The final ACK confirms the server's SYN and completes the ordering. The full timeline shows both endpoints reaching ESTABLISHED with exact sequence and acknowledgment numbers.
highlighted = computed this step
Why the last ACK completes the setup
The final ACK confirms that the client saw the server's sequence number. After this ordered exchange, both lanes are established.
server ack=3001
The client's next sequence number
The client already used SYN at 1000, so its final ACK carries sequence number 1001.
1000+1=1001
Acknowledging the server SYN
The server SYN used sequence number 3000. The client acknowledges 3001, which is one past that server number.
3000+1=3001
Both sides are established
The timeline now has SYN, SYN-ACK, and ACK in order. The states reach ESTABLISHED on both lanes.
messages=3
Summary
The full handshake pins both initial sequence numbers and both acknowledgments. Connection setup ordering and exact sequence numbers only; timing, retransmission, and round-trip time are not modeled here.