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Heartbeat service API

Description​

VAPIX® Heartbeat service API enables devices to send heartbeats to monitor the connection between a device and a master.

The master is typically an Axis door controller connected to another Axis device, for example an I/O module with additional I/O functionality. The master could also be a video management system. The master sends heartbeats to the connected device at regular intervals. If a heartbeat call is not issued successfully within a predefined time, the connection is considered interrupted and the connected device emits a heartbeat lost event. The heartbeat lost event can be used to trigger fallback actions.

Identification​

VAPIX ® Heartbeat service API is supported if:

  • Property: Properties.API.Heartbeat.Heartbeat=yes
  • Property: Properties.API.Heartbeat.Version=1.0 and later.

Using heartbeats​

Use axhbt:Heartbeat to send a heartbeat to a device. The device responds with a session identifier.

Heartbeats should be sent at regular intervals, typically within a few seconds. The Duration field specifies the heartbeat duration, that is, the time the heartbeat is alive. To keep the heartbeat alive, send a new heartbeat before the time expires.

If a heartbeat expires, the session identifier in the device’s response changes. The connection to the device is considered lost and the heartbeat lost event tns1:Device/tnsaxis:Monitor/Heartbeat becomes true.

The heartbeat lost event indicates that the heartbeat has not reached the device. By setting up action rules that listen to the event, the Axis product can be configured to, for example, change I/O port states or send notification messages if a heartbeat is lost. Action rules are described in section Event and action services.

The following pseudocode shows a typical setup that triggers an action rule set_wanted_port_states() if the heartbeat is lost. A new heartbeat is sent every 10 seconds. If the heartbeat is lost, the session identifier changes and the action rule triggers.

info

A changed session identifier indicates that a heartbeat lost event has been emitted. Make sure that action rules and software that use the event are reset.

Pseudocode:

{
  setup_port_action_rules()

    loop {
      session_id = axhbt.Heartbeat(10000)

      if (session_id != old_session_id)
        set_wanted_port_states()

      old_session_id = session_id

       wait_until(current_time + 5 seconds)
    }
}

API calls can be constructed using JSON or using SOAP.

The following example show how to send a heartbeat with duration 10 seconds.

Request using JSON:

POST /vapix/axhbt HTTP/1.1
Host: root:pass@192.168.0.90
Content-Type: application/json

{
  "axhbt:Heartbeat":{
    "Duration": 10000,
  }
}

JSON response:

HTTP/1.1 200 OK
Content-Type: application/json

{
  "SessionId": "14b795e4-507a-44b8-b68c-f98be55bc1dd"
}

Request using SOAP:

POST /vapix/services HTTP/1.1
Host: root:pass@192.168.0.90
Content-Type: text/xml

<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://www.w3.org/2003/05/soap-envelope" xmlns:SOAP-ENC="http://www.w3.org/2003/05/soap-encoding" xmlns:axgpio="http://www.axis.com/vapix/ws/Heartbeat" xmlns="http://www.axis.com/vapix/ws/Heartbeat">
  <SOAP-ENV:Header></SOAP-ENV:Header>
  <SOAP-ENV:Body>
    <axhbt:Heartbeat>
      <axhbt:Duration>10000</axhbt:Duration>
    </axhbt:Heartbeat>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

SOAP response body:

<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope xmlns:SOAP-ENV="http://www.w3.org/2003/05/soap-envelope" xmlns:SOAP-ENC="http://www.w3.org/2003/05/soap-encoding" xmlns:axgpio="http://www.axis.com/vapix/ws/Heartbeat" xmlns="http://www.axis.com/vapix/ws/Heartbeat">
  <SOAP-ENV:Header></SOAP-ENV:Header>
  <SOAP-ENV:Body>
    <axhbt:HeartbeatResponse>
      <axhbt:SessionId>14b795e4-507a-44b8-b68c-f98be55bc1dd</axhbt:SessionId>
    </axhbt:HeartbeatResponse>
  </SOAP-ENV:Body>
</SOAP-ENV:Envelope>

Heartbeat command​

Use the Heartbeat command to send a heartbeat. The heartbeat is valid during the time specified by the Duration field.

  • Command: axhbt:Heartbeat
  • Access class: ACTUATE

Message name: Request

{
  "Duration": "<int>"
}

with the following data fields:

Data fieldValid valuesDescription
DurationIntegerHeartbeat duration, that is, the time before a heartbeat lost event is emitted.Unit: milliseconds

Message name: Response

{
  "SessionId": "<string>"
}

with the following data fields:

Data fieldValid valuesDescription
SessionIdStringSession identifier. The session identifier remains the same as long as the heartbeat is kept alive. If the session identifier changes between two successive calls, action rules and software that use the heartbeat lost event might have triggered and might need to be reset.

Heartbeat lost event​

The heartbeat lost event tns1:Device/tnsaxis:Monitor/Heartbeat is a stateful event which becomes true when the heartbeat duration expires.

To retrieve the event declaration, use aev:GetEventInstances.

Event declaration:

<tns1:Device aev:NiceName="Device">
  <tnsaxis:Monitor aev:NiceName="Monitor">
    <Heartbeat wstop:topic="true" aev:NiceName="Heartbeat">
      <aev:MessageInstance aev:isProperty="true">
        <aev:DataInstance>
          <aev:SimpleItemInstance aev:NiceName="Heartbeat lost" Type="xsd:boolean" Name="lost" isPropertyState="true">
          </aev:SimpleItemInstance>
        </aev:DataInstance>
      </aev:MessageInstance>
    </Heartbeat>
  </tnsaxis:Monitor>
</tns1:Device>
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