8.16 Summary

Converting our echo client/server to use UDP instead of TCP was simple. But lots of features provided by TCP are missing: detecting lost packets and retransmitting, verifying responses as being from the correct peer, and the like. We will return to this topic in Section 22.5 and see what it takes to add some reliability to a UDP application.

UDP sockets can generate asynchronous errors, that is, errors that are reported some time after a packet is sent. TCP sockets always report these errors to the application, but with UDP, the socket must be connected to receive these errors.

UDP has no flow control, and this is easy to demonstrate. Normally, this is not a problem, because many UDP applications are built using a request-reply model, and not for transferring bulk data.

There are still more points to consider when writing UDP applications, but we will save these until Chapter 22, after covering the interface functions, broadcasting, and multicasting.