The OSI model stands for Open Systems Interconnection model. This conceptual model characterizes and standardizes the communication system by participating in the abstraction layers. This model was produced at the International Organization for Standardization (ISO). It has seven layers. The layers are as follows:
- Data Link
Among the above seven layers, four layers namely Application, Presentation, Session and Transport layers lie in the category of host layers and the remaining layers which includes Network, Data Link and Physical layers lie in the category of Media Layers. Also the Application, Presentation and Session layer works on the whole data, while the Transport Layer divides the Data into segments, the Network Layer divides the Data into packets or datagrams, the Data Link Layer divides the Data into Bit Frames and last but not the least the Physical Layer divides the Data into smallest units, i.e., Bits and then after dividing the layers do their respective works on the data.
Let us see what these layers function.
This layer is the lowest layer of the OSI model, and it is concerned with the transmission and. It provides:
- Data encoding which modifies the simple digital signal pattern used by the PC to better accommodate the characteristics of the physical medium
- Physical medium attachment, accommodating various possibilities in the medium and Transmission technique, determines whether the encoded bits will be transmitted by baseband (digital) or broadband (analog) signaling. it, transmits bits as electrical or optical signals appropriate for the physical medium, and determines What physical medium options can be used.
DATA LINK LAYER
- This layer provides error-free transfer of data frames from one node to another over the physical layer.
- The data link layer provides:
- Link establishment and termination, establishes and terminates the logical link between two nodes.
- Frame traffic control, tells the transmitting node to “back-off” when no frame buffers are available.
- Frame sequencing, receives frames sequentially.
- Frame acknowledgment.
- This layer controls the operation of the subnet, deciding which physical path the data should take based on network conditions.
- Routing which is use to routes frames among networks.
- Subnet traffic is use to control the routers.
- It ensures that messages are delivered error-free, in sequence, and with no duplications. The size and complexity of a transport protocol depends on the type of service it can get from the network layer.
- It provides:Message segmentation, Message acknowledgment ,Message traffic control.
- This layer allows session establishment between processes running on different stations.
- It provides: Session establishment, maintenance and termination
- It uses to performs the functions that allow these processes to communicate over the network, performing security, name recognition, logging, and so on.
- The presentation layer provides: Character code translation, Data conversion, Data compression,Data encryption
- The application layer serves as the window for users and application processes to access network services. It provides: Resource sharing and device redirection, Remote file access, Inter-process communication, Network management.
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