Communication can be described as a successful data exchange between a source and a destination. In computer networks, this process involves end devices, also known as endpoints or hosts, creating messages transmitted over networks to reach their destinations, as well as networking devices such as switches, routers, or firewalls exchanging user and control data.
Due to the complexity of networks that interconnect various devices produced by different manufacturers and operating on diverse transmission media, successful communication becomes difficult.
Without standardized methods, efficiently exchanging information becomes impossible. In the early years of networking, the absence of a common approach posed a significant challenge. Various vendors used proprietary methods, which limited interoperability. The ISO OSI reference model and the TCP/IP protocol suite were developed as solutions to address this.
As you can see from the image above, these models describe the functions of internetworking and the protocols that govern them. They serve as network architecture guidelines, ensuring compatibility and streamlined communication among devices from various manufacturers. In essence, the ISO OSI and TCP/IP models unite the diverse networking landscape, allowing for seamless data exchange and encouraging innovation.
OSI Reference Model Overview
The ISO OSI reference model was introduced to address the challenges of interoperability and standardization in today's digital world communications. This model serves as a foundation for a protocol suite that enables seamless communication regardless of hardware or software differences.
It comprises seven distinct layers, each in charge of a specific task. Using seven layers ensures a clear separation of functions, making complex network processes easier to understand and troubleshoot. Today, the OSI model serves as a common language for networking professionals, assisting in network design, implementation, and maintenance.
Its advantages include promoting compatibility, simplifying troubleshooting, facilitating vendor communication, and building a deeper understanding of network interactions. Although TCP/IP gained prominence due to its rapid implementation, the OSI reference model played an important role in modern networking.
The OSI reference model divides network tasks into seven layers, so let’s take a closer look at their responsibilities:
- Layer 1 (Physical): This layer is in charge of defining the network's physical characteristics, such as cables, connectors, and voltage levels. It manages the transmission of raw binary data in the form of electrical signals over a physical medium.
- Layer 2 (Data Link): This layer is responsible for framing data for transmission, detecting and correcting errors, and managing access to the physical medium. It identifies devices within the same network segment using MAC addresses and ensures reliable data transfer.
- Layer 3 (Network): Manages the logical addressing, routing, and forwarding of data packets across network parts using IP addresses. It chooses the best data delivery path and manages network connectivity on a larger scale.
- Layer 4 (Transport): Segments and reassembles data, controls flow to avoid congestion, and ensures dependable data transfer between devices. It uses port numbers to differentiate between different services on the same device.
- Layer 5 (Session): Establishes, maintains, and terminates device communication sessions. It manages dialog control, checkpoints, and recovery mechanisms to ensure continuous data exchange over long periods.
- Layer 6 (Presentation): Handles data translation, encryption, and compression to ensure data exchange compatibility and security. It converts data from its native format to a common communication format.
- Layer 7 (Application): The layer closest to the user, providing network services to applications directly. It includes user-facing services such as email, web browsing, and file transfer, allowing applications to seamlessly interact with the network.
TCP/IP Protocol Suite Overview
Similar to the OSI model, the TCP/IP model divides protocols into layers to explain their functions within a protocol suite. TCP/IP, in contrast to the OSI model, actively guides protocol implementation in systems. It consists of four layers of protocols, most notably TCP and IP, that are required for network communication.
While TCP/IP is widely used in all devices, the OSI model primarily serves network engineers in troubleshooting and explanations. Although the TCP/IP protocol suite is also referred to as protocol stack, the industry term for this is "IP stack."
The TCP/IP protocol suite divides network tasks into four layers, so let’s take a closer look at their responsibilities:
- Link Layer: Also known as the media access layer, this layer interfaces with the local network, handling physical features and characteristics. Physical addresses (MAC addresses) are introduced here to identify devices within a network segment. Ethernet is a TCP/IP connection layer protocol that is widely used.
- Internet Layer: This layer handles routing data, obtaining route information, and reporting errors. It employs logical addressing (IPv4 and IPv6 addresses) to identify hosts globally.
- Transport Layer: TCP and UDP protocols are used in this layer and help support a variety of application protocols. It manages data preparation, transport, and application segregation, while the applications within a host are distinguished by unique addressing.
- Application Layer: The application layer focuses on user interaction, delivering protocols and network services. It supports protocols such as HTTP, FTP, DNS, and others, making web surfing, file transfer, email, remote access, and other user tasks easier.