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Bluetooth Connection and pairing

Micro tracker and Smart Badge:

  • Scenarios that will trigger Bluetooth advertisement:

    • The tracker resets: the advertisement is activated during ble_cnx_adv_duration time. It begins as soon as the tracker attempts the join request. After this period,

      • If the tracker is bonded, it continues to advertise
      • If the tracker is not bonded, the advertisement is stopped

    • The tracker is turned ON with the button press or if it exits shipping state: If the bit 5 of the config_flags parameter is set, the advertisement is activated during ble_cnx_adv_duration time. After this period,

      • If the tracker is bonded, it continues to advertise
      • If the tracker is not bonded, the advertisement is stopped

    • CLI command(1): Enter "ble connect start" on CLI with tracker connected to USB port. The tracker starts the advertisement for a fixed duration of 60 seconds. a parameter can be added to the command to specify an advertisement duration. After this period:

      • If the tracker is bonded the trackers continue to advertise.
      • If not the advertisement is stopped

    • A LoRa downlink(2): It advertises during the duration set in the downlink. After this period:

      • If the tracker is bonded the trackers continue to advertise.
      • If not the advertisement is stopped

Compact and industrial tracker:

  • Scenarios that will trigger Bluetooth advertisement:

    • The tracker resets: the advertisement is activated during ble_cnx_adv_duration time. It begins in join step After this period,

      • If the tracker is bonded the trackers continue to advertise
      • If the tracker is not bonded, the advertisement is stopped

    • The tracker exits shipping state: If the bit 5 of the config_flags parameter is set, the advertisement is activated during ble_cnx_adv_duration time. After this period, the advertisement is stopped no matter the bond state

    • CLI command(1): Enter "ble connect start" on CLI with tracker connected to USB port. The tracker starts the advertisement for a duration of 60 seconds or ble_cnx_adv_duration time (if this parameter value is smaller than 60 seconds). A parameter can be added to the command to specify an advertisement duration. After this period, the advertisement is stopped no matter the bond state

    • A LoRa downlink(2): Advertises during the minimum value between the value set in the downlink and ble_cnx_adv_duration time. After this period, the advertisement is stopped no matter the bond state.

    • A reed switch sequence(3): if it is configured for and if the bit 5 of the config_flags parameter is set. The advertisement is activated during ble_cnx_adv_duration time. After this period, the advertisement is stopped no matter the bond state.

For all trackers, the user can stop at any time the BLE connectivity (communication or advertisement) using:

  • CLI command(1): Enter "ble connect stop" with the tracker connected to USB port of computer.
  • LoRa downlink(2): with a duration of (0 - 0xFF010B0000) seconds
Notes

(1) Refer to the application note AN-013_CLI_description for more details.

(2) Refer to the section BLE scan and communication parameters and Start and Stop BLE Advertisement for more details.

(3) Only for compact trackers, refer to Reed switch interface for more details.

Bonding procedure​

When the tracker advertises and is not bonded (fast advertisement), the buzzer beeps during the first 15 seconds.

Once the connection has been established, the Client application should send a bond request within a fixed delay of 1 minute. If no bond request is received during this period, the BLE module is switched off. If the bonding fails, advertisement should be restarted to attempt a new bonding procedure.

Bluetooth Secured connection​

A secured connection is established when a known Central device (for ex. mobile phone) initiates a connection request and the tracker is not bonded.

Security keys are stored in both the tracker and Central device if the bonding process was successful. The connection is encrypted.

As soon as the BLE secure connection is established (with the bond information), the tracker enters a special mode where the following applies:

  • Accelerometer and battery monitoring tasks are maintained.
  • An event uplink is sent, refer to the section BLE communication events.
  • All LoRaWAN™ communications are stopped (except shutdown message in case the tracker is turned off).
  • No geolocation is performed.
Notes
  1. Once connected, the tracker does not accept any other BLE connections.
  2. If the tracker has the bond information, only the paired central device can connect to it.
  3. When the tracker is bonded and securely connected to the central device, the geolocation is done by the central device.
  4. If a bonded central device lost its security keys, it can establish the bond again with the tracker, if the bit 11 of the config_flags parameter is set to 0. See Asymmetric BLE pairing section below for more details

Disconnection with a bonded device​

The BLE connection on the tracker is considered lost if no messages are received for 6 seconds (Supervision timeout). 30 seconds after a secured connection is lost, the last configured operational mode of the tracker is restored.

Clear bond event​

The bond information can be cleared by:

  • A LoRaWAN™ Downlink (Refer to the sections BLE parameters and Reset the device for more details)
  • A specific BLE command
  • A CLI command (Refer to the application note AN-013_CLI_description for more details)
  • A specific button sequence (see Micro Tracker Commands for more details):
    • Hold the button for more than 14 sec to enter ESC sequence. The tracker will play melody indicating the fact that special sequence can be started.
    • Once inside the special sequence, do the following: 1 click, 1 click or more, 1x press (between 1 and 4 sec)

Once bluetooth bond is removed, the tracker is disconnected from the central device and switches to its configured operational mode. An event payload bond deleted is systematically sent regardless of the bonding state. In prior MCU/Application Firmware version 2.2-1 and below, this uplink was only sent if the tracker was bonded.

The Bluetooth advertisement restarts during ble_cnx_adv_duration time.

Asymmetric BLE pairing​

The asymmetric BLE pairing feature is configurable in the config_flags (bit 11) and controls if the device can renew the bond in case the central device has lost its bond information with the tracker:

  • If set to 1, the tracker cannot renew the bond and it won't be able to reconnect with another central device (this configuration enhances the security, however, the device's bond can be reset by sending BLE bond reset downlink message, with CLI OR with button sequence)
  • If set to 0, the tracker allows to renew the bond with the central device with which its already bonded.
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