One situation to use UDP rather than TCP is with SNMP, which monitors the network, sending frequent intermittent messages with status, updates and alerts. The cost in overhead to establish, maintain, and close a TCP connection for each one of those small messages would induce a really high CPU resource consumption. Another situation is with Real time communications services like Voice over IP, which do not need a completely reliable transport layer protocol. Errors like packet loss usually only have minor impacts on the audio output. It is better to drop a packet and have a few milliseconds of silence rather than have seconds of lag. The last situation for optimal use of UDP is with DNS requests, because the user will retry an operation if the DNS resolution fails.