OSI Layers: What Is The Open System Interconnection Used For?


OSI is the abbreviation for "Open System Interconnection." It is a reference model that illustrates how data travels from an application software on one desktop to a software program on another gadget via a physical link.

OSI has 7 layers, and then each layer has a specific job to do in a network. The International Organization for Standardization (ISO) created the OSI model in 1984, and it is now used as a model for how computers talk to each other.

The OSI model breaks the whole job down into 7 subtasks that are easier to handle. Each layer has a different job to do. Each layer works in silos, which means that the tasks that are given to one layer are done on their own.

Well, today, we will dive deep into the 7 OSI layers and explain the functions of each and what it's used for.

Various uses of the 7 layers of an OSI

As we already mentioned, an OSI comprises 7 layers and each of them does something different. So, let's get started!

1. Physical layer

The physical layer's primary function is to send bits from one node to another. It is also the OSI model's bottom layer.

It sets up, keeps up, and turns off the physical connection. It lists the structural, electronic, and operational details of the local network.

Uses of the physical layer

  • Data Transmission: It sets the mode of data transmission between any two gadgets on the network. It can be simplex, half-duplex, or full-duplex.
  • Topology: It describes how the equipment in a system is set up.
  • Signals: It tells what kind of signal is being used to send the information.

2. Data-link layer

This layer is in place to make sure that data frames are sent without any mistakes. It tells how the information on the system is put together.

It lets multiple devices talk to each other in an efficient and consistent way. Its main job is to make sure that each device on a local area network can be identified by its own unique number.

It has two layers inside:

  • Control layer for logical links

It's in charge of sending the packet data to the network level of the receiving device. It looks at the header to find out the location of the network interface. It also controls the flow.

  • The media access control layer

A connection between both the logical link control layer and also the physical layer of a network is the media access control layer. It is used to move packets across the network.

Uses of the data-link layer

  • Framing: A data link layer uses raw bitstreams from the physical layer and turns it into data packets called frames. The header plus the frame's end are added to the frame by the data link layer.
The equipment location and address of the source are stored in the header, that is incorporated in the frame.

  • Physical addressing: A data link layer brings a header toward the frame which has the address of the destination in it. The frame is sent to the address in the header that says where it should go.
  • Flow control: The primary function of a data-link layer is to control the flow of data. It is the method for keeping both sides of the connection at the same data rate such that no data gets lost or changed. It makes sure that the sending station, like a server, doesn't have a faster processing speed than the receiving station, which has a slower speed.
  • Error control: Error regulation is accomplished by summing a premeditated valuation CRC (Cyclic Redundancy Check) to the text frame's data link layer trailer before sending it to the physical layer. If it seems that there is a problem, the receiver sends a confirmation that the tainted frames need to be sent again.
  • Access control: Once multiple devices are linked to one channel of communication, a data link layer guidelines can be used to figure out which gadget is in charge of the link at any given point in time.

3. Network layer

The network layer is the third one among the seven layers of OSI model. It is utilized to offer routing services within an internetwork.

Network layer protocols are the rules that tell the network how to route traffic. Protocols are things like IP and IPv6 – functionalities of next-gen firewalls.

Uses of the network layer

  • Internetworking: The network layer's main job is to make sure that things work together. It lets different devices talk to each other in a logical way.
  • Addressing: The input and output addresses are added to the frame's header by a network layer. Addressing is how the gadget on the web is found.
  • Routing: Routing serves as the most important part of the network layer. It decides which of the many paths from the sender to the recipient is the ideal one.
  • Packetizing: The upper layer sends packet data to the network layer, which turns them into packets. This method is called "packetizing." It's done with the help of internet protocol (IP).

4. Transport layer

The transport layer, which is part of layer 4, makes sure that texts are shared in the sequence they were meant to be sent and that information isn't sent more than once.

The transport layer's primary function is to get the data from one place to another. It gets the information from the layer above it and breaks it up into tiny chunks called segments.

