5) (10 pts) a particular ARQ protocol is being implemented with a sending and receiving window size of 3 frames (SWS = RWS = 3). Frames are sequenced using numbers 1, 2, 3, etc. Acknowledgments are sent for each frame that is received in order. If a higher sequence numbered frame is received out of order, that frame is not acknowledged until all earlier frames have been acknowledged. For example, frames 1, 2 and 3 are sent, and frame 1 is received (ACK1 sent back), frame 2 is delayed and frame 3 is received. Upon receiving Frame 3, the receiver retransmits ACK1. When frame 2 arrives ACK3 is transmitted (acknowledges frames 2 and 3 being received). Complete the timeline for this protocol given the following information: Sender needs to send 9 frames only with sequence numbers 1 through 9. Show all transmissions (frames and acks) that will occur when transmitting these nine frames and ack9 is received by the sender During transmissions, ACK 2 and Frame 5 are lost Bandwidth is infinite, so transmit time of frames is instantaneous (Frames are transmitted and received instantly though they still have a propagation time) The sender (when allowed) will transmit one frame every of a RTT transmission time is instantaneous, but the sender can only perform one transmission every of a RTT A frame experiencing no delay is received of a RTT after transmission starts (propagation delay) (Frame 1 and ACK 1 are shown) and processing time is instantaneous. At a specific time, frames or ACKs are received and processed(instantly) before a transmission decision occurs o receiver receives a frame and then sends the ACK if required o sender receives an ACK and then determines if a timeout has occurred; it then determines the next frame to transmit (provided the SWS has not been exhausted) If the receiver receives a frame that it has already acknowledged, the receiver repeats its most recent acknowledgment. For example, the last ACK sent by the receiver is ACK6. If frame 5 is received again, ACK6 is repeated. The timeout period is 2 Round Trip Times (2.0 RTT) Timing diagram is on the next page. The grading is based on checking the action at 1RTT, 2RTT, , 5RTT in both sender and receiver; partial credits will be given for correctness at other time instants.

Sender Receiver A1 1 RTT 1 RTT 2 RIT - 2 RTT 3 RTT 3 RTT 4 RTT 4 RTT 5 RTT 5 RTT