Selective Repeat

Overview

A simple prototype of reliable data transfer using Selective Repeat Protocol.

Usage

First, run the receiver program:

receiver PORT LOSSPROB OUTPUTFILENAME

Second, run the sender program:

sender PORT RECVHOST RECVPORT LOSSPROB FILENAME

LOSSPROB is the simulated probability that a packet (either data or ack) is dropped.

MECHANICS

The sender side sends DATA packets and the receiver side sends ACK packets. The format of both packet types are outlined below. Each DATA packet transfers at maximum 500 bytes and uses sequence number for in-order data transfer. Sequence number starts at 0 and resets when it reaches 60000. The sender side will resend a DATA packet if it is not acknowledged by the receiver after 500msec.

DATA
 0       1        2       3            4
 0123456701234567 012345670123 4 5 6 7 01234567
+----------------+------------+-+-+-+-+--------
|SEQ NUM         |LENGTH      |/|/|F|E|DATA...
+----------------+------------+-+-+-+-+--------
                                   | |
                                   | +-> last packet bit
                                   +---> first packet bit

ACK
 0       1        2       3
 0123456701234567 0123456701234567
+----------------+----------------+
|SEQ NUM         |ACC SEQ NUM     |
+----------------+----------------+
                  |
                  +-> left side of receiving window