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Reliable Data Transfer

Computer Networking Lab Project to implement a File Transfer service in Java using ARQ Protocols. In this project, we are required to implement in Java a Reliable Data Transfer protocol (RDT). RDT provides reliability and flow control using the Automatic Repeat Request (ARQ) and Sliding Window protocols. RDT is supposed to be implemented in the OS Kernel at the Data Link Layer.

However, that being too complex, let us implement RDT as a transport-layer File Transfer service over UDP, using the Sliding Window concepts we have learnt in the context of the Data Link Layer.

adapted from here: (http://nsl.cs.sfu.ca/teaching/09/371/prj3_reliableTransferProtocol.html)

Objective

To implement a File Transfer service in Java using ARQ Protocols:

  • Stop-and-Wait
  • Go-Back-N
  • Selective Repeat

General Protocol Requirements

Client File Request Format

REQUEST filename CRLF, with no spaces between REQUEST, filename and CRLF

Server Message Format

RDT sequence_number payload CRLF, where the payload is a byte array of 512, and the sequence_number represents the consignment number and is an ascending number between 0 and 255 stored in 1 byte

At the very last consignment, the message format is as follows:

RDT sequence_number payload END CRLF In the last consignment, the payload is less than, or equals to 512 bytes.

Client Acknowledgement Format

ACK sequence_number CRLF The sequence_number represents the consignment that the Client is expecting next, so it will be 1, 2, 3, 4, ... until the Client is notified of the last consignment.

Upon receiving the last consignment, the Client sends an ACK with sequence_number 0, waits for 500ms and terminates the connection. Negative ACK is not required.

Requirements for Stop-and-Wait

Time-Out = 30ms