OSI Model In Networking : Understanding Network 7 Layers.

29Sep 2023 by Tejas Mule No Comments

How to recall the seven layers of the OSI model and its explanation

The OSI (Open Systems Interconnection) is a network reference model for how applications communicate over a network. Each layer has its own functions and characteristics in network layer. OSI model is a conceptual framework used to understand and standardize how different networking protocols and technologies interact within a computer network.

OSI Model Developed by the International Organization for Standardization (ISO), the OSI Model provides a structured way to break down the complex process of network communication into seven distinct layers. Each layer has its own specific functions and responsibilities, and together, they ensure that data can be transmitted reliably and efficiently across networks.

Here’s a brief overview of each of the seven layers of the OSI Model:

The OSI Model 7 layers are as follows:

Layer 1: Physical

Layer 2: Data Link

Layer 3: Network

Layer 4: Transport

Layer 5: Session

Layer 6: Presentation

Layer 7: Application

The Development of OSI Model started in year 1970. In 1977, the International Organization for Standardization (ISO) initiated efforts to create a universal networking model that could facilitate international communication between computer systems. OSI Model provides a standard for different computer systems to be able to communicate with each other. OSI Model is still very useful for troubleshooting network problems. OSI Model can help to break down the problem and isolate the source of the trouble for solution using layered technology.

Human-readable data must travel down the seven layers of the OSI Model on the sending device and then up the seven layers on the receiving end to be exchanged data over a network from one device to another. Each layer responsible for performing specific tasks according to sending and receiving data.

7 layers of the OSI model with detail explanation:

What is the function of each layer of the OSI model? The seven OSI (Open Systems Interconnection) layers are the following.

Layer 7. Application layers:

When a user chooses to receive messages, transfer files, or do other network-related actions, the application layer allows him or her to engage with the program or network. Layer 7 application protocols are used by web browsers and other internet-connected apps such as Outlook and Skype.

This layer is very closest to end users. It receives information or data from end users directly and show incoming data to users.

Web browsers (Google Chrome, Firefox, Safari, and so on), Telnet, and FTP are examples of Layer 7 communications. This layer interacts with end users or software to interact or connect with the application or network when user perform any task such as read message, share files into network etc.

HTTP (Hypertext Transfer Protocol) as well as SMTP (Simple Mail Transfer Protocol is one of the protocols that enables email communications) are the part of Application layer.

Layer 6 – Presentation

The Presentation Layer, the sixth layer in the OSI Model, plays a vital role in network communication by focusing on data translation and formatting. This layer is responsible for ensuring that data sent from one system can be properly understood by another. It handles tasks such as data compression, character encoding, and encryption/decryption, ensuring that data is not only secure but also in a format that the receiving system can interpret accurately. The Presentation Layer acts as an interpreter, bridging the gap between the lower-level layers responsible for raw data transmission and the upper-level Application Layer where end-user applications interact.

Application layer takes or used data which is prepared by presentation layer. The presentation layer is responsible for translate data with encryption and compression. It will add extra layer of data security for data. Presentation layer is also responsible for compressing data it receives from application layer and transmit that data to fifth layer which is Session Layer. Presentation layer is also called as translation layer as it converts data from complex format into simple one that will understand by application layer. It includes MPEG, HTTP/HTML Protocol determine the page displayed over internet.

Presentation layer is responsible for speed and efficiency of communication by minimizing amount of data will be transmitted to next layer.

Layer 5 – Session

The Session Layer, positioned as the fifth layer in the OSI (Open Systems Interconnection) Model, is a crucial component of network communication responsible for managing and maintaining communication sessions between devices or applications on a network. Its primary purpose is to establish, maintain, synchronize, and terminate these sessions, ensuring that data exchanges occur smoothly and efficiently.

some examples of how the Session Layer is used in networking:

Web Browsing: When you visit a website, your web browser establishes a session with the web server using protocols like HTTP. The Session Layer manages this session, ensuring that data is exchanged correctly for you to view web pages.
Video Conferencing: Video conferencing applications create communication sessions between participants. The Session Layer synchronizes audio and video data, ensuring that participants see and hear each other in real-time.
Online Gaming: Online multiplayer games rely on the Session Layer to manage game sessions. It ensures that game data is synchronized between players and that the game progresses smoothly.
File Transfer: When transferring files over a network, protocols like FTP (File Transfer Protocol) establish sessions. The Session Layer manages these sessions, ensuring that files are transferred accurately.
Email Communication: Email clients and servers establish sessions using protocols like SMTP (Simple Mail Transfer Protocol) for sending emails and POP3/IMAP for receiving emails. The Session Layer manages these email sessions.
Remote Desktop Access: Remote desktop applications create sessions that allow users to access and control remote computers. The Session Layer ensures that keyboard and mouse inputs are synchronized between the local and remote systems.
VoIP (Voice over IP) Calls: Voice and video calls over the internet, such as those made through Skype or Zoom, rely on the Session Layer to manage communication sessions. It synchronizes voice and video data between callers.
Online Banking: When you access your bank account online, the Session Layer manages the session to ensure that your transactions are secure, and that data is exchanged accurately.
Video Streaming: Streaming services like Netflix establish sessions with users. The Session Layer manages the streaming session, ensuring that video and audio data is delivered without interruption.
Database Queries: When applications communicate with databases, sessions are established to execute queries and retrieve data. The Session Layer ensures that data is transmitted accurately between the application and the database.

