Stop-and-Wait ARQ Protocol using UDP Sockets

Overview

This project implements the Stop-and-Wait Automatic Repeat Request (ARQ) protocol using UDP socket programming in C. The protocol ensures reliable data transmission by using acknowledgments (ACKs), sequence numbers, timeouts, and retransmissions.

Features

• UDP-based client-server communication
• Stop-and-Wait ARQ implementation
• Sequence numbers (0 and 1)
• ACK-based reliability
• Timeout handling
• Packet retransmission
• Simulated packet loss (10%)
• Duplicate packet detection

Project Structure

.
├── client.c
├── server.c
└── README.md

How It Works

Sender (Client)

1. Sends a packet with a sequence number.
2. Waits for an acknowledgment.
3. Retransmits if ACK is not received within 2 seconds.
4. Sends the next packet after receiving the correct ACK.

Receiver (Server)

1. Receives packets from the sender.
2. Simulates packet loss with a 10% probability.
3. Sends ACK for correctly received packets.
4. Detects duplicate packets and resends the previous ACK.

Packet Format

Data Packet

<sequence_number>|<message>

Example:

0|Hello

ACK Packet

ACK<sequence_number>

Example:

ACK0

Compilation

Compile the programs using GCC:

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

Execution

Start the Server

./server

Start the Client

Open a new terminal and run:

./client

Sample Output

Server

Stop-and-Wait Receiver started...

Received packet seq 0: Hello
Received packet seq 1: from
Packet lost (simulated).
Received packet seq 0: Stop-and-Wait
Received packet seq 1: ARQ

Client

Sent packet seq 0: Hello
Received ACK0

Sent packet seq 1: from
Received ACK1

Sent packet seq 0: Stop-and-Wait
Timeout or error, resending...
Sent packet seq 0: Stop-and-Wait
Received ACK0

Sent packet seq 1: ARQ
Received ACK1

Concepts Demonstrated

• UDP Socket Programming
• Reliable Data Transfer
• Stop-and-Wait ARQ
• Sequence Numbers
• Acknowledgments
• Timeout Handling
• Packet Loss Recovery

Applications

• Data Link Layer Protocols
• Reliable Communication Systems
• Networking Simulations
• Educational Networking Projects

Author

M R Krishni