What is the Trail-Trace Identifier Message?

This blog post defines the contents within the Trail Trace Identifier Messages, that we transport throughout the Optical Transport Network.

What is the Trail-Trace Identifier (TTI) Message?

We transport Trail Trace Identifier (TTI) messages at the OTU Layer, the ODU Layer, and for the (as many as 6) TCM Layers. In this blog post, I will talk about the type of data we transport within TTI Messages.

I illustrate the byte format of the Trail-Trace Identifier (TTI) message below in Figure 1.

Byte Format of the SM-TTI Message - Showing Synchronization between TTI Message and the MFAS Byte

Figure 1, Illustration of the Byte Format of the Trail-Trace Identifier (TTI) Message

Figure 1 shows that the Trail-Trace Identifier message is:

  • 64 bytes in length,
  • It consists of the following fields:
    • 16 bytes of SAPI (Source Access Point Identifier)
    • 16 bytes of DAPI (Destination Access Point Identifier), and
    • 32 bytes of Operator Specific data
  • We always synchronize our transmission of the TTI Messages with the MFAS byte.
    • This means that we always transmit the first byte of the SAPI field (SAPI[0]) whenever the six LSBs of the MFAS value are [0, 0, 0, 0, 0, 0], and
    • We transmit the last (or 64th byte of the TTI Message) whenever the six LSBs of the MFAS value are [1, 1, 1, 1, 1, 1].

Hence, we not only show the byte format of the Trail-Trace Identifier Message (in Figure 1), but we also show the sequence in which we transmit the byte within the TTI Message.

What Does SAPI (or Source Access Point Identifier) and DAPI (Destination Access Point Identifier) Mean?

The SAPI is a 16-byte sequence (or a subset of data) within the TTI Message.

The first byte of the SAPI field (SAPI[0]) is always set to 0x00.

The remaining 15 bytes (e.g., SAPI[1] to SAPI[15] contain the 15-byte (or 15-character) Source Access Point Identifier.

The first bit of the SAPI field (within bytes 1 through 15) will be set to “0”. Hence, each SAPI byte field is a 7-bit character field.

I highlight the 16-byte SAPI field within the TTI Message in Figure 2.

The SAPI (Source Access Point Identifier) field within a Trail Trace Identifier Message

Figure 2, The 16-byte SAPI field.

Likewise, for the DAPI (Destination Access Point Identifier) field.

We always transmit the first byte of the DAPI field, DAPI[0] coincident whenever the 6 LSBs of MFAS are [0, 1, 0, 0, 0, 0].

I highlight the 16-byte DAPI field within the TTI Message in Figure 3.

The DAPI (Destination Access Point Identifier) bytes within the Trail Trace Identifier Message

Figure 3, The 16-byte DAPI field.

Access Point Identifier (SAPI and DAPI) Features

Each API (or Access Point Identifier) must have the following features (and I’m quoting ITU-T G.709):

  • Each API must be globally unique in its layer network.
  • Where it may be expected that the access point may be required for path set-up across an inter-operator boundary, the access point identifier must be available to other network operators.
  • The access point identifier should not change while the access point remains in existence.
  • The access point identifier should identify the country and network operator responsible for routing to and from the access point.
  • The set of all access point identifiers belonging to a single administrative layer network should form a single access point identification scheme.
  • The scheme of access point identifiers for each administrative layer network can be independent of the scheme in any other administrative layer network.

The standards recommend that the ODUk, OTUk, and OTS each have the access point identification scheme based on a tree-link format to aid routing control search algorithms. The access point identifier should be globally unambiguous.

Additionally, according to Figures 1, 2, and 3, the network must set the first bit (within each byte of the SAPI and the DAPI) to “0”. Hence, we represent the SAPI and DAPI values with 15 7-bit characters.

What Kind of Data Do We Transport via the SAPI and DAPI Fields within the TTI Messages?

