| a random number that is not used as source port for any established connection of the host |
| a random number that is not used as source port for any established connection of the host and is not an reserved port |
| if possible the destination port. If this is used it for any other connection it is increased by one until it becomes available. |
| the host does not choose a source port number. A number bigger than 1000 is assigned by the server in his SYN ACK Message during the three way handshake. |