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OSI stands for Open Systems Interconnection , where open stands to say non-proprietary. It is a 7-layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe. The OSI reference model was developed by ISO – ‘International Organization for Standardization ‘, in the year 1984.
The OSI model provides a theoretical foundation for understanding network communication . However, it is usually not directly implemented in its entirety in real-world networking hardware or software . Instead, specific protocols and technologies are often designed based on the principles outlined in the OSI model to facilitate efficient data transmission and networking operations
Data link layer (dll) – layer 2, network layer – layer 3, transport layer – layer 4, session layer – layer 5, presentation layer – layer 6, application layer – layer 7.
The OSI model, created in 1984 by ISO , is a reference framework that explains the process of transmitting data between computers. It is divided into seven layers that work together to carry out specialised network functions , allowing for a more systematic approach to networking.
When we transfer information from one device to another, it travels through 7 layers of OSI model. First data travels down through 7 layers from the sender’s end and then climbs back 7 layers on the receiver’s end.
Data flows through the OSI model in a step-by-step process:
Each layer adds specific information to ensure the data reaches its destination correctly, and these steps are reversed upon arrival.
Let’s look at it with an Example:
Luffy sends an e-mail to his friend Zoro.
Step 1: Luffy interacts with e-mail application like Gmail , outlook , etc. Writes his email to send. (This happens in Layer 7: Application layer )
Step 2: Mail application prepares for data transmission like encrypting data and formatting it for transmission. (This happens in Layer 6: Presentation Layer )
Step 3: There is a connection established between the sender and receiver on the internet. (This happens in Layer 5: Session Layer )
Step 4: Email data is broken into smaller segments. It adds sequence number and error-checking information to maintain the reliability of the information. (This happens in Layer 4: Transport Layer )
Step 5: Addressing of packets is done in order to find the best route for transfer. (This happens in Layer 3: Network Layer )
Step 6: Data packets are encapsulated into frames, then MAC address is added for local devices and then it checks for error using error detection. (This happens in Layer 2: Data Link Layer )
Step 7: Lastly Frames are transmitted in the form of electrical/ optical signals over a physical network medium like ethernet cable or WiFi.
After the email reaches the receiver i.e. Zoro, the process will reverse and decrypt the e-mail content. At last, the email will be shown on Zoro’s email client.
The OSI model consists of seven abstraction layers arranged in a top-down order:
The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for transmitting individual bits from one node to the next. When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together.
Note: Hub, Repeater, Modem, and Cables are Physical Layer devices. Network Layer, Data Link Layer, and Physical Layer are also known as Lower Layers or Hardware Layers .
The data link layer is responsible for the node-to-node delivery of the message. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. When a packet arrives in a network, it is the responsibility of the DLL to transmit it to the Host using its MAC address . The Data Link Layer is divided into two sublayers:
The packet received from the Network layer is further divided into frames depending on the frame size of the NIC(Network Interface Card). DLL also encapsulates Sender and Receiver’s MAC address in the header.
The Receiver’s MAC address is obtained by placing an ARP(Address Resolution Protocol) request onto the wire asking “Who has that IP address?” and the destination host will reply with its MAC address.
Note: Packet in the Data Link layer is referred to as Frame. Data Link layer is handled by the NIC (Network Interface Card) and device drivers of host machines. Switch & Bridge are Data Link Layer devices.
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 address es are placed in the header by the network layer.
Note: Segment in the Network layer is referred to as Packet . Network layer is implemented by networking devices such as routers and switches.
The transport layer provides services to the application layer and takes services from the network layer. The data in the transport layer is referred to as Segments . It is responsible for the end-to-end delivery of the complete message. The transport layer also provides the acknowledgment of the successful data transmission and re-transmits the data if an error is found.
At the sender’s side: The transport layer receives the formatted data from the upper layers, performs Segmentation , and also implements Flow and error control to ensure proper data transmission. It also adds Source and Destination port number s in its header and forwards the segmented data to the Network Layer.
