Question

Consider a Stop-and-Wait protocol. Assume constant delays for all transmissions and the same delay for packets sent and ACKs sent. Assume no errors occur during transmission.
(a) Suppose that the timeout value is set to 1/2 of what is required to receive an acknowledgement, from the time a packet is sent. Give the complete sequence of frame exchanges when the sender has 3 frames to send to the receiver.
(b) Suppose that the timeout value is sent to 2 times the round trip time. Give the sequence of frame exchanges when 3 frames are sent but the first frame is lost.

Answer 1

Explanation:

question a) answer:

At the moment when it sends the package, then it has a waiting time for the acknowledgement from the receiver, however, the time will be split in two when the frameset size becomes two, meaning that two packages have been sent together, causing the receiver to acknowledge only one package.

question b) answer:

The timeout is equal to two times.

In cases when the frame size is 3, the frame will be lost since the timeout turns to be 2 times. Because the sender has to wait for the acknowledgement, therefore it will send other of the parcels.