The Open Systems Interconnection (OSI) model is a conceptual framework used to understand and implement interactions in telecommunications and computing systems. The data model provides a universal language for computer networking, enabling diverse technologies to communicate using standard protocols or rules of communication. This allows data to be sent over various hardware and software technologies that must work together across geographic and political boundaries.[1]
Despite its theoretical nature, the OSI model remains a fundamental tool in understanding network architecture, guiding the development of networking protocols, and helping classify networking products and technologies.
The OSI model, referred to as ISO/IEC 7498-1, was developed and is maintained by the International Organization for Standardization (ISO) in collaboration with the International Telecommunication Union (ITU). It was first introduced in the late 1970s as part of the ISO’s initiative to provide a clear and comprehensive framework for designing and understanding network systems that would facilitate multivendor equipment interoperability.
This week, we will explore the seven layers of the OSI model, detailing core functions and illustrating each layer with practical examples of their application and usage.
The OSI model divides the network communication system into seven layers, each responsible for a specific aspect of the network’s communication (Figure 1). Additionally, each layer serves the layer above it and is served by the layer below it.
Figure 1: Each layer of the OSI model has a specific responsibility for network communication, with every layer connected to the function of its surrounding layers. (Source: Author)
Starting at the base, the physical layer is responsible for transmitting raw data bits over a medium. Above it, the data link layer organizes these bits into frames and manages their delivery to the correct destination, with Ethernet being a common technology in this layer. The network layer comes next and is tasked with routing data frames across different networks, characterized by the Internet Protocol (IP).
The fourth layer, the transport layer, is crucial for end-to-end communication, where protocols like Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) reside. TCP ensures reliable communication by breaking data into segments and providing error checking, while UDP offers a simpler, faster alternative without the same level of error checking. The subsequent layers—session, presentation, and application—deal with managing communication sessions, data representation, and end-user protocols, respectively. However, in practical applications, these higher layers are often considered together, especially in application protocols like HTTP.
Physical Layer
This layer deals with transmitting and receiving the unstructured raw bit stream (data) over a physical medium. It defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. This includes the layout of connector pins, voltages, cable specifications, hubs, repeaters, network adapters, and more. For instance, when you plug an Ethernet cable into a computer, you are working with the physical layer.
Data Link Layer
This layer provides node-to-node data transfer—a link between two directly connected nodes. It also handles error correction from the physical layer. You'll find Ethernet, Point-to-Point Protocol (PPP), and switches in this layer. The data link layer organizes the raw bits from the physical layer into frames. For instance, the Media Access Control (MAC) sublayer controls how devices on the network gain access to the data and grants permission to transmit it, while the Logical Link Control (LLC) handles frame synchronization, flow control, and error checking in addition to acting as an interface between the MAC sublayer and the network layer.
Network Layer
This layer manages device addressing, tracks the location of devices on the network, and determines the best way to move data. This includes routing through different routers in the network. The IP, which is the basis for the internet, operates here. Routers function at this layer, directing data packets based on their IP addresses.
Transport Layer
This layer is responsible for variable-length data transfer sequences from a source to a destination host while maintaining the quality-of-service functions. Protocols like TCP and UDP operate at this layer. TCP manages the individual conversations between web servers and clients, ensuring that packets are delivered in order and without errors, while UDP provides a faster but less reliable transmission without extensive error checking.
Session Layer
This layer manages sessions between applications. It establishes, controls, and terminates the connections between the local and remote applications. For example, functions like setting up, managing, and then dismantling the sessions between presentation layer entities occur in this layer. This includes service requests and responses and session checkpointing and recovery.
Presentation Layer
This layer ensures data is in a usable format and is where data encryption occurs. This layer translates data between a networking service and an application; for example, it converts an EBCDIC-coded text file to an ASCII-coded file. This layer is responsible for protocol conversion, character conversion, data compression, and encryption/decryption. Formats like JPEG, GIF, and TIFF (for images), as well as MIDI, MPEG, QuickTime, and RealAudio (for multimedia) are part of this layer.
