If reliability is not essential, User Datagram Protocol (UDP), a TCP complement, offers a connectionless datagram service that guarantees neither delivery nor correct sequencing of delivered packets (much like IP). Higher-level protocols or applications might provide reliability mechanisms in addition to UDP/IP. UDP data checksums are optional, providing a way to exchange data over highly reliable networks without unnecessarily consuming network resources or processing time. When UDP checksums are used, they validate the integrity of both the header and data. ACKs are also not enforced by the UDP protocol; this is left to higher-level protocols.
UDP also offers one-to-many service capabilities, because it can be either broadcast or multicast.