You’ll hear about TCP/IP model even if you are new to networking land. If you are taking preparation for a certification exam, which is related to networking, then this post is a must-read for you. In this post, you will get the clearest explanation of TCP/IP model. So, let’s begin!
Before we enter in the busy roads of TCP/IP land, we have to understand what is networking model in general. In simple words, a networking model explains how a message or data travels from sender’s device to receiver’s device.
In today’s world, there are numerous vendors who make their own hardware. As a result, any data communication completes through devices of multiple vendors. The whole process of communication through various devices and networks is explained by networking model.
As we already know, there are millions of networking devices made by thousands of vendors, communicating with each other would be impossible without any standard or common method. This is what TCP/IP model does. It does not describes the rules or protocols itself. Instead, it references the protocols required for communication. So, we can call it as a standard to create standards.
Layers of TCP/IP Model
For simplification, this model breaks down a complete communication processes into for parts, which are called layers. Each layers has many sets of rules, which are called protocols.
Next, we will discuss about each layers. We will also discuss about one of the most popular protocol of each layers.
Application layer defines the services which serve different applications running on network devices. One popular sevice of this layer is HTTP. It defines how a web browser can pull the contents of a website from a web server. Main purpose of application layer is, creating a interface between a running application and the network.
How HTTP works: Assume that you wan to visit whilenetworking.com. So at first, you run your web browser. Then you the address. After a while you see the home page of whilenetworking.com’s home page. All of this possible because of HTTP protocol or service.
In above scenario, when you type a web address in your web browser, it uses HTTP protocol. It sends a HTTP GET request to web server. If web server has requested web page, then it replies with desired files. If required, web server sends multiple files.
Transport layer has fewer protocols. Main purpose of this layer, is to provide service to application layer. The most popular protocol of this layer is TCP protocol.
How TCP works: We prefers TCP protocol when reliability is an issue. There are situations, when sender needs assurance that, expected receiver receives the message without any loss or error. This is where TCP comes.
From the above example, assume that requested web page needs three files to work. First, web server sends a file with SEQ-1. User receives that successfully. But during the transmission of second file with SEQ-2, error occurs. So second file is lost. Then third file with SEQ-3 is received by the user successfully. When users computer sees that SEQ-2 is missing, then it again sends a request to web server for that file. Then web server send the requested file again. Now users web browser has all three required files. This how usually TCP recovers from transmission errors.
This layer also has very few protocols. But only one protocol is used: IP or Internet Protocol. IP servers many services. Two most important services are addressing and routing.
Obviously you have heard about ip address. Internet Protocol provides this addressing scheme. It gives every network device a unique address. Every device send and receives messages or data using this address. This protocol also provides routing. Routing means choosing the best route or path from sender to receiver if there is more than one path. Finding best route is very important for the overall performance of data communication.
Link layer defines both protocols and hardware required for communication. The term Link refers to the connection between network device. This layer also serves it upper layers. One of the most used protocol of this layer is Ethernet protocol.
TCP/IP model has only four layers. But its area is vast. It has many protocols referred by each layers. Now we have discussed the basics of TCP/IP model and its layers. As IP addressing is a major part of networking, we’ll discuss about that in a separate post.
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