OSI-MODEL OVERVIEW
In this article I'm going to discuss about OSI model. Let’s begin with a straight forward , It’s a deal with systems that open for communication
“Conceptual framework for describes the functions of a networking system”
What is exactly OSI ?
OSI stands for Open System Interconnection
Layered model that describes how information moves from an application program running on one networked computer to an application program running on another networked computer.
Developed by the International Organization for Standardization (ISO) in 1984.Now considered as an architectural model for the inter-computer communications. The full acronym of the OSI is ISO OSI.
Why do we need OSI Model?
Guide technology vendors and developers so the digital communications products and software products and software programs they create can interoperate and to promote a clear framework that describes the functions of a networking or telecommunications that’s in use.
How data transfer across the OSI model
Data travels from the sending computer down through all the layers to the physical layer where the data is put onto the network cabling, and then sent to the physical layer of the receiving computer where the process reserves and the data travels up through the layers to the application layer of the receiving computer.
Advantages of OSI
- Standardize the router, switch, motherboard, and other hardware.
- Reduce complexity and standardizes interfaces.
- Facilitates modular engineering.
- Ensure interoperable technology
- Accelerate the evolution
- Protocols can be replaced by new protocols when technology changes
- Provide support for connection-oriented services as well as connectionless service
- Standard model in computer networking
- Supports connectionless and connection-oriented services
- Offers flexibility to adapt to various types of protocols.
Structure of the OSI model
It’s a seven layer architecture with each layer having specific functionality to perform. All these seven layers work collaboratively to transmit the data from one person to another across the globe.
How to remember order
”Please Do Not Throw Salami Pizza Away”- for bottom-to-top.
“All People Seem To Need Data Processing”- a top-to-bottom reminder.
Let’s discuss one by one..
The Upper Layers
It deals with application issues and mostly implemented only in software. The highest is closest to the end system user. In this layer, communication from one end-user to another begins by using the interaction between the application layer. It will process all the way to end-user.
The Lower Layers
These layers handle activities related to data transport. The physical layer and datalink layers also implemented in software and hardware.
7. Application layer
Application layer, both the end user and the application layer interact directly with the software application. This layer sees network services provided to end-user applications such as a web browser or Office 365. The application layer identifies communication partners, resource availability, and synchronizes communication.
6.Presentation Layer
Presentation layer allows you to define the form in which the data is to exchange between the two communicating entities. It also helps you to handles data compression and data encryption. This layer transforms data into the form which is accepted by the application. It also formats and encrypts data which should be sent across all the networks. This layer is also known as a syntax layer.
5.Session Layer
This is the layer responsible for opening and closing communication between the two devices. The time between when the communication is opened and closed is known as the session. The session layer ensures that the session stays open long enough to transfer all the data being exchanged, and then promptly closes the session in order to avoid wasting resources. The session layer also synchronizes data transfer with checkpoints.
4.Transport Layer
The transport layer is responsible for transferring data across a network and provides error-checking mechanisms and data flow controls. It determines how much data to send, where it gets sent and at what rate. TCP within the TCP/IP suite is the best-known example of the transport layer. This is where the communications select TCP port numbers to categorize and organize data transmissions across a network. Transport layer helps you to control the reliability of a link through flow control, error control, and segmentation or DE segmentation.
(i) TCP(Transmission Control Protocol)
The TCP/IP relationship is similar to sending someone a message written on a puzzle through the mail. The message is written down and the puzzle is broken into pieces. Each piece then can travel through a different postal route, some of which take longer than others. When the puzzle pieces arrive after traversing their different paths, the pieces may be out of order. The Internet Protocol makes sure the pieces arrive at their destination address. The TCP protocol can be thought of as the puzzle assembler on the other side who puts the pieces together in the right order, asks for missing pieces to be resent, and lets the sender know the puzzle has been received. TCP maintains the connection with the sender from before the first puzzle piece is sent to after the final piece is sent.
When an email is sent over TCP, a connection is established and a 3-way handshake is made. First, the source send an SYN “initial request” packet to the target server in order to start the dialogue. Then the target server then sends a SYN-ACK packet to agree to the process. Lastly, the source sends an ACK packet to the target to confirm the process, after which the message contents can be sent. The email message is ultimately broken down into packets before each packet is sent out into the Internet, where it traverses a series of gateways before arriving at the target device where the group of packets are reassembled by TCP into the original contents of the email.
(ii) UDP(User Datagram Protocol)
On the other hand, is a connectionless internet protocol that allows communication between the server and the client. User datagram protocol (UDP) operates on top of the Internet Protocol (IP) to transmit datagrams over a network. UDP does not require the source and destination to establish a three-way handshake before transmission takes place. Additionally, there is no need for an end-to-end connection.
3.Network Layer
The network layer works for the transmission of data from one host to the other located in different networks. It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available. The sender & receiver’s IP addresses are placed in the header by the network layer.
2.Data Link Layer
The data-link , or protocol layer, in a program handles moving data into and out of a physical link in a network. This layer handles problems that occur as a result of bit transmission errors. It ensures that the pace of the data flow doesn’t overwhelm the sending and receiving devices. This layer also permits the transmission of data to Layer 3, the network layer, where it’s addressed and routed.
Data Link Layer is divided into two sublayers:
- Logical Link Control (LLC)
- Media Access Control (MAC)
1.Physical Layer
The lowest layer of the OSI Model is concerned with electrically or optically transmitting raw unstructured data bits across the network from the physical layer of the sending device to the physical layer of the receiving device. It can include specifications such as voltages, pin layout, cabling, and radio frequencies. At the physical layer, one might find “physical” resources such as network hubs, cabling, repeaters, network adapters or modems.
I hope you will get an idea about OSI model and how it works apparently.
I will see you in next article.
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