GO Classes Test Series 2024 | Mock GATE | Test 14 | Question: 38

Question

Consider a sliding window protocol with a window size of $5$ using cumulative ACKs (and ACK is being sent for each segment).

Assume that the retransmission timeout timer is long enough and timeout has not occurred for any packet in this question.

The numbering of data packets start from $1.$ Also, assume the TCP receiver sends an ACK for every segment it receives.

The notation $A x$ is used to mean that the ACK packet is acknowledging the receipt of all packets up to and including data packet $x$. That is, $A 5$ is acknowledging the receipt of packet 5; to be clear, the notation does not mean that the receiver is expecting packet 5 as the next data packet. Assume that the following ACK packets arrive (just the ordering is shown, no timing information is provided):
$$A1 A2 A3 A3 A5 A6$$
Which scenarios would have produced such a series of ACKs? (mark all that apply)

• A. Data packet number 4 was dropped.
• B. Data packet number 4 was delayed, and arrived immediately after data packet 5
• C. Data packet 3 was duplicated by the network
• D. ACK packet A3 was duplicated by the network

Answer 1

If A3 is not duplicated by network then why it's appearing  2 times ..anyone please clear my doubts .. @GO Classes 

Comments

@Sachin Mittal 1

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In Morning I will upload video solution

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OK thank you so much sir , no problem

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A1 {1} Received 1 (We have all packets up to 1)

A2 {1, 2} Received 2 (We have all packets up to 2)

A3 {1, 2, 3} Received 3 (We have all packets up to 3)

A3 {1, 2, 3, 5} Received 5 (We have all packets up to 3 only as 4th is not here so can't say up to 5)

A5 {1, 2, 3, 4, 5} Received 4 (We have all packets up to 5)

A6 {1, 2, 3, 4, 5, 6} Received 6 (We have all packets up to 6)