TCP connection and release process
Three-way handshake process
1) A host sends a TCP connection request packet to the host B, where the initial sequence number comprises seq (A) = x host A. (Wherein the packet synchronization flag bit SYN = 1, ACK = 0, indicates that this data is a TCP connection request packet; sequence number seq = x, indicates that the first data byte sequence number when the transmission data is x);
2) After the host B receives the request, it sends back the connection acknowledgment packet. (Wherein acknowledgment segments, flag SYN = 1, ACK = 1, indicates that this is a TCP connection response data packet, and comprising an initial sequence number seq host B (B) = y, and the host B to host A the initial sequence number acknowledgment number ack (B) = seq (a) + 1 = x + 1)
3) Third, the host A receives the acknowledgment message from the host B, the need to confirm that a transmission sequence number seq (A) = x + 1; acknowledgment number ack (A) = y + 1 is reported Wen;
Four waving process
Assume that the host of the client A, B is a host server, the TCP connection release procedure is as follows:
1) the client closes the connection to the server: a first client A sends the FIN, for closing the client to the data transmission server, and then wait confirm the server. Wherein the termination flag FIN = 1, the sequence number seq = u.
2) server receives the FIN, it sends back an ACK, acknowledgment number is a sequence number received ack plus 1.
3) Close the server connected to the client: a FIN is sent to the client.
