What is the difference between UDP and TCP?

In computer network communications, transport layer protocols play a vital role. They are responsible for transmitting data between different hosts in the network. Among them, UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) are the two most common transport layer protocols. Although they are both used for data transmission, they have significant differences in many aspects. This article will explore the differences between UDP and TCP protocols in depth to help readers better understand the characteristics and applicable scenarios of these two protocols.

I. Basic feature comparison

1.1 Connectivity

• ​TCP protocol​: TCP is a connection-oriented protocol. Before data transmission, a connection needs to be established and the connection needs to be disconnected after the end. This connection mechanism ensures the reliability and sequentiality of data transmission.
• ​UDP protocol​: UDP is a connectionless protocol. No connection needs to be established before sending data, and data is sent directly. This connectionless feature makes the UDP protocol have lower latency and higher efficiency.

1.2 Reliability

• ​TCP protocol​: TCP provides reliable data transmission. It ensures the accurate arrival of data through sequence numbers, confirmation mechanisms, retransmission mechanisms, etc. Even in the case of unstable network, TCP can ensure the integrity of data by retransmitting lost data packets.
• ​UDP protocol​: UDP does not guarantee the reliable delivery of data. Data may be lost, out of order or duplicated. The UDP protocol is only responsible for sending data to the target host as quickly as possible, without caring whether the data arrives or is complete.
  
  

2. Data transmission and processing

2.1 Data order

• ​TCP protocol​: TCP ensures that data arrives at the receiving end in the order in which it is sent. Each data packet has a sequence number, and the receiving end will sort the data packets according to the sequence number to ensure the order of data.
• ​UDP protocol​: UDP does not guarantee the order of data. The order of data received by the receiving end may be different from that of the sending end. The UDP protocol is only responsible for sending data packets, without caring about the order of data.

2.2 Flow Control and Congestion Control

• ​TCP Protocol​: TCP has flow control and congestion control mechanisms. Through the sliding window protocol and congestion avoidance algorithm, TCP can dynamically adjust the sending rate to avoid network congestion and data loss.
• ​UDP Protocol​: UDP has no flow control and congestion control mechanisms. It sends data as fast as possible without considering the current state of the network. This feature makes UDP likely to cause packet loss or network congestion when the network load is high.
  
  

III. Header Overhead and Efficiency

3.1 Header Overhead

• ​TCP Protocol​: TCP has a large header overhead and contains more control information, such as sequence number, acknowledgment number, window size, checksum, etc. These control information ensures the reliability and order of data, but also increases the header overhead.
• ​UDP Protocol​: UDP has a small header overhead of only 8 bytes, which contains basic information such as source port number, destination port number, length and checksum. Smaller header overhead makes UDP more efficient in data transmission.

3.2 Transmission efficiency

• ​TCP protocol​: Since TCP needs to establish connections, perform additional operations such as flow control and congestion control, its transmission efficiency is relatively low. But this also ensures the reliability and order of data.
• ​UDP protocol​: UDP does not have these additional operations and sends data directly, so it has a higher transmission efficiency. But this also makes UDP face problems such as data loss and disorder during data transmission.
  
  

IV. Applicable scenarios

4.1 Applicable scenarios of TCP protocol

• ​Applications with high requirements for data accuracy and order​: such as file transfer, email, web browsing, etc. These applications need to ensure the integrity and order of data, so it is more suitable to use TCP protocol.
• ​Applications that require reliable delivery​: such as financial transactions, remote login, etc. These applications have high requirements for data reliability, so they are also more suitable to use TCP protocol.

4.2 Application scenarios of UDP protocol

• ​Applications with high real-time requirements and not very sensitive to data loss​: such as live video, audio calls, online games, etc. These applications require low-latency data transmission, and even if a small amount of data is lost, it will not have much impact on the overall effect, so it is more suitable to use UDP protocol.
• ​Applications for broadcast or many-to-many communication​: such as video conferencing, Internet phone, etc. These applications need to support real-time communication between multiple participants, so it is also more suitable to use UDP protocol.
  
  

V. Summary

UDP protocol and TCP protocol each play an important role in computer network communication. TCP protocol focuses on the reliability and sequence of data, and is suitable for applications with high requirements for data accuracy and sequence; while UDP protocol focuses more on the efficiency and real-time of data transmission, and is suitable for applications with high real-time requirements and not very sensitive to data loss. In practical applications, it is necessary to select the appropriate protocol according to specific needs. By deeply understanding the characteristics and applicable scenarios of these two protocols, we can better use them to meet different network communication needs.