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copied!<p><a href="http://en.wikipedia.org/wiki/Distributed_Interactive_Simulation" rel="noreferrer">Distribued Interactive Simulation</a> (DIS), which is defined under <a href="http://standards.ieee.org/" rel="noreferrer">IEEE</a> Standard 1278, uses a default heartbeat of 5 seconds via UDP broadcast. A DIS heartbeat is essentially an Entity State PDU, which fully defines the state, including the position, of the given entity. Due to its application within the simulation community, DIS also uses a concept referred to as dead-reckoning to provide higher frequency heartbeats when the actual position, for example, is outside a given threshold of its predicted position.</p> <p>In your case, a DIS Entity State PDU would be overkill. I only mention it to make note of the fact that heartbeats can vary in frequency depending on the circumstances. I don't know that you'd need something like this for the application you described, but you never know.</p> <p>For heartbeats, use UDP, not TCP. A heartbeat is, by nature, a connectionless contrivance, so it goes that UDP (connectionless) is more relevant here than TCP (connection-oriented).</p> <p>The thing to keep in mind about UDP broadcasts is that a broadcast message is confined to the <a href="http://en.wikipedia.org/wiki/Broadcast_domain" rel="noreferrer">broadcast domain</a>. In short, if you have computers that are separated by a layer 3 device, e.g., a router, then broadcasts are not going to work because the router will not transmit broadcast messages from one broadcast domain to another. In this case, I would recommend using multicast since it will span the broadcast domains, providing the time-to-live (TTL) value is set high enough. It's also a more automated approach than directed unicast, which would require the sender to know the IP address of the receiver in order to send the message.</p>

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