User Datagram Protocol. A Transport Layer host-to-host protocol in the TCP/IP protocol suite, UDP is a connectionless protocol for datagram-oriented applications. Like the Transmission Control Protocol (TCP), UDP uses the Internet Protocol (IP) for addressing and routing purposes. Unlike TCP, UDP provides no sequencing, error control, or flow control mechanisms. An application program that uses UDP assumes full responsibility for all issues of reliability, including data loss, data integrity, packet latency, data sequencing, and loss of connectivity. UDP is used extensively in voice over Internet Protocol (VoIP) and stream-oriented multimedia applications, where compression techniques are designed to mitigate such issues over a highly shared packet network. UDP also works well where transactions are of such short duration that connection setup overhead comprises a large proportion of overall transaction traffic, as exemplified by Simple Network Management Protocol (SNMP) exchanges. The standard size of the UDP header is eight octets, as illustrated in Figure U-1. The UDP header comprises the following fields.