Question

With respect to a TCP connection between a client and a server, which one of the
following statements is true?

• A. The client and server use a two-way handshake mechanism before the start of data transmission
• B. The server cannot initiate closing of the connection before the client initiates closing of the connection
• C. The TCP connection is half-duplex
• D. The client and server can initiate closing of the connection at the same time

Hint:

Remember TCP uses a three-way handshake to connect and is full-duplex, so either endpoint can independently send a FIN, meaning both sides can initiate closing simultaneously.

Answer 1

The Correct Option is D

Eliminate the wrong options one at a time using what you know about TCP's connection state machine.

Option A claims a two-way handshake sets up the connection. TCP actually needs three segments - SYN from the client, SYN plus ACK from the server, and a final ACK from the client - so this is wrong; it is a three-way handshake.

Option B claims the server cannot close first. Since TCP treats the two directions of data flow independently, either endpoint owns the right to send a FIN whenever it has no more data to send, regardless of the peer's state, so the server can absolutely initiate the close.

Option C calls TCP half-duplex, meaning only one side could send at a time. This contradicts the very design of TCP, which supports simultaneous, independent data flow in both directions - it is full-duplex, not half-duplex.

That leaves the correct statement: because both endpoints can independently decide to stop sending data and issue a FIN, nothing prevents both the client and the server from doing so around the same instant. The TCP state machine has a dedicated CLOSING state exactly to handle this simultaneous-close case.

So the true statement is that the client and server can initiate closing of the connection at the same time, Option D.