I earlier mentioned the following:

  • Each TTI Message contains a 16-byte SAPI and 16-byte DAPI field
  • However, the network set the first byte of each SAPI and DAPI field to an all-zeros pattern.
  • In the remaining 15 bytes (of the SAPI and DAPI fields), the most significant bit-field is set to “0”.
  • This means that the SAPI and DAPI fields carry 15 7-bit fields.

ITU-T G.709 states that “the access point identifier (SAPI, DAPI) shall consist of a three-character international segment (or sequence) and a twelve-character national segment.” I illustrate the basic structure for the Access Point Identifier (SAPI and DAPI) below in Figure 4.

SAPI and DAPI Field Formats - within the Trail Trace Identifier Message

Figure 4, Access Identifier Structure (for both SAPI and DAPI)

The international segment (or international sequence) field consists of a three-character ISO 3166 geographic/political Country Code (G/PCC). The country code (CC) shall be based on the three-character uppercase alphabetic ISO 3166 country code (e.g., USA, FRA).

The national segment field consists of two subfields: the ITU carrier code (ICC) is followed by a unique access point code (UAPC).

The ITU carrier code is a code assigned to a network operator service provider, maintained by the ITU-T Telecommunication Standardization Bureau (TSB) as per ITU-T M.1400. This code shall consist of 1 to 6 left-justified characters, alphabetic, or leading alphabetic with trailing numeric.

The unique access point code shall be a matter for the organization to which the country code and ITU carrier code have been assigned, provided that uniqueness is guaranteed. This code shall consist of 6 to 11 characters, with trailing NUL, completing the 12-character national segment.

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So What Does All This Mean for STE Equipment?

All of this means the following:

  • Each piece of Section Terminating Equipment (STE) contains a unique 15-character (7-bit) Access Point Identifier value.
  • In other words, no two STEs (in the world) can share the same 15-character Access Point Identifier value.
  • The ITU and the nation (that the STE resides within) dictate the exact Access Point Identifier value (that we assign to a given STE).
  • Whenever a given STE transmits a TTI message to another STE, it will use the SAPI value to identify itself (the Source STE). It will also use the DAPI value to identify the Destination STE (that it sends the TTI Message to).

We Also Deal with TTI Messages with PTE (Path Terminating Equipment) and TCMTE (Tandem Connection Terminating Equipment) – Do These Rules apply to the ODU Layer and the ODUT Layers as Well?

The answer is yes.

  • Each piece of Path Terminating Equipment (PTE) contains a unique 15-character (7-bit) Access Point Identifier value.
  • The ITU and the nation (that the PTE resides within) dictate the exact Access Point Identifier value (that we assign to a given PTE).
  • Whenever a given PTE transmits a TTI message to another, it will use the SAPI value to identify itself (the Source PTE). It will also use the DAPI value to identify the Destination PTE (that it sends the TTI Message to).

Each of the four bullet points (above) applies to as many as 6 ODUT (or Tandem Connection Monitoring) Layers (within the TCMTE).

How About the Operator-Specific Portion of the TTI Message

We have no defined use for the Operator Specific Portion of the TTI Message for the time being. For now, we would reserve this 32-byte field for future use.

Which Byte-Fields Do We Use to Transport the TTI Message within an OTN Signal?

We transport TTI Messages within each of the following OTN Layers:

  • OTU – Section Monitoring Overhead
  • ODU – Path Monitoring Overhead, and
  • As many as 6 Tandem Connection Monitoring Layers (TCM01 to TCM06)

Transporting TTI Messages at the OTU-Layer

At the OTU Layer, we will use the SM (Section Monitoring) field within each OTU frame to transport TTI Messages. I illustrate an OTU frame with the SM field highlighted in Figure 5.

OTUk Framing Format - Identifying Section Monitoring field

Figure 5, We Use the Section Monitoring (SM) field to transport the TTI Messages.

The SM field is a 3-byte field. In Figure 6, I zoom in and expand the SM field (to reveal the 3 bytes within the SM field). We transport the TTI Messages (within an OTU frame) via the TTI byte I show below in Figure 6.

