OSI Model

The OSI (Open Systems Interconnection) model was developed by the International Organization for Standardization (ISO) as a conceptual framework to standardize the functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal was to support the emergence of diverse computer networking methods and facilitate interoperability among different systems and vendors, which was increasingly important as computer networks grew more complex. 

The OSI model's development and evolution span several decades. In the 1970s, as computer networks began to emerge, there was a growing need for standardization to enable communication between different systems and vendors. Various organizations, including the International Organization for Standardization (ISO), initiated efforts to develop a standardized model for networking. In 1977, the ISO formed the ISO/TC97/SC16 committee to develop standards for data communication. In 1980, the ISO published the OSI Reference Model as ISO 7498, providing a conceptual framework for understanding network communication. The OSI model consisted of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer had specific functions and responsibilities, with clear interfaces defined between adjacent layers. Throughout the mid-1980s, efforts to promote the OSI model gained momentum, with many countries and organizations endorsing it as the preferred networking standard. The OSI model was seen as a comprehensive framework that could accommodate a wide range of networking technologies and protocols.  

The OSI model has significantly contributed to the fulfill the need for equipment manufacturers to have a set of design standards that would enable their products to communicate with each other, addressing the lack of standardization that previously existed. This hierarchical architecture logically partitions the functions required to support system-to-system communication, making it easier to design and implement complex network architectures. The OSI Model operates by breaking down the communication process into smaller, more manageable 7 layers, From the physical transmission of data signals to the presentation of information to end-users, each layer has its own function as follows: 

At the base of the OSI Model lies the Physical Layer which is responsible for the physical and electrical transmission of data over network connections. It defines the hardware equipment, cabling, signaling, and the electrical aspects of the data transfer. At the Physical Layer, signaling methods encompass both analogue and digital modulation techniques. Analog methods like Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM) modify carrier signal properties, such as amplitude, frequency, or phase, to encode data. Digital modulation techniques like Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK) also alter carrier frequency characteristics to represent binary data. Additionally, the Physical Layer defines physical media characteristics for data transmission, specifying cable types, fiber optics, or wireless channels for carrying encoded signals. 

Above the Physical Layer is the Data Link Layer, which provides node-to-node data transfer—a link between two directly connected nodes. It also handles error correction from the physical layer, ensuring reliable data transfer. This layer is divided into two sublayers: Logical Link Control (LLC) and Media Access Control (MAC), where the latter assigns unique addresses to devices on the network. PROFINET IRT, for example, operates on this layer, providing error detection, framing, and flow control mechanisms. 

The Network Layer comes next, tasked with transferring data from one host to another located in different networks. It is responsible for routing packets across the network by determining the optimal path for data delivery. The Network Layer uses logical addressing—such as Internet Protocol (IP) addresses—to route packets to their destination node. This task is supported by protocols such as IP and ICMP overseeing tasks related to addressing, routing, and network management. 

Following the Network Layer is the Transport Layer, which breaks down data into smaller packages for transmission and is responsible for the end-to-end delivery of those packets. This layer ensures that data is sent at an appropriate rate and manages error correction, providing reliable data transfer. Protocols such as TCP and UDP protocols comes into play, offering a choice between reliable, connection-oriented communication and faster, connectionless exchanges at this layer. 

The Session Layer establishes, manages, and terminates connections between applications. It sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It manages sessions by initiating opening and closing of connections.  

The Presentation Layer, prepares or translates data for the application or the network. It ensures that data is in a usable format and is responsible for data encryption and decryption, as well as data compression. Data representation and encoding standards such as ASCII, Unicode and Binary Encoding is used here to facilitate exchange of a variety of data. 

At the top of the OSI Model is the Application Layer, which provides protocols that allow software to send and receive information and present meaningful data to users. It supports application and end-user processes, facilitating communication between software applications and lower layers of the OSI model. Communication protocols like OPC UA, Modbus, and PROFIBUS commonly provide services for data exchange, device configuration, and monitoring at this layer. 

