OSI(Open Source Interconnection) Model

OSI Model

The Open Systems Interconnection (OSI) model describes 7 layers that computer systems use to communicate over a network. The OSI model became so popular when it was first released as a teaching tool in the 1980s that it has become a common standard in networking.

OSI (Open Systems Interconnection) is a reference model for how applications communicate over a network and a reference model is a conceptual framework for understanding relationships. This model focuses on providing a visual design of how each communications layer is built on top of the other, starting with the physical cabling, all the way to the application that’s trying to communicate with other devices on a network.

OSI Model

Application Layer (Layer 7)

1. It provides services directly to user applications such as email or file transfers.

2. It provides protocols that allow the software to send and receive information and present meaningful data to users.

3. This layer provides the services such as establishing privacy mechanisms, authenticating the intended communication partners, and determining if adequate resources are available.

4. A few examples of application layer protocols are the HyperText Transfer Protocol(HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).

Presentation Layer (Layer 6)

1. It performs data transformation to provide a common interface for user applications, including services such as reformatting, data compression, and encryption.
2. The presentation layer allows us to define the form in which the data is to be exchanged between the two communicating entities. It also helps you to handle data compression and data encryption.
3. This layer transforms data into the form which is accepted by the application. It also formats and encrypts data that should be sent across all the networks. This layer is also known as a syntax layer.
4. A few examples of presentation layer protocols are the MPEG, Secure Socket Layer(SSL), and Transport Layer Security(TLS).

Session Layer (Layer 5)

1. The session layer creates communication channels, called sessions, between devices.
2. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends.
3. This layer handles all the important log-on or password validation.
4. A few examples of session layer protocols are the Session Announcement Protocol(SAP), and Network Basic Input/Output System(NetBIOS).

Transport Layer (Layer 4)

1. The transport layer builds on the network layer to provide data transport from a process on a source machine to a process on a destination machine.
2. It provides error recovery, flow control, segmentation, or desegmentation between the 2 endpoints of network connections.
3. A few examples of transport layer protocols are the Transmission Control Protocol(TCP) and User Datagram Protocol(UDP).

Network Layer (Layer 3)

1. The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end. The other is routing packets by discovering the best path across a physical network.
2. A few examples of network-layer protocols are the Internet Protocol version 4/6(IPv4/v6), Internet Message Control Protocol (ICMP), Address Resolution Protocol(ARP), Internet Group Management Protocol(IGMP), and Routing Information Protocol(RIP).

Data Link Layer (Layer 2)

1. The data link layer establishes and terminates a connection between two physically-connected nodes on a network. It breaks up packets into frames and sends them from source to destination.
2. This layer is composed of two parts — Logical Link Control (LLC), which identifies network protocols, performs error checking, and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.
3. A few examples of data link layer protocols are the Point-to-Point Protocol (PPP).

Physical Layer (Layer 1)

1. This layer represents the electrical and physical representation of the system. This can include everything from the cable type, radio frequency link (as in a Wi-Fi network), as well as the layout of pins, voltages, and other physical requirements.
2. This layer is responsible for controlling the transmission of the raw bitstream, which is simply a series of 0s and 1s while taking care of bit rate control.

For the networking layer concept refer to the below link

Networking Layers