Heartbeat is not a special component, but rather a set of messages that each REQ component can send to its REP-component(s) or ROUTER component(s) to guarantee two things:
The heartbeat is different from the FM.5 RequestStatus message, as it is not interested in the state of the Model, but rather in the state of the connection to the Model Controller. The heartbeat can also be used to check if a FederateStarter or a LoadBalancer is still up-and-running.
There are two heartbeat messages:
The messages are quite simple, and do not have a payload. See Heartbeat Messages for more information about the messages. The Heartbeat message can be sent as often as required, e.g. once a minute or once every 10 seconds, depending on the speed by which a time-out or frozen / crashed component should be detected.