What is TCP/UDP protocol?

Before understanding TCP/UDP protocol, let's first understand TCP/IP protocol.

TCP/IP refers to a suite of protocols that can transmit information between multiple different networks. The TCP/IP protocol not only refers to the two protocols TCP and IP, but also refers to a protocol cluster composed of FTP, SMTP, TCP, UDP, IP and other protocols. Just because in the TCP/IP protocol, the TCP protocol and the IP protocol The most representative, so it is called TCP/IP protocol. The TCP/IP protocol includes a series of network protocols that form the basis of the Internet. It is the core protocol of the Internet, including application protocols, transmission protocols, Internet protocol and routing control protocols.
Let’s take a look at the differences between TCP and UDP communication rules.
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the two main protocols of the transport layer. They have significant differences in data transmission methods and application scenarios.
The most significant feature of the TCP protocol is that a handshake is required before each transmission of information. The three-way handshake is an important process for TCP to establish a connection. The three-way handshake ensures that the connection and data exchange between the client and the server can be stable and reliable.
Below we introduce the three-way handshake process in detail:
One-time handshake: The client will actively send a SYN packet to the server, and the SYN packet contains its own initial sequence number X. The SYN packet indicates that the client wants to establish a connection with the server. At this point, the client will enter the SYN_SENT state and wait for the server to reply with a confirmation message.
Two-step handshake: After the server receives the SYN packet from the client, it will reply to the client with a SYN+ACK packet as response data. This response packet contains the server's initial sequence number Y, and the server's confirmation of the client's SYN packet (the confirmation number has been updated to X+1 at this time). After the response data is sent, the server enters the SYN_RECV state, which indicates that the server has received the client's synchronization request and is ready to send its own synchronization request.
Three-way handshake: After receiving the SYN+ACK packet from the server, the client will send an ACK confirmation packet to the server. The content of this packet contains the server confirmation number Y+1, which indicates that the client has received the server's synchronization request and confirmed it. At this time, both the client and the server have entered the established connection state. At this time, the TCP connection is successfully established and both parties can start data transmission.

When using the TCP protocol, each data interaction requires a handshake first. After the handshake is successful, the information sent by the other party will be received.
Let's take a look at the common application scenarios of the TCP protocol
1. HTTP (Hypertext Transfer Protocol) and HTTPS (Secure Hypertext Transfer Protocol) are both based on the TCP protocol. When a user accesses a web page, the browser uses the TCP protocol to establish a connection with the server, and data will be transmitted after the connection is established. The three-way handshake mechanism ensures the accuracy of web page access.
2. Email protocols such as SMTP (Simple Mail Transfer Protocol), IMAP (Internet Mail Access Protocol) and POP3 (Post Office Protocol) are also based on the TCP protocol. The TCP protocol ensures the stable transmission of emails and avoids data loss or damage during the transmission process.
3. FTP (File Transfer Protocol) and SFTP (Secure File Transfer Protocol) are also file transfer protocols based on TCP, which ensure stable file transfer between the client and the server and ensure the integrity of the file.
After understanding the TCP protocol, let's take a look at the UDP protocol
The TCP protocol just mentioned requires a three-way handshake before communication, while the UDP protocol does not require this trouble. You only need to know the IP and port of the other party to send information directly, and the other party does not need to confirm. Therefore, the UDP protocol is a connectionless transmission protocol with the characteristics of simplicity and efficiency. It is suitable for scenarios that require fast transmission but do not require high data integrity.
UDP is a simple protocol based on IP that provides connectionless data transmission services. It is mainly used for applications with single small amounts of data transmission, such as DNS, SNMP, etc. The UDP header has a small overhead, including the source port number, destination port number, length, and checksum, totaling 8 bytes.

In summary, the main features of the TCP protocol include:
1. Connection-oriented: TCP must establish a connection before transmitting data, and release the connection after the data transmission is completed
2. Reliability: Reliable transmission is achieved through mechanisms such as checksum, sequence number, confirmation response, and retransmission control
3. Flow control: Use the sliding window protocol to prevent the sender from sending too fast and causing the receiver to be unable to process in time
4. Congestion control: Prevent network congestion through algorithms such as slow start, congestion avoidance, fast retransmission, and fast recovery
5. Full-duplex communication: Allow data to be transmitted in both directions at the same time
6. Byte stream-oriented: Treat the message sent by the application layer as a byte stream, and do not distinguish the data packets sent by the application layer
The main features of the UDP protocol include:
1. Connectionless: No connection is required before sending data, and the sender can send data at any time
2. Unreliable: The order, error, or loss of data packets is not guaranteed
3. Small header overhead: Only necessary fields are included, such as source port, destination port, length, and checksum
4. Support multiple communication modes: support one-to-many, many-to-one and many-to-many communication
5. High transmission efficiency: Since there are no steps such as establishing connections, confirming data, and processing retransmissions, the transmission efficiency is relatively high
The main differences between TCP and UDP
1. Connectivity: TCP is a connection-oriented protocol that requires establishing and closing connections; UDP is a connectionless protocol
2. Reliability: TCP provides reliable transmission services, while UDP does not guarantee data reliability
3. Header overhead: TCP has a large header overhead, while UDP has a small header overhead
4. Transmission efficiency: TCP has a relatively low transmission efficiency, but high reliability; UDP has a high transmission efficiency, but data may be lost
5. Application scenarios: TCP is suitable for scenarios that require reliable transmission, such as file transfer, e-mail, etc.; UDP is suitable for scenarios that have high real-time requirements but low data reliability requirements, such as video streaming, audio streaming, etc.
In general, TCP is suitable for data transmission that requires high reliability, while UDP is suitable for applications that require high transmission efficiency and real-time performance
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