Do you know what is an OSI model or what is an OSI layered model? If not, today’s post will be very good. At first, network development was very messy. The reason for this is that each seller has their own solution. The bad thing about this is that one vendor’s solution was not compatible with the other. Only the OSI model was born to solve this problem.

In this, a multi-layer approach to networks was used, with hardware vendors used to design hardware for the network, while others developed software for the application layer.

Using an open model, where everyone agrees, means creating a network that works for everyone. To resolve this issue, the International Organization for Standardization (ISO) studied the various networks in 1984 and the OSI model preparation. It was compatible with all sellers.

This OSI model is not just a model for making networks compatible, but a very good way to get people to understand networks. That’s why today I thought about why I should give you information about what the OSI model is and what all the OSI layers and functions are. Then what is the delay, let’s start.

What is the OSI model?

The full form of OSI is the Open System Interconnection (OSI) model, an ISO standard for global networking that defines a networking framework so that protocols can be implemented in seven layers.

The OSI layer model was developed by the International Organization for Standardization where OSI stands for Open Systems Interconnection. In this way the communication system is divided into seven different layers.

The layer here is a variety of theoretically comparable functions in which the layer above the services it provides receives more services than the layer below it. The OSI layer model makes it easy for the user to have an error-free transmission in a cross-sectional network while also providing the path required by the applications.

Here the layers throw the packets and also find the path that provides the path to the contents. The OSI layer model provides a framework for networks that use the protocols in these seven layers.

In this the processing control is bypassed from one layer to another and this process continues to the end. In this, processing starts from the bottom layer and then travels through the channel to the next station, and later back in its hierarchy.

What is the OSI layer?

The communication process is layers in a process medium which means the communication process is smaller to partition and easier to deal with related classes.

What are Layer Protocols?

The conventions and rules used in such communications are collectively called Layer Protocol .

When was the OSI model created?

The Open Systems Interconnection (OSI) model was developed by ISO ( International Organization for Standardization ) in 1984. ISO is that organization entirely devoted to defining such communications and global standards.

Why is this model called OSI?

This model is called Open System Interconnection (OSI) because this model allows two different systems to communicate, regardless of their infrastructure.

Therefore, the OSI reference model allows open communication between two different systems, without having to make any changes to its underlying hardware and software.

This is the International Organization for Standards (ISO), an attempt to encourage open networks, along with a reference model for linking open systems.

This model logically groups functions and establishes rules, which are called protocols. It is very important to establish and make connections between two or more parties. The seven functions of this model are often called layers. Each layer is added to its own header from its previous layer of the beam.

The OSI reference model is now considered an essential standard for online work and intercomputer computing .

How are these seven layers grouped together?

In the OSI model, the network/data connection is defined in seven layers. These seven layers are grouped into three groups – network, transport, and application.

1. Layer 1, 2, and 3, ie physical, data link, and network are called network support layers .

2. Layer 4, the transport layer provides reliable end-to-end data transfer.

3. Layer 5, 6 and 7 i.e. Session, Presentation and Application layer are called User Support Layers.

The last three layers are primarily concerned with the organization of terminal software and are not directly concerned with telecom engineers. It is the transport layer that links software-guided protocol communications.

One special thing to note is that this OSI model is just a sample. It is not a protocol that can be installed or run in any system.

How do you remember OSI layers?

Remembering these OSI layers is not really that easy but if you use mnemonic it becomes very easy. Which is: ” It seems that all people need to process data .”

• physical layer – processing
• data link layer – data
• Network Layer – Need
• transport layer – to
• session layer – looks
• Presentation Layer – People
• Application Layer – All

7 layers OSI 

This OSI model layer consists of seven layers and each layer interacts with each other. In this layer one and two are called the media layer and layer 3, 4, 5, 6 and 7 are called the host layers .

The OSI layer model is categorized into 7 categories which are listed below, which we will learn more about.

physical layer

This physical layer is the lowest layer in the OSI model, and is only concerned with sending and receiving a raw, unstructured bit stream through a physical medium.

It describes the electrical/optical, mechanical and functional interfaces in its physical medium, and also transmits signals to all upper layers. The physical layer itself defines the cabling, network cards, and physical aspects.

