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Computer Networks
Transport Protocols & IP Addressing
GATE 2024
Medium

TCP client P successfully establishes a connection to TCP server Q. Let Nₚ denote the sequence number in the SYN sent from P to Q. Let N_Q denote the acknowledgement number in the SYN ACK from Q to P. Which of the following statements is/are CORRECT?

  • The sequence number Nₚ is chosen randomly by P
  • BThe sequence number Nₚ is always 0 for a new connection
  • CThe acknowledgement number N_Q is equal to Nₚ
  • The acknowledgement number N_Q is equal to Nₚ+1

Explanation

Modern TCP implementations choose the Initial Sequence Number (ISN) randomly for security (to resist sequence-number-guessing attacks) — not a fixed value like 0. Since the SYN itself consumes one sequence number, the SYN-ACK's acknowledgement number must be Nₚ+1.

Source: GATE CS 2024 (Session 1 / CS1) (2024)

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