Source Port— This field occupies the first 16 bits of the UDP header. This field typically holds the UDP port number of the application sending this datagram.
Destination Port— This 16-bit field holds the port address to which the UDP software on the receiving machine will deliver this datagram.
Length— This 16-bit field identifies the length in octets of the UDP datagram. The length includes the UDP header as well as the UDP data payload.
Checksum— This 16-bit field is used to determine whether the datagram was corrupted during transmission. The checksums generated at the source and verified at the destination allow the client application to determine if the datagram has been corrupted.