tailieunhanh - The Illustrated Network- P30

The Illustrated Network- P30:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER User Datagram Protocol 10 What You Will Learn In this chapter you will learn about UDP one of the major transport layer protocols in the TCP IP stack. We ll talk about datagrams and the structure of the UDP header. You will learn about ports and sockets and how they are used at the transport layer. The User Datagram Protocol UDP is one the major transport layer protocols that rides on top of IPv4 or IPv6. Most explorations of the TCP IP transport layer treat the other major protocol the connection-oriented Transmission Control Protocol TCP first and present connectionless UDP later. But the complexities ofTCP and the reasons for these often sophisticated procedures are better understood after appreciating the basic connectionless service provided by UDP In addition certain concepts that are shared by both UDP and TCP such as ports can be introduced in UDP and so reduce the number of new ideas that must be covered during TCP discussions to a more manageable level. The UDP acronym shows the effects of early Internet efforts to distinguish connectionless packet delivery It s a datagram not a packet from more conventional connection-oriented schemes in use at the time. The data unit of UDP is not a packet anyway but a datagram the content of a connectionless packet many authors call IP packets datagrams as well but we do not in this book . UDP datagrams have their own headers naturally and the UDP header is about as simple as a header can s only to be expected because UDP operation is also very simple making UDP ideal for a first look at end-to-end functions on a network. In recent years UDP s popularity as a transport layer protocol for applications has been growing. The simple and fast operation of UDP makes it ideal for delay-sensitive traffic like voice samples the digital representation of analog speech multicast digital video and other types of real-time traffic that cannot be resent if lost on the network. This use of UDP is not as originally .