Question 1 options: Consider communication between a sender and receiver. Using

Question

Question 1 options:

Consider communication between a sender and receiver. Using a time-space diagram, illustrate reliable transmission of a message consisting of 5 segments using the selective-repeat protocol with N=3. In your illustration include acknowledgments and fixed timeout intervals of your choice. Assume that segment 2 is lost and that the acknowledgment for segment 4 is lost as well. Include the sequence number in your drawings.

From the diagram answer the following question. How many acknowledgments did the receiver transmit to the sender? (Enter a number only)

Explanation / Answer

Selective Repeat is a connection oriented protocol in which both transmitter and receiver have a window of sequence numbers.

Operation of Selective Repeat. The sender transmits four PDUs (1-4). The first PDU (1) is corrupted and not received. The receiver detects this when it receives PDU(2), which it stores in the receive buffer and requests a selective repeat of PDU(1). The sender responds to the request by sending PDU(1), and then continues sending PDUs (5-7). The receiver stores all subsequent out-of-sequence PDUs (3-4), until it receives PDU(1) correctly. The received PDU (1) and all stored PDUs (2-4) are then forwarded, followed by (5-7) as each of these is received in turn.

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