TCP client P successfully establishes a connection to TCP server Q. Let $N_P$ 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?

During the TCP 3-way handshake:

1. Initial Sequence Number (ISN): The initial sequence number $N_P$ is chosen dynamically/randomly (often using a clock-based or pseudo-random algorithm) by client P to prevent sequence number prediction attacks and avoid confusion with old duplicate packets from previous connections. Hence, $N_P$ is not always $0$. Thus, (A) is correct and (B) is incorrect.

2. SYN Packet Consumption: A TCP segment with the SYN flag set consumes one logical sequence number (even though it carries no user data).

3. Acknowledgement Number: The server acknowledges the receipt of the SYN by sending a SYN+ACK segment with an acknowledgement field containing the next expected sequence number from client P, which is $N_P + 1$. Thus, $N_Q = N_P + 1$. Hence, (D) is correct and (C) is incorrect.

Therefore, statements (A) and (D) are correct.