Message send protocol
TCP Based Message Send Service
One message send service is defined as a connection based application on TCP. A service listens for TCP connections on port 18. Once a connection is established, a short message is transmitted from the sender to the receiver over the connection. The sender closes the connection after sending the message.
UDP Based Message Send Service
Another message send service is defined as a datagram based application on UDP. A service listens for UDP datagrams on port 18. When a datagram is received by the receiver, an answering datagram is sent back to the sender containing exactly the same data.