Section Monitoring Field with the TTI (Trail Trace Identifier) Byte-field highlighted

Figure 6, We Identify the TTI (Trail Trace Identifier) Byte within the SM Field – That We Use to Transport TTI Messages via an OTU signal.

Transporting TTI Messages at the ODU Layer

At the ODU Layer, we will use the PM (Path Monitoring) field within each ODU frame to transport TTI Messages. I illustrate an ODU frame with the PM field highlighted in Figure 7.

An ODU Frame with the PM or PMOH Field Highlighted

Figure 7, We Use the Path Monitoring (PM) field to transport the TTI Messages.

The PM field is also a 3-byte field. In Figure 8, I zoom in and expand the PM field (to reveal the 3 bytes within the PM field). We transport the TTI Messages (within an ODU signal) via the TTI byte that I show below in Figure 8.

Path Monitoring Field with the Trail Trace Identifier Byte-field highlighted

Figure 8, We Identify the TTI (Trail Trace Identifier) Byte within the PM Field – That We Use to Transport TTI Messages via an ODU signal.

Transporting TTI Messages at (as many as) 6 ODUT Layers – for Tandem Connection Monitoring

At the ODUT Layers, we will use the SM (Section Monitoring) field within as many as six (6) TCMOH fields within each ODUT frame to transport TTI Messages. I illustrate an ODU/ODUT frame with the 6 TCMOH fields highlighted in Figure 9.

The 6 TCMOH (TCM Overhead Fields) within an ODU Frame

Figure 9, An ODU Frame with each of the 6 TCMOH Fields Highlighted

Each of the TCM fields is also a 3-byte field. In Figure 10, I zoom in and expand the TCM field (to reveal the 3 bytes within each TCM field). We transport the TTI Messages (within an ODUT signal) via the TTI byte that I show below in Figure 10.

A Given TCM Overhead Byte (of the 6 within an ODU frame) - broken into the 3 byte-fields. TTI Byte is highlighted

Figure 10, We Identify the TTI (Trail Trace Identifier) Byte within a given TCM Field – That We Use to Transport TTI Messages via an ODUT signal.

To be clear, we can transport as many as 8 TTI messages independently through an OTN signal at a given time.

  • One TTI Message at the OTU Layer (via the TTI-byte-field within the SM byte)
  • One TTI Message at the ODU Layer (via the TTI-byte-field within the PM byte), and
  • As many as 6 TTI Messages at each (of 6 possible) ODUT/TCM Layers (via the TTI byte-field within the SM byte).

Please see the relevant post for more details on how we transport TTI Messages at a given OTN Network Layer.

OTN – Lesson 12 – APS Features within Atomic Functions – Part 2

This blog post presents a video that discusses the APS features within some fo the Atomic Functions that we discussed in Lesson 11.

Lesson 12 – Video 13 – Detailed Implementation of APS within the Atomic Functions – Video 2

This blog post continues 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 ODUT/ODU_A_So and ODUT/ODU_A_Sk functions (ODUT/TCM Layer – SNC/S Monitoring)
    • How do we implement the APS features within these Atomic Functions to support TCM Layer i SNC/S Monitoring and Protection-Switching?
    • How do we implement a complete System-Level design (using these atomic functions along with the ODUT_TT_So and ODUT_TT_Sk Atomic Functions)?
      • NOTE: We discussed these atomic functions in Lesson 11. However, we did not discuss the APS features (within those functions) then.

More specifically, we discuss how our system should implement APS and the APS Communication Protocol whenever the upstream ODUT_TT_Sk Atomic Function declares either a Service-Affecting or the TCMi-dDEG defect.

Check Out the Video Below

Continue reading “OTN – Lesson 12 – APS Features within Atomic Functions – Part 2”

OTN – Lesson 12 – Introduction to APS and the APS Communication Protocol for Protection Switching

This blog post presents a video that shows how to implement APS (Automati Protection Switching) both with and without using an APS Communication Protocol.

Lesson 12 – Video 8 – Detailed Discussion of APS without and with the APS Communication Protocol – Video 1

This blog post describes how we can implement APS (Automatic Protection Switching) without using an APS Communication Protocol. Afterward, this blog introduces how to implement APS using the APS Communication Protocol. This video serves as the first of several videos on this topic.

