TCP/IP Analysis and Troubleshooting Toolkit

CHAPTER 5

User Datagram Protocol

UDP stands for User Datagram Protocol. Its name reflects the type of service it provides. The term datagram is defined by the Free Online Dictionary of Computing (FOLDOC) (http://foldoc.doc.ic.ac.uk/foldoc/index.html) as:

A self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.

UDP does not use a connection setup to transfer data nor does it rely on any other processes, as would a protocol like TCP. Hence, UDP is referred to as an unreliable and connectionless datagram service. Similar to IP, UDP does not guarantee the delivery of data. IP's responsibility is to forward upper-layer data throughout the IP network but it does not make a guarantee that it will arrive at the destination. UDP is a Layer 4 transport layer protocol. In Chapter 1, I briefly discussed the roles of the transport layer, but before moving on to the details of the UDP protocol, it is important I revisit those roles to convey a solid understanding of the transport layer.

Revisiting the Transport Layer

As I state in Chapter 1, the transport layer can provide reliable or unreliable service to an application or other upper-layer protocol. Depending on the type of application, the services of the transport layer required will be different. The term transport does not mean that the transport ...