I really had no idea between TCP and UDP.
This did a nice comparsion: Transmission Control Protocol ensures a reliable and ordered delivery of a stream of bytes from user to server or vice versa. User Datagram Protocol is not dedicated to end to end connections and communication does not check readiness of receiver.
- HTTP uses TCP connection. But HTTP uses only one TCP connection.
- Use persistent plain TCP sockets if both client and server independently send packets but an occasional delay is OK (e.g. Online Poker, many MMOs).
- Use UDP if both client and server may independently send packets and occasional lag is not OK (e.g. Most multiplayer action games, some MMOs).