OSI Model
Tags: networking, osimodel
Published: 2020-08-30 18:45:33

**OSI** or **Open Systems Interconnection** is a conceptual model explains how networks communicate. It describes the characteristics and standards for any communication of a telecom or computing system without getting into the details of the internal structure and the technology involved. Its sole purpose is to ensure that diverse communication systems operate with standard communication protocols.

**Application Layer:** It is the layer closest to the end user, meaning this layer interacts with the user directly. The Application Layer functions typically includes identification of the communication patterns, determining resource availability and synchronizing communication

**Presentation Layer:** This layer is responsible for establishing context between various entities. various applications might use different syntax and semantics, this layer relieves the application of the concerns regarding syntactical differences in data representation within the systems. Basically it takes care of encryption and decryption of data.

**Session Layer:** This layer controls the connections between various systems. It establishes, manages and terminates the connections between the sender and the receiver applications. It also establishes protocols for check-pointing, suspending, restarting and terminating a session. Basically it provides dialogue between the application processes.

**Transport Layer:** This layer provides the means of transferring data sequences from source to destination while maintaining the quality of the service functions. It controls the reliability of the data through flow control, segmentation/de-segmentation and error control. It keeps a track of the data segments and also re transmits the failed packets. It also provides acknowledgement of the successful data transmission and send the next data packet if no error occurred.It creates segments out of the message, meaning it divides a long message into smaller messages.

**Network Layer:** This layer helps in routing information in the network. It provides the functions for the telecommunication resources that provide the paths for transfer of data between systems. Anything that has to do with inter-network connections takes place at the network layer. This includes setting up the routes for data packets to take, checking to see if a server in another network is up and running, and addressing and receiving IP packets from other networks.

**Data Link Layer:** This layer detects and corrects possible errors that might occur during transmission. It is responsible for multiplexing data streams, data frame detection, medium access, and error control. It ensures reliable point-to-point and point-to-multipoint connections in a communication network. 

**Physical Layer:** This layer describes the physical properties of various communication media as well as the electrical properties. It is responsible for the transmission and reception of unstructured raw data between a device and a physical transmission medium. It converts the digital bits into electrical, radio, or optical signals.

There are some easy ways to remember all the network layers:

1) *Andhra* (Application Layer) *Pradesh* (Presentation Layer) *Se* (Session Layer) *Train* (Transport Layer) *Nikli* (Network Layer) *Delhi* (Datalink layer) *Pahunchi* (Physical Layer).

2) *All* (Application Layer) *People* (Presentation Layer) *Seem* (Session Layer) *To* (Transport Layer) *Need* (Network Layer) *Data* (Datalink Layer) *Protection* (Physical Layer).

Youtube Link for ease of understanding(in Hindi):
https://www.youtube.com/watch?v=Dppl6iA2G8Q