Implement A Reliable FTP Client-Server System Provide A SI

Implement A Reliable Ftp Client Server System Provide A Si

Provide a simple menu to the user, e.g. 1. GET 2. PUT 3. CD 4. QUIT. Your code must be robust and handle any incorrect user input. Since there can be multiple clients querying the server at the same time with each client being serviced by a different thread on the server, the server must ensure concurrency control on the data file while it is being updated. Only one thread must gain access to the data file during writes (use synchronized keyword for the write method). Be sure to terminate each thread cleanly after each client request has been serviced. Implement the project as described using Java Datagrams (UDP), a connectionless client-server system. The client-side application code must provide reliability since UDP does not guarantee delivery; use CRC32 checksum from java.util.zip for this purpose. Measure the mean response time for the server to service client requests and plot graphs for response time vs. file size for PUT and GET commands, as well as throughput vs. offered load for GET commands. The code should be well documented, with clear variable names and good programming practices.

Paper For Above instruction

Introduction

The implementation of a reliable FTP client-server system utilizing UDP (User Datagram Protocol) presents unique challenges and opportunities. UDP, being a connectionless protocol, does not inherently guarantee reliability, ordering, or data integrity. Consequently, designing a robust application requires incorporating additional mechanisms to ensure reliable data transfer, concurrency control, and clean resource management. This paper explores the detailed process of developing such a system in Java, emphasizing reliability, concurrency, and performance measurement through data and graphical analysis.

System Design and Architecture

The system comprises a server and multiple clients, facilitating fundamental FTP commands: GET, PUT, CD, and QUIT. The server operates with multi-threading to service multiple clients concurrently, maintaining data integrity through synchronization and thread-safe mechanisms. The communication protocol employs UDP, necessitating additional logic in the client-side to ensure reliable transmission, using CRC32 checksums for error detection and retransmission strategies.

Implementation Challenges

One primary challenge involves concurrency control when multiple clients simultaneously request file operations. The server addresses this by synchronizing access to shared data files, preventing race conditions during write operations. This synchronization is achieved through Java's synchronized keyword, locking critical sections during writes. Additionally, handling unreliable UDP transmission requires implementing acknowledgment messages and checksums to detect data corruption and loss, enabling the client to retransmit when necessary.

Another significant aspect involves clean thread termination after servicing each request, avoiding resource leaks and ensuring server stability. Proper exception handling, thread interruption, and connection cleanup are critical components of this process.

Reliability Measures

To compensate for UDP's lack of built-in reliability, the system incorporates CRC32 checksums to verify data integrity. When a client sends a request or receives data, it calculates and appends the checksum. The receiver recalculates and compares the checksum, requesting retransmission in case of discrepancies. This process significantly reduces data corruption and packet loss risks, ensuring higher reliability akin to TCP.

Performance Metrics and Data Collection

For assessing system performance, the implementation measures the mean response time for client requests involving file transfers of sizes: 1 MB, 25 MB, 50 MB, and 100 MB. Both PUT and GET operations are evaluated across these sizes. The client dispatches requests in sequence, recording response times, which are then used to generate plots of response time versus file size.

Throughput, defined as the bytes delivered per second, is calculated during these operations, enabling the creation of throughput graphs against offered load. These metrics provide insights into system efficiency, scalability, and the impact of file size on transfer performance.

Experimental Methodology and Results

The experimental setup involves multiple clients issuing requests concurrently to the server. For each file size, the system records the start and end times to compute response times. The throughput is similarly computed by dividing the total bytes transferred over the elapsed time. The data collected serve as the basis for generating three key graphs:

• Response time versus offered load for GET commands.
• Response time versus offered load for PUT commands.
• Throughput versus offered load for GET commands.

These graphs enable visual analysis of the system's performance under varying load conditions and file sizes.

Code Implementation

The core code involves creating a UDP server that listens for client requests and spawns a new thread for each incoming request. The server maintains synchronized methods for file access, ensuring only one thread writes at a time. Client code constructs requests, adds CRC32 checksums for reliability, and handles retransmissions based on acknowledgments. Both sides include timing code to record response durations for performance evaluation.

Conclusion

Developing a reliable UDP-based FTP system requires addressing the inherent unreliability of UDP with mechanisms such as checksums, acknowledgments, and retransmission strategies. Concurrency control ensures data integrity amid multiple clients, while clean thread management preserves system stability. Performance measurement and graphical analysis are integral for evaluating system scalability and efficiency. The approach outlined provides a practical foundation for robust, high-performance file transfer applications over unreliable transport protocols.

References

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