GATE CS 2024 Set 1 — Question 29
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Computer Networks → Transport Layer → TCP Handshake
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Question
TCP client successfully establishes a connection to TCP server . Let denote the sequence number in the SYN sent from to . Let denote the acknowledgement number in the SYN ACK from to . Which of the following statements is/are CORRECT?
Correct answer
(A) The sequence number N_P is chosen randomly by P; (D) The acknowledgement number N_Q is equal to N_P + 1
Solution
In the TCP three-way handshake process:
1.Step 1 (SYN): The client sends a SYN segment to the server to initiate a connection. This segment contains an Initial Sequence Number (ISN), denoted as . According to TCP standards (RFC 793, RFC 6528), the ISN is chosen using a pseudo-random generator to ensure uniqueness and security against sequence number prediction attacks. Therefore, statement (A) is correct.
2.Step 2 (SYN ACK): The server responds with a SYN ACK segment. This segment includes its own ISN and an acknowledgement number. The acknowledgement number confirms the receipt of the client's SYN. Since the SYN flag logically consumes one sequence number, the acknowledgement number is set to the client's sequence number plus one (). The question defines as this acknowledgement number. Thus, , making statement (D) correct.
Statement (B) is incorrect because the ISN is randomized, not fixed at 0. Statement (C) is incorrect because the acknowledgement number must be to account for the SYN flag.Continue learning with Success Tracker
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