The three way handshake for TCP connection establishment is shown below. Which…

Answer: S1 and S4 are true; S2 and S3 are false.

Key ideas:

• Three-way handshake sequence (no packet loss): client sends SYN → server receives SYN and moves LISTEN → SYN_RCVD and sends SYN+ACK → client receives SYN+ACK and sends ACK → both sides move to ESTABLISHED.

• Server state transitions on passive open: LISTEN → SYN_RCVD → ESTABLISHED (it does not go to SYN_SENT, which is a client active-open state).

Statement-by-statement explanation:

• S1 (Loss of SYN+ACK from the server will not establish a connection): True. If the client does not receive the SYN+ACK, it will not send the final ACK, so the connection is not established at that time (the server remains in SYN_RCVD and will retransmit).

• S2 (Loss of ACK from the client cannot establish the connection): False. The client sends the ACK and moves to ESTABLISHED; if that ACK is lost, the server will retransmit the SYN+ACK and the client will send the ACK again. Thus a lost ACK does not permanently prevent establishment — the connection can still become established via retransmission.

• S3 (The server moves LISTEN → SYN_RCVD → SYN_SENT → ESTABLISHED on no packet loss): False. SYN_SENT is the state used by the active opener (client), not the passive opener (server). The server does not enter SYN_SENT in the normal passive-open handshake.

• S4 (The server moves LISTEN → SYN_RCVD → ESTABLISHED on no packet loss): True. This matches the standard passive-open state transitions when the handshake completes without loss.

Conclusion: The correct true statements are S1 and S4.