A set of rules is needed for any means of communication. Human intercommunication requires rules of conversation Computers are no different. .

.If the two people talk at the same time then we get what is known in networking terms as data collision. . .

Therefore, we need regulations and rules to how we communicate over a computer network. For example to remote login, telnet, FTP or email. . .The set of rules and regulations is called a Protocol. A network protocol has to define how all the operations within a network, and also how entities outside the network must interact.

How data gets from point A to Point B. How computers and devices communicate. For example how a file is printed on a printer , how data is transmitted over a telephone line etc.

.To provide all these requirements the TCP/IP Model for computer network protocols created in the 1970s by DARPA, an agency of the United States Department of Defense. . .TCP/IP defines a set of rules to enable computers to communicate over a network, specifying how data should be packaged, addressed, shipped, routed and delivered to the right destination. The specification defines protocols for different types of communication between computers and provides a framework for more detailed standards.

.Structure Of TCP-IP. .

Networking protocols are normally developed in layers, with each layer responsible for a different facet of the communications. A protocol suite, such as TCP/IP, is the combination of different protocols at various layers. TCP/IP is normally considered to be a 4-layer system as follows. .

Application Layer. .The application layer handles the details of the particular application. There are many common TCP/IP applications that almost every implementation provides: . .Telnet for remote login.

. .FTP, the File Transfer Protocol. .

.SMTP, the Simple Mail Transfer protocol, for electronic mail, . .SNMP, the Simple Network Management Protocol. .Transport Layer.

.The transport layer provides a flow of data between two hosts, for the application layer above. In the TCP/IP protocol suite there are two vastly different transport protocols TCP and UDP. . .TCP provides a reliable flow of data between two hosts, acknowledging received packets, setting timeouts to make certain the other end acknowledges packets that are sent etc.

. .UDP on the other hand, provides a much simpler service to the application layer. It just sends packets of data called datagram’s from one host to the other, but there is no guarantee that the datagram’s reach the other end. Any desired reliability must be added by the application.

.Network Layer. .The network layer handles the movement of packets around the network. Routing of packets, for example, takes place here. IP, Internet Control Message Protocol, and Internet Group Management Protocol provide the network layer in the TCP/IP protocol suite.

It is concerned with the physical transmission of the data from computer to computer. . .

There is one further level of software to be considered, the network level. It routes the packages across a particular network. .Data Link Layer.

.The data link layer, sometimes called the data-link layer or network interface layer, normally includes the device driver in the operating system and the corresponding network interface card in the computer. Together they handle all the hardware details of physically interfacing with the cable or whatever type of media is being used. .

.This layer also represents the boundary between hardware e.g. CRC and software implementation e.

g. physical addressing. .

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