---
description: Understand the shared Operation Handshake control nodes used by Track In, Track Out, and Abort.
alias: userguide-equipment-integration-opcua-standard-operation-handshake
---

# Operation Handshake

## Control Nodes

**Track In**, **Track Out**, and **Abort** use the same three-bit contract.

| Node                        | Owner           | Meaning                                                                                                                                    |
| --------------------------- | --------------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
| `MachineOperationRequest`   | Machine         | Requests that Connect IoT execute the MES operation |
| `MESOperationPerformed`     | Connect IoT | Indicates that MES performed the operation within the current transaction and starts the machine-confirmation phase |
| `MachineOperationConfirmed` | Machine         | Confirms that the machine consumed the MES result, allowing the MES transaction to complete |

All three bits are `Boolean` and are normally `false` while the operation is idle.

## Communication Flows

### Machine-Initiated

```mermaid
--8<-- "docs/userguide/equipmentintegration/opcua-standard/_includes/mermaid-sequence-theme.txt"
sequenceDiagram
    autonumber
    participant M as Machine / PLC
    participant S as OPC UA Server
    participant I as Connect IoT
    participant E as Critical Manufacturing MES

    M->>S: Write Material
    M->>S: MachineOperationRequest = true
    S->>I: Request and payload change notification
    I->>I: Validate Resource, request, and Material Name
    I->>E: Execute MES operation
    E->>E: Validate and perform within transaction

    alt MES validation and processing succeed
        E-->>I: Operation performed, awaiting machine confirmation
        I->>S: MESOperationPerformed = true
        S-->>M: Performed signal available
        M->>M: Consume result

        alt Confirmation before MachineReplyTimeout
            M->>S: MachineOperationConfirmed = true
            S-->>I: Confirmation change notification
            I-->>E: Machine confirmed
            E->>E: Commit transaction
            E-->>I: Operation succeeded
            I->>S: MESOperationPerformed = false
            M->>S: Request and confirmation = false
        else MachineReplyTimeout expires
            I-->>E: Machine confirmation timeout
            E->>E: Roll back transaction
            I->>S: MESOperationPerformed = false
            I-->>I: Record failure diagnostic
        end
    else MES validation or processing fails
        E-->>I: Failure and rollback
        I-->>I: Record diagnostic, performed remains false
    end
```

Step by step:

1. The machine writes the operation payload, including `Material.Name` when available.
2. The machine sets `MachineOperationRequest = true` once.
3. **Connect IoT** resolves the applicable Resource and Material.
4. **Connect IoT** invokes the corresponding MES operation.
5. MES applies its normal preconditions and performs the operation within the current transaction.
6. **Connect IoT** sets `MESOperationPerformed = true` and starts waiting for the machine confirmation.
7. The machine consumes the result and sets `MachineOperationConfirmed = true`.
8. When confirmation arrives before `MachineReplyTimeout`, MES commits the transaction.
9. **Connect IoT** resets `MESOperationPerformed`.
10. The machine resets its request and confirmation bits.
11. If the confirmation does not arrive in time, the command fails and the MES transaction rolls back.

### Operator-Initiated and Hybrid

```mermaid
--8<-- "docs/userguide/equipmentintegration/opcua-standard/_includes/mermaid-sequence-theme.txt"
sequenceDiagram
    autonumber
    actor O as Operator
    participant U as MES UI
    participant E as Critical Manufacturing MES
    participant I as Connect IoT
    participant S as OPC UA Server
    participant M as Machine / PLC

    O->>U: Perform Track In, Track Out, or Abort
    U->>E: Execute standard MES operation
    E->>E: Validate and perform within transaction
    E-->>I: Operation event, awaiting machine confirmation

    I->>S: MESOperationPerformed = true
    S-->>M: Performed signal available
    M->>M: Consume MES-originated result

    alt Confirmation before MachineReplyTimeout
        M->>S: MachineOperationConfirmed = true
        S-->>I: Confirmation change notification
        I-->>E: Machine confirmed
        E->>E: Commit transaction
        E-->>U: Operation succeeded
        U-->>O: Success
        I->>S: MESOperationPerformed = false
        M->>S: MachineOperationConfirmed = false
    else MachineReplyTimeout expires
        I-->>E: Machine confirmation timeout
        E->>E: Roll back transaction
        E-->>U: Operation failed
        U-->>O: Failure
        I->>S: MESOperationPerformed = false
    end
```

In this path:

- The operator acts through the MES UI.
- MES validates and performs the standard operation within its transaction.
- `MachineOperationRequest` remains `false`.
- The affected Material is taken from the MES operation context, not from the OPC UA Material node.
- The machine must monitor `MESOperationPerformed` even when it did not issue a request.
- MES commits the operation only after the machine confirms within `MachineReplyTimeout`.

## Material Resolution

For a machine-initiated request, Connect IoT resolves the Material in this order:

1. If `Operation.<Operation>.Material.Name` is non-empty, resolve that exact MES Material.
2. Otherwise, read `IndEqAutomationOperationAllowFIFO` from the Resource attribute.
3. If FIFO is disabled, reject the request.
4. If FIFO is enabled, select the first eligible Material for the operation.

| Operation     | FIFO source when enabled                                             |
| ------------- | -------------------------------------------------------------------- |
| **Track In**  | First eligible queued/dispatched Material for the Resource and Step |
| **Track Out** | First eligible in-process Material at the Resource and Step         |
| **Abort**     | First eligible in-process Material at the Resource and Step         |

FIFO does not mean an arbitrary Material. The selected Material must still satisfy the normal MES operation rules.

## Missing Acknowledgement and Recovery

After setting `MESOperationPerformed = true`, Connect IoT waits for `MachineOperationConfirmed = true` for the period configured by `/IndEq/Automation/OpcUaServer/MachineReplyTimeout/`.

- If confirmation is received in time, the MES operation completes and its transaction commits.
- If the timeout expires first, the command fails, the MES operation is not successful, and its transaction rolls back.
- A rollback restores the MES transaction, but it cannot prove that the physical machine did not already react to the performed signal.
- Recovery must reconcile MES, handshake values, and the physical machine state before resetting or retrying.

See [Automation Timeout Settings](../configuration/opcua-connection.md#automation-timeout-settings) for configuration guidance.

## Reset Contract

The idle state is:

```text
MachineOperationRequest   = false
MESOperationPerformed     = false
MachineOperationConfirmed = false
```

The machine must not raise a new request until the previous cycle has returned to idle. Connect IoT must not interpret a bit that remained high from the preceding cycle as a new request.