Some Useful Applications

In this section, you’ll see several Internet servers and clients that use DatagramPacket and DatagramSocket. Some of these will be familiar from previous chapters because many Internet protocols have both TCP and UDP implementations. When an IP packet is received by a host, the host determines whether the packet is a TCP packet or a UDP datagram by inspecting the IP header. As I said earlier, there’s no connection between UDP and TCP ports; TCP and UDP servers can share the same port number without problems. By convention, if a service has both TCP and UDP implementations, it uses the same port for both, although there’s no technical reason this has to be the case.