Peer-To-Peer File Sharing System Using Bittorrent Protocol

Abstract

Peer-to-peer (P2P) file sharing has evolved significantly since its early adoption in platforms like Napster and Gnutella, offering a decentralized alternative to traditional client-server architectures. Despite their scalability and bandwidth efficiency, P2P systems often face challenges such as network congestion, peer misbehavior, and lack of fairness in data distribution. To address these issues, this research presents a python-based BitTorrent-like file sharing system that implements dynamic peer selection through choking and optimistic unchoking mechanisms, secure handshake protocols, and multithreaded socket communication for efficient and resilient data exchange. The system ensures secure remote deployment using SSH and incorporates a detailed logging mechanism to monitor peer interactions. Experimental results demonstrate improved download speeds, balanced bandwidth allocation, and enhanced fault tolerance. The findings validate the effectiveness of the proposed Framework as a robust and scalable solution for decentralized file sharing.

Introduction

Introduction & Background

Peer-to-peer (P2P) file sharing is a decentralized method of distributing data by having peers share resources like storage and bandwidth. Early systems like Napster and Gnutella laid the foundation but suffered from limitations such as low bandwidth efficiency and poor fault tolerance. Modern P2P systems, especially BitTorrent, offer improved performance by splitting files into pieces and enabling parallel downloads, leveraging tit-for-tat strategies to encourage participation and fairness.

Challenges in P2P Systems

While advantageous over traditional client-server models in terms of scalability and fault tolerance, P2P systems face challenges:

• Free-riding behavior

• Fair bandwidth allocation

• Malicious nodes

• High churn rates

• Lack of centralized integrity and reliability controls

BitTorrent & System Inspiration

BitTorrent revolutionized P2P sharing with:

• Piece-wise parallel downloading

• Tit-for-tat reciprocity

• Choking and optimistic unchoking to manage peer performance

These principles form the core of the proposed system, which is implemented in Python using socket programming and multithreading to simulate decentralized communication.

Literature Survey

• BitTorrent Protocol (Cohen): Incentive-based strategies that reduce free-riding.

• Overlay Architectures (Lua et al.): Structured vs unstructured networks.

• Churn Management (Rhea et al.): Stabilization in DHTs.

• Chord Protocol (Stoica et al.): Efficient distributed lookup using consistent hashing.

• P2P Streaming (Xu et al.): Real-time buffering and scheduling insights.

• BitTorrent Modeling (Qiu & Srikant): Effects of peer capacity on performance.

• Adaptive Choking (Zhang et al.): Performance-based peer selection.

• Economic Models (Li, Guo): Reputation and virtual incentives.

• Sybil Attack Mitigation (Levine et al.): Importance of authentication and trust.

Proposed Framework

1. Flow Diagram Overview

Peers follow a loop:

• Handshake → Request → Receive → Check completion → Repeat → Assemble full file.

2. System Design Phases

• Knowledge Gathering: Deep understanding of BitTorrent protocol behavior.

• Architecture: Fully decentralized; all peers are equal.

• Peer Discovery: Via config or broadcast; handshake initiates connection.

• Chunking and Transfer: Files split into pieces, exchanged with integrity checks.

• Choking/Unchoking: Top peers are prioritized; one random peer is optimistically unchoked periodically.

• Logging: Real-time logging of all events for monitoring and debugging.

• Remote Execution: Peers are deployed on remote machines using SSH to simulate real-world conditions.

• Fault Tolerance: Resumes interrupted downloads; safe shutdown and cleanup.

Evaluation & Results

1. Download Completion Time vs Peers

• Performance improves as more peers are optimally unchoked.

• Dynamic choking strategy leads to faster file completion under load.

2. Bandwidth Utilization

• High concurrency leads to bandwidth peaks, showing efficient multithreading.

• Active peers show better performance, especially during optimistic unchoking.

3. Peer Fairness Index (PFI)

• Measures upload/download balance; value near 1.0 is ideal.

