Achieving reliable data transfer over UDP by utilizing selective repeat mechanism in the application layer. Assignment for Computer Networks course. The receiver code was not written by me.
Every packet in the transmission window is handled by a new thread. A thread sends the packet and starts waiting. If the main process receives an ACK message, it interrupts the thread. If the retransmission timer expires before an interrupt the packet is retransmitted.
To simulate packet losses and transmission delays packet_loss_probability and max_packet_delay arguments are used in the receiver.
The receiver drops the data packets with the specified probability p, and it delays the reception of the data packets with the
amount of delay randomly chosen from the interval [0, Dmax]. This emulates the effects of network delay.
First start the receiver from the console:
python receiver.py <bind_port> <window_size_N> <packet_loss_probability_p> <max_packet_delay_Dmax>
Then run the client code:
java Sender <file_path> <receiver_port> <window_size_N> <retransmission_timeout>
Example:
python3 receiver.py 112 20 0.1 100 and
java Sender image.png 112 100 120