Question

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

• A. TCP connection is half duplex
• B. The client and server use a three-way handshaking mechanism
• C. Before starting data transmission, client and server can initiate closing the connection at the same time
• D. The server cannot initiate closing of the connection unless the client initiates closing of the connection

Hint:

Key TCP facts for GATE: \textbf{TCP is full duplex} and uses \textbf{3-way handshake for connection establishment} and \textbf{4-way handshake for connection termination}.

Answer 1

The Correct Option is B

The correct statement regarding a TCP connection between a client and a server is: "The client and server use a three-way handshaking mechanism". Let's explore this in detail along with the reasoning for ruling out other options:

1. The three-way handshake mechanism is an essential part of establishing a TCP connection. Here's how it works:
   • The client sends a SYN (synchronize) message to the server to initiate the connection.
   • The server responds with a SYN-ACK (synchronize-acknowledge) message.
   • The client sends an ACK (acknowledge) message back to the server, completing the handshake.
   This process ensures that both the client and server are ready to transmit data and can communicate with each other. This is a fundamental aspect of TCP, which makes this option correct.
2. Option: TCP connection is half-duplex is incorrect because TCP connections are, in fact, full-duplex. This means that data can be transmitted in both directions simultaneously.
3. Option: Before starting data transmission, client and server can initiate closing the connection at the same time is misleading. While it is possible for both sides to attempt to close the connection, such a scenario usually results in a proper handshake for disconnecting (known as a four-way termination), not simultaneous closing before transmission starts.
4. Option: The server cannot initiate closing of the connection unless the client initiates closing of the connection is incorrect. Either the client or the server can initiate the closing of a TCP connection independently.

Conclusion: The only accurate statement about TCP connections pertaining to the process between a client and server is the use of the three-way handshaking mechanism.

Answer 2

Step 1: Recall basic properties of TCP.
TCP (Transmission Control Protocol) is a connection-oriented, reliable, and full-duplex transport layer protocol.
It ensures reliable communication between a client and a server using well-defined connection establishment and termination procedures.
Step 2: Analyze option (a).
TCP supports simultaneous data transmission in both directions.
Hence, TCP is full duplex, not half duplex.
Option (a) is incorrect.
Step 3: Analyze option (b).
TCP connection establishment uses the three-way handshake:
\[ \text{SYN} \rightarrow \text{SYN+ACK} \rightarrow \text{ACK} \] This mechanism synchronizes sequence numbers and establishes a reliable connection.
Option (b) is correct.
Step 4: Analyze option (c).
Connection termination in TCP involves a four-segment handshake.
Although both sides may close independently, closing is not related to data transmission start and cannot occur simultaneously in the described manner.
Option (c) is incorrect.
Step 5: Analyze option (d).
In TCP, either the client or the server can initiate connection termination.
There is no restriction that only the client must initiate closing.
Option (d) is incorrect.
Step 6: Conclusion.
The correct statement regarding TCP connections is: \[ \boxed{\text{The client and server use a three-way handshaking mechanism}} \]