UDP header consists of four parts, two of which are optional:
Source port and destination port used to mark each 16bit application process sent and received. Because UDP does not require a response, so the source port is optional, if not the source port, then set to zero.
Destination port behind a fixed length in bytes of the packet length field, used to specify the UDP datagram comprises a length, the minimum length of the data portion is 8byte.
The remaining portion of the header is used to 16bit header and data portions do together checksum (Checksum) of this part is optional, but generally use this feature in practical applications.
UDP and TCP checksum both to cover their header and data, but before the introduction of the IP header checksum covers only the IP header.