User Datagram Protocol (UDP) or sometimes, incorrectly, referred to as the Unreliable Data Protocol. The UDP protocol is used to send data between two IP addresses, but there is no guarantee (unlike tcp/ip) that the data will be transmitted.

UDP is important in video surveillance because it often is used as the protocol in video streaming. When streaming video, it is not always desired that all the data be transmitted. For example, when streaming video in realtime data can sometimes be lost during transmision. However, retransmitting the lost data will only increase the bandwidth required and the overhead associated with assuring that all the data is passed correctly will increase network latency. Under these circumstances it is desirable to simply ignore the lost data and continue to show video as close to realtime as possible.

For a detailed explanation udp see: www,protocols,com/pbook/tcpip1,htm