GATE CS 2025 Set 1 Q12 — Transport Layer: Flow Control, Congestion Control, UDP, TCP, Sockets

In TCP, the connection establishment process uses a 3-way handshake protocol. The three packets exchanged in order ($\text{P1}$, $\text{P2}$, and $\text{P3}$) have the following TCP header flag configurations:

1. Packet 1 ($\text{P1}$): Client to Server (Connection Request)
   • The client initiates the connection by setting the SYN flag.
   • Flags: $\text{SYN} = 1$, $\text{ACK} = 0$.
2. Packet 2 ($\text{P2}$): Server to Client (Connection Acknowledgment)
   • The server acknowledges the client's request and sends its own synchronization request.
   • Flags: $\text{SYN} = 1$, $\text{ACK} = 1$.
3. Packet 3 ($\text{P3}$): Client to Server (Acknowledgment)
   • The client acknowledges the server's request. The synchronization phase is complete, so the SYN flag is cleared.
   • Flags: $\text{SYN} = 0$, $\text{ACK} = 1$.

Let's evaluate the given options based on these rules:

• Option A: $\text{P3: SYN} = 1, \text{ACK} = 1$ — Incorrect (In $\text{P3}$, $\text{SYN} = 0$).
• Option B: $\text{P2: SYN} = 1, \text{ACK} = 1$ — Correct.
• Option C: $\text{P2: SYN} = 0, \text{ACK} = 1$ — Incorrect (In $\text{P2}$, $\text{SYN} = 1$).
• Option D: $\text{P1: SYN} = 1$ — Correct (In $\text{P1}$, $\text{SYN}$ is indeed set to $1$).