8.2.2.1
General description
The MQTT (Message Queuing Telemetry Transport) protocol is an open network protocol
for machine-to-machine communication that enables the transmission of telemetric
data between devices. The built-in MQTT client allows the device to publish a specific
set of information to an MQTT broker.
Messages are published once after the device is started and then when the corre‐
sponding value is changed. However, the sending of the message does not take place
immediately, but cyclically, every 5 seconds. In addition to the payload, so-called topics
are also transmitted in the messages. This allows for mapping and hierarchical identifi‐
cation.
The data structure of the messages is in JSON format and is directly oriented on the
schema of the REST API (
Quality of Service cannot be configured and is set to “At most once”, i.e. messages are
only sent once without confirmation from the client or broker.
If the connection is lost, a
Last Will
is sent with the following message:
Table 18: Last Will message
Topic
Message
EXIT
“Publisher”: “Offline”
The MQTT functions are activated in the delivery state. The MQTT client can be deacti‐
vated either via the web interface or directly via the rotary switches.
8.2.2.2
Messages – topics
The following gives an overview of the available messages. The composition of the
topics is based on the REST API schema and is composed as follows:
{client head topic}/[BasePath]/[Domain]/{Parameter}
•
The
{clientHeadTopic}
variable can be assigned via the WebUI. The MAC address is
used as the default value.
•
The
BasePath
is oriented on the REST API standard and is defined at:
/iolink/v1
•
Via [
Domain]
/{
Parameter}
, the respective message is identified:
e.g.: /masters/
{masterNumber}
/ports/
{portNumber}
/configuration
•
The payload of the message is formatted equivalent to the REST API and can
be taken from the OPEN API document,
see "Available variables and methods",
.
Table 19: MQTT topics
Domain Topic
Description
gateway {clientHeadTopic}/iolink/v1/gate‐
way/identification
Read out of identification data (e.g. MAC
address or serial number of the device)
{clientHeadTopic}/iolink/v1/gate‐
way/capabilities
Information on device functions
{clientHeadTopic}/iolink/v1/gateway/con‐
figuration
Read out of device or Ethernet configura‐
tion (e.g. DHCP or IP address)
OPERATION
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