ESTABLISHED
     | (application close; send FIN)
     v
FIN_WAIT_1 ----(recv ACK for FIN)----> FIN_WAIT_2 ----(recv FIN; send ACK)----> TIME_WAIT
     |                                                                              |
     | (recv FIN; send ACK for peer FIN)                                            | (after 2*MSL or 30s)
     v                                                                              v
CLOSING ----(recv ACK for our FIN)----> TIME_WAIT ------------------------------> CLOSED