OSI Model and TCP/IP Model

Learn the similarities and contrasts between the OSI and TCP/IP models, the two most well-known computer network models.

Models of computer networks make it easier to connect the transmitter and receiver and convey data seamlessly. The OSI Model and the TCP/IP (Transport Control Protocol/Internet Protocol) Model are the two most widely used computer network models. While TCP/IP is the set of communication protocols used to link network devices to the Internet, OSI is a reference model specifying a networking system’s operations. 

We shall examine these two models in-depth in this article. We shall study their layers and the differences between the OSI and TCP/IP models.

TCP/IP Model

The TCP/IP model has four layers: network access, internet, transport and application. These layers function as a set of protocols when combined. When a user sends data via these layers, the TCP/IP model does so in a certain sequence, and then does so again in the opposite order when the data is received.

Network Access Layer

Computers can connect over the internet thanks to the network access layer, commonly referred to as the data link layer. This includes network interface cards, wireless networks, ethernet connections, and computer device drivers.

The technological framework that enables network connections, such as the code that transforms digital data into transmittable signals, is also a part of the network access layer.

Internet Layer

The network layer, commonly referred to as the internet layer, manages traffic flow and routing to guarantee timely and correct data transmission. This layer also puts the data packet back together at its destination. The internet layer may take a bit longer to transfer a file when there is a lot of internet traffic, but there is a lower likelihood that an error would destroy the file.

Transport Layer

The transport layer offers a dependable data link between two communicating devices. The transport layer separates the data into packets, recognizes the packets it has received from the sender and ensures the receiver acknowledges the packets it gets, much like mailing an insured package.

Application Layer

The set of programs known as the application layer enables user access to the network. That often refers to email, messaging services, and cloud storage services. When delivering and receiving data, this is what the end user sees and interacts with.

OSI Model

Physical Layer

The lowest layer of the OSI Model is concerned with conveying physical pieces of raw, unstructured data over the network from the sending device’s physical layer to the receiving device’s physical layer. Specifications like voltages, pin layouts, cables, and radio frequencies may be included. Physical resources like network hubs, cabling, repeaters, network adapters, or modems can be found at the physical layer.

Functions:

• Line Configuration: This describes the physical connections that may be made between two or more devices.
• Data Transmission: It specifies the method of transmission between the two devices on the network, such as simplex, half-duplex, or full-duplex.
• Topology: It describes the configuration of network devices.
• Signals: It chooses the kind of signal that will be utilized to send the information.

Data Link Layer

Directly linked nodes are used for node-to-node data transfer at the data link layer, where data is bundled into frames. Errors that could have happened at the physical layer are likewise fixed at the data connection layer.

Two more layers are included in the data link layer itself. For device communications across a network, the first, media access control (MAC), offers flow control and multiplexing. The second, logical link control (LLC), defines line protocols and offers flow and error control over the physical media.

Functions:

• Framing: The physical bit stream is converted by the data connection layer into packets called frames. The header and trailer are added to the frame by the Data link layer. The hardware destination and source addresses are contained in the header that is appended to the frame.
• Physical Addressing: A header with a destination address is added to the frame by the data link layer. The destination address listed in the header is where the frame is sent.
• Flow Control: The Data-link layer’s primary role is flow control. It is a technique used to maintain a consistent communication flow on both ends, preventing data corruption. It makes sure that the processing speed of the receiving station, which is slower, does not surpass that of the sending station, such as a server.
• Error Control: To control errors, a computed number called a CRC (Cyclic Redundancy Check) is added to the message frame’s trailer in the data link layer before it is delivered to the physical layer. The receiver delivers the acknowledgment for the retransmission of the corrupted frames if any error appears.
• Access Control: The data link layer protocols are used to identify which device is in control of the connection at any one time when two or more devices are connected to the same communication channel

Network Layer

The network layer is in charge of taking frames from the data link layer and sending them, based on the addresses they contain, to their intended destinations. The network layer locates the target using logical addresses, such as IP addresses. Routers are essential at this tier because they route information across networks.

Functions:

• Internetworking: The network layer’s primary duty is internetworking. It offers a logical link between many devices.
• Addressing: The network layer adds source and destination addresses to the frame’s header. On the internet, addressing is used to identify the device.
• Routing: Routing, a key element of the network layer, chooses the optimum way from a variety of options to go from one place to another.
• Packetizing:The packets from the higher layer are converted into packets by a network layer, which is known as packetizing. The action in question is called packetizing. Internet Protocol is used to accomplish it (IP).

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Transport Layer

Data packet delivery and error checking are controlled by the transport layer. It controls the amount, order, and final transit of data between hosts and systems. The Transmission Control Protocol, also known as TCP, is one of the most popular instances of the transport layer.

Functions:

• Flow control: The transport layer is also in charge of flow regulation, which is carried out end-to-end rather than across a single connection.
• Error control: Error control is a function of the transport layer. End-to-end error control is used instead of error control over a single connection. The sender transit layer guarantees error-free message delivery to the target location.
• Service-point addressing: Because computers execute several programs at once, data must be sent from source to destination not just from one computer to another, but also from one process to another. The transport layer adds the header with the address known as a service-point address or port address. Data transmission between computers is the job of the network layer, while message transmission to the right process is the responsibility of the transport layer.
• Segmentation and reassembly: After receiving the message from the top layer, the transport layer divides the message into a number of segments and assigns each segment a sequence number that uniquely identifies it.The transport layer then reassembles the message based on their sequence numbers after the message has reached its destination.
• Control of connections: The transport layer offers both connection-oriented and connectionless services. A connectionless service treats each segment as a separate packet, and they all follow different routes to their destination. Before sending the packets, a connection-oriented service establishes a connection with the target machine’s transport layer. All packets in a connection-oriented service use the same path.

