The transport layer manages direct communication between endpoints, guaranteeing dependable data transmission. Its core functions include:- End-to-end delivery: Verifying correct and ordered data arrival at the destination.- Packet loss recovery and duplicate packet detection: The transport layer upholds transmission reliability through acknowledgments, retransmissions, and sequencing to address lost or duplicated packets.As specified in the query, the principal function emphasized is end-to-end delivery.Step 2: Conclusion.
Therefore, the accurate selection is (4) End to end delivery.