Draw and explain the TCP 3-way handshake: (1) Client → Server: SYN (seq=x), (2) Server → Client: SYN-ACK (seq=y, ack=x+1), (3) Client → Server: ACK (ack=y+1). Explain: why sequence numbers are random, what flags are set, how this prevents old duplicate connections. Then explain 4-way termination (FIN/ACK).