It is actually responsible for the actual physical connection between the devices. You can make such a physical connection using twisted pair cable or fiber optic cable or coaxial cable , or modes of wireless communication .

This layer receives the frames sent by the data link layer and converts them into such signals that are compatible with other transmission media.

For example, if a metal cable is used, it will convert the data into electrical signals; Whereas if fiber-optic cable is used, it converts data into optical signals; If a wireless network is used, it will convert data into electromagnetic signals; And it will continue like this.

When receiving data, these layers receive that signal, convert it into zeros and ones, and then send it to the data link layer, which then keeps those frames together, and then checks their integrity. These X.25 protocols operate at the physical, data link, and network layers.

What are the functions of the physical layer

Data encoding: Modifies the patterns of simple digital signals (1 and 0) used by computers to better suit the characteristics of the physical medium, as well as enabling bit and frame synchronization.

Specify the following:
1. Does the signal state represent binary 1?
2. How is this audience receiving station when “bit time” starts.
3. How does this receiving station define a frame.

Transmission technology : Specifies whether the encoded bits are transmitted over a baseband (digital) or broadband (analog) signal.

Physical Medium Transmission: Transmits bits into electrical or optical signals suitable for the physical medium, specifying:

1. What physical broker options can be used.
2. How many volts/dB must be used so that a given signal state can be represented, using a given physical medium.

The protocols used in the physical layer are ISDN, IEEE 802, and IEEE 802.2 .

Bit Synchronization : This physical layer provides synchronization of the bits for which a clock is used. This clock controls both the sender and the receiver providing synchronization at the bit level.

Provides the physical properties of the interfaces and the medium: The physical layer manages how a device communicates with network media. For example, if the physical connection of a device uses a coaxial cable to connect to the network, the device that performs the functions in the physical layer must be designed in such a way that it can operate in a particular type of network. All components including connectors are identified in the physical layer.

Bit rate control: The physical layer determines the transmission rate, that is, the number of bits sent per second. Sets the duration a little.

Line configuration : The physical layer then determines how devices are connected to the medium. Two different shapes of lines are used for point-to-point formation and multi-point formation. Use it to activate, maintain, and deactivate a physical connection.

Transmission mode : The physical layer defines how data flows between two connected devices. The different possible transmission modes are – Simplex, half-double and full-double.

Physical Topology : The physical layer defines how different devices/nodes are arranged in a network i.e. a bus, star or network.

Multiplexing : The physical layer can use different multiplexing techniques, so that the channel efficiency can be improved.

Circuit switching : The physical layer also provides how to communicate with other networks through circuit switching.

data link layer

The OSI data link layer provides physical addressing. This layer provides procedural and functional resources during data transmission in networks.

It also identifies physical layer errors and also tries to correct them. The main purpose of this data link layer is point-to-point multi-media processing.

It is also responsible for reliable data delivery from node to node. It receives data from the network layer and creates frames, adds physical addresses to those frames and then passes them to the physical layer.

This data link layer provides error-free transmission of data, and this is also on top of the physical layer from one node to another, which together allows the layers above it to assume an almost error-free transmission.

The data link layer defines the format of the data in the network. Network data consists of frame and packet along with checksum, source and destination address and data.

This data link layer deals with the physical and logical connections to the packet destination, which also uses the network interface.

This layer receives data packets sent through the network layer and converts them into frames that are sent to the network media, in this they add your computer’s network card. The address, in addition to the physical address of the destination network card, control data and checksum data, also known as CRC.
These X.25 protocols operate at the physical, data link, and network layers.

Sub – layer data link layer 
1. layer sub – control logical link (LLC Note )
2. class sub – control medium access (MAC)

The LLC sublayer provides an interface between media access methods and network layer protocols such as the Internet Protocol, which is part of the TCP/IP protocol suite.

The LLC sub-layer also determines whether this connection will be connectionless or connection-configured at the data link layer.

The MAC sublayer is responsible for communication with the physical media. In the MAC sublayer of the data link layer, the actual physical address of the device, also known as the MAC address, is added to the packet.

This packet is called the frame that stores all the addressing information necessary to go from the source device to the destination device.

A MAC address is a 12-digit hexadecimal number, which is unique to every computer worldwide.

