Network Working Group J. Postel Request for Comments: 863 ISI May 1983
One discard service is defined as a connection based application on TCP. A server listens for TCP connections on TCP port 9. Once a connection is established any data received is thrown away. No response is sent. This continues until the calling user terminates the connection.
Another discard service is defined as a datagram based application on UDP. A server listens for UDP datagrams on UDP port 9. When a datagram is received, it is thrown away. No response is sent.