At sender
- If OK is received, proceed with the next n characters. Otherwise, if NAK is received, send the data + CRC bits again to the receiver after randomly introducing the error.
Final outcome: Input and output files should match. A log file should show how many frames were in error and how many retries were done for each frame.
Python – Stop & Wait Implementation using CRC
Stop and wait protocol is an error control protocol, in this protocol the sender sends data packets one at a time and waits for positive acknowledgment from the receiver’s side, if acknowledgment is received then the sender sends the next data packet else it’ll resend the previous packet until a positive acknowledgment is not received.
Note: To get more info on what is stop and wait protocol, refer Stop and Wait ARQ article.
CRC aka Cyclic redundancy check is an error detection mechanism, its procedure is as follows.