Lesson 5 – PT = 0x20 Approach

This blog post provides information and Video Training on the PT = 0x20 Approach for Mapping/Multiplexing Lower-Speed ODUj Tributary Signals into an ODUk Server Signal.

Lesson 5 – PT = 0x20 Approach to Mapping/Multiplexing Lower-Speed ODUj Tributary Signals into an ODUk Server Signal.

This portion of Lesson 5 presents information, along with a Training Video on how we Map and Multiplex Lower-Speed ODUj Tributary Signals into a Higher-Speed ODUk Server Signal using the PT = 0x20 Approach.

This Lesson includes four (4) videos discussing mapping/multiplexing lower-speed ODUj Tributary Signals into an OPUk/ODUk Server Signal using the PT = 0x20 scheme.

Introduction to the PT = 0x20 Scheme and Mapping/Multiplexing up to 2 ODU0 Tributary Signals into an ODU1 Server Signal

This video covers the following topics.

  • An overall discussion of the PT = 0x20 Scheme to Mapping and Multiplexing Lower-Tributary ODUj signals into an ODUk Server signal.
  • How do we use the PT =0x20 Approach to mapping/multiplexing 2 ODU0 signals into an ODU1 server signal? As this video discusses this particular mapping/multiplexing scheme, it will cover the following items in detail.
    • Using the AMP (Asynchronous Mapping Procedure) to map each ODU0 tributary signal into an ODTU01 frame/signal.
    • How do we combine each ODTU01 signal and map this data into the ODU1 payload?
    • Transporting these AMP Justification parameters from the Source PTE (where we map/multiplex these ODU0 tributary signals into the ODU1 server signal) and the Sink PTE (where we de-multiplex and de-map out the ODU0 tributary signals).
    • The Multiplexed Structure Identifier within this type of ODU1 server signal.

You can watch the Video Training that Introduces the PT = 0x20 Scheme and discusses Mapping/Multiplexing up to 2 ODU0 Tributary Signals into an ODU1 Server below.

Continue reading “Lesson 5 – PT = 0x20 Approach”

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

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 two different types of PSI Messages.
      • The Non-Multiplexed Traffic Type of PSI Message, and
      • The Multiplexed Traffic Type of PSI Message.  

Suppose we’re discussing the MSI (Multiplex Structure Identifier), which involves OPU/ODU server signals transporting multiple lower-speed ODUj tributary signals.  In that case, we will deal 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 (transmitting an ODUk signal to the remote Sink PTE) has set the PT byte value (within each PSI Message) to 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 discuss 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 server signal carries.

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 this ODUk/OPUk server signal is transporting.  

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

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, the MSI will consist of 2 bytes.
  • If we’re working with an OPU2/ODU2 server signal, the MSI will consist of 4 bytes.
  • An OPU3/ODU3 server signal will use 16 bytes for its MSI.  
  • For PT = 0x20, each MSI byte (or entry) represents 2.5Gbps of bandwidth.  

For PT = 0x21

  • If we’re working with an OPU2/ODU2 server signal, 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.  
  • For PT = 0x21, each MSI byte (or entry) represents 1.25Gbps of bandwidth.

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, that we are transporting via the OPU4/ODU4 server signal.  

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 shown 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.  In this case, we are using this bandwidth to transport the individual ODUj tributary signal. 

Conversely, suppose this bit-field is set to “0”.  In that case, this particular time slot (or bandwidth) within the OPU4/ODU4 server signal is NOT allocated (or is 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 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 it 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 it is most likely an ODU1 signal.  

And so on.  

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 to 0x4F (or 79 in decimal format). 

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 (Coming Soon to this Blog)

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

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What is the PSI – Payload Structure Identifier Byte

This post describes the role of the PSI (Payload Structure Identifier) byte, within the OPUk Overhead, is used within the OTN.

What is the PSI – Payload Structure Identifier (Byte and Message)?

The PSI Byte

The PSI (or Payload Structure Identifier) byte is an Overhead byte within the OPUk structure.

Figure 1 presents an OPU frame with the location of the PSI byte identified.

Generic OPU Frame with PSI Byte Highlighted

Figure 1, Illustration of an OPUk Frame Structure with the Overhead Bytes (along with the PSI Byte) Identified  

The purpose of the PSI byte is to permit an OTN Path Terminating Equipment (PTE) to transport a 256-byte PSI (payload structure identifier) message throughout the OTN (Optical Transport Network).

The primary purpose of this 256-byte PSI Message is to permit the Source PTE to alert the OTN (Network) of the type of data (or traffic) we are transporting within this particular OPU data stream.

Since each OPUk frame contains only 1 PSI byte, an OTN PTE will have to transmit 256 consecutive OPU frames to transmit this PSI message completely.

The OTN PTE will align its transmission of this 256-byte PSI message with the MFAS byte.

Please see the OTUk Frame Structure post for more information on the MFAS byte.

In other words, whenever the OTN PTE is transmitting an OTUk frame with the MFAS byte set to “0x00”, then the OTN PTE will also be sending the first byte of the PSI message (e.g., PSI[0]) via the PSI byte-field.

Likewise, whenever the OTN PTE is transmitting an OTUk frame with the MFAS byte set to “0x01”, then the OTN PTE will also be sending the second byte within this 256-byte message (e.g., PSI[1]) via the PSI byte field, and so on.

Two Types of PSI Messages

An OTN Source PTE will transport one of two types of PSI Messages.

  • The Non-Multiplexed Traffic – PSI Message, and
  • The Multiplexed Traffic – PSI Message.

I will describe each of these types of PSI Messages below.  

