This article is contributed by Vivek Reddy.We will discuss the TCP/ip model and the OSI model to better understand how communication works. References-Connection establishment Wikipedia TCP 3-Way Handshake TCP 3-Way Handshake TCPIPguide. Note Initial sequence numbers are randomly selected while establishing connections between client and server. In this chapter, we will look at the layered models that are used in communication over networks.How does TCP work TCP provides communication between an application program and the Internet Protocol (they are frequently written as TCP/IP.) An application.With these, a full-duplex communication is established. TCP/IP can also be used as a communications protocol in a private network (an intranet or an extranet ).In the previous chapter we were introduced to computer networks and we got to know their importance in everyday lives. TCP/IP (Transmission Control Protocol/Internet Protocol): TCP /IP, or the Transmission Control Protocol/Internet Protocol, is a suite of communication protocols used to interconnect network devices on the internet.

A layered model shows how the protocols work at each layer as well as how the layers interact with the layers either above them or below them. As shown in the figure, control bits in the TCP header indicate the progress and status of the connection.To better understand the various protocols and how they work with each other, we use layered models. To establish the connection, the hosts perform a three-way handshake. Use of layered modelsTCP is a full-duplex protocol, where each connection represents two one-way communication sessions.

This means that if a change in technology or capabilities is made in one layer, it will not affect another layer either above it or below it. The layered model is useful since it allows for independence between other layers. Competitions between different vendors is increased, this is because the models define standards and therefore product superiority is not based on the use of certain protocols since all products support them. Each layer in a model defines different protocols, therefore by using a layered model, network engineers can be able to define and design protocols which conform to the specific layer.

However, the TCP/IP model is an open standard and therefore no company has control of the definitions. The protocols that are defined in this model are usually based on vendor specifications. However, these two models are different.The TCP/IP model is protocol model and it describes the functions at each of its layers.

A good analogy would be a cityвЂ™s building regulations committee, this body would be in charge of the regulations on where a person can put up a structure, the strength specifications, the maximum height and other regulations, however, it cannot prescribe the specific design of the building to be put up. It does not give strict regulations on how or what protocols and services should work at each layer, rather, it works as a guideline. The TCP/IP model was introduced in the 1970вЂ™s by the USвЂ™s DOD (Department Of Defense).NOTE: although you are not required to know all the background information, you will be expected to understand some of the RFCвЂ™s for the course as well as the CCNA examinations.The OSI model is a reference model and it is used to provide or maintain consistency and standardization among the various protocols and services that are used in networks.

The application layer, is the component that interfaces with the user, when you are using a web browser, this is a component of the application layer.The transport layer defines the various ports and helps differentiate the different types of communication from a single user. Network communications were first defined using this model and for successful communication to occur, the functions of each layer must be in place in a network.From the output below, you can see the function of each and every layer of this model. There are four categories as you can see from the output above. This does not mean that the TCP/IP model is not relevant as we will see as we proceed in this course.This model was first introduced in the 1970вЂ™s. Network engineers use it in designing, operating and troubleshooting networking equipment where necessary.

If a message is to be sent from one computer to another on a remote network, it is the work of the internet layer to make sure the message gets to the intended recipient. The transport layer also helps in interoperability between different network devices such as a PDA and a computer.The internet layer is meant to provide the best path to remote networks, this differentiates the different devices on a network. It is the work of the transport layer to differentiate the different types of communications.

(more on logical addressing will be discussed later) The segments would then be passed down to the internet layer and encapsulated into packets, in this layer, logical addressing would be added. In this case, the PDU at the transport layer is the segment.

This process is illustrated below.As mentioned above, each form that the data takes at each layer of the TCP/IP model is known as a PDU, we have already discussed the transport and internet layer PDUs. The data would then be passed to the user. When the data is received at the destination, the reverse process would happen, i.e., removal of protocol specific information вЂ“ decapsulation as well as reassembly into the application data would be carried out.

Packet вЂ“ in the internetwork layer, the packets are the PDUs and they include the logical addressing for remote delivery. Segment вЂ“ as mentioned earlier, this is the PDU at the transport layer. This is the information presented to the user. Data вЂ“ the end user information, this may include, email content, website information among others.

In this model, as shown in the diagram above, the application and network access layer are broken down to define more functions. It also describes the interaction of each layer with the layers directly above and below it.The protocols that are discussed in the TCP/IP model, can be clearly defined and described in the OSI mode. Bits вЂ“ the form that is carried over the physical media form is Bits, these may be in many forms such as electrical signals, light signals and others.The OSI model provides an extensive list of functions and services that can occur at each layer.

We will look at these in future topics. In the OSI model, the protocols that mainly work here are the UDP and TCP protocols. At this layer, the rules define how messages are acknowledged, how the communication recovers from errors, and how the segments are arranged. The functions at these layers are the same.The transport layer defines how communication between different user machines happens. It does not state what exactly happens at each of them.The network and transport layers of the OSI model are very similar to those of the TCP/IP model. At the data link and physical layer, the OSI model only describes how data is handled from the network layer to the physical layer.

As we mentioned earlier, the data is usually broken down into different PDUs and the layers in the OSI model define how each PDU is controlled so as to make communication successful.Addresses are one of the ways that communication is made successful in the network.

Tcp Communication Process