The OSI (Open Systems Interconnection) model is developed by the International Standard Organization. It is a layered framework for the design of network systems that allows communication between all types of computer systems. Its primary purpose is to provide a set of structural guidelines for exchanging information between computers, workstations, and networks.
|Layers No.||Layers Name||Function|
|Layer 1||Physical Layer||Transmission method used to propagate bits through a network|
|Layer 2||Data Link Layer||Frame formatting for transmitting data across a physical communication line.|
|Layer 3||Network Layer||Network addressing and packet transmission on the network.|
|Layer 4||Transport Layer||Data tracking as it moves through a network.|
|Layer 5||Session Layer||Job management tracking|
|Layer 6||Presentation Layer||Encoding the language used in transmission.|
|Layer 7||Application Layer||User networking applications and interfacing to the network.|
The Physical Layer is the lowermost layer in the OSI model and its major responsibility includes the actual propagation of the unstructured data bits (0’s and 1’s) across the network, from the physical layer of the sending device to the physical layer of the receiving device.
The Physical layer contains information in the form of bits. It transmits individual bits from one node to the next node. The transmission media defined by the physical layer include metallic cable, optical fiber, and the wireless radio-wave.
Physical Layer Includes −
It is the second layer of the OSI model. The data link layer is responsible for providing error-free communication across the physical link connecting the primary and secondary nodes within a network. It provides hop-to-hop delivery. It packages the data from the physical layer into a group called blocks.
The data link layer provides the final framing of the information signal, and it provides synchronization facilities for the orderly flow of data between the nodes.
The network layer provides details that enable data to be routed between devices in an environment using multiple networks, sub-networks, or both.
The networking components that operate at the network layer include routers and their software. It determines which network configuration is most appropriate for the function provided by the network and addresses and routes data within a network by establishing, maintaining, and terminating connectors between them.
It provides the upper layers of the hierarchy with independence from the data transmission and switching technologies used to interconnect systems.
It also provides the source and destination network addresses, subnet information, and source and destination node addresses. In this, the network is subdivided into subnet-work that is separated by routers.
We can say that the transport layer controls and ensures the end-to-end integrity of the data message propagated through the network between two devices, providing the reliable, transparent transfer of data between the endpoints.
The session layer creates communication channels between devices. It is responsible for opening sessions, ensuring they remain open and functional while the data is being transferred, and close the session when the communication ends.
The session layer can also set checkpoints during a data transfer. If a session is interrupted, then the devices can resume data transfer from the last checkpoint.
The session layer is responsible for network availability for data storage and processes capacity. It provides the logical connection entities at the application layer.
The presentation layer prepares the data for its upper layer or the application layer. It defines how two devices should encode, encrypt, and compress the data.
The application layer is the topmost layer in the OSI model and acts as the general manager of the network by proving access to the OSI environment. This layer provides distributed information services and controls the sequence of activities within an application and also the sequence of events between the computer application and the user of the application. It communicates directly with the user’s application program.
The application layer uses HTTP, FTP, POP, SMTP, and DNS protocols that allow the software to send and receive information and present meaningful data to users.