In particular, this video will discuss the following topics:

  • Executing APS without using the APS Communication Protocol
    • Under what conditions can we implement APS without using an APS Communication Protocol?
    • Why can we implement APS (without an APS protocol) in this case?
    • When not supporting an APS Communication Protocol, the Architecture/Design of the Protection-Switching Controllers.
    • How to implement Automatic Protection Switching – without implementing an APS Communication Protocol.
  • Executing APS with an APS Communication Protocol
    • Under what conditions must we implement APS with an APS Communication Protocol?
    • Why do we need to use an APS Communication Protocol for these cases?
    • How to implement Automatic Protection Switching – while using an APS Communication Protocol
      • Introduction to the APS/PCC Field for OTN/Linear Protection Switching Applications (per ITU-T G.873.1).
      • The Architecture/Design of the Protection-Switching Controllers – 1+1 Protection Architecture
      • The Architecture/Design of the Protection Switching Controllers – 1:N Protection Architecture
      • The NR (No Request) Command

To Learn How to Implement APS, with and without an APS Communication Protocol, Check Out the Video Below.

Continue reading “OTN – Lesson 12 – Introduction to APS and the APS Communication Protocol for Protection Switching”

OTN – Lesson 12 – Detailed Discussion of SNC/S Monitoring (Protection Switching)

This blog post presents a video that describes (in detail) SNC/S (Subnetwork Circuit Protection – Sublayer) Monitoring for Protection Switching.

Lesson 12 – Video 7 – Detailed Discussion of SNC/S (Subnetwork Circuit – Sublayer) Monitoring for Protection Switching

This blog post contains a video that presents a detailed discussion of SNC/S (Subnetwork Circuit – Sublayer) Monitoring for Protection Switching purposes at the ODU Layer.

In particular, this video will discuss the following topics:

  • A Detailed Review of SNC/S (Subnetwork Circuit Protection/Sublayer) Monitoring.
  • This video shows example locations/conditions of where we would use SNC/S Monitoring and why we would use this form of monitoring.
  • This video also highlights similarities of SNC/S with SNC/I Monitoring.
  • It also shows the differences between SNC/S and SNC/Ne or SNC/Ns monitoring.
  • Finally, this video reviews a Multi-Administrative Domain Network (and
    Tandem Connection Monitoring) and describes how SNC/S works within a given “Protect Domain.”

Check Out the Video Below.

Continue reading “OTN – Lesson 12 – Detailed Discussion of SNC/S Monitoring (Protection Switching)”

OTN – Lesson 12 – Detailed Discussion of SNC/N Monitoring (Protection Switching)

This blog post presents a video that describes (in detail) SNC/N (Subnetwork Protection – Non-Intrusive) Monitoring for Protection Switching.

Lesson 12 – Video 6 – Detailed Discussion of SNC/N (Subnetwork Circuit – Non-Intrusive) Monitoring for Protection Switching

This blog post contains a video that presents a detailed discussion of SNC/N (Subnetwork Circuit – Non-Intrusive Monitoring, for Protection-Switching purposes, at the ODU Layer.

In particular, this video will discuss the following topics:

  • A Detailed Review of SNC/Ne (Subnetwork Circuit Protection/Non-Intrusive End-to-End) Monitoring, and
  • A Detailed Review of SNC/Ns (Subnetwork Circuit Protection/Non-Intrusive Sublayer) Monitoring.
  • This video shows example locations/conditions of where we would use SNC/Ne or SNC/Ns Monitoring and why we would use this form of monitoring.
  • This video also highlights the similarities and differences between SNC/Ne and SNC/Ns Monitoring.

Check Out the Video Below

Continue reading “OTN – Lesson 12 – Detailed Discussion of SNC/N Monitoring (Protection Switching)”

OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part TWO

This blog post contains the second of two videos that analyzes how the Multi-Administrative Domain uses Tandem Connection Monitoring to respond to service-affecting defects within an ODU signal passing through it.