A device’s MAC address is located on its Network Interface Card (NIC). In the 12 digits of the MAC address, the first six digits indicate the manufacturer of the NIC and the last six digits are completely unique.

for example. 31-16-a6-32-72-0c is a 12-digit hexadecimal MAC address . So the MAC address represents the physical address of the device in the network.

Data Link Layer Functions

Link creation and termination: establishes and terminates a logical link between two nodes.

Physical Addressing : After the frames are created , the data link layer adds physical addresses (MAC address) to the header of each frame for both the sender and receiver.

Frame Motion Control : Tells the sending node the “undo algorithm” when no frame buffers are available.

Frame Sequence : Transmits/receives frames sequentially.

Framework Acknowledgment: Provides/expects framework acknowledgments. They detect and recover from errors in the physical layer, so they send back unacknowledged

Frames and also handle duplicates of the frame receipt.

Frame delineation : Establishing and recognizing frame boundaries.

Frame Fault Check : Checks the integrity of received frames.

Media Access Management : Specifies when a node has the “right” to access a physical medium.

Flow control : This is a traffic regulatory mechanism that is implemented through the data link layer and prevents slow receivers from flooding fast senders. If the rate at which the receiver absorbs data is less than the rate at which the transmitter produces it, the data link layer imposes on the flow control mechanism.

Error Control : The data link layer provides an error control mechanism by which it detects and retransmits damaged and missing frames. It also deals with the redundant frame problem, so it provides reliability to the physical layer.

Access Control : When a single communication channel is shared with multiple devices, the MAC sub-layer of the data link layer helps determine which device is controlling the channel at a particular time.

Feedback : Once frames are submitted, the system waits for feedback. Then the receiver sends the acknowledgment frames to the back source, from which it provides a receipt for the frames.

network layer

The OSI network layer is used for logical addressing like virtual circuits, and it is used to specify node to node and path for data transmission.
The OSI network layer also provides routing and switching technologies with it. Besides, error handling, packet sequencing, online working, addressing, and congestion control are all essential functions of the network layer.

It also offers the best quality service when the transport layer is requested. These are the IPX and TCP/IP protocols implemented in this layer.

There are three sub-layers of the network layer, let’s get acquainted with them: –
Subnet access: Subnet access is considered protocols and is responsible for making the interface deal with the network on X.25 lines.

Subnet Dependent Convergence : This is responsible for moving the transport network level to any side of the network level.

Subnetwork Independent Convergence : It is used across multiple networks to manage transport.

This layer is also responsible for packet addressing, converting logical addresses into physical addresses. Together, they are responsible for delivering packets from source to destination over multiple networks (links).

This layer is responsible for setting up the directive. Although the packages will reach the destination on their own, it also depends on some factors such as traffic and priorities. This same network layer determines how data is transferred between network devices.

If two systems are connected at the same link, then no network layer is needed. The same if two systems are connected to two different networks that also have devices connected like routers between these two networks, then the network layer is required in this space.

It also translates the logical address into a physical address, for example a computer name into a MAC address.

It is also responsible for setting the path. Besides, it also manages network and addressing issues.

It also controls the operation of the network layer subnetwork, deciding whether to specify a physical path based on data based on network conditions, service priority, and other factors. These X.25 protocols operate at the physical, data link, and network layers.
This network layer lies between the data link layer and the transport layer. These services take the data link and provide the service to the transport layer.

Network Layer Functions

1. Control subnet traffic : Routers (intermediate systems of the network layer) can easily instruct a sending station to “re- control network traffic ” when the router’s buffer is filled.

2. Logical-physical address mapping : translation of logical addresses, names, physical addresses.

3. Subnet usage accounting : They have accounting functions so that they can keep track of the number of frames forwarded from the subnetting intermediate systems, so that they can produce billing information.

In the network layer and the layers below it, peer protocols exist between a node and its immediate neighbor, but this neighbor can also be a node through which data is routed, not the destination station.

In this, the source and destination stations are separated from several intermediate systems.

