On Wednesday, April 6, 2011, ratheesh kannoth <ratheesh.ksz@xxxxxxxxx> wrote: > connect() system call establishes a connection as shown in below steps. > > 1. Â |client | Â----------------- syn ---------------> Â| server | > > 2. Â|Server| Â--------------syn+ ack --------------> | client | > > 3. Â| Client | -----------------ack --------------------> | Server | > > > But establishing connection , client calls close() system call. Client > is sending FIN+ ACK to server Â[ i expected only FIN to be sent from > client to server ] > > Is this a valid scenario.? Âwhat could be the problem ? > > > -Ratheesh The problem is that both sides can never coordinate to close the connection. So TCP does the best it can. It notifies the other side that the connection will be closed and start a timer. If the othet side gets the FIN + ACK its send an ACK. When the sender gets the ACK closes the connection. If the ACK doesnt arrive and the timer expires, it just close the connection, the other side will eventually will notice that the connection was closed so it will also close its side. So you dont need a handshacking protocol. In fact you cant design a robust protocol. This is a particular case of a more general problem known as the two army problem [1] [1] http://en.m.wikipedia.org/wiki/Two_Generals'_Problem Hope it helps, Javier -- ----------------------------------------- Javier MartÃnez Canillas (+34) 682 39 81 69 PhD Student in High Performance Computing Computer Architecture and Operating System Department (CAOS) Universitat AutÃnoma de Barcelona Barcelona, Spain -- To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