Lesson 11 – Video 11 – Tandem Connection Monitoring (TCM) Multi-Administrative Domain Defect Analysis – Part TWO

This blog post contains a video covering the second (and final) part of the Multi-Administrative Domain Walk-Through when defects occur.

In particular, this video discusses how the Multi-Administrative Domain will respond to the presence of defects.

This video will analyze the Multi-Administrative Domain’s response to the following two cases.

Case 2 – Whenever a Service-Affecting defect occurs within Serving Operator Domain – Operator B, and

Case 3 – Whenever a Service-Affecting defect occurs within the Protect Domain.

NOTE: In the previous video, we analyzed Case 1 (Service-Affecting defect occurs within the ODU signal but outside of any of the administrative regions).

As we analyze the Multi-Administrative Domain’s response to these defects (for Cases 2 and 3), we will cover the following topics:

  • What exactly occurs within an ODU signal that experiences a service-affecting defect?
  • How do ODU-layer, ODUT-layer, and OTU-layer circuitry respond to such defects?
  • How does the circuitry within these Administrative Domains respond to the service-affecting defects associated with Cases 2 and 3?
  • What does the Path Terminating Equipment (at the remote terminal) do in response to these service-affecting defects?

This video will close out our discussion of Lesson 11 – Tandem Connection Monitoring.

Check Out the Video Below.

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part TWO”

OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part ONE

This blog post contains the first of two videos that analyzes how the Multi-Administrative Domain uses Tandem Connection Monitoring to respond to service-affecting defects within the ODU signal passing through it.

Lesson 11 – Video 10 – TCM Multi-Administrative Domain Defect Analysis – Part ONE

This blog post contains a video covering the first part of the Multi-Administrative Domain Walk-Through when defects occur.

In particular, this video discusses how the Multi-Administrative Domain will respond to the presence of defects.

During this video, we assume that we are experiencing a service-affecting defect within the ODU signal (that passes through the Multi-Administrative Domain). However, in this case, we assume that the defect occurs outside any administrative regions. As we analyze the Multi-Administrative Domain’s response to this defect, we will cover the following topics:

  • What exactly occurs within an ODU signal that experiences a service-affecting defect?
  • How do ODU-layer, ODUT-layer, and OTU-layer circuitry respond to such defects?
  • How does each Administrative Domain respond to the presence of a service-affect defect outside of the Service-Requesting (or any other Domain) using Tandem Connection Monitoring?
  • What does the Path Terminating Equipment (at the remote terminal) do in response to this service-affecting defect?

I hope the student will better understand Tandem Connection Monitoring as we go through this and the following video.

Check Out the Video Below.

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administrative Domain Defect Analysis – Part ONE”

OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administration Domain Walk-Thru – Part TWO

This post serves as Part TWO (and the Final Part) for the Multi-Administrative Domain Walk Through and Analysis for our study of Tandem Connection Monitoring.

Lesson 11 – Video 9 – TCM Multi-Administration Domain Walk Through – Part TWO

This blog post contains a video that covers the second (and final) part of the Multi-Administrative Domain Walk-Through.

In particular, this video covers the following topics:

  • Part TWO of our Multi-Administration Domain Walk-Through (using our knowledge of TCM-related atomic functions to analyze this network).

In particular, this post covers the following parts of the Multi-Administration Domain Walk-Through.

  • Initializing the Serving Operating Domain (Operator B) – TCM Level 3
  • Terminating the Serving Operating Domain (Operator B) – TCM Level 3
  • Initializing the Serving Operating Domain (Operator C) – TCM Level 3
  • Initializing the Protect Domain – TCM Level 4
  • Terminating the Protect Domain – TCM Level 4
  • Terminating the Serving Operating Domain (Operator C) – TCM Level 3
  • Terminating the Leased Service Serving Operator Domain – TCM Level 2
  • Terminating the Service Requesting Domain – TCM Level 1

This video serves as Part TWO (and the Final Part) of our Multi-Administration Domain Walk-Through and Analysis.