Note: The sender needs to know the port number associated with the receiver’s application. Generally, this destination port number is configured, either by default or manually. For example, when a web application requests a web server, it typically uses port number 80, because this is the default port assigned to web applications. Many applications have default ports assigned.
At the receiver’s side: Transport Layer reads the port number from its header and forwards the Data which it has received to the respective application. It also performs sequencing and reassembling of the segmented data.
1. Connection-Oriented Service: It is a three-phase process that includes:
In this type of transmission, the receiving device sends an acknowledgment, back to the source after a packet or group of packets is received. This type of transmission is reliable and secure.
2. Connectionless service: It is a one-phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. This approach allows for much faster communication between devices. Connection-oriented service is more reliable than connectionless Service.
Note: Data in the Transport Layer is called Segments . Transport layer is operated by the Operating System. It is a part of the OS and communicates with the Application Layer by making system calls. The transport layer is called as Heart of the OSI model. Device or Protocol Use : TCP, UDP NetBIOS, PPTP
This layer is responsible for the establishment of connection, maintenance of sessions, and authentication, and also ensures security.
Note: All the below 3 layers(including Session Layer) are integrated as a single layer in the TCP/IP model as the “Application Layer”. Implementation of these 3 layers is done by the network application itself. These are also known as Upper Layers or Software Layers. Device or Protocol Use : NetBIOS, PPTP.
Let us consider a scenario where a user wants to send a message through some Messenger application running in their browser. The “ Messenger ” here acts as the application layer which provides the user with an interface to create the data. This message or so-called Data is compressed, optionally encrypted (if the data is sensitive), and converted into bits (0’s and 1’s) so that it can be transmitted.
Communication in Session Layer
The presentation layer is also called the Translation layer . The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.
Note: Device or Protocol Use: JPEG, MPEG, GIF.
At the very top of the OSI Reference Model stack of layers, we find the Application layer which is implemented by the network applications. These applications produce the data to be transferred over the network. This layer also serves as a window for the application services to access the network and for displaying the received information to the user.
Example : Application – Browsers, Skype Messenger, etc.
Note: The application Layer is also called Desktop Layer. Device or Protocol Use : SMTP .
The main functions of the application layer are given below.
Note: The OSI model acts as a reference model and is not implemented on the Internet because of its late invention. The current model being used is the TCP/IP model.
|
|
|
|
|
---|---|---|---|---|
7 | Helps in identifying the client and synchronizing communication. | Message | ||
6 | Data from the application layer is extracted and manipulated in the required format for transmission. | Message | , , | |
5 | Establishes Connection, Maintenance, Ensures Authentication and Ensures security. | Message (or encrypted message) | ||
4 | Take Service from Network Layer and provide it to the Application Layer. | Segment | ||
3 | Transmission of data from one host to another, located in different networks. | Packet | ||
2 | Node to Node Delivery of Message. | Frame | , | |
1 | Establishing Physical Connections between Devices. | Bits | , , , Cables |
TCP/IP protocol ( Transfer Control Protocol/Internet Protocol ) was created by U.S. Department of Defense’s Advanced Research Projects Agency (ARPA) in 1970s.
Some key differences between the OSI model and the TCP/IP Model are:
OSI vs TCP/IP
Even though the modern Internet doesn’t strictly use the OSI Model (it uses a simpler Internet protocol suite), the OSI Model is still very helpful for solving network problems. Whether it’s one person having trouble getting their laptop online, or a website being down for thousands of users, the OSI Model helps to identify the problem. If you can narrow down the issue to one specific layer of the model, you can avoid a lot of unnecessary work.
Imperva security solutions protect your applications at different levels of the OSI model. They use DDoS mitigation to secure the network layer and provide web application firewall (WAF), bot management, and API security to protect the application layer.
To secure applications and networks across the OSI stack, Imperva offers multi-layered protection to ensure websites and applications are always available, accessible, and safe. The Imperva application security solution includes:
The OSI Model defines the communication of a computing system into 7 different layers. Its advantages include:
In conclusion, the OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has specific responsibilities and interacts with the layers directly above and below it, ensuring seamless communication and data exchange across diverse network environments. Understanding the OSI model helps in troubleshooting network issues, designing robust network architectures, and facilitating interoperability between different networking products and technologies.
