Revealing the three-way handshake and four-way wave of the TCP protocol

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Revealing the three-way handshake and four-way wave of the TCP protocol

introduction

TCP (Transmission Control Protocol) is a reliable transmission protocol that plays a vital role in network communication. In the process of establishing and closing a TCP connection, the three-way handshake and the four-way wave are essential steps. This blog will introduce in detail the principles, processes and practical applications of the three-way handshake and four-way wave.

three handshake

The three-way handshake is the process of establishing a TCP connection, which includes three steps: SYN, SYN-ACK and ACK.

The client sends a data packet with the SYN flag to the server, indicating a request to establish a connection.
After receiving the request, the server sends a data packet with SYN and ACK flags to the client, indicating that it agrees to establish a connection.
After receiving the confirmation from the server, the client sends a data packet with an ACK flag to the server, indicating that the connection is successfully established.

The purpose of this process is to ensure that both parties are willing to establish a connection and can communicate normally. If there is a problem with either party during this process, the connection will not be established.

The specific process of the three-way handshake is as follows:

客户端 -> 服务器：SYN=1，seq=x
服务器 -> 客户端：SYN=1，ACK=1，seq=y，ack=x+1
客户端 -> 服务器：ACK=1，seq=x+1，ack=y+1

In actual applications, you may encounter some problems, such as timeout, retransmission, etc. In order to solve these problems, some strategies can be adopted, such as setting appropriate timeouts and retransmission times, and using sliding window mechanisms.

waved four times

Four waves is the process of closing a TCP connection, which includes four steps: FIN, ACK, FIN and ACK.

The client sends a packet with the FIN flag to the server, indicating a request to close the connection.
After receiving the request, the server sends a data packet with an ACK flag to the client, indicating that the shutdown request has been received.
The server then sends a data packet with the FIN flag to the client, indicating that the server is also preparing to close the connection.
After receiving the server's closing request, the client sends a data packet with an ACK flag to the server, indicating that the connection has been closed.

The specific process of waving four times is as follows:

客户端 -> 服务器：FIN=1，seq=u
服务器 -> 客户端：ACK=1，seq=v，ack=u+1
服务器 -> 客户端：FIN=1，ACK=1，seq=w，ack=u+1
客户端 -> 服务器：ACK=1，seq=u+1，ack=w+1

During the four waves, it should be noted that the server can still receive the data sent by the client after sending the FIN. This is because the server may not have processed all the data yet, so it needs to wait for a while until all the data has been processed before closing the connection.

The relationship between three handshakes and four waves

The three-way handshake and four-way wave are important steps in the establishment and closing process of a TCP connection. The three-way handshake is performed when establishing a connection, while the four-way handshake is performed when closing the connection. Through these two processes, it can be ensured that both parties can establish and close the connection normally, thereby achieving reliable data transmission.

The relationship between the three-way handshake and the four-way wave is that a three-way handshake is required when establishing a connection to ensure that both parties are willing to establish the connection. When closing the connection, four waves are required to gradually close the connection to ensure that both parties can safely close the connection. This is because closing the connection requires both parties to confirm that the other party has processed all data and no more data will be exchanged.

Through the three-way handshake and four-way wave process, the TCP protocol can provide reliable connection and data transmission, ensuring data integrity and reliability.

Frequently Asked Questions and Notes

When using the TCP protocol for network communication, you may encounter some common problems, such as timeouts, retransmissions, etc. To address these issues, the following strategies and considerations can be adopted:

Set an appropriate timeout and number of retransmissions: Set an appropriate timeout and number of retransmissions based on the network environment and application requirements to ensure that data can be transmitted and received in a timely manner.
Use the sliding window mechanism: The sliding window mechanism can improve the efficiency and reliability of data transmission and adapt to network conditions by dynamically adjusting the window size.
Handle the semi-closed state: During the four waves, you need to pay attention to handling the semi-closed state, that is, you can still receive data before closing the connection. Make sure all data has been processed before closing the connection.
Avoid too many connections and long periods of idle time: Too many connections and long periods of idle time will occupy resources and affect network performance. Therefore, it is necessary to manage connections reasonably and close connections that are no longer used in a timely manner.
Regular connection testing and maintenance: Regular connection testing and maintenance can detect and solve connection problems in a timely manner and ensure the stability and reliability of the network.

Optimization and improvement of TCP protocol

In order to improve the performance and efficiency of the TCP protocol, many optimization methods and improvement plans have been proposed. Some common optimization methods include:

Fast retransmission: By monitoring lost data packets and duplicate acknowledgment packets, lost data is retransmitted in a timely manner to improve the speed and reliability of data transmission.
Congestion control: Avoid network congestion and improve network throughput and stability by dynamically adjusting the sending rate of the sender.
Delayed confirmation: Delayed confirmation can reduce the number of confirmation packets and improve network transmission efficiency.
Nagle algorithm: The Nagle algorithm can reduce network transmission overhead and improve transmission efficiency by delaying the sending of small data packets.

These optimization methods and improvement solutions can improve the performance and efficiency of the TCP protocol in network communication, thereby better meeting the needs of different application scenarios.

Practical application scenarios

Three-way handshake and four-way wave play an important role in practical applications. Here are some examples of practical application scenarios:

Web browsing: When we access a website through a web browser, the browser will establish a TCP connection with the server and perform a three-way handshake to ensure the establishment of the connection. The browser then sends an HTTP request, the server returns an HTTP response, and finally the connection is closed with four waves.
File transfer: During the file transfer process, a TCP connection needs to be established between the client and the server to transfer files. After the connection is established through a three-way handshake, the client sends a file request, the server returns the file data, and finally the connection is closed by waving four times.
Mail transmission: When sending an email, a TCP connection needs to be established between the client and the mail server. After establishing a connection through a three-way handshake, the client sends the email content, the mail server receives and processes the email, and finally closes the connection with four waves of hands.

The above are just some examples of practical application scenarios. In fact, in almost all network communications, a three-way handshake and four waves are involved to ensure the establishment and closing of the connection.

Summarize

The three-way handshake and four-way wave of the TCP protocol are indispensable and important steps in network communication. Through the three-way handshake, both parties can establish a reliable connection and transmit data. With four waves, both parties can safely close the connection to ensure data integrity. In practical applications, we need to pay attention to handling connection issues and optimizing network performance to provide better user experience and data transmission efficiency.