Consider the three-way handshake mechanism followed during TCP connection establishment between hosts P and Q. Let X and Y be two random 32-bit starting sequence numbers chosen by P and Q respectively. Suppose P sends a TCP connection request message to Q with a TCP segment having SYN bit = 1, SEQ number = X, and ACK bit = 0. Suppose Q accepts the connection request. Which one of the following choices represents the information present in the TCP segment header that is sent by Q to P?

During the TCP 3-way handshake:

1. Step 1 (P to Q): P sends a SYN packet:

   $$\text{SYN} = 1, \text{ACK} = 0, \text{SEQ} = X, \text{FIN} = 0$$

2. Step 2 (Q to P): Q accepts the connection by responding with a SYN-ACK packet:

   • Since Q is also synchronizing its sequence number, $\text{SYN bit} = 1$.

   • Since Q is acknowledging P's SYN segment, $\text{ACK bit} = 1$.

   • Q's own starting sequence number is $\text{SEQ number} = Y$.

   • Since a SYN packet consumes 1 sequence number, Q acknowledges it with $\text{ACK number} = X + 1$.

   • Connection termination is not taking place, so $\text{FIN bit} = 0$.

Therefore, the header contains: $\text{SYN bit} = 1, \text{SEQ number} = Y, \text{ACK bit} = 1, \text{ACK number} = X+1, \text{FIN bit} = 0$, which corresponds to option (C).