Understanding how data gets from point A to point B is really a key in computer networking. Whatever may be the process-e-mail sending, video streaming, or viewing web pages-in short, any kind of networking, it will depend on various sequential interactions of several devices at some network.
This complicated process was somehow simplified through conceptualization called OSI model into seven layers which makes the whole networking process manageable.
In this article, we shall discuss the OSI model in greater detail. For each layer, its role in the process is elaborated on.
What is the OSI Model?
The OSI (Open Systems Interconnection) Model is a conceptual framework that describes how different components of a networking system interact. Developed by the International Organization for Standardization (ISO) in 1984, its purpose is to standardize network design and equipment manufacturing. By establishing a common set of communication rules and protocols, it allows different technologies to communicate with each other seamlessly.
Before the introduction of the OSI model, network architecture lacked standardized protocols for efficient data communication and infrastructure design. As a result, setting up and configuring new equipment within existing networks was a difficult and often inconsistent process.
Importance of OSI model
What is the importance of the OSI model? Or why does it matter?
This model holds utmost importance because it provides a standardized way of understanding and organizing how data moves between devices, regardless of where it resides. When network issues arise, whether due to equipment failure or application malfunction, the OSI model helps troubleshoot.
However, the modern Internet does not strictly follow the OSI Model, but it still proves helpful for troubleshooting network problems.
Benefits of The OSI Model
The OSI (Open Systems Interconnection) model offers several benefits, as explained below.
Secures Cloud Infrastructure
This model can be adapted to enhance the security of cloud infrastructure. It can be tailored according to the unique characteristics and requirements of the cloud infrastructure to create a more targeted and effective security program.
Whether it’s a public, private, or hybrid cloud environment, a customized OSI model can help strengthen the overall security posture and mitigate risks associated with cloud-based operations.
Troubleshooting
The OSI model has a layered architecture that facilitates troubleshooting, allowing network administrators to identify and diagnose problems at specific layers. For instance, an issue with data transmission may be related to the physical layer or the data link layer.
By isolating the problem to a specific layer, administrators can more efficiently focus their efforts on diagnosing and resolving issues.
Standardization
Formalizing communication protocols across internal and external networks, such as the cloud or the internet, is vital for efficient data transmission. The OSI model establishes a standardized framework that facilitates faster communication between devices and networks, regardless of where the data originates, its destination, or its path.
What are the 7 Layers of the OSI Model?
The OSI model comprises seven layers, each performing a defined function to maintain smooth data flow in the network. Below it is explained, from top to bottom:
Application layer (Layer 7)
- It is the topmost layer of the OSI model that directly interacts with end-users and applications.
- The application layer supports communication protocols that enable applications to interact with the network.
- Examples of this layer include FTP (File Transfer Protocol), DNS (Domain Name System), SMTP (Simple Mail Transfer Protocol), and HTTP (Hypertext Transfer Protocol).
Presentation layer (Layer 6)
- This layer prepares data into a format that the application layer can understand. Simply, it is responsible for translation, encryption, and data compression.
- If the devices connect over an encrypted connection, the presentation layer adds encryption on the sender’s side and decodes it on the receiver’s end.
- It compresses the data received from the application layer before delivering it to layer 5, i.e., the session layer.
Session layer (Layer 5)
- The session layer is majorly responsible for establishing communication sessions between communicating entities. The period when the communication is opened and closed is known as the session.
- It manages the beginning and ending of a one-to-one application connection and synchronization.
- Also, this layer synchronizes data to maintain smooth data flow. This means when large chunks of data are sent, it breaks down into smaller chunks by adding checkpoints.
- For instance, if a 1000-page document needs to be sent, the session layer can add checkpoints at 50 or 100 pages. This way, the document will be transferred without interruption in case of network or system failure.
Transport Layer (Layer 4)
- The transport layer maintains end-to-end communication between two devices. It gets data from the session layer and breaks it down into small segments before sending it to layer 3, i.e., the network layer.
- It is also responsible for two main functionalities: flow control and error control.
- Flow control monitors the speed at which data is transferred between devices and ensures it is transmitted at a rate that can be effectively handled, preventing overwhelm and congestion. While error control performs error checking to detect any corruption or loss of data during transmission.
- Examples of transport layer protocols include transmission control protocol (TCP) and user datagram protocol (UDP).
Network Layer (Layer 3)
- The network layer facilitates data transfer between two networks and is necessary when two devices communicate with the same network.
- It receives data segments from the transport layer and breaks them into smaller units called packets.
- Further, this layer handles routing functionality, finding the best route or path for efficient data transfer.
- The Internet Protocol v4 (IPv4) and IPv6 are the primary network layer protocols.
Data Link layer (Layer 2)
- The data link layer is somewhat similar to the network layer; the only difference is that, unlike layer 3, it facilitates data transfer between two devices on the same network.
- This layer takes packets from layer 3 and breaks them into smaller pieces called frames before sending them to the destination.
- It is split into two sub-layers: media access control (MAC) and logical link control (LLC). The MAC layer deals with how data frames are sent over physical connections like wires or cables. If there are any issues with sending data, the LLC helps manage resending packets.
Physical Layer (Layer 1)
- The physical layer manages the physical network components involved in the data transfer, including cables, switches, or routers.
- This layer transmits data as ones (1s) and zeros (0s). It takes bits from the sender, turns them into a signal, sends them over the network, and decodes them at the receiving end. Without this layer, data couldn’t move between devices through physical media.
How Does Communication Happen In The OSI Model?
In the OSI model, human-readable information is transferred over a network from layer 7 down to layer 1 from the sender and then layer 1 to layer 7 on the recipient side.
