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Definition: UDP

(User Datagram Protocol) A TCP/IP protocol that is widely used for streaming audio and video, voice over IP (VoIP) and videoconferencing. UDP is considered an unreliable delivery protocol because it does not check for errors. When transmitting voice and video, there is no time to retransmit erroneous or dropped packets. In contrast, when financial and other data are transmitted, TCP is used, which does check for errors.

UDP is "connectionless" and does not use a handshake to start a session like TCP does. For example, in a broadcast session with multiple destinations, UDP does not set up a connection with each receiver beforehand. See TCP, TCP/IP and RTP.

UDP Within an Ethernet Frame
A UDP packet is framed just like a TCP packet. This shows a UDP packet in an Ethernet frame ready for transmission over the network.

The Transport Layer of TCP/IP
The transport layer of the TCP/IP protocol defines both unreliable (UDP) and reliable (TCP) delivery methods.