I wrote an application in c++ which send data over tcp connection to several machines.as part of the protocol I use in my application, the other side sends hearbeat messages from time to time, then I know that the connection is still alive. now, I want this application to work on 100 machines or more at the same time. but, I see that sometimes I don't get these heartbeat messages although they sent: I see in wireshark that the packet arrived, then my OS doesn't ack on this message, so there are some retransmit without any ack from my OS. if I look in the window size property - I saw that there is no issue in this part. what can be the root cause for this behavior? it is something in my code that I should change? this is my select code:

int res = select(fdCount, &readFds, NULL, NULL, NULL );

I'm using server 2008 r2. Please help me!

thanks