Internet Core Protocols: The Definitive Guide

UDP Is an Unreliable, Datagram-CentricTransport Protocol

As we discussed in Chapter 1, sending a message via UDP is somewhat analogous to sending a postcard in that it is totally untrustworthy, providing no guarantees of any kind of delivery. UDP messages are sent and then forgotten about immediately. As such, applications that need a reliable transport protocol should not use UDP.

However, UDP’s lightweight model does provide some distinct benefits, particularly in comparison to TCP’s highly managed connection model. While TCP provides high levels of reliability through highly managed virtual circuits, UDP offers high performance from having so little overhead. If reliability comes at the expense of performance, then conversely, performance can be gained by eliminating some of the overhead associated with reliability.

In addition, many applications simply cannot use TCP, since TCP’s virtual circuit design requires dedicated end-to-end connections between two (and no more than two) endpoints. If an application needs to use broadcasts or multicasts in order to send data to multiple hosts simultaneously, then that application will have to use UDP to do so.