Check Out the Video Below.

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring Multi-Administration Domain Walk-Thru – Part TWO”

OTN – Lesson 11 – Tandem Connection Monitoring Controller and Multi-Administration Domain Walk-Thru – Part ONE

This blog post briefly introduces the Tandem Connection Monitoring Controller Atomic Function. This post also serves as Part ONE for the Multi-Administrative Domain Walk Through and Analysis.

Lesson 11 – Video 8 – TCM Controller and Multi-Administration Domain Walk-Through – Part ONE

This blog post contains a video that covers the first part of the Multi-Administrative Domain Walk-Through.

In particular, this video covers the following topics:

  • An Introduction to the TCM (Tandem Connection Monitoring) Controller Atomic Function
  • An Overview of What We Have Covered thus far – In Lesson 11 and Where We’re Going
  • Introduction to Compound (Atomic Functions)
    • Definition/Introduction to the Source Compound Function
    • Definition/Introduction to the Sink Compound Function
  • Part ONE of our Multi-Administration Domain Walk-Through (using our knowledge of TCM-related atomic functions to analyze this network).

In particular, this post covers the following parts of the Multi-Administration Domain Walk-Through.

  • Initializing the Service Requesting Domain – TCM Level 1
  • How We Initialize the Leased Service Serving Operator Domain – TCM Level 2
  • Initializing the Serving Operating Domain (Operator A) – TCM Level 3
  • Terminating the Serving Operating Domain (Operator A) – TCM Level 3

This video serves as Part ONE of our Multi-Administration Domain Walk-Through and Analysis.

Check Out the Video Below

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring Controller and Multi-Administration Domain Walk-Thru – Part ONE”

OTN – Lesson 11 – Tandem Connection Monitoring – Sink Atomic Functions – Video 5

This blog post includes a video that discusses both the ODUTm_TT_Sk (Non-Intrusive Monitoring) Function and the ODUT/ODU_A_Sk Atomic Function. This is the last blog post to describe and define the TCM-related Atomic Functions.

Lesson 11 – Video 7 – Tandem Connection Monitoring – ODUTm_TT_Sk and ODUT/ODU_A_Sk Atomic Functions

This blog post contains a video that covers the fifth part of the Sink Direction Tandem Connection Monitoring (TCM) related Atomic Functions.

In particular, this video covers the following two atomic functions:

  • ODUTm_TT_Sk (Atomic Function for Non-Intrusive Monitoring – TCM Applications), and
  • ODUT/ODU_A_Sk

More specifically, this video covers the following aspects of each of these Atomic Functions.

  • ODUTm_TT_Sk Atomic Function
    • Applications in which we would use the ODUTm_TT_Sk Atomic Function (e.g., Non-Intrusive Monitoring for TCM Subnetworks)
    • A brief overview of this function’s capabilities and attributes
    • How this function differs from the ODUT_TT_Sk Atomic Function?
      • When the ODUT_TT_Sk Function is operating in the OPERATIONAL Mode
      • If the ODUT_TT_Sk Function is running in the MONITOR Mode, and
      • When the ODUT_TT_Sk Function is working in the TRANSPARENT Mode
  • ODUT/ODU_A_Sk Atomic Function
    • Where this function fits into the Tandem Connection Monitoring Network
    • The Architecture/Functionality of the ODUT/ODU_A_Sk Function
      • Operation in the various TCM Modes (e.g., OPERATIONAL and MONITOR/TRANSPARENT).
      • The Protection Port (for Automatic Protection Switching support).
      • The Removal Block – How this function terminates the “Selected TCMOH and APS/PCC field.”
      • Replacing the Normal ODU signal (carrying client data) with either the ODU-AIS or ODU-LCK Maintenance Signals.
      • Asserting CI_SSF and CI_SSD in response to upstream defect conditions.

This video completes our discussion/review of the TCM-related Atomic Functions.

Check Out the Video Below.

Continue reading “OTN – Lesson 11 – Tandem Connection Monitoring – Sink Atomic Functions – Video 5”