Layer 4 – Transport:

The Transport Layer, positioned as the fourth layer in the OSI (Open Systems Interconnection) Model. It is responsible for exchange of data between devices and host on network. This is essential bridge that ensures secure, reliable, and efficient data transmission between devices on networks.

Port numbers are utilized to identify specific services or applications on devices. When data arrives at a device, the Transport Layer uses port numbers to determine which application or service should receive the data. For example, web traffic typically uses port 80 (HTTP). For instance, port 25 is associated with SMTP (Simple Mail Transfer Protocol) for email.

Layer 3 – Network:

This layer is responsible for transport data between two networks. It is a layer 3 that manages device addressing, tracks the location of devices on the network.

If the two communicating devices are on the same network, the network layer is unneeded. On the sender’s device, the network layer divides segments from the transport layer into smaller pieces called packets, which are then reassembled on the receiving device. Routers are the layer 3 devices; Routing is the process by which the network layer determines the optimum physical path for data to take to reach its destination. The Data link layer is responsible for routing and forwarding the packets. The protocols used to route the network traffic are called as Network layer protocols. Examples of protocols are IP and Ipv6. This network layer is responsible for packetizing, addressing, and routing with multiple paths including source and destination.

IP (Internet Protocol), the Internet Control Message Protocol (ICMP), the Internet Group Message Protocol (IGMP), and the IPsec suite are examples of network layer protocols.

Note:

In the Data Link layer, a packet is referred to as a frame.

The NIC (Network Interface Card) and device drivers of host machines handle the Data Link layer.

Data Link Layer devices include switches and bridges.

Layer 2: Data Link Layer:

The Data Link Layer, is the second layer of OSI (Open Systems Interconnection) Model, is responsible for managing the physical connection between devices on a local network. Its primary function is to ensure reliable and error-free data transmission over a physical medium, such as Ethernet cables or Wi-Fi. Here’s a detailed explanation of the Data Link Layer:

Physical Addressing (MAC Address): The Data Link Layer assigns a unique physical address to each network device, known as a MAC (Media Access Control) address. This address helps identify devices on the same local network and enables the efficient delivery of data packets.
Frame Creation and Encapsulation: Data is divided into smaller units called frames at the Data Link Layer. Each frame contains both data and control information, including source and destination MAC addresses. This encapsulation ensures that data is transmitted in an organized and structured manner.
Frame Addressing: When a device wants to send data to another device on the same local network, it uses the recipient’s MAC address to address the frame.
Error Detection and Correction: The Data Link Layer includes mechanisms for error detection, such as checksums or cyclic redundancy checks (CRC). These checks help identify any data corruption that may occur during transmission, allowing for error correction or retransmission when needed.
Flow Control: Flow control techniques are implemented to manage the rate of data transmission between devices. This ensures that a fast sender does not overwhelm a slower receiver, preventing data loss and congestion on the network.
Media Access Control: In shared network environments, such as Ethernet, the Data Link Layer employs protocols like CSMA/CD (Carrier Sense Multiple Access with Collision Detection) or CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to determine when devices can transmit data without causing collisions.
Ethernet Switching: Ethernet switches operate at the Data Link Layer and use MAC addresses to make forwarding decisions. They intelligently filter and forward frames only to the devices that need them, reducing network traffic and improving efficiency.
VLAN (Virtual LAN): The Data Link Layer supports VLANs, which allow networks to be logically divided into separate segments, even if they share the same physical infrastructure. VLANs improve network management and security.
Bridging: Bridges, which operate at the Data Link Layer, connect and filter traffic between different network segments. They help control network traffic and prevent data from unnecessarily traversing the entire network.
Wireless Communication: In wireless networks, the Data Link Layer manages access to the wireless medium and handles issues related to signal interference, collisions, and security.

Layer 1: Physical Layer:

This is the lower layer in the OSI (Open Systems Interconnection) Model, serves as the foundation of network communication. Main role is to define how data is physically transmitted over the network. The physical layer contains information in the form of bits (0/1). It is responsible for transmitting individual bits from one host to the next.

The Physical Layer’s Functions

Bit synchronization: The physical layer synchronizes the bits by supplying a clock. This clock controls both the sender and the receiver, allowing for bit-level synchronization.

The Physical layer also defines the transmission rate, or the number of bits transferred each second.

Physical topologies: The physical layer determines how different devices/nodes in a network are grouped, such as a bus, star, or mesh topology.

Transmission mode: The physical layer dictates how data flows between two linked devices. Simplex, half-duplex, and full-duplex transmission modes are available.