Go-Back-N Simulator

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Introduction

This is a GO-BACK-N simulation writen in C# 2.0. Go-Back-N ARQ is a specific instance of the Automatic Repeat-reQuest (ARQ) Protocol, in which the sending process continues to send a number of frames specified by a window size without receiving an ACK packet from the receiver. The receiver process keeps track of the sequence number of the next frame it expects to receive, and sends that number with every ACK it sends. If a frame from the sender does not reach the receiver, the receiver will stop acknowledging received frames. Once the sender has sent all of the frames in its window, it will detect that all of the frames since the first lost frame are outstanding, and will go back to sequence number of the last ACK it received from the receiver process and fill its window starting with that frame and continue the process over again.

Work Structure

The simulation includes two different programs. One of them does server operations and the other one does client operations. Firstly client accepts a 10240(40*256) Bytes long file. It splits these bytes into 40 segments. Then user selects the probability of corruption while client is sending segments to the server, the probability of corruption while server is sending acknowledges to the client side and window size which determines the number of segments that are sent in the same time.

The client sends segments to the server with the probability of corruption that user has chosen. If packets are dropped, acknowledges are not sent back to client. If packets are received, server can not send acknowledges to client side. Because of the probability of corruption in acks, acks can be dropped.

After all segments are sent, user can defrag all segments and get the file.

Multi threads are used to send segments.

Conclusion

This simulation performs an unreliable channel using TCP!!! Packets and acknowledges are consciously dropped to show working structure of Go-Back-N.