Internet

1. This is a major responsibility of the network layer as it provides internet service to different networks.

2. It also provides logical connections in different types of networks.

3. Only because of this layer, we can merge different networks together to create one big network.

logical addressing

1. Many different networks can be combined together to form a large network or the Internet.

2. To uniquely identify each device in the interface network, the network layer defines the addressing scheme.

3. These titles uniquely and globally distinguish each device.

routing

1. When independent networks or links are combined together to create Internet business, it is possible that there are multiple routes from the source device to the destination device.

2. These network layer protocols specify only the best path or path from source to destination. The function of the network layer itself is called routing.

3. Frame paths are only in grids.

Packaging

1. This network layer receives data from higher layers and creates its own packets, for which it encapsulates packets. This same process is called packetization.

2. This packetization is done through the Internet Protocol (IP) which defines its packet format.

fragmentation

1. Fragmentation means dividing large packages into smaller parts.

2. The maximum packet size transmitted is determined by the physical layer protocol.

3. For this purpose, the network layer divides large packets into fragments so that they can be easily transmitted in a physical medium.
4.

If the downstream router’s maximum transmit unit (MTU) size is determined to be less than its own frame size, the router can segment that frame for transmission and then reassemble at the destination station.

Protocols: The protocols that operate at the network layer are IP, ICMP, ARP, RIP, OSI, IPX, and OSPF.

transport layer

Transport layer (also called end-to-end layer), it manages the end-to-end (source to destination) (process-to-process) message delivery over the network as well as providing error checking, thus providing a guarantee that no redundancy or errors occur in data transmission over the network.

It places more emphasis on the fact that messages for all packets must arrive intact and in the correct order.

The transport layer also provides acknowledgment of successful data transfer and also retransmission of data if an error is found. The transport layer ensures that messages are delivered error-free, sequentially, and without any losses or duplication.

The size and complexity of the transport protocol depends on the type of service it receives from the network layer.

You can think of the transport layer as the core of the OSI model. The transport layer provides services to the application layer and takes services from the network layer.

The transport layer splits the message into packets that it receives from the upper layer and then reassembles them into packets again so that they can get a message at the destination.

The transport layer provides two types of services:

Contact directed transmission
(a) In this type of transmission, the receiver sends a notification to the back source as soon as a packet or group of packets is received.

(b) This type of transmission is also called reliable transmission method.

(c) Since connection-oriented transmission requires more packets to be sent through the network, it is considered as a slower transmission method.

(d) If there are problems with the data to be transmitted, the destination requests retransmit to the source, where only the packets received are recognized and recognized.

(e) Once the destination computer receives all the data needed to be reassembled into a packet, the transport layer assembles that data into a valid sequence and then passes it to the session layer.

Offline transmission
(a) In this type of transmission the receiver does not acknowledge receipt of the packet.

(b) The transmitter assumes that the packet has arrived correctly.

(c) This approach allows for very fast communication between two devices.

(d) Its disadvantage is that transmission without connection is less reliable as compared to directed connection.

Transport Layer Functions:

Fragmenting the message into a packet and reassembling the same packets into the message: accepts a message from the above (session) layer, breaks that message into smaller units (if it isn’t already smaller) and then passes those messages down into smaller units at the network layer . The transport layer at the destination station is similar to the message itself.
Message Acknowledgment: Provides reliable end-to-end message delivery with acknowledgments.

Message Traffic Control : Instructs the sending station to “undo” when no message buffers are available.

Session multiplexing : Multiplexes multiple message streams or sessions into a logical link and also keeps track of which messages belong to which sessions.

Service Point Addressing : Incidentally, the purpose of the transport layer is to deliver the message from one process (running in the source device), to another process (running in the destination device).

It may also happen that many different programs and processes are running simultaneously in both devices. To do message delivery in the correct process, the transport layer header is a type of address that is added to the service point address or port address. By selecting the correct address from this, the transport layer provides assurance that the message is delivered in the correct operation of the destination device.

Flow control: Like the data link layer, the transport layer also controls the flow. The transport layer ensures that the sender and receiver communicate at a rate that both can handle. So control flow prevents the source from sending data packets faster to the destination than it can handle. Here flow control is implemented end-to-end rather than via a link.

Error control: Like the data link layer, the transport layer also performs error control. Here error control is implemented end-to-end and not over a single link. Here the sending transport layer ensures that the entire message reaches the receiving transport layer without any error (damage, loss or duplication). The error is corrected by retransmission.