The OSI model has a profound impact on fieldbus, industrial Ethernet, and IIoT protocols, serving as a foundational framework that guides the standardization and interoperability of network communication in industrial environments. 

Fieldbus protocols, such as PROFIBUS and Modbus, rely on the OSI model to segment communication processes into manageable layers. For example, the Application Layer handles user interactions and process data exchange, while the Data Link Layer manages the reliable transmission of data between devices. By adhering to the OSI model, fieldbus protocols ensure that industrial control systems can communicate effectively despite diverse manufacturers and equipment types, fostering greater integration and more streamlined operations. 

Industrial Ethernet protocols, like EtherNet/IP and PROFINET, extend the principles of traditional Ethernet to the industrial sector. They leverage the OSI model to enhance real-time data exchange, reliability, and scalability in automation systems. By using standardized layers from the OSI model, these protocols address critical requirements such as real-time performance (Layer 2 - Data Link Layer) and network safety (Layer 4 - Transport Layer). This ensures robust operations and compatibility across different network infrastructures, allowing for seamless integration between IT and OT (Operational Technology). 

IIoT technologies, such as MQTT and OPC UA, owe much of their structural efficacy to the OSI model. They span multiple OSI layers, ensuring secure and efficient data transmission crucial for advanced industrial applications. For instance, MQTT operates mainly at the Application Layer, facilitating lightweight and efficient communication in resource-constrained environments. Meanwhile, the Transport Layer Security (TLS), integral to these protocols, provides secure data communication by enabling encrypted connections across networks. 

The OSI model significantly enhances industrial communication through the following advantages: 

Layered architecture

Divides the communication process into seven distinct layers, each with specific functions, simplifying network design, implementation, and troubleshooting. This modularity allows for the introduction of new protocols or technologies at specific layers without disrupting the entire network, facilitating scalability and incremental upgrades. 

Interoperability

By adhering to a common framework, devices and software from different vendors can communicate effectively, regardless of their origins. This vendor neutrality is crucial for industrial organizations, allowing them to select the best hardware and software solutions from a wide range of options while ensuring compatibility and seamless integration. 

Flexibility

Each layer of the OSI model serves a specific function and can operate independently of the others. This design provides the flexibility to select the most appropriate protocols or services at each layer based on the specific needs and objectives of the network or system. 

Rapid Fault isolation and troubleshooting

By localizing issues to specific layers, engineers can more easily identify and resolve communication problems, thereby reducing downtime and enhancing network reliability. 

Conceptual understanding

It provides a comprehensive framework for understanding how communication systems operate, which is invaluable for engineers, technicians, and stakeholders involved in the design and implementation of industrial communication systems. This conceptual understanding, combined with the model's flexibility in protocol selection, enables industrial organizations to tailor their communication systems to meet specific requirements and integrate legacy systems with newer technologies. 

As a leading company in the field of industrial communication, Hilscher offers a broad portfolio of technologies and solutions for networking industrial environments. 

This includes a wide range of interface solutions for connecting sensors, actuators and controllers to industrial communication networks. The communication controllers of the netX family form the basis for this. The multi-protocol-capable SoCs can be integrated into automation components as required and their extensive chip peripherals enable powerful, efficient and flexible solutions. A protocol change is achieved by simply reloading Hilscher's own netX firmware. Building on this, the company also offers embedded modules and PC cards in all form factors in order to realize the netX communication interface with less integration effort. 

Hilscher also offers a comprehensive managed industrial IoT range under the netFIELD brand. This ranges from edge gateways as an application-oriented computer platform with integrated container management and the Edge OS Runtime running on it to the central cloud portal, via which the docker containers are deployed to the edge devices, through to turnkey containers for communication applications. 

Gateways and switches, devices for network diagnostics as well as masters and bridges for the wireless connection of IO-Link sensors round off the automation portfolio.