Assignment 3: Go-Back-N ARQ Protocol Simulation

Overview

This assignment simulates a reliable data transmission protocol using Go-Back-N Automatic Repeat reQuest (ARQ). The system manages data transmission, acknowledgments, timeouts, and retransmissions within a sliding window protocol. It simulates packet loss and tracks events via a logger, ensuring proper retransmission of unacknowledged packets.

Objectives

• Implement the Go-Back-N ARQ protocol for reliable transmission.
• Manage packet transmission, acknowledgment, and timeouts.
• Simulate packet loss and retransmissions.
• Implement a sliding window to manage flow control.
• Log all events including sends, ACKs, drops, and timeouts.

Features

• Packet segmentation from an input file.
• Sliding window-based sender with configurable window size.
• Acknowledgment tracking and retransmission logic.
• Packet drop simulation every n-th packet.
• Logging of all major sender-side events.
• Threaded architecture using Python's threading and queue modules.

How It Works

• The sender reads from an input file and breaks the content into fixed-length packets.
• It sends up to window_size packets at a time.
• A packet is marked for retransmission if an acknowledgment is not received before timeout_interval.
• Every n-th packet (as defined by nth_packet) is simulated to drop, forcing retransmission.
• Events are logged consistently using the provided logger.

Running the Simulation

Requirements

• Python 3.x

Configuration Parameters

• input_file: Path to the file to transmit
• window_size: Size of the sliding window
• packet_len: Number of characters per packet
• nth_packet: Frequency of dropped packets (simulated)
• timeout_interval: Timeout duration for retransmissions
• send_queue and ack_queue: Queues to simulate the sender-receiver channel
• logger: Logger instance for tracking events

Example Usage

sender = GBN_sender(
    input_file="data.txt",
    window_size=4,
    packet_len=10,
    nth_packet=5,
    send_queue=send_q,
    ack_queue=ack_q,
    timeout_interval=2.0,
    logger=your_logger
)

Notes

• Adheres to the Go-Back-N ARQ protocol.
• Logs must be formatted consistently to allow result tracking.
• Use timeouts and exception handling to prevent blocking and crashes.
• Designed for educational simulation purposes, not real-time transmission.

License

This project is part of CS 3357A - Computer Networks I at Western University. For academic use only.