Let’s take the email application as an example to understand more about how communication happens in this model.
Mr. R wants to email Ms. J. As soon as he clicks the “send” button, his message will be sent to the application layer. From there, it will pick a defined protocol, STMP (for outgoing email), and data will be passed to the presentation layer.
Then, the presentation layer compresses the data and sends the message to the session layer. The communication session between the sender’s device and the outgoing server will be initialized from this step.
Now, the data will enter the sender’s transportation layer, which will be segmented and broken into packets. These packets are then sent to the data link layer, where these are further broken into frames.
Further, the frames will be delivered to the physical layer, where data is converted into the bitstream from 1s and 0s.
Once the Receiver (J) receives the message, the data will flow through the same sequences of layers but in reversible order. Firstly, the physical layer converts the bitstream from 1s and 0s into frames, from where the data link layer reconstructs the frames into packets for the network layer.
Now, the network layer will make segments from packets so that the transport layer can reassemble the segments into one piece of data.
Finally, the data flows into the receiver’s session layer, which is then passed to the presentation layer, and the communication session ends. The presentation layer removes the compression, and raw data is passed to the application layer, allowing Ms. J to read the mail.
So, next time you browse the web or send an email, remember that the OSI model is working behind the scenes to make it all happen!
OSI vs. TCP/IP Model: What’s the Difference?
One of the primary differences between the TCP/IP and OSI models is how they organize and categorize networking functions.
In the OSI model, the networking functions are divided into seven layers, each performing specific tasks. On the contrary, the TCP/IP model groups similar functions into fewer layers. For instance, the network access layer of TCP/IP is the combination of OSI’s physical and data link layers.
Further, the troubleshooting process in the OSI model is easy as one can focus specifically on a particular layer. In contrast, in the TCP/IP model, consolidated layers make it very difficult to find the exact source of a problem.
Now the Question Arises: TCP/IP vs. OSI Model: Which one should you choose?
No doubt, the OSI Model is the preferred choice due to the below apparent reasons:
- Segment the functions of the network into more layers
- Make troubleshooting easier
- Improve network performance But this doesn’t mean the TCP/IP model is not used! It is particularly leveraged in current networking structures.
Real-World Applications of the OSI Model
Below are some of the practical applications of the OSI model.
Web Browsing and HTTP
Vast amounts of information and resources can be accessed online within seconds. The credit for these seamless experiences goes to the Hypertext Transfer Protocol (HTTP), which operates within the Application Layer of the OSI model. It facilitates the exchange of hypertext documents, such as web pages, between web servers and clients.
In a nutshell, the credit for seamless browsing over the Internet goes to the OSI model.
Ethernet and Local Area Networks
Ethernet is the backbone of all Local Area Network (LAN) connections and is the fundamental element of the OSI model. It provides the infrastructure to link computers, servers, and other network devices.
The OSI model is vital for understanding how Ethernet works within LAN connections.
Ethernet cables transmit signals at the OSI’s physical layer to establish the physical connection between devices. On the other hand, the Data Link Layer ensures reliable digital transmission by organizing data into frames.
Email Communication and SMTP
Everyone uses Gmail for everyday tasks, but only a few know that there is a Simple Mail Transfer Protocol (SMTP) behind every email sent or received linked to the OSI model.
SMTP creates a standard protocol between mail servers, allowing entities to send and receive messages or emails seamlessly. No matter what technologies are involved in networks or devices, SMTP facilitates smooth and reliable routing of emails.
IP Addressing
The Internet is an integral part of our lives, and the OSI model plays a very important role. Here’s how!
IP Addressing is a fundamental aspect of Internet communication that allows devices to identify and communicate with each other across the global network. It functions within the OSI model’s network layer and transfers data over the Internet.
The process starts by assigning unique identities to devices to transmit the data between senders and recipients.
Additionally, the network layer ensures that the data packets reach the destinations by enabling logical addressing, routing, and packet forwarding.
Alternatives to the OSI Model
While the OSI (Open Systems Interconnection) model is widely used and recognized, there are alternatives to it as well. Let’s have a look!
TCP/IP Model: Definition
The TCP/IP model is an alternative to the OSI Model. Developed by the United States Department of Defense, this model is the default data communication method on the Internet.
How does the TCP/IP Model Work?
The process of sending an email using a Simple Mail Transfer Protocol or SMTP from an email server starts when the TCP layer divides the message into packets, numbers them, and then forwards them to the IP layer.
The IP layer then transports each packet to the destination email server. Upon arrival, the packets are handed to the TCP layer to be reassembled into the original email message format.
The SMTP protocol, which operates at the application layer, handles the message delivery to the recipient’s email inbox, allowing the user to access and read the email.
4 Layers of TCP/IP Model:
1. Datalink / Network Access Layer:
Also known as the network access layer, the datalink layer monitors how data is transmitted. It manages the physical transmission of data, including signaling and handling the hardware involved in sending and receiving data.
This layer combines functions from the OSI model’s physical and data link layers to ensure standardized communication across networks.
2. Internet Layer:
This layer facilitates the responsibility for routing packets across networks and monitors till they reach their intended destinations. Also, it manages the transfer of data sequences between devices and applications on different networks.
3. Transport Layer:
It provides a solid data connection between the original device and its intended destination. The transport layer divides data into packets, assigns them sequence numbers, and ensures error-free transmission.
4. Application Layer:
The application layer is the level with which the user interacts, such as email systems and messaging platforms. This layer combines the OSI model’s session, presentation, and application layers.
The Bottom Line
Now that the blog is about to be completed, it’s pretty clear that the OSI model plays a vital role in standardizing a networking system and solving troubleshooting concerns.
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