This command is sent in response to a ping command. Ping commands are most commonly issued by IRC servers to test if clients are still connected. If a client fails to answer a ping within a specified time limit, then the client is automatically disconnected from the server. Most IRC clients will automatically respond to ping commands with pong. Telnet connections however, will have to manually issue a pong command to avoid disconnecting. This command takes one argument, the server that pinged you.