What is the OSI Model? – A Definitive Guide
The OSI model is a seven-layer model for describing and designing computer networking. It has become the basic conceptual model used by the majority of networking professionals. This article will provide an overview of what the Open Systems Interconnection (OSI) model is, how it was designed, and its impact on technology today.
Basics of OSI Model
The OSI model was created by the International Organization for Standardization (ISO) in 1978 and is commonly used today. It is a seven-layer model that uses abstractions to describe how data, information, and communication move through a system.
Layer 1 – Physical layer: This layer deals with the physical properties of devices such as electrical interfaces, connectors, circuits, media types, speeds, etc.
Layer 2 – Data link layer: The data link layer defines how network devices exchange data over a physical connection.
Layer 3 – Network layer: The network layer provides an interface between the end systems and the network. This is where routing decisions are made and service flows are established.
Layer 4 – Transport layer: The transport layer ensures that packets arrive at their destination without any errors or delays. It handles most of the addressing and signaling related to delivery of packets across multiple hops on a path to their ultimate destination.
Layer 5 – Session layer: The session layer establishes connections between applications using secure channels such as SSL/TLS or IPSec. This ensures private communications are maintained even if there are multiple layers of encryption in place between two systems.
Layer 6 – Presentation layer: This is where user interaction takes place like mouse clicks, keyboard entries, etc., which will then be passed on to the application or operating system itself.
Layer 7 – Application layer: This is where applications interact with each other through APIs and provide services like email and web browsing
The 7 Layers of the OSI Model
The OSI model is a seven-layer model that provides an overview of the process an application goes through to send and receive data. This process starts at the physical layer and ends at the application layer. The 7 layers are:
1) Physical Layer
2) Data Link Layer
3) Network Layer
4) Transport Layer
5) Session Layer
6) Presentation Layer
7) Application Layer.
Physical Layer
The physical layer of the OSI model is the first layer in which we encounter when attempting to send or receive data. The physical layer is responsible for sending, receiving, and locating the medium on which data is sent. Other responsibilities of this layer include the transmission of data by encoding it into a specific type of signal that can move through a given medium (e.g., digital-to-analog conversion) and determining how to transmit multiple signals simultaneously over a shared medium (e.g., frequency division multiplexing).
Data Link Layer
The Data Link Layer (layer 2) is responsible for physical and data-link layer communication between stations. This layer provides the following services:
– Transmission Media Access Control (MAC)
– Physical Layer (PHY)
– Link Frame Formats
– Multiplexing & Demultiplexing.
Network Layer
The network layer, also known as the data link layer, is the first and lowest layer of the OSI model. It is mostly concerned with providing reliable communication between devices on a network. This layer is responsible for creating an end-to-end connection through which packets are sent. The most important function of this layer is to guarantee reliable delivery of data from one device to another.
Transport Layer
The transport layer is the lowest-level layer in the OSI model. The purpose of this layer is to move information from one point to another. It does this by using various protocols for transferring data, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Although it is the lowest level of the OSI model, the transport layer must be implemented on every operating system. The transport layer uses a connection-oriented protocol that ensures that all data packets are accurately delivered to their destination without being dropped or corrupted, even if there are network errors in between.
Session Layer
The session layer is the first layer in the OSI model. It is the lowest level of the seven-layer model and it is responsible for maintaining and managing communications between two communicating devices, regardless of how many layers they are separated by. The session layer provides communication services like flow control, error checking, reliable data transfer and message sequencing among other things that enable the exchange of messages between two devices.
Presentation Layer
The presentation layer is the interface between the physical and data-oriented aspects of the network. It deals with how information is transmitted between two systems, such as a client and server, and how it is converted into different formats that are understandable by either party. An example of this would be translating characters from one type of language to another for ease of reading.
Application Layer
The Application layer is the highest layer of the OSI model. It is where all the “application-specific” data takes place. This includes network applications, such as email and file sharing, as well as any other communication that takes place on a computer network.
OSI vs TCP/IP Model
The Open Systems Interconnection (OSI) model was created in the early 1970s to help reduce the complexity of data transferred between computers and networks. It became important during this time because it was designed in a way that it could easily be used to transfer data across different types of networks. The OSI model is different from TCP/IP, which is the current standard for computer networking. The OSI model consists of seven layers, while TCP/IP only has four layers. The difference between these two models is that TCP/IP does not have a layer for communicating with other devices, like humans, for example.
The OSI model also differs from TCP/IP in the way that it has a greater number of entities involved in each layer and includes more responsibilities than just those assigned to one layer. For example, Layer 3d includes both hardware and software devices as well as other layers like Layer 5 that includes both application software and network devices. This leads to an increase in complexity on any given system as there are now many entities involved at each level with many responsibilities assigned to each one.