What is the OSI Model?
The OSI model is a conceptual model that represents the network protocol stack. Its seven layers are more focused on the various functions that are performed to make network communications work than the actual technology.
Each layer in the OSI model fulfills an important role, and information is exchanged between the layers in the form of protocol data units (PDUs), which differ based on the layer. The seven layers of the OSI model can be referred to by name or number and, from the top down, include:
#7. Application: Connects directly to end-user applications, providing various services (browsing, email, etc.).
#6. Presentation: Translates data between the formats used by an application when transmitting data over the network. It also manages encryption and data compression.
#5. Session: Responsible for session management, synchronization, and organizing traffic.
#4. Transport: Responsible for ensuring that data is completely and reliably transferred between networks.
#3. Network: Routes, forwards, and addresses packets between networks.
#2. Data Link: Manages the transfer of data between devices on the network and corrects errors from the physical layer.
#1. Physical: Includes the physical components connecting devices (cables, routers, etc.).
The OSI model has several advantages, including:
- Standardization: The OSI model is a widely used reference model for network protocol stacks. This provides a shared basis for conversation where referencing a particular layer provides useful information.
- Independent Layers: The OSI model defines more layers than the TCP/IP model. This ensures that each layer performs a single function, while some TCP/IP layers combine multiple functions.
- Easier Troubleshooting: The independent layers of the OSI models simplify the process of troubleshooting networking issues. Each layer can be considered independently rather than considering the various purposes of a single layer.
- Connection-Oriented and Connectionless Services: The Transmission Control Protocol (TCP) is a connection-oriented network protocol, while the User Datagram Protocol (UDP) is a connectionless protocol. The OSI model supports both of these paradigms.
What is the TCP/IP Model?
The TCP/IP model is a network model that is based on the structure of the network protocol stack. Each of the four layers in the TCP/IP model is visible within a TCP/IP network packet.
These four layers include:
- Application: The Application layer combines the OSI Application, Presentation, and Session layers and is responsible for high-level application protocols, representation, and session management.
- Transport: The Transport layer maps to the OSI Transport layer and is responsible for end-to-end connectivity, data integrity, and flow control.
- Internet: Like the Network layer in the OSI model, the TCP/IP Internet layer manages routing and packet forwarding.
- Data Link: The Data Link layer in the TCP/IP model maps to the Data Link and Physical layers in the OSI model and is responsible for the physical and logical connections between devices.
The TCP/IP model also has advantages over similar models, including:
- Connection Establishment: The TCP/IP model outlines the protocols used for establishing a connection between two systems. IP provides routing, while TCP manages the connection and provides error handling.
- Real-World Model: TCP/IP is a networking model built around the protocols used to establish connections between computers. This means that it has real-world applicability rather than being just a reference model.
Key Differences between TCP/IP and OSI Model
The OSI and TCP/IP models are both designed to provide a structure for thinking about and discussing network traffic. However, the two models have a few significant differences, including:
- Layers: The OSI model has seven different layers built around the various functions that network traffic must perform. The TCP/IP has a total of four layers that are tied directly to specific protocols that exist in network traffic.
- Real-World Applicability: The OSI model is designed as a conceptual, reference model, meaning that it doesn’t map directly to real-world network protocols. In contrast, the TCP/IP model is based on standard protocols used to create network connections.
- Protocol Dependency: The TCP/IP model is based on specific protocols designed to achieve a particular goal. The OSI model is protocol-agnostic, allowing it to be used with any protocol stack.
- Traffic Types: The OSI model is a general model that supports both connection-oriented and connectionless network traffic. The TCP/IP model is designed specifically for connection-oriented TCP traffic.
TCP/IP vs. OSI Model: How To Choose
The TCP/IP and OSI models both serve the purpose of providing a conceptual framework for modeling and thinking about network protocols. However, the two models have significant differences. The right choice depends on an organization’s intended use case. The OSI model is more widely used and is helpful for planning due to its distinct, independent layers. In contrast, the TCP/IP model provides a direct mapping to certain network protocols designed to achieve a particular purpose.
Network Security with Check Point
The OSI and TCP/IP models provide a model for network protocols as well as a way to describe and classify different network security solutions. Cyberattacks are performed at different layers of these models, and understanding the models can help protect against these attacks.
Check Point’s Quantum next-generation firewall (NGFW) provides protection across all layers of the OSI and TCP/IP models. For more information about its capabilities, sign up for a free demo.
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