UDP is called a connectionless protocol, but it really is not. The operating system maintains information about each active UDP socket, which implies a connection-oriented service. In a true connectionless service (such as IP) there are no sockets maintained. Data units are sent to a specific destination, with a port address. The socket is not needed because the data unit is processed when it is received by the application, and there is no further action to take with the originating host.

What UDP does not provide is error correction and flow control. There are no acknowledgments sent for received UDP data units; they are assumed received. The application using UDP services is responsible for determining if there have been errors or if data units are missing. This makes UDP an unreliable service, but reliability is not always a concern with applications such as e-mail and some network management functions. Upper-layer protocols can make up for what UDP is lacking. This provides a streamlined protocol that does not require a lot of processing at the originating or destination hosts. If a lot of processing is not required, data units can be sent and received with very little delay. Many newer protocols operating at this layer (layer 4) and the lower layers use this philosophy.