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6. UDP-Client Example
UDP-Client Example
UDP-Client ExampleRoutine IntroductionCode Analysisfunctionconnect_wififunctionstart_udp_clientSend a test messageClosing a SocketMain program entryUDP protocol1. Basic knowledge of UDP1.1 What is UDP?1.2 UDP vs TCP Core Differences2. UDP protocol structure (diagram)2.1 Datagram Format2.2 Header Structure3. UDP key working mechanism3.1 Connectionless Communication3.2 Checksum calculation4. UDP Advanced Features4.1 Multiplexing and Demultiplexing4.2 Application layer reliability implementation5. Typical UDP application scenarios5.1 Real-time audio and video transmission5.2 Game Communication5.3 Network Service Discovery5.4 IoT Communications
Routine Introduction
In this section, we will introduce how to use K230 as a UDP server
We open the example code in this section and modify the WIFI connection information part in the code to your home WIFI or mobile hotspot
sta.connect("WIFI SSID", "WIFI PASSWORD") # 连接到指定WiFi / Connect to specified WiFiThen we open the network debugging assistant and enter the IP address of the machine (check with ipconfig)
Then we go back to the code and modify this part of the code (modify it to the IP address and port number filled in above)
x
# 设置服务器参数 / Set server parametersserver_ip = '192.168.2.109'server_port = 8080Click the run button in the lower left corner, and the console will output the information sent to the server.
x发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 1发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 2发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 3发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 4发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 5发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 6发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 7发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 8发送字节数 / Bytes sent: 29发送消息 / Sending: K230 UDP client send test 9发送字节数 / Bytes sent: 29客户端已结束 / Client ended.At the same time, we will go to the network debugging assistant and find that the information sent by K230 has also been received here
xxxxxxxxxx[2025-02-21 10:37:01.615]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 0 [2025-02-21 10:37:01.679]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 1 [2025-02-21 10:37:01.862]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 2 [2025-02-21 10:37:02.188]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 3 [2025-02-21 10:37:02.378]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 4 [2025-02-21 10:37:02.466]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 5 [2025-02-21 10:37:02.779]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 6 [2025-02-21 10:37:02.869]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 7 [2025-02-21 10:37:03.096]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 8 [2025-02-21 10:37:03.272]# RECV ASCII/30 from 192.168.1.253 :49153 <<<K230 UDP client send test 9
Code Analysis
For complete comments and code, please refer to the file [Source Code/11.Network/04.udp/udp_client.py]
xxxxxxxxxximport socketimport osimport timeimport networkAt the beginning of the code, the necessary modules are imported:
socket: Provides network communication functions and supports TCP and UDP protocols.os: Provides functionality for interacting with the operating system, such as exiting a program.time: Provides time-related functions, such as delay.network: Provides network related functions, here for WiFi connection.
functionconnect_wifi
xxxxxxxxxxdef connect_wifi(ssid="[WIFI SSID]", password="[WIFI PASSWORD]"): """ 连接WiFi并返回IP地址 Connect to WiFi and return IP address 参数 / Parameters: ssid: WiFi名称 / WiFi name password: WiFi密码 / WiFi password 返回 / Returns: str: IP地址 / IP address """This function is used to connect to the specified WiFi network and return the IP address after successful connection. Its parameters include the WiFi name (SSID) and password.
xxxxxxxxxx wifi_station = network.WLAN(0) # 创建WiFi站点对象 / Create WiFi station object wifi_station.connect(ssid, password) # 连接到指定WiFi / Connect to specified WiFiHere a WiFi site object is created and a connection is made to the WiFi network using the provided SSID and password.
xxxxxxxxxx # 等待直到获取到IP地址 / Wait until IP address is obtained while wifi_station.ifconfig()[0] == '0.0.0.0': os.exitpoint()Check if the IP address has been obtained by ifconfig()the method. If not (that is, the IP address is 0.0.0.0), enter the loop and keep checking until a valid IP address is obtained. The here os.exitpoint()may be an error, usually it should be os._exit(1)or raise SystemExit.
xxxxxxxxxx return wifi_station.ifconfig()[0] # 返回IP地址 / Return IP addressOnce a valid IP address is obtained, it is returned.
functionstart_udp_client
xxxxxxxxxxdef start_udp_client(): """ 启动UDP客户端，发送测试消息 Start UDP client and send test messages """This function is responsible for starting the UDP client and sending a test message.
xxxxxxxxxx # 连接WiFi网络 / Connect to WiFi network connect_wifi()Call connect_wififunction to connect to WiFi.
xxxxxxxxxx # 设置服务器参数 / Set server parameters server_ip = '192.168.2.89' server_port = 8080Defines the IP address and port of the UDP server to connect to.
xxxxxxxxxx # 获取服务器地址信息 / Get server address information address_info = socket.getaddrinfo(server_ip, server_port) print("地址信息 / Address info:", address_info) server_address = address_info[0][-1] print("连接地址 / Connect address:", server_address)Use socket.getaddrinfo()to obtain the server's address information and extract the actual connection address (the last element of the tuple).
xxxxxxxxxx # 创建UDP套接字 / Create UDP socket udp_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)Create a UDP socket.
