App RFID LLRP Inventory - Inventory Events

There are 3 basic inventory events that are generated and sent to the EdgeX MessageBus. Here are some example EdgeX Events with accompanying EdgeX Readings.

Note

The readings field of the EdgeX Event is an array and multiple Inventory Events may be sent via a single EdgeX Event. Each EdgeX Reading corresponds to a single Inventory Event.

Arrived

Arrived events are generated when ANY of the following conditions are met:

A tag is read that has never been read before
A tag is read that is currently in the Departed state
A tag aged-out of the inventory and has been read again

Example InventoryEventArrived Event

{
  "apiVersion": "v3",
  "id": "6def8859-5a12-4c83-b68c-256303146682",
  "deviceName": "app-rfid-llrp-inventory",
  "profileName": "app-rfid-llrp-inventory",
  "sourceName" : "app-rfid-llrp-inventory",
  "origin": 1598043284109799400,
  "readings": [
    {
      "apiVersion": "v3",
      "id": "8d15d035-402f-4abc-85fc-a7ed7213122a",
      "origin": 1598043284109799400,
      "deviceName": "app-rfid-llrp-inventory",
      "resourceName": "InventoryEventArrived",
      "profileName": "app-rfid-llrp-inventory",
      "valueType": "String",
      "value": "{\"epc\":\"30340bb6884cb101a13bc744\",\"tid\":\"\",\"timestamp\":1598043284104,\"location\":\"SpeedwayR-10-EF-25_1\"}"
    }
  ]
}

Moved

Moved events are generated when ALL of the following conditions are met:

A tag is read by an Antenna (Incoming Antenna) that is not the current Location
The Incoming Antenna's Alias does not match the current Location's Alias
The Incoming Antenna has read that tag at least 2 times total (including this one)
The moving average of RSSI values from the Incoming Antenna are greater than the current Location's adjusted moving average (See: Mobility Profile)

Example InventoryEventMoved Event

{
  "apiVersion": "v3",
  "id": "c78c304e-1906-4d17-bf26-5075756a231f",
  "deviceName": "app-rfid-llrp-inventory",
  "profileName": "app-rfid-llrp-inventory",
  "sourceName" : "app-rfid-llrp-inventory",
  "origin": 1598401259697580500,
  "readings": [
    {
      "apiVersion": "v3",
      "id": "323694d9-1a48-417a-9f43-25998536ae8f",
      "origin": 1598401259697580500,
      "deviceName": "app-rfid-llrp-inventory",
      "resourceName": "InventoryEventMoved",
      "profileName": "app-rfid-llrp-inventory",
      "valueType": "String",
      "value": "{\"epc\":\"30340bb6884cb101a13bc744\",\"tid\":\"\",\"timestamp\":1598401259691,\"old_location\":\"Freezer\",\"new_location\":\"Kitchen\"}"
    }
  ]
}

Departed

Departed events are generated when:

A tag is in the Present state and has not been read in more than the configured DepartedThresholdSeconds

Note

Departed tags have their tag statistics cleared, essentially resetting any values used by the tag algorithm. So if this tag is seen again, the Location will be set to the

first Antenna that reads the tag again.

Example InventoryEventDeparted Event

{
  "apiVersion": "v3",
  "id": "4d042708-c5de-41fa-827a-3f24b364c6de",
  "deviceName": "app-rfid-llrp-inventory",
  "profileName": "app-rfid-llrp-inventory",
  "sourceName" : "app-rfid-llrp-inventory",
  "origin": 1598062424894043600,
  "readings": [
    {
      "apiVersion": "v3",
      "id": "928ff90d-02d1-43be-81a6-a0d75886b0e4",
      "origin": 1598062424894043600,
      "deviceName": "app-rfid-llrp-inventory",
      "resourceName": "InventoryEventDeparted",
      "profileName": "app-rfid-llrp-inventory",
      "valueType": "String",
      "value": "{\"epc\":\"30340bb6884cb101a13bc744\",\"tid\":\"\",\"timestamp\":1598062424893,\"last_read\":1598062392524,\"last_known_location\":\"SpeedwayR-10-EF-25_1\"}"
    },
    {
      "apiVersion": "v3",
      "id": "abfff90d-02d1-43be-81a6-a0d75886cdaf",
      "origin": 1598062424894043600,
      "deviceName": "rfid-llrp-inventory",
      "resourceName": "InventoryEventDeparted",
      "profileName": "rfid-llrp-inventory",
      "valueType": "String",
      "value": "{\"epc\":\"30340bb6884cb101a13bc688\",\"tid\":\"\",\"timestamp\":1598062424893,\"last_read\":1598062392512,\"last_known_location\":\"POS Terminals\"}"
    }
  ]
}

Tag State Machine

Below is a diagram of the internal tag state machine. Every tag starts in the Unknown state (more precisely does not exist at all in memory). Throughout the lifecycle of the tag, events will be generated that will cause it to move between Present and Departed. Eventually once a tag has been in the Departed state for long enough it will "Age Out" which removes it from memory, effectively putting it back into the Unknown state.

Tag State Diagram