Unreliable – When a UDP message is sent, it cannot be known if it will reach its destination; it could get lost along the way. There is no concept of acknowledgment, retransmission, or timeout. Not ordered – If two messages are sent to the same recipient, the order in which they arrive cannot be guaranteed. Lightweight – There is no ordering of messages, no tracking connections, etc. It is a very simple transport layer designed on top of IP. Datagrams – Packets are sent individually and are checked for integrity on arrival. Packets have definite boundaries which are honored upon receipt; a read operation at the receiver socket will yield an entire message as it was originally sent. No congestion control – UDP itself does not avoid congestion. Congestion control measures must be implemented at the application level or in the network. Broadcasts – being connectionless, UDP can broadcast - sent packets can be addressed to be receivable by all devices on the subnet. Multicast – a multicast mode of operation is supported whereby a single datagram packet can be automatically routed without duplication to a group of subscribers. Standards – User Datagram Protocol – Internet Protocol, Version 6 (IPv6) Specification – IPv6 Jumbograms – Management Information Base for the UDP – UDP Usage Guidelines See also Comparison of transport layer protocols Datagram Transport Layer Security (DTLS) List of TCP and UDP port numbers Micro Transport Protocol (μTP) Reliable Data Protocol (RDP) Reliable User Datagram Protocol (RUDP) UDP-based Data Transfer Protocol UDP flood attack UDP Helper Address UDP-Lite – a variant that delivers packets even if they are malformed References External links IANA Port Assignments The Trouble with UDP Scanning (PDF) Breakdown of UDP frame UDP on MSDN Magazine Sockets and WCF UDP connections Internet protocols Internet Standards Transport layer protocols 1980 introductions