UDP

User Datagram Protocol (UDP) is a connectionless, stateless, and unreliable protocol that was designed for applications that do not need to have a reliable transport mechanism, such as NTP, DNS (for lookup queries), and NFS. UDP relies on the network to provide the reliability, and the actual application handles any retransmission of lost data. Consequently, UDP requires less processing overhead than TCP, because there is no setup and termination of a virtual connection and no acknowledgement mechanism.

UDP uses datagrams as its basic units of transfer, which are shorter than TCP segment headers and contain fewer fields. The format of the UDP datagram header is shown in Figure 9.4.

Figure 9.4. UDP header format.

UDP uses the following UDP header fields:

• Source Port ” Identifies the UDP application program on the sending side.

• Destination Port ” Identifies the UDP application program on the receiving side.

• Length ” A 16-bit integer for the length of the datagram (in bytes), including the data portion.

• Checksum ” A 16-bit integer used to verify the integrity of the UDP datagram header and the data.