What is the OSI Model?

The seven layers of the OSI model explained with physical layer security

The OSI Model (Open Systems Interconnection Model) is a conceptual framework that defines network communication through seven distinct layers, each with a specific role in transmitting data across a computer network. Understanding the OSI Model is essential for grasping how network protocols like TCP/IP, Ethernet, and Internet Protocol (IP) interact to ensure seamless end-to-end communication.

In this article, we will break down the seven layers of the OSI Model, emphasizing the physical layer and its role in network security. Securing the physical layer is crucial for protecting network interfaces and preventing unauthorized access, ensuring a resilient cybersecurity strategy.

The Seven Layers of OSI Model Explained

The OSI Model (Open Systems Interconnection Model) structures network communication into seven layers, each playing a crucial role in data transmission. Understanding these layers is vital for enhancing network security, particularly at the physical layer, where data is physically transmitted and vulnerabilities can be exploited.

Physical Layer of the OSI Model
Seven layers of OSI Model

Physical Layer: The Foundation of Network Communication

The physical layer of the OSI Model is responsible for the transmission and reception of raw data between network devices. Examples of Physical layer devices range from repeaters to hubs. Data units, such as bits, derive from energy in the form of radio waves or electricity. These units are subsequently conveyed through a physical medium, like fiber optic cables or copper wiring. Essentially, this layer manages the physical link connecting a network with its nodes.

Physical layer security is critical to prevent unauthorized devices from infiltrating the network. Without proper safeguards, rogue devices or network implants can bypass traditional firewalls and remain undetected. Securing this layer helps mitigate cyber threats and ensures seamless interoperability within the OSI Model’s protocol stack.

Data Link Layer: Managing Local Networks

The OSI model Data Link layer technically consists of two sub-layers. One being Media Access Control (MAC) and the other is Logical Link Control (LLC). This layer is responsible for managing access to the physical layer and facilitating local network communication. Both sub-layers serve as a bridge between Layer 1 (Physical Layer) and Layer 3 (Network Layer), ensuring smooth data transmission.

The MAC layer transports data between itself and Layer 1, while LLC communicates with Layer 3 (LAN – Network Devices). This establishes the data link between the two sub-layers that use switches and bridges.

Network Layer: Routing Data Across Networks

The Network Layer of the OSI Model is responsible for routing data between devices across different networks. This layer includes key components such as routers and IP addresses, which facilitate the efficient movement of network packets.

At this layer, IP protocols like IPv4 and IPv6 determine the optimal routing paths to ensure reliable data transmission across local and wide-area networks (LANs and WANs). By managing packet forwarding, addressing, and traffic control, the Network Layer plays a crucial role in enabling seamless end-to-end communication within the OSI Model.

Transport Layer: Ensuring Reliable Communication

The Transport Layer of the OSI Model manages packet sequencing, flow control, and error detection to ensure reliable data transmission. It breaks data into segments, allowing for re-sequencing or retransmission if needed.

The protocols used in Layer 4 are Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). Both of these protocols enable different types of data transmission. TCP is known to be a more reliable method, and UDP prioritizes the speed of data transfer.

Session Layer: Managing Communication Channels

The Session Layer of the OSI Model establishes and manages communication channels between devices. It ensures uninterrupted data transfer by overseeing the functionality of active sessions. Layer 5 not only initiates and terminates communication channels but also sets up checkpoints during data transfer, enabling the session to resume if interrupted.

The Session Layer uses different communication modes: simplex, half-duplex, and full-duplex, each representing a distinct transmission mode for effective data communication.

Presentation Layer: Data Formatting and Encryption

The Presentation Layer of the OSI Model receives data and prepares it for the Application Layer, making it comprehensible. This is achieved through processes like compression, encoding, and encryption, ensuring that data can be properly received and understood on the opposite end.

Common concepts within layer 6 include known formats such as JPEG, GIF and TIFF.  

Application Layer: End-User Interaction

The Application Layer of the OSI Model is the final interface where users interact with computer applications, commonly known as end-user software. This layer supports protocols like File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), and Domain Name System (DNS).

Users engage with end-user software daily, whether browsing the web or using instant messaging, making the Application Layer essential for seamless user interaction with the network.

OSI Model and Physical Layer Network Security

The Physical Layer of the OSI model is the lowest layer and provides hardware security overview. This layer is responsible for the actual physical connection between the devices by identifying the equipment involved in the data transfer. Layer 1 defines the hardware equipment, cabling, wiring, frequencies and pulses. The data exists in the form of bits and nodes transmit it from one to another.

Existing cybersecurity solutions overlook physical layer network visibility. Performing no data verification at layer 1. Without physical layer visibility, the physical data specifications of the network are not captured. Hence, network implants – Rogue Devices which operate on the Physical Layer – are not detected. Similarly, spoofed peripherals – Rogue Device manipulated on the Physical Layer – are identified as legitimate Human Interface Devices (HID).

Without physical layer data verification, enterprises are at risk of Rogue Devices infiltrating their network and conducting harmful hardware attacks. To stop the cyber attacks from Rogue Devices at the very first instant, It is crucial to have adequate physical level security.

Sepio’s Physical Layer Security

Sepio’s platform introduces innovative patented technology aimed to enhance the network security of your organization. The Physical Layer within the OSI Model serves as the network infrastructure level where real data transmission takes place. Leveraging advanced visibility and control capabilities, Sepio effectively mitigates risks and rapidly identifies potential security threats to your network. In contrast to other cybersecurity solutions, Sepio places its focus on security against threats at the Physical Layer, such as network implants, rogue devices, and malicious activities, including spoofed peripherals like malicious USB devices.

Sepio's Discovered Assets
Sepio’s Discovered Assets

What distinguishes Sepio is its non-intrusive methodology. When deployed, the system abstains from probing network traffic or utilizing discovery protocols, ensuring that it does not monitor any proprietary data. Consequently, your organization can enjoy a straightforward and efficient implementation process.

Minimize Risks and Strengthen Security with Sepio

Sepio substantially reduces the risk of employee negligence, bolstering your overall network security posture. By optimizing your security efforts and minimizing breach-related costs, Sepio provides unmatched protection at the Physical Layer of the OSI Model. Gain control over both known and shadow assets to prioritize and mitigate risks with Sepio’s patented technology.

Talk to an expert. It will help you understand how to use Sepio’s patented technology to gain control of your asset risks.

November 22nd, 2022