# How Should an OTN STE Declare and Clear the dAIS Defect Condition (OTUk-AIS)?

In another post, we describe the OTUk-AIS Maintenance Signal.

Further, in that post, I stated that ITU-T G.709 does not require that an OTN STE be able to generate and transmit the OTUk-AIS Maintenance Signal.

However, I also stated that ITU-T G.709 DOES require that an OTN STE be capable of receiving and processing the OTUk-AIS Maintenance signal, such that it can declare and clear the OTUk-AIS defect condition.

## What about this Post?

In this post, we will discuss how an STE should declare and clear the * dAIS (OTUk-AIS) defect condition*.

**NOTE:** Please do not confuse this particular dAIS Defect (in response to the detection of the OTUk-AIS Maintenance signal) with the other AIS Defect (in response to receipt of the ODUk-AIS Maintenance Signal).

Although their names are similar, they are two very different maintenance signals and defects.

In the OTUk-AIS Maintenance Signal Post, we state that the OTUk-AIS Maintenance Signal is an * Unframed PN-11 Pattern*. More specifically, ITU-T G.709 defines this PN-11 sequence by the generating polynomial: 1 + x

^{9}+ x

^{11}.

## How to Detect the PN-11 Pattern?

If we want to be able to detect, declare, and also clear the * dAIS condition*, then we need to have some ability to detect this

*.*

**unframed PN-11 pattern**Fortunately, the ITU-T Standard Committee did a lot of the work for us and defined such a circuit within ITU-T G.798.

I show this * Inverse PN-11 Circuit*, below in Figure 1.

**Figure 1, Illustration of the Inverse PN-11 Circuit**

### How Does this Inverse PN-11 Circuit Work?

This * Inverse PN-11 Circuit* makes up a big part of our

*(that we also mention in the post on the OTSi/OTUk_A_Sk atomic function).*

**dAIS Detection Circuit**The user should apply both the Recovered OTUk Data and Clock Signal at the * IN* and

*inputs of our*

**Clock***, respectively.*

**Inverse PN-11 Circuit**If our OTUk data-stream is carrying the OTUk-AIS Maintenance signal (e.g., an * Unframed PN-11 signal*) and if we are applying this data to the

*input (of our circuit), then our*

**IN***will generate an*

**Inverse PN-11 circuit***at the Node, that I’ve labeled*

**All-Zeros Pattern***.*

**OUT**I show our Inverse PN-11 Circuit, again, below in Figure 2. However, in this figure, I also highlight these two reference points.

**Figure 2, Illustration of the Inverse PN-11 Circuit – with the Locations of the OTUk-AIS Maintenance Signal and the Resulting All-Zeros Pattern Highlighted. **

Now before we get too excited, we need to recognize that two conditions will cause our * Inverse PN-11 circuit* to generate an

*at the*

**All-Zeros Pattern***node.*

**OUT**- Our
will generate the All-Zeros pattern at the**Inverse PN-11 Circuit**Node, whenever the**OUT**is present at the**OTUk-AIS Maintenance Signal**input (to this circuit), and**IN** - Our
will also generate the AIl-Zeros pattern (at the**Inverse PN-11 Circuit**Node), whenever someone applies an**OUT**at the**All-Zeros Pattern**Input.**IN**

### OTUk-AIS Maintenance Signal or All-Zeros Pattern Signal at the IN input?

Hence, whenever we are using the Inverse PN-11 Circuit to check for the OTUk-AIS Maintenance signal, we (of course) need to check the * OUT* Node (or our Inverse PN-11 Circuit).

However, we also need to check and make sure that we are NOT receiving an All-Zeros pattern at the * IN* input.

If we are TRULY receiving the OTUk-AIS Maintenance Signal, then we will see an All-Zeros pattern at the * OUT* Node, while the signal that is present at the

*input is NOT an All-Zeros pattern.*

**IN**I summarize how the * Inverse PN-11 Detector circuit* works for various signals (at the IN input) below in Table 1.

**Table 1, A Truth-Table presenting How the Inverse PN-11 Detector Circuit responds to Various Signals (at the IN input)**

IN Input | OUT Node | Comments |
---|---|---|

All-Zeros Signal | All-Zeros Signal | An All-Zeros pattern at the Input results in an INAll-Zeros pattern at the Node.OUT No OTUk-AIS. |

Ordinary OTUk Traffic | Non All-Zeros Pattern Signal | Normal Traffic Situation |

OTUk-AIS Maintenance Signal | All-Zeros Signal | The Presence of an All-Zeros Signal at the Node, and the Non OUTAll-Zeros pattern at the input indicates INOTUk-AIS. |

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## Criteria for Declaring the dAIS Defect?

OK, we now have a basic understanding of how the * Inverse PN-11 Detector circuit *works. We also know what signals to look for, to determine if the

*is detecting the OTUk-AIS Maintenance signal.*

**Inverse PN-11 Circuit**Let’s now move on to the full criteria for declaring the * dAIS defect*.

When checking for * dAIS*, ITU-T G.798 recommends that we continuously monitor both of the signals at the

*input signal and the*

**IN**

**OUT**Node of our**Inverse PN-11 Circuit**.ITU-T G.798 goes on to (effectively) state, that we should continuously check these signals over a rolling 8192 bit-interval (or sliding window, if you will).

If our * Inverse PN-11 circuit* detects a set of three (3) consecutive strings each of 8192-bit periods (in length), such that BOTH of the following conditions are TRUE for each of these three 8192 bit-periods, then we MUST

*.*

**declare the dAIS defect condition**- The number of 1s bits at the
Node is less than 256; AND**OUT** - the number of 1s bits at the
Input is at 256 or more.**IN**

I show an illustration of the * dAIS Defect Declaration Criteria*, below in Figure 3.

**Figure 3, Illustration of the dAIS (OTUk-AIS) Defect Declaration Criteria**

## Criteria for Clearing the dAIS Defect Condition

On the other hand, while we are declaring the * dAIS defect* if our

*detects a set of three (3) consecutive strings, each of 8192-bit periods (in length) such that EITHER of the following conditions is TRUE for each of these three 8192 bit periods, then we MUST clear the*

**Inverse PN-11 circuit***.*

**dAIS defect condition**- If the number of 1s bits at the
Node is 256 or more, OR**OUT** - If the number of 1s bits at the
input is less than 256 in three consecutive 8192-bit intervals.**IN**

I show an illustration of the * dAIS Defect Clearance Criteria*, below in Figure 4.

**Figure 4, Illustration of the dAIS (OTUk-AIS) Defect Clearance Criteria**

## What Entities or Atomic Functions declare and clear the dAIS (OTUk-AIS) defect condition?

The OTSi/OTUk_A_Sk function is the only atomic function that contains an * Inverse PN-11 Detector circuit*. Hence, it is the one atomic function that will declare or clear the

*.*

**OTUk-dAIS Defect condition****NOTE:** For Multi-Lane Applications, the OTSiG/OTUk_A_Sk function does not contain an * Inverse PN-11 Detector circuit*, nor does it declare or clear the

*.*

**dAIS Defect condition**If for some reason, an OTL3.4 or OTL4.4 signal were carrying the OTUk-AIS Maintenance Signal (which, again is an * Unframed PN-11 Pattern*), then the OTSiG/OTUk_A_Sk function (that is receiving this signal) would instead, continuously declare the

*(*) within each of the 4 or 20 Logical Lanes.*

**dLOFLANE defect condition**This atomic function would also declare the * dLOL defect*(*) as well.

* NOTE: (*) *– Indicates that you need to be a member of

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