TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic language of the communication or protocol of the Internet. It can also be used as a communication protocol in a private network (either an Intranet or a extranet).

TCP/IP Models Layers:
Model protocol TCP/IP uses four span layers that, logically, the equivalent of the six layers of the model of reference OSI, The physical layer are not covered by model protocol TCP/IP because the data link layer is regarded as the point where interface occurs; interface between pile TCP/IP and the material subjacent network. The following text is model protocol TCP/IP of layers, while starting with bottom.

1. Application Layer:
   In TCP/IP, the layer application also includes/understands the layer OSI Presentation and Session Layer. In this document, an application is a process which occurs above the layer of transport. That includes/understands all of the processes together which imply the interaction of user. The application determines the presentation of the data and controls of the session. In TCP/IP, the socket and the port terms are used to describe the way on which applications to communicate. There exists many level of TCP/IP application of protocols TCP/IP, including Simple Mail Transfer Protocol (smtp) and POP (Post Office Protocol) used for the e-mail, Hyper Text Transfer Protocol (HTTP) used for the World-Wide-Web, and of file Transfer Protocol (ftp). Majority of the protocols of level of the application are associated with one or more number of port.
   
   
2. Transport Layer:In TCP/IP, there exist two protocols of layer of transport. Transmission Control Protocol (TCP) guarantees that the information is received as it was sent. The UDP (User Datagram Protocol) does not carry out end at the end of the reliability of controls.
   
   
3. Internet Layer:
   In the model of reference OSI the network layer isolates the protocols from roadbase, the details of the sub-network and manages connections on the network. Protocol IP (Internet Protocol) is generally described like the TCP/IP Network Layer. Because of the Inter-Networking accent of TCP/IP, this commonly layer Internet commonly is called. All in top and bottom Travels through the layer of communication IP such a way that they are transmitted by the intermediary of protocol TCP/IP protocol stack.
   
   
4. Network Access Layer:
   In TCP/IP, the data link layer and the physical layer are normally gathered. TCP/IP allows the use of the data links and the physical layer of the standards rather than to define its own means. The majority of the RFC which refers to the data link layer describe how the existing intellectual property of data link uses protocols such as Ethernet, Token-ring, FDDI, HSSI, and the ATM. The characteristics of the material which transmits the signal of communication are generally defined by the physical layer.
   

The four layers of TCP/IP is built on the basis of information transmitted to leave the applications of the physical layer of the network. When data are sent, each milked layer all information it receives layer above that the data and adds information of control to before these data. This control of the information is called a heading, and the addition in the a heading is called encapsulation. When the data are received, the procedure proceeds opposite each layer removes its head before passing the data to the layer above.

Models are useful because they help to understand our difficult terms and wrapped systems. If it concerns networks, there be several models which are used for the role of different technologies, and how them interact. Of these, most popular and most used the open Systems Interconnection (OSI) are Reference model.

Definition: An abstract description of the digital communication between an application processes in separate systems.

Layers: The model has a hierarchical structure of the seven layers. Each low service with added value performs at the request of adjacent higher low and, for its part, request more basic provisions of adjacent lower layer:

1. Physical Layer (Layer 1)
   Physical layer services perform services at the request of the data link layer. Performs the most important functions and services by physical layer is:
   
   • Determining and the suspension a connection with a communication medium.
     
     
   • Participation to the process where the communication resources is effectively shared with several users.
     
     
   • Conversion between the representation of the digital data of sent the users and the corresponding indicators concerning a communication channel.
     


2. Data Link Layer (Layer 2) These low reacts to requests of the service network layer and questions service requests to physical low. The data risky Layer possibly stipulates the functional and procedural resources to transfer of data between network and entities to trace and corrects of errors which can appear in physical low.


3. Network Layer (Layer 3) These low reacts to requests of the service transport Layer and questions service requests to the data risky Layer. The Network Layer stipulate the functional and procedural resources of the transfer of variable length data sequences of a source to a destination by means of one or more networks, with conservation of the quality of the service by the transport Layer. The Network Layer conduct network routing, flow control, segmentation/de-segmentation and wrongly control functions.
   
   
4. Transport Layer (Layer 4) These low reacts to requests of the service Session Layer and questions service requests to the network layer. The aim of the transport Layer is supplying transparent transfer of data between end-users, so that the upper layers of only concern concerning supplying reliable and cost effective data transfer.
   
   
5. Session Layer (Layer 5) these low approach to the requests of the service presentation Layer and questions service requests to the transport Layer. The Session Layer offer application processes to the mechanism for the management of the dialogue between end-user. It provides for a duplex or half-duplex-working and puts check pointing, discontinuance, suspension, and restart procedures.
   
   
6. Presentation Layer (Layer 6) These low reacts to requests of the service Application Layer and questions service requests to the Session Layer. The presentation Layer lighted the Application Layer of care on the syntactic differences in data representation in end-user the systems.
   
   
7. Application Layer (Layer 7) These low interfaces directly and run into common application for the application processes, but also questions request Layer to the presentation. The common application services offer, semantic conversion linked between application processes.