Reliable Data Transfer (RDT) Protocol Implementation

A Python implementation of a reliable data transfer protocol using TCP sockets. This project demonstrates network programming concepts including error detection, packet loss handling, and reliable data transmission.

🌟 Overview

This implementation consists of three main components that work together to ensure reliable data transfer across an unreliable network:

• Sender (sender.py)
• Receiver (receiver.py)
• Utility Functions (util.py)

🚀 Features

• Reliable Data Transfer

  • Sequence numbering (0,1 alternating)
  • Acknowledgment system
  • Packet retransmission
  • Checksum verification

• Error Handling

  • Packet loss detection
  • Corruption detection
  • Timeout mechanism (5 seconds)
  • Automatic retransmission

• Network Simulation

  • Simulated packet loss (every 6th packet)
  • Simulated corruption (every 3rd packet)
  • Logging of received packets

🔧 Technical Details

Packet Structure

[COMP][NETW][Checksum(2B)][Length+ACK+SEQ(2B)][Data]

Components

1. Sender (sender.py)

Key Features:
- Sequence number management
- ACK processing
- Retransmission logic
- Three states:
  1. Original message
  2. Retransmission
  3. Socket timeout

2. Receiver (receiver.py)

Key Features:
- Packet verification
- ACK generation
- Error simulation
- Packet logging

3. Utility Functions (util.py)

Key Functions:
- create_checksum()
- verify_checksum()
- make_packet()
- extract_message()
- extract_seq_num()

📋 Prerequisites

• Python 3.x
• Basic understanding of:
  • Socket programming
  • Network protocols
  • Binary operations

💻 Installation

1. Clone the repository:

git clone [repository-url]
cd [repository-name]

2. No additional dependencies required (uses standard Python libraries)

🎮 Usage

1. Start the receiver:

python receiver.py

2. Start the sender:

python sender.py

3. The receiver port is calculated as:

receiver_port = 10100 + (4196840 % 500)

🔄 Protocol Flow

Sender                        Receiver
  |                             |
  |-------- Data Packet ------->|
  |                             | (Verify Checksum)
  |                             | (Process Packet)
  |<------- ACK Packet ---------|
  |                             |

📝 Implementation Details

Error Detection

• 16-bit checksum calculation
• Binary operations for integrity verification
• Packet structure verification

Retransmission Mechanism

• Timeout-based retransmission
• ACK-based reliability
• Sequence number verification

Logging

• Received packets are logged in "received_pkt.txt"
• Packet details and status are printed to console

🧪 Testing Scenarios

1. Normal Operation

   • Successful packet transmission
   • Proper ACK reception

2. Error Scenarios

   • Every 6th packet: Simulated loss
   • Every 3rd packet: Simulated corruption
   • Timeout handling

🔍 Debugging

Common issues and solutions:

1. Packet Loss

   • Check timeout settings
   • Verify network connectivity

2. Corruption

   • Verify checksum calculation
   • Check packet structure

3. Connection Issues

   • Confirm port numbers
   • Check socket bindings

🛠️ Development

Adding New Features

1. Extend error simulation
2. Add more packet types
3. Implement sliding window
4. Add congestion control

Code Style

• Follow PEP 8 guidelines
• Document new functions
• Maintain error handling

📈 Performance Considerations

• Socket timeout set to 5 seconds
• Buffer size: 1024 bytes
• Maximum packet size considerations
• Checksum calculation efficiency

🤝 Contributing

1. Fork the repository
2. Create feature branch
3. Commit changes
4. Push to branch
5. Create Pull Request

🔮 Future Improvements

1. Implementation Options:

   • Add sliding window protocol
   • Implement selective repeat
   • Add congestion control
   • Enhance error simulation

2. Performance Enhancements:

   • Optimize checksum calculation
   • Improve buffer management
   • Add compression

⚠️ Limitations

• Basic implementation for educational purposes
• No encryption
• Limited error types simulation
• Fixed sequence number (0,1)
• Single connection handling

📚 References

• Computer Networking: A Top-Down Approach
• Socket Programming in Python
• RFC Documents on Reliable Transfer
• TCP/IP Protocol Suite

👥 Authors

Krushikesh Thotange