Send a test message
xxxxxxxxxx # 发送测试消息 / Send test messages try: for msg_count in range(10): # 构建消息 / Build message message = f"K230 UDP client send test {msg_count}\r\n" print("发送消息 / Sending:", message) # 发送消息并获取发送字节数 / Send message and get bytes sent bytes_sent = udp_socket.sendto(message.encode(), server_address) print("发送字节数 / Bytes sent:", bytes_sent) # 等待200ms / Wait 200ms time.sleep(0.2)In trythe block, a loop sends 10 test messages:
- The message content is a formatted string, including the message number.
- Use
sendtothe method to send a message and print the number of bytes sent. - After each message is sent, the program will wait 200 milliseconds.
Closing a Socket
xxxxxxxxxx finally: # 关闭套接字 / Close socket udp_socket.close() print("客户端已结束 / Client ended.")Regardless of whether the message sending process is successful or not, finallythe UDP socket will be closed in the block and the end information will be printed.
Main program entry
xxxxxxxxxx# 启动客户端 / Start clientif __name__ == '__main__': start_udp_client()If this script is the main program running, the function is called start_udp_client()to start the UDP client.
UDP protocol
1. Basic knowledge of UDP
1.1 What is UDP?
- Positioning : Transport layer protocol (OSI layer 4)
- Features : connectionless, best effort delivery, lightweight header, low latency
- Analogy : Like the post office's "normal postcard service" (no guarantee of delivery, but fast delivery)
1.2 UDP vs TCP Core Differences
| characteristic | UDP | TCP |
|---|---|---|
| Connection Establishment | No handshake | Three-way handshake |
| Data transmission guarantee | Order and arrival are not guaranteed | Completely reliable (logically reliable only from this layer) |
| Header overhead | 8 bytes | 20-60 bytes |
| Transport Control | No flow control/congestion control | Fine-grained control |
| Applicable scenarios | Real-time communication | Reliable transmission |
2. UDP protocol structure (diagram)
2.1 Datagram Format
2.2 Header Structure
xxxxxxxxxx 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Source Port | Destination Port |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Length | Checksum |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| Data |+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Source Port (16 bits): Optional field, 0 indicates a passive port
- Destination Port (16 bits): Required destination port
- Length (16 bits): Total number of bytes of header + data (minimum 8 bytes)
- Checksum (16 bits): Checksum (optional for IPv4, mandatory for IPv6)
3. UDP key working mechanism
3.1 Connectionless Communication
- Unicast : one-to-one transmission
- Multicast : one-to-many transmission (IP multicast address range: 224.0.0.0~239.255.255.255)
- Broadcast : One-to-all transmission (limited broadcast address 255.255.255.255)
3.2 Checksum calculation
- Coverage : pseudo header + UDP header + data
- Pseudo header structure :
xxxxxxxxxx| Source IP address (32 bits) | Destination IP address (32 bits) | Protocol (8 bits) | UDP length (16 bits) |4. UDP Advanced Features
4.1 Multiplexing and Demultiplexing
- Port number : Different applications are distinguished by port number (0~65535)
4.2 Application layer reliability implementation
- Custom retransmission : such as packet loss detection in the QUIC protocol
- Forward Error Correction : Adding Redundant Data to Deal with Packet Loss
- Sequence number mechanism : add custom sequence numbers in data payload
5. Typical UDP application scenarios
5.1 Real-time audio and video transmission
- Zoom/Teams : Allowing a small amount of packet loss in exchange for low latency
- Streaming protocol : RTP over UDP
5.2 Game Communication
- MOBA games : high-frequency position updates (20-30 times per second)
- FPS shooting game : quickly transmit operation instructions
5.3 Network Service Discovery
- DHCP : Dynamically obtain an IP address
- mDNS : LAN device discovery (such as printers)
5.4 IoT Communications
- CoAP : A lightweight protocol for constrained devices
- MQTT-SN : Sensor Network Protocol