Tcp/ip

I'm studying TCP/IP in game. I try to catch the sign if one of the member disconnect, but I can't. I solve this problem by sending a message "CLOSE" before disconnecting. But in the situation of network problem, how can the player knows that the other one is disconnected? Please help me as soon as possible !!!

I'm not sure about how to implement this.. but why not try a timeout feature. Where if a packet hasn't been recieved from the peer for x amount of time the peer is dropped.

Just a suggestion