TCP什么时候发送ACK？

Question

I have an application and I am seeing packets being re-transmitted multiple times. connection is reset after multiple re-transmits. In Wireshark, I can see the packet reaching the server, but I do not see the packet at the application level. I want to know how I can check if the packet is dropped at the TCP layer? When does TCP send DATA packet ACK? After delivering the packet to an application or after receiving the DATA packet on the socket?

Answer 1

ACK is sent to the server by the client after it has established a connection following the SYN-ACK packet.

Answer 2

When does TCP send DATA packet ACK? After delivering the packet to an application or after receiving the DATA packet on the socket?

The ACK is sent by the OS after the data are successfully put into the sockets read buffer. No application logic is involved here yet.