• Tit-for-tat and optimistic unchoking ensure fairness and deter free-riding.

Key Contributions

• A modular, secure Python-based BitTorrent-like file sharing system.

• Improved fairness, efficiency, and fault tolerance.

• Logging and SSH-based deployment for real-world simulation.

• Focus on scalability and resilience to common P2P attacks.

Conclusion

The proposed peer-to-peer (P2P) file sharing system, inspired by the BitTorrent protocol, successfully addresses the fundamental challenges associated with decentralized data distributionnamely fairness, bandwidth optimization, and robustness against peer misbehavior. By leveraging python-based multithreading, socket communication, and dynamic peer selection strategies, the system ensures efficient and reliable transmission of file chunks across a distributed network of peers. The implementation of handshake authentication, piece-wise exchange, and choking/unchoking mechanisms collectively contributes to the system’s stability and equitable resource allocation, validating its relevance as a solution to the scalability and fairness concerns outlined in the initial problem statement. The evaluation metrics, including download completion time, bandwidth utilization, and peer fairness index, confirm that the framework not only meets but exceeds performance expectations in distributed environments. The system maintains high throughput, ensures balanced participation among peers, and provides resilience in the presence of network volatility. Additionally, the real-time logging and monitoring capabilities enable transparent tracking of operations, making the system auditable and maintainable for extended use. These results collectively demonstrate that the framework is not only technically sound but also practical for real-world deployment in large-scale file distribution scenarios. Looking forward, the current system can be further enhanced by integrating advanced encryption protocols such as AES for end-to-end security and blockchain-based trust models to prevent Sybil and spoofing attacks. Additionally, the incorporation of AI-driven peer selection algorithms and bandwidth prediction models could further optimize resource allocation. Expanding the system with a user-friendly graphical interface and mobile support would also improve accessibility and adoption. These future directions aim to evolve the framework into a scalable, intelligent, and secure platform suitable for next-generation decentralized content delivery networks (CDNs) and edge-based data systems.

References

[1] Cohen, B. (2003). Incentives build robustness in BitTorrent. In Workshop on Economics of Peer-to-Peer Systems. [2] Lua, E. K., Crowcroft, J., Pias, M., Sharma, R., & Lim, S. (2005). A survey and comparison of peer-to-peer overlay network schemes. IEEE Communications Surveys & Tutorials, 7(1), 72-93. [3] Rhea, S. C., Geels, D., Roscoe, T., & Kubiatowicz, J. (2004). Handling churn in a DHT. In USENIX Annual Technical Conference. [4] Stoica, I., Morris, R., Karger, D., Kaashoek, M. F., & Balakrishnan, H. (2001). Chord: A scalable peer-to-peer lookup protocol for internet applications. ACM SIGCOMM Computer Communication Review, 31(4), 149-160. [5] Xu, M., Liu, J., & Liu, J. (2011). A survey of P2P streaming applications. Future Internet, 3(4), 329-366. [6] Qiu, D., & Srikant, R. (2004). Modeling and performance analysis of BitTorrent-like peer-to-peer networks. ACM SIGCOMM Computer Communication Review, 34(4), 367-378. [7] Zhang, H., Xie, G., Li, M., & He, H. (2014). Adaptive choke algorithms in BitTorrent-like P2P networks. IEEE Transactions on Parallel and Distributed Systems, 25(3), 579-589. [8] Li, X., Li, B., & Lau, W. C. (2005). A BitTorrent-like P2P system with incentive mechanisms. IEEE International Conference on Communications (ICC). [9] Guo, L., Chen, S., & Deng, L. (2006). BitTorrent-like file sharing with fairness and incentives. IEEE Transactions on Multimedia, 8(6), 1166-1177. [10] Levine, B. N., Shields, C., & Margolin, N. B. (2006). A survey of solutions to the Sybil attack. ACM Computer Surveys, 38(4), 1-28.

Copyright

Copyright © 2025 Ambika R, Dr. SDN Hayath Ali. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.