Is osi layer still used.
Yes, the OSI model is still used by networking professionals to understand data abstraction paths and processes better.
Layer 7 or Application layer is highest layer of OSI model.
Layer 8 doesn’t actually exist in the OSI model but is often jokingly used to refer to the end user. For example: a layer 8 error would be a user error.
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So I feel I pretty well understand the application layer, and everything below (and including) the transport layer.
The session and presentation layers, though, I don't fully understand. I've read the simplistic descriptions in Wikipedia, but it doesn't have an example of why separating out those layers is useful.
The session layer is meant to store states between two connections, like what we use cookies for when working with web programming.
The presentation layer is meant to convert between different formats. This was simpler when the only format that was worried about was character encoding, ie ASCII and EBCDIC. When you consider all of the different formats that we have today(Quicktime, Flash, Pdf) centralizing this layer is out of the question.
TCP/IP doesn't make any allocation to these layers, since they are really out of the scope of a networking protocol. It's up to the applications that take advantage of the stack to implement these.
The reasons there aren't any examples on wikipedia is that there aren't a whole lot of examples of the OSI network model, period.
OSI has once again created a standard nobody uses, so nobody really know how one should use it.
Layers 5-6 are not commonly used in today's web applications, so you don't hear much about them. The TCP/IP stack is slightly different than a pure OSI Model.
One of the reasons TCP/IP is used today instead of OSI is it was too bloated and theoretical, the session and presentation layer aren't really needed as separate layers as it turned out.
I think that presentation layer protocols define the format of data. This means protocols like XML or ASN.1. You could argue that video/audio codecs are part of the presentation layer Although this is probably heading towards the application layer.
I can't help you with the session layer. That has always baffled me.
To be honest, there are very vague boundaries in everything above the transport layer. This is because it is usually handled by a single software application. Also, these layers are not directly associated with transporting data from A to B. Layers 4 and below each have a very specific purpose in moving the data e.g. switching, routing, ensuring data integrity etc. This makes it easier to distinguish between these layers.
Presentation Layer The Presentation Layer represents the area that is independent of data representation at the application layer - in general, it represents the preparation or translation of application format to network format, or from network formatting to application format. In other words, the layer “presents” data for the application or the network. A good example of this is encryption and decryption of data for secure transmission - this happens at Layer 6.
Session Layer When two devices, computers or servers need to “speak” with one another, a session needs to be created, and this is done at the Session Layer. Functions at this layer involve setup, coordination (how long should a system wait for a response, for example) and termination between the applications at each end of the session.
For the presentation layer :because most of communication done between heterogeneous systems (Operating Systems,programing langages,cpu architectures)we need to use a unified idepedent specification .like ANS1 ans BRE.
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Prerequisite : OSI Model. Introduction : Presentation Layer is the 6th layer in the Open System Interconnection (OSI) model. This layer is also known as Translation layer, as this layer serves as a data translator for the network. The data which this layer receives from the Application Layer is extracted and manipulated here as per the required ...
2. Data link layer. 1. Physical layer. v. t. e. In the seven-layer OSI model of computer networking, the presentation layer is layer 6 and serves as the data translator for the network. [ 2][ 3][ 4] It is sometimes called the syntax layer. [ 5]
The presentation layer is located at Layer 6 of the OSI model. The tool that manages Hypertext Transfer Protocol ( HTTP) is an example of a program that loosely adheres to the presentation layer of OSI. Although it's technically considered an application-layer protocol per the TCP/IP model, HTTP includes presentation layer services within it.
Chloe Tucker. This article explains the Open Systems Interconnection (OSI) model and the 7 layers of networking, in plain English. The OSI model is a conceptual framework that is used to describe how a network functions. In plain English, the OSI model helped standardize the way computer systems send information to each other.
