Reliable Transport Protocol Lite

This project implements a simple unidirectional reliable data transfer protocol over UDP. The protocol is designed to handle packet loss and ensure reliable delivery using a sliding window, fast retransmission, and simulated packet loss. It also features basic connection establishment and termination, as well as logging of key events.

Features

1. Handshake and Termination:

   • A single exchange handshake is implemented to establish a connection between the sender and receiver, using a SYN segment followed by an ACK segment.
   • A simplified termination process is used, where the sender sends a FIN segment and waits for an ACK from the receiver.

2. Sliding Window Protocol:

   • The sender uses a sliding window mechanism to manage the flow of data packets, ensuring that multiple packets can be in transit simultaneously to optimize throughput.

3. Fast Retransmission:

   • The sender implements a fast retransmission mechanism. If three duplicate ACKs are received, the sender immediately retransmits the unacknowledged segment without waiting for a timeout.

4. Packet Loss Simulation:

   • The system simulates packet loss for both data and ACK segments using user-specified probabilities. Forward loss probability (flp) simulates data packet loss, while reverse loss probability (rlp) simulates ACK packet loss.

5. Event Logging:

   • Both the sender and receiver log significant events (such as sending, receiving, and dropping of packets) to sender_log.txt and receiver_log.txt. These logs also include statistical information about original data sent, retransmissions, and dropped packets.

Requirements

• Python 3.x

Usage

Running the Sender

To run the sender, use the following command:

python3 sender.py sender_port receiver_port txt_file_to_send max_win rto flp rlp

Where:

• sender_port: The UDP port the sender binds to.
• receiver_port: The port of the receiver.
• txt_file_to_send: The file path of the text file to send.
• max_win: The maximum sliding window size in bytes.
• rto: The retransmission timeout (in milliseconds).
• flp: Forward loss probability (for simulating data packet loss, 0 ≤ flp ≤ 1).
• rlp: Reverse loss probability (for simulating ACK packet loss, 0 ≤ rlp ≤ 1).

Example:

python3 sender.py 5000 6000 data.txt 4096 200 0.1 0.05

This sends the data.txt file from the sender on port 5000 to the receiver on port 6000, using a sliding window of 4096 bytes, a retransmission timeout of 200 milliseconds, and packet loss probabilities of 10% for data and 5% for ACK packets.

Running the Receiver

To run the receiver, use the following command:

python3 receiver.py receiver_port sender_port txt_file_received max_win

Where:

• receiver_port: The UDP port the receiver listens on.
• sender_port: The port of the sender.
• txt_file_received: The file name to save the received text.
• max_win: The maximum sliding window size in bytes.

Example:

python3 receiver.py 6000 5000 received_data.txt 4096

This saves the received data from the sender into the file received_data.txt.

Log Files

• Sender Log (sender_log.txt): Logs all major events such as sending, receiving, dropping, retransmitting packets, and summarizes statistics like original data sent, retransmitted segments, duplicate ACKs, etc.
• Receiver Log (receiver_log.txt): Logs events such as receiving data packets, duplicate packets, and final statistics on the data received and duplicate segments.

Protocol Details

1. Connection Establishment:

   • The sender initiates the connection by sending a SYN segment.
   • The receiver acknowledges the SYN by sending an ACK segment.
   • The connection is established after this single SYN-ACK exchange.

2. Data Transmission:

   • The sender transmits data using a sliding window.
   • The receiver acknowledges the successfully received segments. If a segment is out of order, it will be buffered until the expected segment is received.
   • If the sender receives three duplicate ACKs for the same data, it triggers a fast retransmission of the lost segment.

3. Connection Termination:

   • The sender initiates the termination by sending a FIN segment once all data has been sent.
   • The receiver responds with an ACK to confirm the connection termination.
   • If the FIN or ACK is lost, retransmissions are handled until confirmation is received.

Error Handling and Packet Loss Simulation

• Timeouts: If the sender doesn't receive an ACK within the specified retransmission timeout (RTO), the oldest unacknowledged segment is retransmitted.
• Simulated Packet Loss: You can configure the forward loss probability (flp) and reverse loss probability (rlp) to simulate packet loss in the network. This feature helps test the protocol's behavior under unreliable conditions.