What is OSI ?
Open Systems Interconnection (OSI) model was approved as an international standard for communications architecture by International standard organization (ISO).
The word “open” refers to the capacity to link any two structures that conform to the model of reference and related norms. The OSI model explains how information or data move from application programs (such as spreadsheets) to another application program situated on another network through a network medium (such as wire).
OSI architecture layers:
The OSI reference model divides the issue of shifting data across a network medium between computers into SEVEN smaller and more manageable problems. The layers of seven are:
- Physical layer
- Data link layer
- Network layer
- Transport layer
- Sessions layer
- Presentation layer
- Application layer
The physical layer is the smallest layer in the OSI hierarchy and coordinates the features necessary for transmitting a bit stream over a physical medium. It also describes the processes and functions to be performed for transmission by physical appliances and interfaces.
The transmission media defined by the physical layer includes metal cable, optical fiber cable, or propagation of wireless radio waves. Also included in the physical layer is the carrier system used to propagate information signals between points in the network.
The data link layer converts the physical layer, a raw transmission facility, into a secure link and is accountable for delivering node to node. It makes the bottom layer (network layer) appear error free from the physical layer.
The data link layer packages data in groups called blocks, frames or packets from the physical layer. The data link layer adds a header to the frame to define the physical address of the frame’s sender (source address) and/or receiver (destination address) if frames are to be distributed to different systems on the network.
The network layer offers information that allow information to be transmitted through various networks, subnetworks or both between machines in an setting.
This is accountable for sending emails and information to the right location and for translating logical addresses and names into physical addresses (such as a machine name FLAME).
This layer is also responsible for finding a path through the network to the destination computer
The transport layer checks and guarantees the end-to-end integrity of the information signal between two appliances propagated through the network, offering secure, transparent information transfer between two endpoints.
Transport layer responsibilities include routing of messages, segmentation, recovery of errors and two types of basic services to an upper layer protocol: connection oriented and connectionless.
Session layer, sometimes referred to as the dialog controller, offers a mechanism to control the dialog between the two end devices. It describes how to begin, regulate and end inter-applications discussions (called sessions).
The logical connection entities on the application layer are provided by session layer protocols. These applications include protocols for file transfer and email sending. Session responsibilities include processes for network log-on and log-off and authentication of users.
The presentation layer gives the application procedures independence by addressing any code or syntax transformation needed to present the information to the network in a common communications format.
Translated between various information formats and protocols, the presentation layer. Presentation features include data file formatting, encoding, information message encryption and decryption, dialog processes, algorithms for data compression, synchronization, disruption, and termination.
The application layer is the largest layer in the hierarchy and by offering access to the OSI setting is similar to the network’s general manager.
The application layer provides distributed information services and controls the sequence of activities within and application, as well as the sequence of events between the computer application and another application user.