the ODUk Server Signal set of paths.

1GbE to ODU0 to ODU4 - Path Terminating Equipment

Figure 3, A Closer Look at the ODUk Server Path

NOTE: We described the Non-OTN Client Signal path earlier in this post.  Hence, the reader should be familiar with this particular type of Path.

Handling the 1000BASE-X/OPU0/ODU0 Signals

In Figure 3, we have a 1000BASE-X (1GbE) signal that we first map into an OPU0 signal (in the Upper-Left-Hand corner of this figure).

We earlier stated that this point of mapping a non-OTN signal (such as a 1000BASE-X signal) into an OTN signal (e.g., an OPU0 in this case) is the beginning of the Non-OTN Client Signal Path.

Once we’ve mapped this signal into an OPU0, then we will also, in turn, map this OPU0 signal into an ODU0 signal.

Afterward, this ODU0 signal goes through some different processes (that we discuss in detail in other posts) before we map/multiplex this ODU0 tributary signal into an OPU4 signal.

Once we’ve mapped the ODU0 tributary signal (along with 79 other such signals) into an OPU4 signal, this point serves as the entry point for the ODU0 to OPU4/ODU4 Path.  We can also call this the ODUk Server Signal Path entry point.  

Figure 3 labeled this point as the ODU0 to OPU4 Path Demarcation Line.

This is where this OPU4 signal begins (and serves as the starting point for this particular Path).

Handing the OPU4/ODU4 Server Signal

We then quickly map this OPU4 signal into an ODU4 signal and then (eventually) into an OTU4 signal.

Afterward, we convert this OTU4 signal into an optical signal and transmit it through three additional sets of STEs before arriving at the XCVR and Optical I/F at the Remote Terminal (in the lower-left-hand corner of Figure 3).  

The remote terminal converts this signal back into the electrical format and terminates the OTU4 and ODU4 signals.

Finally, the circuitry routes the resulting OPU4 signal to the OPU4 De-Mapper block.  The OPU4 De-Mapper block then terminates this OPU4 signal.

This point serves as the OPU4 to the ODU0 Path Demarcation point.  This point is where this OPU4 signal (and its Path) ends.  We can also say that this is the end of the ODUk Server Signal Path.  

NOTE:  If you wish to learn more about how we map/multiplex lower speed ODUj tributary signals into an ODU4 Server signal, then you can check out Lesson 5 within THE BEST DARN OTN TRAINING PERIOD!!!

This circuitry will then de-map out the ODU0 tributary signal (of interest) along with as many as 79 other ODU0 tributary signals from this OPU4 signal.

Next, the ODU0 Terminator block will terminate this ODU0 signal and extract the OPU0 signal.

Afterward, it will transmit this data to the OPU0 De-Mapper block.

The OPU0 De-Mapper block will then de-map out the 1000BASE-X (1GbE) client signal from its incoming OPU0 signal.

Once the OPU0 De-Mapper block de-maps the 1000BASE-X signal from the OPU0 signal, this point serves as the Non-OTN Client Path Demarcation point.

In other words, this is the point at which this particular OPU0 signal (and its Path) ends.

How the PTE Operates in the Optical Transport Network

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

Path Termination Equipment will process data (in the electrical format) by doing many of the following functions:

In the Transmit Direction

  • Mapping data (either Non-OTN client data or lower-speed ODUj tributary data) into an OPUk signal and generating the new OPUk signal and overhead.
  • Generating the ODUk overhead or the ODUk-PMOH (Path Monitoring Overhead) and attaching the ODUk-PMOH to each outbound OPUk frame.
  • Sending this data downstream, the circuitry will either map this signal into another higher-speed ODUk signal or an OTUk frame and precondition it for transmission across the optical fiber.

NOTE:  Throughout many of the postings on this blog, we will refer to this ODUk overhead data as the ODUk-PMOH (ODUk-Path Monitoring Overhead) data.

In the Receive Direction

  • Receive ODUk data from the upstream OTUk Framer block
  • Process and Terminate the ODUk overhead (or ODUk-PMOH).  While the PTE is processing the ODUk-PMOH, it will check for the following errors and defects within the incoming ODUk signal.
    • Defects or Failures (e.g., dTIM, dPLM, dDEG, dAIS, dOCI, dLCK and PM-BDI)
    • Errors (e.g., PM-BIP-8, PM-BEI)
  • Terminate the OPUk data stream and de-map either the Non-Client OTN signal or some lower-speed ODUj tributary signals.
  • Route the de-mapped data downstream for further processing.

Mapping Data (either Non-OTN client data or lower-speed ODUj tributary data) into an OPUk/ODUk signal

Anytime the PTE maps data (be it non-OTN client data or lower-speed ODUj tributary signals) into an OPUk signal, it will do so by using some of the following mapping procedures.

As the PTE uses one of these mapping procedures to load client data into the OPUk payload, it will load its mapping parameters into the OPUk overhead.

The PTE will also alert the network of the type of traffic that it is transmitting via this OPUk signal by sending the appropriate PSI message via the PSI byte.

Please see the relevant posts for more information on this functionality.

Generating the ODUk Overhead (ODUk-PMOH)

As the PTE receives an OPUk data stream from upstream circuitry, it will precondition all this data for transport through the Path by computing and attaching the ODUk overhead fields to each outbound OPUk frame.

In particular, the PTE will attach some ODUk-PMOH fields to the OPUk frame, which will help it to detect errors and declare and clear certain defect conditions.

Other ODUk overhead fields support maintenance/monitoring features such as Tandem Connection Monitoring, the transport of APS (Automatic Protection Switching) Commands, and other forms of Equipment to Equipment (non-client related) commands and information.