Session Layer

The session layer governs the conversation between several machines. At layer 5, a session or connection between devices is established, controlled, and ended. Authentication and reconnections are also part of the session layer services.

Functions:

• Dialog control: The session layer serves as a dialog controller, facilitating communication between two processes that can be either half-duplex or full-duplex.
• Synchronization: The session layer adds various checkpoints while delivering the data in a series. If a transmission error occurs, the data will be transmitted once again from the checkpoint. Synchronization and recovery is the name of this procedure.

Presentation Layer

The presentation layer prepares or transforms data for the application layer based on the syntax or semantics that the application accepts and it is also known as the syntax layer.This layer can also handle the encryption and decryption tasks required by the application layer.

Functions:

• Translation: The processes in two systems communicate via character strings, integers, and other data types. The presentation layer manages the compatibility between the various encoding methods used by various systems. The data is transformed from a sender-dependent format into a common format, which is then transformed at the receiving end into a receiver-dependent format.
• Encryption: To guarantee privacy, encryption is necessary. Encryption is a technique that transforms the data sent by the sender into a different format before sending the final message across the network.
• Compression: Reducing the amount of bits required to convey the compressed data is the process of data compression. Data compression is crucial for multimedia content including text, music, and video,

Application Layer

Direct communication with the program occurs at this layer between the end user and the application layer.A web browser or Office 365 are end-user programs that get network services from this layer. The application layer determines resource availability and communication synchronization.

Functions:

• File transfer, access, and management (FTAM): A user can access files on a distant computer, recover files from a computer, and manage files on a remote computer using an application layer.
• Mail services: An application layer makes email forwarding and archiving possible.
• Directory services: An application is used to give global information about diverse objects and distributed database sources.

Similarities: TCP/IP Model &OSI Model

• Both specify networking protocols and both are logic models.
• Both offer a framework for developing and using networking standards and tools.
• Both provide levels for the network communication process.
• Both approaches describe a certain functionality and just those standards for that functionality in a single layer.
• With either model, a manufacturer can provide network components and devices that can coexist and function with those produced by other manufacturers.
• By breaking down complicated functions into simpler components, both approaches make the troubleshooting process easier to understand.
• Both approaches referred to the already established standards and protocols rather than establishing them. Before the development of these models, for instance, IEEE had already established the Ethernet standards. Therefore, both models utilized them as IEEE Ethernet standards rather than redefining them.

Differences: OSI model & TCP/IP model

• While the TCP/IP model only has four levels, the OSI Layer model contains seven.
• TCP/IP is still utilized in computer networking while the OSI Layer model is no longer in use.
• The OSI model employs three distinct levels (Application, Presentation, and Session) to specify the functionality of upper tiers, but the TCP/IP model only uses one layer (Application).
• The OSI model employs two different levels (Physical and Data-link), but TCP/IP just uses one layer (Link layer), to specify the capabilities of the lower layers, much like the top layers.
• The OSI model employs the Network layer, whereas the TCP/IP model uses the Internet layer, to establish the routing protocols and standards.
• The OSI model has more documentation than the TCP/IP model.
• The TCP/IP model offers a simplified version of each standard and protocol, whereas the OSI model provides a detailed explanation of each.

Differences:Original TCP/IP Model & Updated TCP/IP Model

• The original TCP/IP model and the upgraded TCP/IP model differ.
• The TCP/IP model that is now in use differs somewhat from the original TCP/IP model. The upgraded TCP/IP model contains five layers, unlike the old model’s four.
• The functionality and parts responsible for data transfer are defined in the original version using a single layer (the link layer). For the same, the revised version employs two layers (Data Link and Physical).
• In the Physical layer, it specifies the functions that are directly connected to data transmission, and in the Data-link layer, it defines the functions that are indirectly related.
• The Internet layer is now referred to as the Network layer in the upgraded version.
• The OSI reference model, the outdated TCP/IP model, and the original TCP/IP model are all contrasted in the following diagram.
• Any model may be easily correlated with another after it has been learnt, regardless of which one you study or understand initially. With the exception of the Application layer, the revised TCP/IP model is mostly comparable to the OSI model. For educational purposes, you might imagine that the TCP/IP model’s Application layer performs the same functions as the OSI model’s top three levels (Application, Presentation, and Session).

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Conclusion

The TCP/IP Model is more trustworthy than the OSI Model.We employ TCP/IP for end-to-end connections to send data across the internet. Therefore, TCP/IP is reliable, adaptable, and tangible. It also makes recommendations on how data should be transferred across the internet.

The TCP/IP Model’s transport layer determines if the data has arrived in order, whether there is an error, whether lost packets have been resend, whether an acknowledgment has been received, and other factors.

In contrast, the OSI model provides a conceptual framework for understanding how applications interact with networks.