Suppose you have to develop an error recovery protocol for a link that is unreliable and delay sensitive, which of the following protocol would you choose?

(i) Stop & wait.

(ii) Selective Repeat.

(iii) Go back.

Justify your answer.

Selective- repeat and Go -back both work well if errors are rare. Although if error rate is high than many bandwidth will be wasted in retransmission of frames. Therefore both the above methods are not appropriate for a link which is unreliable and delay sensitive. For such type of link stop and wait protocol is most appropriate protocol. In such protocol sender waits after transmitting all packets. While the receiver is ready for other packet, the receiver sends a control message, as a rule in form of acknowledgement. Though such protocol prevents over run, they can reason extremely inefficient utilization of network capacity.