heartbeat message

A UDP (User Datagram Protocol) data packet used to monitor a data connection, polling to see if the connection is still alive.
 In general terms, a heartbeat is a signal emitted at regular intervals by software to demonstrate that it is still alive. In networking, a heartbeat is the signal emitted by a Level 2 Ethernet transceiver at the end of every packet to show that the collision-detection circuit is still connected.