Security
Security can be divided into the following three topics.
Identification
If multiple clients are to communicate with the same server, it might be necessary for the clients to identify themselves. Usually this is used in conjunction with authentication and encryption.
<Heartbeat Id="103" ClientId="012345"></Heartbeat>
Authentication
Authentication is as simple as adding a password to each datagram. Both server and client may require authentication.
<Heartbeat Id="103" Authentication="dz80mi0pql+js9028jm8c89jv8"></Heartbeat>
Encryption
Authentication is essentially pointless without encryption. If authentication is used, the TCP socket should be encrypted using SSL.