This message requests a Heartbeat <35=0> from the opposing application, to verify it is still responsive. The other application responds with a Heartbeat <35=0> echoing back the given TestReqID (112).

TestReqID (112) ensures that the opposite application has generated the Heartbeat as the result of a specific Test Request and not a normal timeout. The opposite application includes the TestReqID in the resulting Heartbeat. Any string can be used as the TestReqID, but uniqueness is preferable for debugging purposes. Timestamps, sequences, or UUIDs are sensible choices.