BitTorrent Network Simulation

A Java-based educational simulation of the BitTorrent protocol, demonstrating peer-to-peer file distribution concepts through practical implementation.

Overview

This project implements a distributed network simulation that models core BitTorrent concepts including:

• Peer discovery and tracking
• Segmented file transfers
• Bandwidth management
• Network topology
• Progress monitoring

Project Structure

.
├── src/                    # Source code
│   ├── base/              # Core network components
│   │   └── torrent/       # BitTorrent protocol implementation
│   ├── model/             # Data models
│   ├── simulation/        # Simulation runtime
│   ├── test/             # Test suites
│   └── util/             # Utility classes
├── student/               # Student implementation directory
└── solution/             # Reference implementation

Key Components

Network Layer

• NetworkDevice.java: Base class for all network-capable devices
• Router.java: Network routing and connection management
• Computer.java: Extended network node with storage/bandwidth constraints
• Hub.java: Network hub implementation
• Switch.java: Network switch implementation

BitTorrent Implementation

• TorrentClient.java: Peer node for file transfer operations
• TorrentServer.java: Seeding node with peer coordination
• TorrentTracker.java: Centralized peer discovery service

Data Models

• TorrentFile.java: File representation with piece management
• Piece.java: Individual file segment unit
• PeerStatus.java: Transfer metrics and statistics
• SwarmInfo.java: Peer group state tracking

Technical Specifications

Runtime Parameters

public static final int PIECE_SIZE = 262144;    // 256 KB
public static final long FILE_SIZE = 10485760L; // 10 MB
public static final int SIMULATION_CYCLES = 20;
public static final long SLEEP_TIME = 1000;     // 1 second

Sample Usage

Creating a torrent client:

TorrentClient client = new TorrentClient(
    "CLIENT1",           // Device ID
    "192.168.1.10",     // IP address
    "NYC",              // Location
    1000,               // Bandwidth (Mbps)
    50.0,               // Max upload speed
    100.0,              // Max download speed
    10000000L           // Storage capacity (bytes)
);

Initializing a file transfer:

TorrentFile file = new TorrentFile(
    "hash123",          // Info hash
    "test.mp4",         // Filename
    1048576L,           // File size (bytes)
    262144              // Piece size (bytes)
);
client.initializeDownload(file);

Running the simulation:

Simulation simulation = new Simulation();
simulation.runSimulation();

Features

Network Implementation

• IPv4 address validation and management
• Bandwidth and storage constraints
• Router-based network topology
• Connection tracking
• Device discovery

BitTorrent Protocol

• Piece-based file segmentation
• Peer discovery and tracking
• Progress monitoring
• Transfer speed calculations
• Swarm management
• Multiple simultaneous transfers

Testing

Comprehensive test suite covering:

• Network device functionality
• Torrent protocol operations
• Data model integrity
• Edge cases and error conditions

Getting Started

Prerequisites

• Java JDK 21 or higher
• JUnit 5.7.0+ for testing

Building the Project

1. Clone the repository
2. Navigate to the project directory
3. Run the tests: ./gradlew test or mvn test
4. Run the simulation: ./gradlew run or mvn exec:java

Design Notes

Limitations

The simulation intentionally excludes:

• Actual file I/O
• Network protocol headers
• Socket communications
• Cryptographic verification
• Request pipelining
• Advanced peer selection

Educational Focus

This implementation prioritizes:

• Code clarity and readability
• Demonstrable protocol concepts
• Testability
• Modular design
• Clear separation of concerns