The presentation layer is the lowest layer at which application programmers consider data structure and presentation, instead of simply sending data in the form of datagrams or packets between hosts. This layer deals with issues of string representation - whether they use the Pascal method (an integer length field followed by the specified ...
Data Link Layer. Network Layer. Transport Layer. Session Layer. Presentation Layer. Application Layer. Summary. The Open Systems Interconnection (OSI) networking model defines a conceptual framework for communications between computer systems. The model is an ISO standard which identifies seven fundamental networking layers, from the physical ...
Presentation Layer is the Layer 6 of the seven-layer Open Systems Interconnection (OSI) reference model. The presentation layer structures data that is passed down from the application layer into a format suitable for network transmission. This layer is responsible for data encryption, data compression, character set conversion, interpretation ...
The presentation layer is the sixth layer of the OSI model. It is primarily used to convert different file formats between the sender and the receiver. The OSI model is a reference model that is used to define communication standards between two devices within a network. The development of this standard began in the 1970s and it was first ...
The Presentation Layer, situated at Layer 6 of the OSI model, acts as an intermediary between the Application Layer (Layer 7) and the Session Layer (Layer 5). Its primary function is to ensure ...
Layer 6: Presentation. The Presentation Layer represents the area that is independent of data representation at the application layer. In general, it represents the preparation or translation of ...
Presentation Layer: The presentation layer is layer 6 of the 7-layer Open Systems Interconnection (OSI) model. It is used to present data to the application layer (layer 7) in an accurate, well-defined and standardized format. The presentation layer is sometimes called the syntax layer.
Functionalities of the Presentation Layer. Specific functionalities of the presentation layer are as follows: 1. Translation. The processes or running programs in two machines are usually exchanging the information in the form of numbers, character strings and so on before being transmitted. The information should be changed to bitstreams ...
The Presentation Layer. The sixth layer of the OSI model is the Presentation layer. Applications running on the local system may or may not understand the format that is used to transmit the data over the network. The presentation layer works as a translator.
The presentation layer is the sixth layer of the OSI model. It is primarily used to convert different file formats between the sender and the receiver. The OSI model is a reference model that is used to define communication standards between two devices within a network. The development of this standard began in the 1970s and it was officially ...
What is Presentation Layer? Definition: Presentation layer is 6th layer in the OSI model, and its main objective is to present all messages to upper layer as a standardized format.It is also known as the "Translation layer". This layer takes care of syntax and semantics of messages exchanged in between two communication systems. Presentation layer has responsible that receiver can ...
The presentation layer is the 6 th layer from the bottom in the OSI model. This layer presents the incoming data from the application layer of the sender machine to the receiver machine. It converts one format of data to another format of data if both sender and receiver understand different formats; hence this layer is also called the ...
Conclusion. In conclusion, the OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.
The presentation layer is the sixth layer of the Open Systems Interconnection (OSI), model. In computer networking, the OSI model is a concept that describes the transmission of data from one computer to another. Each layer in the model is a packet of protocols, or procedures that govern data transmission, which allow the layer to execute ...
The session layer is meant to store states between two connections, like what we use cookies for when working with web programming. The presentation layer is meant to convert between different formats. This was simpler when the only format that was worried about was character encoding, ie ASCII and EBCDIC. When you consider all of the different ...
What is presentation layer? The functions of presentation layer The presentation layer is located at the sixth level of the OSI model, it is responsible for the delivery and formatting of information to the application layer for further processing or display. The functions and protocols of presentation layer in OSI model you can read here.
Presentation layer: The OSI presentation layer is the sixth layer and translates data across the network. Application layer: Topmost seventh layer which stipulates the interface methods for the ...
Presentation layer definition. The presentation layer is the sixth layer in the Open System Interconnection (OSI) model. It serves as the data translator for the network — it takes data formats from different sources and presents it to the application layer in an accurate, well-defined, and standardized manner.
The OSI Model can be seen as a universal language for computer networking. It is based on the concept of splitting up a communication system into seven abstract layers, each one stacked upon the last. Each layer of the OSI Model handles a specific job and communicates with the layers above and below itself. DDoS attacks target specific layers ...