The UDP protocol is also one of the Internet's basic protocols. It shares the same protocol as the TCP in the transport layer.
However, the UDP protocol is a connectionless protocol (TCP is a protocol for face-to-face connections). The establishment of a UDP connection does not require server-side interception like the TCP protocol, nor does it require a client-side request connection and a server-side connection to establish communication.
UDP datagram formatIn this datagram format, the source port is an optional field, and when it makes sense, it refers to the UDP port that sends the application. If you don't use it, fill in 0 in this field. The destination port is meaningful when there is a specific destination network address and refers to the UDP port of the target application. The length refers to the octal representation of the length of this user datagram (this indicates that the minimum datagram length is 8). The checksum is also a simple mathematical operation used to check for bit-level errors in UDP messages. The IP header, the UDP header, and the digits of the packet header in the data are reversed and then inverted. The UDP protocol packet does not have the complex reliability and control mechanism of the TCP protocol packet, and there are no two fields of "sequence" and "confirm".
Main features of the UDP protocolUDP is a connectionless, unreliable transport layer protocol;
Limited error checking functionality is provided in the completion of process-to-process communication;
The purpose of designing a relatively simple UDP protocol is to achieve the purpose of process communication in the network environment with minimal overhead;
The UDP protocol can be used because the packets sent by the process are short and the reliability of the packets is not high.
Basic working process of UDPEncapsulation and unpacking during UDP user datagram transmission
UDP packet transmission queue
The port number is used in the TCP/IP protocol suite to identify the process;
The port number is an integer between 0 and 65535;
The temporary port number randomly selected by the client program;
Each server program is assigned a determined globally consistent well-known port number;
Each client process knows the well-known port number of the corresponding server process.
Well-known port number used by UDP
Pseudo head
UDP header
Application layer data
Some readers may ask, since UDP is an unreliable network protocol, what is the use value or necessary? In fact, in some cases the UDP protocol may become very useful. Because UDP has the speed advantage that TCP can't match. Although various security functions are embedded in the TCP protocol, a large amount of system overhead is incurred in the actual execution process, which undoubtedly causes the speed to be seriously affected. In contrast, UDP eliminates the reliable transmission mechanism of information, and transfers security and sorting functions to the upper-layer application, which greatly reduces the execution time and ensures the speed.
The earliest specification for the UDP protocol was RFC768, which was released in 1980. Although the time is already long, the UDP protocol continues to play a role in mainstream applications. Many applications, including video teleconferencing systems, have proven the value of the UDP protocol. Because these applications are more focused on actual performance than reliability, a certain degree of reliability (eg, meeting quality) can often be sacrificed in order to achieve better use (eg, higher frame frame refresh rate). This is the trade-off between UDP and TCP. According to different environments and characteristics, both transmission protocols will play a more important role in the future network world.
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