Implementation of UDP Client-Server Communication using Sockets in C

 

Experiment 

Implementation of UDP Client-Server Communication using Sockets in C

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Aim

To implement a simple UDP client-server program for sending and receiving messages.

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Objective

• To understand connectionless communication using UDP
• To implement message passing between client and server
• To compare UDP with TCP

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Theory

What is UDP?

User Datagram Protocol (UDP) is a connectionless protocol:

• No connection establishment
• No guarantee of delivery
• Faster than TCP
• No ordering or retransmission

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Key Difference from TCP

Feature	TCP	UDP
Connection	Yes	No
Reliability	High	Low
Speed	Slower	Faster
Use Case	File transfer	Streaming, DNS

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Working of UDP

• No listen() or accept()
• Data sent using sendto()
• Data received using recvfrom()

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Algorithm

Server

1. Create socket
2. Bind socket to port
3. Receive message from client
4. Send response
5. Close socket

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Client

1. Create socket
2. Send message to server
3. Receive response
4. Close socket

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💻 Program

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🔹 Server Program (UDP in C)

#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

#define PORT 12345

int main() {
    int sockfd;
    char buffer[1024];
    struct sockaddr_in server_addr, client_addr;
    socklen_t len;

    // Create socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(PORT);

    // Bind
    bind(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));

    printf("UDP Server is running...\n");

    len = sizeof(client_addr);

    // Receive message
    recvfrom(sockfd, buffer, sizeof(buffer), 0,
             (struct sockaddr *)&client_addr, &len);

    printf("Client: %s\n", buffer);

    // Send response
    char *msg = "Hello from UDP server";
    sendto(sockfd, msg, strlen(msg)+1, 0,
           (struct sockaddr *)&client_addr, len);

    close(sockfd);
    return 0;
}

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🔹 Client Program (UDP in C)

#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <unistd.h>

#define PORT 12345

int main() {
    int sockfd;
    char buffer[1024];
    struct sockaddr_in server_addr;
    socklen_t len;

    // Create socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

    char *msg = "Hello from UDP client";

    // Send message
    sendto(sockfd, msg, strlen(msg)+1, 0,
           (struct sockaddr *)&server_addr, sizeof(server_addr));

    len = sizeof(server_addr);

    // Receive response
    recvfrom(sockfd, buffer, sizeof(buffer), 0,
             (struct sockaddr *)&server_addr, &len);

    printf("Server: %s\n", buffer);

    close(sockfd);
    return 0;
}

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▶️ Compilation and Execution

gcc server.c -o server
gcc client.c -o client

Run:

• Terminal 1 → ./server
• Terminal 2 → ./client

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📌Output

Server

UDP Server is running...
Client: Hello from UDP client

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Client

Server: Hello from UDP server

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Key Points

• UDP is connectionless → no connect()
• Uses:
  • sendto()
  • recvfrom()
• Faster but unreliable
• Suitable for:
  • Video streaming
  • Online gaming
  • DNS

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🧾 Result

The UDP client-server communication was successfully implemented and messages were exchanged without establishing a connection.

This experiment demonstrates connectionless communication using UDP sockets and highlights its speed and simplicity compared to TCP.