Stop-and-wait ARQ

Stop-and-wait ARQ, also referred to as alternating bit protocol, is a method in telecommunications to send information between two connected devices.

Typically the transmitter adds a redundancy check number to the end of each frame.

Another problem is when the transmission medium has such a long latency that the sender's timeout runs out before the frame reaches the receiver.

To avoid these problems, the most common solution is to define a 1 bit sequence number in the header of the frame.

Similarly, if two subsequent ACKs reference the same sequence number, they are acknowledging the same frame.

To solve this problem, one can send more than one packet at a time with a larger sequence number and use one ACK for a set.