Reading TCP/IP Protocol

Training target: Read the following reading materials and use the reading skills mentioned in the passages above. You may also choose some parts of this passage to practice.

Text Network communication is defined by various network protocols. Protocols like TCP and IP provide the rules for communication. They contain the details of message format ， describe how a computer responds when a message arrives ， and specify how a computer handles errors or other abnormal conditions.

Most important ， they allow us to discuss computer communication independent of any particular vendor’s network hardware. In a sense ， protocols are to communication while algorithms are to computation ， a communication protocol allows one to specify or understand data communication without depending on detailed knowledge of a particular vendor’s network hardware.

A wide variety of network protocols models exist ， which are defined by many standard organizations worldwide and technology vendors over years of technology evolution and development. One of the most popular network protocol model is TCP/IP ， which is the heart of Internetworking communications.

The name TCP/IP refers to a suite of data communication protocols. The name is misleading because TCP and IP are only two of dozens of protocols that compose the suite. Its name comes from two of the most important protocols in the suite: the Transmission Control Protocol （ TCP ） and the Internet Protocol （ IP ）.

TCP/IP originated out of the investigative research into networking protocols that the Department of Defense （ DoD ） initiated in1969. In the early 1980s ， the TCP/IP protocols were developed. In1983 ， they became standard protocols for ARPANET. Because of the history of the TCP/IP protocol suite ， it is often referred to as the DoD protocol suite or the Internet protocol suite.

 TCP/IP protocol suite includes more than 100 protocols ， now let’s see some:  （ 1 ） The Hypertext Transfer Protocol The Hypertext Transfer Protocol （ HTTP ） is an application-level protocol for distributed ， collaborative ， hypermedia information systems. It has been in use by the World Wide Web global information initiative since1990.It is a stateless protocol which can be used for many tasks beyond its use for hypertext ， such as name servers and distributed object management systems ， through extension of its request methods ， error codes and headers. A feature of HTTP is the typing and negotiation of data representation ， allowing systems to be built independently of the data being transferred.

（ 2 ） File Transfer Protocol File Transfer Protocol （ FTP ） enables file sharing between hosts. FTP uses TCP to create a virtual connection for controlling information and then creates a separate TCP connection for data transfers. The control connection uses an image of the TELNET protocol to exchange commands and messages between hosts.

 （ 3 ） Internet Control Message Protocol  Internet Control Message Protocol （ ICMP ） is used for network error reporting and generating messages that require attention. The errors reported by ICMP are generally related to datagram processing. ICMP only reports errors involving fragment0of any fragmented datagrams. The IP ， UDP or TCP layer will usually take action based on ICMP messages. ICMP generally belongs to the IP layer of TCP/IP but relies on IP for support at the network layer. ICMP messages are encapsulated inside IP datagrams.

（ 4 ） Transmission Control Protocol Transmission Control Protocol （ TCP ） supports the network at the transport layer. TCP specifies the format of the data and acknowledgement that two computers exchange to achieve a reliable transfer ， as well as the procedure the computers use to ensure that the data arrives correctly. It specifies how TCP software distinguishes among multiple destinations on a given machine ， and how communicating machines recover form errors like lost or duplicated packets. The protocol also specifies how two computers initiate a TCP stream transfer and how they agree when it is complete. Because TCP assumes little about the underlying communication system ， TCP can be used with a variety of packet delivery systems ， including the IP datagram delivery service. In fact ， the large variety of delivery systems TCP can use is one of its strengths.

 （ 5 ） User Datagram Protocol  User Datagram Protocol （ UDP ） supports the network at the transport layer. UDP provides the primary mechanism that application programs use to send datagrams to other application programs. UDP provides protocol ports used to distinguish among multiple programs executing on a single machine. UDP uses the underlying IP to transport a message from one machine to another ， and provides the same unreliable ， connectionless datagram delivery semantics as IP. It does not use acknowledgement to make sure messages arrive ， it does not order incoming messages ， and it does not provide feedback to control the rate at which information flows between the machines.

 （ 6 ） Internet Protocol  Internet Protocol （ IP ） provides support at the network layer. IP provides three important definitions. First the IP protocol defines the basic unit of data transfer used throughout a TCP/IP internet. Thus ， it specifies the exact format of all data as it passes across a TCP/IP internet. Second ， IP software performs the routing function ， choosing a path over which data will be sent. Third ， IP includes a set of rules that embody the idea of unreliable packet delivery ， meaning there is no guarantee that the data will reach the intended host. The datagram may be damaged upon arrival ， out of order ， or not arrive at all. IP is such a foundational part of the design that a TCP/IP internet is sometimes called an IP-base technology.

 Evolution of TCP/IP technology is intertwined with revolution of the global Internet. With millions of users at tens of thousands of sites around the world depending on the global Internet as part of their daily work environment. We have passed the early stage of development in which every user was also an expert ， and entered a stage which few users understand the technology. Despite appearance ， however ， neither the Internet nor the TCP/IP protocol suite is static. Researchers solve new networking problems ， and engineers improve the underlying mechanisms.In short ， TCP/IP technology continues to evolve.

 The End