Which TCP/IP host-to-host protocol makes every effort but cannot guarantee data delivery?

Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are the two host-to-host protocols (UDP). TCP guarantees packet delivery via a virtual circuit and data acknowledgments, whereas UDP does not. As a result, TCP is frequently referred to as connection-oriented, whereas UDP is connectionless. IP and ICMP do not qualify as host-to-host protocols.