Protocols: The protocols that run in the transport layer are TCP, SPX, NETBIOS , ATP, and NWLINK.

session layer

The primary responsibility of the session layer is to assist in the initiation, maintenance and termination of communication between two devices, this is called a session.

It provides an orderly communication between devices, so they have to regulate the flow of data.

This session protocol defines the format of the data that is transmitted in communications. The session layer creates and manages the session between any users, also at two different ends of the network.

The session layer also manages who transmits data over a certain period of time and for how long.

Examples of session layers are interactive logins and file transfer sessions. The session layer reconnects the session if it is disconnected. It also reports and logs upper layer errors.

This session layer allows a session to be created between two such processes running on different terminals.

The control of dialogue and management of the token are all the responsibility of the session layer.

Session Layer Functions:

Session creation, maintenance, and termination: Allows creation, use, and termination of two application processes, called a session, in different devices.

Session Support : It performs functions that allow these operations to be communicated with each other over the network, perform security, name recognition, registration and much more.

Control dialog box : Control dialog box is a function of the session layer that identifies the device that will continue to be first and the amount of data that must be sent.

When the device is first communicated, the session layer is responsible for determining which device participating in that connection will send at a given time, as well as how much of that data.control is sent to the transmission. This is called dialog control.

The types of dialog control are simple , half duplex and full duplex .

Dialogue separation and synchronization : This session layer is also responsible for adding checkpoints and flags to the message.

This process of inserting tags into a data stream is called dialog separation.

Protocols : The protocols that run at the session layer are NetBIOS, Mail Slots, Names Pipes, and RPC.

display layer

The presentation layer is also called the translation layer. This presentation layer presents the data in a standardized format and hides the difference in data format between two different systems.

OSI Presentation layer data representation, it converts plain text into code as it happens in cipher and also decrypts the data.

The OSI Presentation layer together provides freedom from compatibility issues, hence it is also called the syntax layer. It also sets up a perspective between other application layer entities.
The OSI Presentation Layer decodes the presentation of data from the application format to the network format and vice versa.

It formats the display layer data that is presented in the application layer. You can also consider it as a network translator.

This translates the layer data into a format used by the application layer in a format common to the sending station, and then translates this common format back into a format known to the application layer. at the receiving station.

Layer Display Functions:

1. Character code translation : eg, ASCII to EBCDIC.
2. Data transformation : bit order, CR-CR/LF, integer floating point, etc.
3. Data compression : It reduces the number of bits that have to be transmitted in the network.
4. Data encryption : It encrypts data for security purposes. For example password encryption.

Application layer

This application layer acts as a window for users and application processes to be able to access network services.

It is always implemented in the end system itself. This application layer creates an interface between the program sending or receiving data and the protocol stack.

When you download or send email messages, your email program communicates with this layer. This layer provides network services to end users such as mail, ftp, telnet, and dns.

What are the functions of the application layer?

• Resource sharing device forwarding
• Remote file access
• remote printer access
• interprocess communication
• Network management
• Directory Services
• Electronic messages (such as mail)

virtual network station

A network virtual terminal is a version of the software, a physical terminal that allows a user to log into a remote host. For this, the application layer creates a software simulation of a terminal on a remote host.

Now the user’s computer talks to the software terminal which in turn talks to the host and vice versa. In this, the remote host thinks it is communicating with any of its terminals and allows the user to log in.

File Transfer and Access Management (FTAM):

This application allows a user to access a file in a remote host, so that they can make changes or read data, retrieve files from a remote computer that can access them on the local computer, and manage them or you can control files locally in a remote computer.

Mail Services : This app provides various email services such as email forwarding and storage.

Directory Services : This application provides distributed database sources and access to global information about many different objects and services.

The protocols used in the application layer are FTP, DNS, SNMP, SMTP, FINGER, and TELNET.

What did you learn today

I hope you liked my article What is the OSI Model  . I’ve always been trying to provide complete information about the OSI layer model to my readers so that they don’t have to search other sites or the Internet in the context of that article.

This will also save their time and they will also have all the information in one place. If you have any doubts about this article or if you want there to be some improvement in it, you can write low comments on it.

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