This layer can be called an end-to-end layer because it offers a complete point-to-point link between the sender and recipient.

Here are the two methods that are used:

a) Transmission control protocol

It is a set of rules that lets computers talk to each other over the internet. It sets up a link between servers and keeps it going.

When information is sent over a TCP connection, the TCP protocol breaks the information into smaller pieces called segments.

Each piece traverses over the web in various ways, and they reach the desired location in various orders.

At the receiver section, the transmission control protocol moves the packets around so that they are in the right order.

b) User datagram protocol

A user datagram protocol is used in the transport layer. It is an unverified transport protocol since once the packet date arrives, the receiver does not send an acknowledgement and the sender does not wait for an acknowledgement.

Because of this, a protocol can't be trusted.

Uses of the transport layer

  • Service-point tackling: Because computers run various programs at the same time, data can be sent from the input to the output not just from one desktop to the other, but even from one procedure to another.

The service-point location aka port address goes in the header, which is added by the transport layer. The network layer is in charge of sending the file from one device to another, and the transport layer is in charge of sending the right messages to the right process.

  • Clustering and reinstallation: Whenever the transport layer gets a signal from a higher layer, it breaks the message into several segments and gives each segment an identifier that makes it easy to find. When the message gets to its destination, the transport layer uses the sequence numbers to put the message back together.
  • Connection control: The transport layer offers two services. Connection-based service and service without a connection. A connectionless service thinks of each segment as a separate packet, and they all take different paths to get to the same place.

Before sending the packets to the destination machine, a service that is based on connections connects the dots to a transport layer there. In connection-driven services, all of the packets take the same route.

  • Flow control is also done by the transport layer, but it is done from end to end instead of across a specific node.
  • Error control: Error regulation is also the job of the transport layer. Error control is done from one end to the other instead of across a single link. The sender's transport layer makes sure that the message gets to the right place without any problems.

5. Session layer

A session layer can be used to set up, sustain, and seamlessly integrate how two devices talk to each other.

Uses of the session layer

  • Dialog control: The session layer is a dialogue regulator that makes a conversation between two procedures, or it lets two methods talk to each other in either a half-duplex or a full-duplex way.
  • Synchronization: The session layer makes sure that the data is sent in the right order by adding checkpoints. If something goes wrong in the midst of the data transfer, the transfer will start over from the control point. Syncing and retrieval is the name for this methodology.

6. Presentation layer

A presentation layer is mostly concerned with how the information between two systems is put together and what it means.

It helps a network translate information. It is a component of a computer system that changes the way the information is shown from one template to another. The syntax layer is another name for the presentation layer.

Uses of the presentation layer

  • Information is passed between two systems in the context of strings, numbers, and other things. Different machines use various methodologies of encoding.
  • The presentation layer makes sure that the various encryption methods can work together. It changes the data from a format that depends on the sender into a common format.
At the receiving end, it alters the standardized framework into a format that depends on the recipient.

  • Encryption: You require encryption to keep your information private. Encryption is a method that changes the data sent by the sender into a different guise and then submits the new post over the system.
  • Compression: The procedure of compacting data, or reduction in the bits number that need to be sent. Data condensing is very essential for text, audio, and video, among other things.

7. Application layer

An application layer allows users and applications to use network services through a window. It takes care of things like network clarity, allocating resources, etc.

An application layer does not really count as a software application, but it does the things that programs do. This layer gives the end-users the internet services they need.

Uses of the application layer

  • File transfer, access, and management (FTAM): An application layer lets an user access files on a remote host, get records from a desktop, and edit documents on a remotely located computer.
  • Mail services: An application layer lets you forward and stores your emails.
  • Directory services: An application layer provides the distributed data sources and is used to give worldwide information about various objects.


Above, we learned whatever you need to understand regarding the 7 OSI layers, alongside their uses.

Recognizing the OSI configuration can help us learn more about IT security, especially when it comes to figuring out the form and reason of a threat.

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