The OSI MODEL

INTRODUCTION

The OS1 model stands for open system interconnect. it was a model that was developed in the 70s to understand and describe network operations. it gave us a place to categorize and organize various network protocols and the orders they should be processed in. The OSI model is divided into seven distinct layers, each representing a specific aspect of network functionality. These layers are:

1. PHYSICAL LAYER(Layer 1): This is the lowest layer of the OSI model and is concerned with the physical connection between devices, including the transmission of raw data bits over a physical medium like cables, radio frequencies, or fiber optics. When you think of physical layers, think of cables.
2. The next layer, the Data Link Layer(Layer2), enables the transfer of information over physical cables. One specific protocol within this layer is Ethernet, which facilitates data transmission from a workstation to a wireless router, then to a cable modem, on to an internet provider, and finally to servers and switches within the server infrastructure. All these protocols, which fall under the Data Link Layer, establish the necessary structures to utilize the connected cables effectively. They define the rules, protocols, and specifications for electrical signaling and for transmitting messages across links. This layer essentially enables data to be passed from one device to another within the same network. However, if data needs to be transmitted to a device outside the local network, an additional protocol is required from a different layer of the OSI model. This is where higher-level protocols come into play to facilitate communication across broader networks.
3. This is where the Internet Protocol (IP) and IP addressing come into play. IP addressing enables users to communicate with any device across the internet. This functionality is provided by the Network Layer, also known as Layer 3, of the OSI model. To summarize the layers discussed so far:
   The physical Layer includes the cables and physical connections.
   The data Link Layer consists of protocols, such as Ethernet, that allow computers and other devices to communicate locally.
   The network Layer (Layer 3) utilizes the Data Link Layer and Physical Layer to facilitate long-distance message transmission across networks. In essence, the Network Layer allows for the use of IP addressing to send data across vast distances, enabling global communication over the internet.
4. The Transmission Control Protocol (TCP) establishes a session between a workstation and a server, enabling data transmission between these devices. This task is handled by the Transport Layer(layer4), which uses TCP to set up the session. TCP employs a handshake process to build a connection and relies on the Network Layer to determine the locations of the devices involved. Through this layered approach, TCP ensures reliable communication and data exchange across the network.
5. The Presentation and Session Layers(later 5 and 6) of the OSI model are largely considered redundant in present day networking practices. Back in the days, these layers played significant roles in the architecture of network communication, but their functions have largely been absorbed by specifically the application layer( layer 7). The Presentation Layer was responsible for data translation, encryption, and compression. While The Session Layer managed the establishment, maintenance, and termination of communication sessions between applications. The responsibility of the session layer is now integrated into the Transport layer. While presentation later is now integrated into the Application layer.
6. Application Layer: The topmost layer is responsible for interacting directly with end-user applications. It provides various network services like email, file transfer, and remote access.