OSI (Open Systems Interconnection) is reference model for how applications can communicate over a network. The Open Systems Interconnect (OSI) model has seven layers. Networking protocols need to be established for low level computer communication up to how application programs communicate. Each step in this protocol is called a layer.
The main benefits of the OSI model include the following:
• Helps users understand the big picture of networking
• Helps users understand how hardware and software elements function together
• Makes troubleshooting easier by separating networks into manageable pieces
• Defines terms that networking professionals can use to compare basic functional relationships on different networks
• Helps users understand new technologies as they are developed
• Aids in interpreting vendor explanations of product functionality
The physical layer, the lowest layer of the OSI model, Deals with all aspects of physically moving data from one computer to the next over a physical medium.
“The physical layer of the OSI model defines connector and interface specifications, as well as the medium (cable) requirements. Electrical, mechanical, functional, and procedural specifications are provided for sending a bit stream on a computer network.”
This layer sets up links across the physical network, putting packets into network frames.
So that the data link layer provides error-free transfer of data frames from one node to another over the physical layer.
For example - if a packet is corrupted this layer is responsible for retransmitting the packet.
NOTE: Data Link Layer has 2 sub layer
The network layer controls the operation of the subnet, deciding which physical path the data should take based on network conditions, priority of service, and other factors. Or you can say this layer sets up links across the physical network, putting packets into network frames.
It requires logical address such as IP address. Ex – Router.
The transport layer of the OSI model, offers end-to-end communication between end devices through a network. Depending on the application, the transport layer either offers reliable, connection-oriented or connectionless, best-effort communications.
If I divide the work of Transport Layer then it works like –
The session layer, provides various services, including tracking the number of bytes that each end of the session has acknowledged receiving from the other end of the session. This session layer allows applications functioning on devices to establish, manage, and terminate a dialog through a network.
Session Layer Provides duplex, half-duplex, or simplex communications between devices.
Ex - Convert clear text to encrypted text at one end and back to clear text at the other.
It can be viewed as the translator for the network. This layer may translate data from a format used by the application layer into a common format at the sending station, then translate the common format to a format known to the application layer at the receiving station.
You can understand it by example –
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