Four Layers of TCP/IP Model Explained: Difference between TCP/IP and OSI Model

In this article, I am going to explain all the four Layers of TCP/IP Model and also difference between TCP/IP and OSI Model so keep reading this article till the end.

We know that computers can be connected to a network. This enables them to communicate and share resources. The network of computers, therefore, has been of great use for communication, information dissemination, and overall human progress.

There might be different standards and technology used by different types of computers. So, in order for the computers to effectively communicate with each other, there needs to be some agreed-upon rules and standards.

There also has to be an effective architecture, hierarchy, and structure of data flow. From the physical to the software level, a lot of things have to be taken care of, so that the communication within computer networks remain smooth and the data flow remains efficient.

TCP/IP Model (Transmission Control Protocol- Internet Protocol) and OSI (Open System Interconnection) model help us in conceptualizing and standardizing so that computers can communicate over networks. These models help us in laying the theoretical and foundational basis of modern communication systems.

The four layers of the TCP/IP model are:

  1. Application Layer – to allow access to network resources.
  2. Transport Layer – to provide reliable methods to process message delivery and error delivery.
  3. Internet Layer – to move packets from source to destination and to provide networking.
  4. Network Interface Layer – Responsible for the transmission between two devices on the same network.

Each of these layers includes specific protocols. Each layered is defined to perform a specific function. These four layers work in collaboration to transmit data from one layer to another.

A little detail about four layers of the TCP/IP model is given below:

  1. Application Layer: This layer helps in interacting with the Application program or the software which the user uses. Thus, it becomes closest to the end-user. It allows users to interact with other software applications.

This layer interacts with software applications to implement a communicating component. How the data is interpreted by the end-user application program is not the concern or outside the scope of the TCP/IP model.

For instance, file transfer application, email, remote login, etc are the programs at the application layer.

Some of the protocols used in the application layer are TELNET (Telecommunications Network), FTP (File Transfer Protocol), TFTP (Trivial File Transfer Protocol), NFS (Network File System), SMTP (Simple Mail Transfer Protocol), LPD (Line Printer Daemon), SNMP (Simple Network Management Protocol), DNS (Domain Name Service), etc.

The application layer, therefore, helps a user in identifying communication partners, determining resource availability, and synchronizing communication.

  1. Transport Layer: This layer helps in maintaining end-to-end communication across the network. It handles communication between hosts and provides multiplexing and reliability. This layer is built on the message which is received from the application layer.This layer determines data quantity and rates be sent over the network; it also sees to it that the data units are delivered in an error-free and sequential manner. The transport layer ensures that the message is received without any error; otherwise, the entire message is retransmitted again.

The reliability of a link is maintained and controlled through this layer. It helps in flow control, error control, and segmentation or de-segmentation.

Once the data has been successfully sent over the network and no errors occurred, this layer offers an acknowledgment of the same.

  1. Internet layer: The internet layer helps in the transmission of data between the source and the destination computers. It accepts data from the Transport layer and passes the data to the Network Interface layer. It is responsible for the logical transmission of data packets over the internet.

This layer ensures that the data reaches the correct destination. For sending the data, this layer ensures that the shortest available route is used, in case more than one route is available to send the data. By any chance, if there is a problem with the shortest route available to send data, an alternate route is chosen.

The main functions of the internet layer are:

  • Transmitting data packets to the link layer
  • Optimal routing of data packets in an independent way from source to destination.
  • Re-assembling out of order packets when they reach the destination.
  • The errors which happen in the transmission of data packets and fragmentation is handled by this layer.

This layer uses various protocols such as Internet Protocol (IP), Address Resolution Protocol(ARP), Reverse Address Resolution Protocol (RARP), Internet Control Message Protocol (ICMP), Internet Group Message Protocol (IGMP).

  1. Network Interface layer: This layer deals with the network on the physical level. It looks out for hardware addressing. The physical transmission of data is allowed due to the protocols present in this layer.

It also includes how bits should optically be signaled by hardware devices (which directly interfaces with a network medium), like coaxial, optical fiber, or twisted-pair cables.

A network layer is a combination of the data line and defined in the article of the OSI reference model. How the data should be sent physically through the network, is decided by the network layer. When the transmission of data takes place between two devices on the same network, this layer is responsible for it.

Difference between the OSI and TCP-IP model.

TCP/IP modelOSI Model
It is less refined. It doesn’t have a clear distinction between services, interfaces, and protocols.It is more detailed and refined. It has clearly defined points between interfaces, services, and protocols.
Developed in the initial days of ARPANET (Advanced Research Project Agency Network). Therefore, it has its evolution taking place before the advent of the internet.Developed by the ISO (International standards organization). It has been defined and evolved mainly after the advent of the internet.
This has four layers.This has seven layers.
It follows a horizontal approachIt follows a vertical approach
TCP/IP uses the Session and Presentation Layer in the Application Layer itself.This uses different Session and Presentation Layer.
TCP/IP uses only the Internet layer.OSI uses the network layer to define routing standards and protocols.
In TCP, physical and data link are both combined as a single host-to-network layer.In the OSI model, the data link layer and physical are separate layers.
TCP/IP model network layer only provides connectionless services.Connectionless and connection-oriented both services are provided by the network layer in the OSI model.
Protocols cannot be replaced easily in the TCP/IP model.While in the OSI model, Protocols are better covered and are easy to replace with the change in technology.
TCP/IP developed protocols then model.OSI developed model then protocol.
Transport layer in TCP/IP Model does not provide assurance delivery of packets.In OSI model, transport layer provides assurance delivery of packets.

While there are differences between the TCP-IP and the OSI Model, there are a few similarities:

  • Both models are logical. They help in defining standards for networking.
  • Since both models are based on layered architecture; in implementation, they divide the whole communication process into various layers.
  • In both the models, a single layer stands for specific functionality, and that layer defines standards related to that specific functionality only. The protocols are defined in a layer-wise manner.
  • The common standards and protocols are defined already by both models. This helps the manufacturers and operators to make and set up devices and network components. These devices and network components can coexist and work with devices and components made by other manufacturers.
  • Both help in dividing the communication network logically and physically into well-defined levels. This helps in making the troubleshooting process easier, as the complex functions now would be broken into simpler components.
  • In many cases, there were already defined standards and protocols. In such cases, both these models adopt those existing standards instead of defining a new standard. For instance, IEEE had already defined Ethernet standards before the formal inception or adoption of both of these models. In that case, both these models adopted the IEEE Ethernet standards.
  • The layers of both these models are comparable to each other. The Physical and Data Link Layers of the OSI model corresponds to the Link Layer of the TCP/IP model. The application layer of the TCP/IP model is represented by the Session Layer, Presentation Layer, and the Application layer of the OSI model. Finally, in both the models, the Network and Transport Layers are at the same.
  • The data is divided into packets, in both these models. Each of the packets may take the individual route from the source to the destination.

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