In other posts, we will discuss these topics (e.g., Tandem Connection Monitoring and the APS Channel).

The critical thing to note at this point is that the PTE will use the ODUk-PMOH to monitor the overall health of the entire Path (from the point where it creates the ODUk signal to the end where it terminates this signal).

Figure 4 presents an illustration of the ODUk Overhead that the PTE will use to support the monitoring of this signal as it travels through the Path.  NOTE:  The ODUk-PMOH is the orange PM field within Figure 4.  We will discuss the PMOH in another post.  

ODU Frame with ODU Overhead Shown

Figure 4, ODUk Overhead, PMOH, and Payload fields

NOTE:  Please see the ODUk Frame post for more information on the ODUk frames and the PMOH fields.

Terminating the OPUk Overhead

After the OTUk signal has been converted into the optical format, received, and converted back into the electrical domain (by the remote terminal), the remote terminal will terminate the OTUk signal (because this equipment is an STE).

Once the STE has terminated OTUk-SMOH, it will route the resulting ODUk signal towards downstream circuitry for further processing.

At this point, the PTE will proceed to terminate the ODUk-PMOH.

As the PTE performs this task, it will check the ODUk-PMOH for the occurrence of bit errors and defects.

The PTE will report the occurrences of such errors and defects to System Management.

Additionally, the PTE will remove all ODUk-PMOH data from this incoming stream (which leaves us with just an OPUk data stream now).

This OPUk data stream is then routed to a De-Mapper block for further processing.

Important Takeaway

The critical takeaway is that the PTE will rely on the ODUk-PMOH data (as shown in Figure 4) to process, manage, and ultimately terminate the ODUk stream.

NOTE:  Each ODUk signal (whether it is a lower-speed ODUj tributary signal that we map/multiplex into a higher-speed ODUk server signal) or an ODUk signal (that is carrying a single Non-OTN client signal) will have its ODUk-PMOH data.

This means that PTE (whether it is for transporting a single Non-OTN client signal or one of many lower-speed ODUj signals) will manage and monitor its own respective ODU signal.

I have redrawn Figure 2 to show where the circuitry generates and terminates/monitors the ODU4-PMOH within the Non-OTN Client Path (of 100GBASE-R over OPU4/ODU4).  

I have included this figure below in Figure 5.

100GbE to OTU4 PTE w/ ODU4-PMOH

Figure 5, Illustration of the 100GbE to ODU4 Path.  (The Entire ODU4 Path is shaded).  

NOTE:  I have highlighted the locations where the Path Circuitry Generates and Monitors/Terminates the ODU4-PMOH (Non-OTN Client ODU4).

This also means that the circuitry (shown above in Figure 3) would require as many as 81 sets of PTE.

  • 80 sets of PTE would be required to monitor each of the 80 ODU0 signals (that we are transporting via the OPU4/ODU4 signal), and
  • One additional PTE would be required to monitor the more significant ODU4 signal.

I have also redrawn Figure 3 to show where the circuitry generates and terminates/monitors the ODU0-PMOH within the Non-OTN Client Path (of 1000BASE-X over OPU0/ODU0).  

I have included this figure below in Figure 6.

1GbE to ODU0 to ODU4 - ODU0 SMOH Termination

Figure 6, Illustration of the 1GbE to ODU0 -> ODU4 Path.  (The entire ODU0 Path is shaded).

NOTE:  In Figure 6I have highlighted the locations where the Path Circuitry Generates and Monitors/Terminates the ODU0-PMOH (Non-OTN Client ODU0).  

Finally, I have redrawn Figure 3 (again) to show where the circuitry generates and terminates/monitors the ODU4-PMOH within the ODU0 mapped/multiplexed into OPU4/ODU4 Path.   

I have included this figure below in Figure 7.

1GbE to ODU4 with ODU4-PMOH

Figure 7, Illustration of the 1GbE to ODU0 -> ODU4 Path.   (The Entire ODU4 Path is shaded).

NOTE:  I have highlighted the Locations where the Path Circuitry Generates and Monitors/Terminates the ODU4-PMOH (ODU0 Mapped/Multiplexed into OPU4/ODU4).

De-Mapping the Client Signal from the OPUk Payload

Once the OPUk has reached the De-Mapper block, the De-Mapper block will de-map out the client data (be it non-OTN client data or lower-speed ODUj tributary signals) using the mapping parameters that the Source PTE loaded into the OPUk overhead bytes (when it was mapping these clients into the OPUk signal).

This point will be the “end of the line’ for the OPUk frame and overhead.

This circuitry will send the client data downstream for further processing (either by non-OTN system-side circuitry, such as a MAC or other PTE circuitry to handle the lower speed ODUj signals).

Examples of PTE

  • Line Cards or Transceivers take (for instance) 100GBASE-R data from a MAC and transport this data over an OTU4 connection (and vice-versa).
  • Any equipment that performs ODUj switching and grooming
  • ROADMs.

Some Final Comments about the ODUk-PMOH and PTE Equipment.

This post introduced the concept of a Path, Path Terminating Equipment (PTE), and the ODUk-PMOH (Path Monitoring Overhead).

In another post, I describe the Section, Section Terminating Equipment (STE), and the OTUk-SMOH (Section Monitoring Overhead).

STEs will use the OTUk-Layer to manage the data transmission across Sections.

STEs will only generate and process OTUk-SMOH data.  They do not process ODUk-PMOH data AT ALL.

Likewise, PTEs will use the ODUk-Layer to manage data transmission across a Path.

PTEs will only generate and process ODUk-PMOH data.  They do not process OTUk-SMOH data AT ALL.  In most cases, the PTE will not even see the OTUk-SMOH data.

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