Application Layer
This top layer provides services to the software through which the user sends and receives information. It is the layer through which users interact with the network. Email (SMTP, POP3), file transfer (FTP), web browsing (HTTP), and database management are services that operate at this layer.
The OSI model is intended to be a guideline for understanding and designing a network architecture, but not all networks adhere strictly to this model. For example, the IP suite used for the internet does not fit neatly into the OSI model. Instead, it uses a simpler, four-layer model that combines some of the OSI layers.
This week’s New Tech Tuesday features networking devices from Digi International and Lantronix.
The Digi Connect® EZ series represents a state-of-the-art solution for modern operational infrastructure, particularly in terms of network connectivity and functionality. This series is designed to cater to the diverse requirements of today’s applications by offering a range of models with various serial port options. One notable model in this series is the Digi Connect EZ32-C100-US, which stands out with its extensive capabilities.
The EZ32-C100-US model is a robust serial server equipped with 32 serial ports, offering support for RS-232/422/485 communications. This makes it extremely versatile for a wide range of industrial and commercial applications. The device also features dual power supply options, with specifications including a range of 100 to 240VAC and a maximum of 2.4A, ensuring reliable and continuous operation. Additionally, the Digi Connect EZ series is known for its quick setup and “click-to-connect” functionality that allows devices to boot in seconds and configure in minutes, further emphasizing its user-friendly and efficient design. With dual 10/100/1000 Ethernet support, the EZ32-C100-US is not only flexible but also offers enhanced network connectivity, making it a suitable choice for environments requiring extensive serial communication capabilities.
The Lantronix X300 series offers a compact cellular Internet of Things (IoT) gateway solution designed to serve the evolving needs of the IoT landscape. These gateways are specifically engineered for mission-critical applications, presenting robust and reliable connectivity solutions for globally distributed assets. The X300 series includes not just the hardware but also integrates cloud-based device management, which simplifies the monitoring and management of IoT devices.
This series stands out for its compact size, making it an ideal choice for applications where space is at a premium. Despite its small footprint, the X300 series does not compromise on functionality or performance. It is tailored to support extensive connectivity options, ensuring seamless and secure communication between IoT devices and the cloud. The focus on reliable, scalable, and secure connectivity positions the Lantronix X300 series as a strategic solution for businesses looking to leverage the full potential of IoT in their operations.
The Open Systems Interconnection model serves as a foundational conceptual framework for understanding and implementing interactions in telecommunications and computing systems. The model plays a critical role in guiding the development of networking protocols and classifying networking products and technologies, thus facilitating multivendor equipment interoperability.
The networking devices from Digi and Lantronix exemplify cutting-edge solutions that align seamlessly with the OSI model. The Digi Connect EZ32-C100-US, with its versatile range of serial ports and robust server capabilities, demonstrates excellence in the data link and physical layers of the OSI model. Its quick setup and dual Ethernet support make it a powerful tool for modern network infrastructures. Similarly, the Lantronix X300 series, with its compact yet powerful IoT gateway solutions, addresses critical needs in the higher OSI layers like the session, presentation, and application layers, ensuring effective data management and secure communication for IoT applications. Together, these products underscore the relevance of the OSI model in designing and understanding advanced network systems that enhance interoperability and efficiency in today’s diverse technological landscape.
Sources:
[1] “What Is the OSI Model? - OSI Layers Explained - AWS,” Amazon Web Services, Inc., accessed November 28, 2023, https://aws.amazon.com/what-is/osi-model/.
Rudy Ramos brings 35+ years of expertise in advanced electromechanical systems, robotics, pneumatics, vacuum systems, high voltage, semiconductor manufacturing, military hardware, and project management. Rudy has authored technical articles appearing in engineering websites and holds a BS in Technical Management and an MBA with a concentration in Project Management. Prior to Mouser, Rudy worked for National Semiconductor and Texas Instruments..