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Anonymous users2024-02-08To put it simply, this process is called a three-way handshake agreement.
First handshake: When the connection is established, the client sends a SYN packet (syn=j) to the server and enters the SYN send state, waiting for the server to acknowledge.
Second handshake: When the server receives the SYN packet, it must confirm the customer's SYN(ACK=J+1) and send a SYN packet (syn=k), that is, SYN+ACK packet, and the server enters the SYN recv state.
Third handshake: The client receives the SYN ACK packet from the server and sends an acknowledgement packet ACK (ACK=K+1) to the server.
After the three-way handshake, the client and server begin to transfer data, and in the process described above, there are some important concepts:
Unconnected Queue: In the three-way handshake protocol, the server maintains an unconnected queue that opens an entry for each client's SYN packet (syn=j) that indicates that the server has received the SYN packet and issues an acknowledgment to the customer, waiting for the customer's acknowledgment packet. The connection identified by these entries is in the SYN recv state on the server, and when the server receives an acknowledgment packet from the customer, the entry is deleted and the server enters the established state.
backlog parameter: indicates the maximum number of unconnected queues.
Number of SYN-ACK Retransmissions After the server sends the SYN ACK packet, if the customer acknowledgement packet is not received, the server performs the first retransmission, waits for a period of time and does not receive the customer acknowledgement packet, performs the second retransmission, and if the number of retransmissions exceeds the maximum number of retransmissions specified by the system, the system deletes the connection information from the semi-connection queue. Note that the wait time for each retransmission is not necessarily the same.
Semi-connected time-to-live: refers to the maximum time that entries in a semi-connected queue can live, that is, the maximum time from the time the service receives the SYN packet to the time when the packet is invalid, and the time is the sum of the maximum waiting time for all retransmission request packets. Sometimes we also refer to the half-connection live time as the time out time and the syn recv time alive.
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Anonymous users2024-02-07If the chat tool of P2P communication technology does not need to go through the server, it only needs to communicate directly between two computers, and if it is not based on P2P, it must communicate through the server.
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Anonymous users2024-02-06If it is a company computer, of course, it has to go through the server, unless it is your company's computer, which is directly connected! However, even if it is a machine that is directly connected to the wire, the use of the chat tool also needs to go through the bus of telecommunication network. If the Work Safety Supervision Bureau wants to investigate, it will also be found!
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