The Non-Multiplexed Traffic PSI Message

We will use the Non-Multiplexed Traffic PSI Message when transporting Non-Multiplexed Traffic within our OPU data stream.

Examples of Non-Multiplexed Traffic would be:

  • Transporting 1000BASE-X via an OPU0 signal
  • 10GBASE-R via an OPU2e signal.
  • 100GBASE-R via an OPU4 Signal.

In other words, we are handling Non-Multiplexed Traffic whenever we only transport a single Non-OTN client signal via this OPUk data stream.  

I present an illustration of an OPU Frame, with the PSI field highlighted (along with a break-out of the Non-Multiplexed Traffic type of PSI Message) below in Figure 2.

OPU Frame with PSI Byte-Field highlighted and a Breakout of the Non-OTN Client/Non-Multiplexed PSI Message

Figure 2, Illustration of an OPU Frame, transporting the Non-Multiplexed traffic of PSI Message

NOTE:  The easiest way to tell if you’re working with the Non-Multiplexed Traffic type of PSI Message is to check and see if you see the CSF (Client Signal Fail) bit-field in PSI Byte # 2.

If the CSF bit-field is present, you’re dealing with the Non-Multiplexed Traffic type of PSI Message.

If the CSF bit-field is NOT present (within the PSI Message), then you are dealing with the other type of PSI Message.

The Multiplexed Traffic Type of PSI Message

We use the Multiplexed Traffic type of PSI Message anytime we work with an OPU server signal transporting numerous lower-speed ODUj Tributary Signals.

For example, if we mapped and multiplexed 80 ODU0 tributary signals into an OPU4 server signal, then this OPU4 signal would transport the Multiplexed Traffic type of PSI Message.

Figure 3 presents an illustration of an OPU Frame, with the PSI field highlighted, along with a break-out of the Multiplexed Type of PSI Message.

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

Figure 3, Illustration of an OPU Frame transporting the Multiplexed Traffic Type of PSI Message

Again, one big difference between the Multiplexed Traffic type of PSI Message and that for Non-Multiplexed Traffic is that the Multiplexed Traffic type of PSI Message will not have the CSF (Client Signal Fail) bit-field.

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The PSI Message

The PSI (Payload Structure Identifier) message is a 256-byte message that an OTN terminal will transport via the PSI byte for 256 consecutive OPUk/ODUk/OTUk frames.

Let’s talk a little bit about the data that we are transporting within these PSI Messages.  

PSI[0] – or PSI Byte # 0 – PT (Payload Type)

The first byte of the PSI Message (e.g., PSI[0]) carries the Payload Type (or PT) value.  The PT byte identifies the type of client data the OPUk structure is transporting via its payload.  

First, Table 1 presents a list of standard PT values and the corresponding client data types (being transported within the OPUk Structure).

Table 1a, PT (PSI[0]) Values, and the Corresponding Client Data within the OPUk Structure – Part I

PT - Payload Type - PSI Byte - Client Signal into OPUk

Table 1b, PT (PSI[0]) Values, and the Corresponding Client Data within the OPUk Structure – Part II

PT - Payload Type - PSI Byte - Client Signal into OPUk

NOTES: 

  1. We will discuss the PT = 0x07 case when mapping 100GBASE-R into an OPU4 in Lesson 4.  
  2. Access to Lesson 4 requires that you have a membership to “THE BEST DARN OTN TRAINING PERIOD” training.

Table 1c, PT (PSI[0]) Values, and the Corresponding Client Data within the OPUk Structure – Part III

PT - Payload Type - PSI Byte - Client Signal into OPUk

NOTE: 

  1. We will discuss cases where PT = 0x20 and 0x21 in Lesson 5.  
  2. Access to Lesson 5 requires that you have a membership to “THE BEST DARN OTN TRAINING PERIOD” training.

Table 1d, PT (PSI[0]) Values, and the Corresponding Client Data within the OPUk Structure – Part IV

PT - Payload Type - PSI Byte - Client Signal into OPUk

Other posts contain detailed information on how ITU-T G.709 recommends that the System Designer map each client signal into their corresponding OPUk structure.

Click HERE for more information about the PT = 0x21 Method for Mapping/Multiplexing Lower-Speed ODUj signals into a Higher-Speed ODUk Signal.

The Remaining Bytes within the PSI Message

PSI bytes 1 and 3 through 255 are for “Mapping and Concatenation Specific” roles that we will discuss in another post. 

In Multiplexed-Traffic Type of PSI Messages

For the Multiplexed-Traffic type of PSI Message, we use these bytes to transport MSI (Multiplex Structure Identifier) information throughout the OTN.  

In other words, we will transport the MSI information (via these PSI Messages) for applications in which we are mapping/multiplexing lower-speed ODUj tributary signals into higher-speed OPUk/ODUk server signals.

The MSI aims to identify these lower-speed ODUj tributary signals we are transporting via this OPUk/ODUk signal to the OTN.  

You can think of the MSI as a passenger list or manifest of lower-speed ODUj tributary signals riding along (or being transported) within this OPUk server signal.  

In Non-Multiplexed-Traffic Type of PSI Messages

PSI byte 2, Bit 1 (for the Non-Multiplexed Traffic PSI Message) is the CSF (or Client Signal Fail) indicator.  The ITU-T Standards Committee has reserved PSI Byte 2, Bits 2 through 8 for “future standardization.”

We discuss the CSF indicator and the MSI information in other posts.

We also extensively discuss these PSI Messages within THE BEST DARN OTN TRAINING PRESENTATION….PERIOD!!!.  

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