Host A sends 10 TCP packets to Host B. All packets arrive at Host B quickly, but some arrive out of order. What will Host B do?

TCP does not discard out-of-order segments; it buffers them and can use Selective Acknowledgment (SACK) to inform the sender which segments were received.

TCP never drops already-received segments and waits; its buffering mechanism exists precisely to avoid unnecessary retransmission of data that arrived early.

Dropping out-of-order packets is the behavior of UDP, not TCP; TCP's reliability guarantee requires retaining all received segments until gaps are filled.

TCP assigns sequence numbers to every byte of data, allowing the receiver to detect and buffer out-of-order segments rather than discard them. Host B holds the early-arriving segments in its receive buffer, acknowledges them, and reassembles the full stream in order before passing it to the application layer, ensuring reliable and ordered delivery.